William Newsome

All Publications

• Decoding and perturbing decision states in real time. Nature Peixoto, D., Verhein, J. R., Kiani, R., Kao, J. C., Nuyujukian, P., Chandrasekaran, C., Brown, J., Fong, S., Ryu, S. I., Shenoy, K. V., Newsome, W. T. 2021

  Abstract

  In dynamic environments, subjects often integrate multiple samples of a signal and combine them to reach a categorical judgment1. The process of deliberation can be described by a time-varying decision variable (DV), decoded from neural population activity, that predicts a subject's upcoming decision2. Within single trials, however, there are large moment-to-moment fluctuations in the DV, the behavioural significance of which is unclear. Here, using real-time, neural feedback control of stimulus duration, we show that within-trial DV fluctuations, decoded from motor cortex, are tightly linked to decision statein macaques, predicting behavioural choices substantially better than the condition-averaged DV or the visual stimulus alone. Furthermore, robust changes in DV sign have the statistical regularities expected from behavioural studies of changes of mind3. Probing the decision process on single trials with weak stimulus pulses, we find evidence for time-varying absorbing decision bounds, enabling us to distinguish between specific models of decision making.

  View details for DOI 10.1038/s41586-020-03181-9

  View details for PubMedID 33473215

• Remote, brain region-specific control of choice behavior with ultrasonic waves SCIENCE ADVANCES Kubanek, J., Brown, J., Ye, P., Pauly, K., Moore, T., Newsome, W. 2020; 6 (21)

  View details for DOI 10.1126/sciadv.aaz4193

  View details for Web of Science ID 000537235300018

• Value and choice as separable and stable representations in orbitofrontal cortex. Nature communications Kimmel, D. L., Elsayed, G. F., Cunningham, J. P., Newsome, W. T. 2020; 11 (1): 3466

  Abstract

  Value-based decision-making requires different variables-including offer value, choice, expected outcome, and recent history-at different times in the decision process. Orbitofrontal cortex (OFC) is implicated in value-based decision-making, but it is unclear how downstream circuits read out complex OFC responses into separate representations of the relevant variables to support distinct functions at specific times. We recorded from single OFC neurons while macaque monkeys made cost-benefit decisions. Using a novel analysis, we find separable neural dimensions that selectively represent the value, choice, and expected reward of the present and previous offers. The representations are generally stable during periods of behavioral relevance, then transition abruptly at key task events and between trials. Applying new statistical methods, we show that the sensitivity, specificity and stability of the representations are greater than expected from the population's low-level features-dimensionality and temporal smoothness-alone. The separability and stability suggest a mechanism-linear summation over static synaptic weights-by which downstream circuits can select for specific variables at specific times.

  View details for DOI 10.1038/s41467-020-17058-y

  View details for PubMedID 32651373

• Differential encoding in prefrontal cortex projection neuron classes across cognitive tasks. Cell Lui, J. H., Nguyen, N. D., Grutzner, S. M., Darmanis, S. n., Peixoto, D. n., Wagner, M. J., Allen, W. E., Kebschull, J. M., Richman, E. B., Ren, J. n., Newsome, W. T., Quake, S. R., Luo, L. n. 2020

  Abstract

  Single-cell transcriptomics has been widely applied to classify neurons in the mammalian brain, while systems neuroscience has historically analyzed the encoding properties of cortical neurons without considering cell types. Here we examine how specific transcriptomic types of mouse prefrontal cortex (PFC) projection neurons relate to axonal projections and encoding properties across multiple cognitive tasks. We found that most types projected to multiple targets, and most targets received projections from multiple types, except PFC→PAG (periaqueductal gray). By comparing Ca2+ activity of the molecularly homogeneous PFC→PAG type against two heterogeneous classes in several two-alternative choice tasks in freely moving mice, we found that all task-related signals assayed were qualitatively present in all examined classes. However, PAG-projecting neurons most potently encoded choice in cued tasks, whereas contralateral PFC-projecting neurons most potently encoded reward context in an uncued task. Thus, task signals are organized redundantly, but with clear quantitative biases across cells of specific molecular-anatomical characteristics.

  View details for DOI 10.1016/j.cell.2020.11.046

  View details for PubMedID 33338423

• Opportunities and limitations of genetically modified nonhuman primate models for neuroscience research. Proceedings of the National Academy of Sciences of the United States of America Feng, G. n., Jensen, F. E., Greely, H. T., Okano, H. n., Treue, S. n., Roberts, A. C., Fox, J. G., Caddick, S. n., Poo, M. M., Newsome, W. T., Morrison, J. H. 2020

  Abstract

  The recently developed new genome-editing technologies, such as the CRISPR/Cas system, have opened the door for generating genetically modified nonhuman primate (NHP) models for basic neuroscience and brain disorders research. The complex circuit formation and experience-dependent refinement of the human brain are very difficult to model in vitro, and thus require use of in vivo whole-animal models. For many neurodevelopmental and psychiatric disorders, abnormal circuit formation and refinement might be at the center of their pathophysiology. Importantly, many of the critical circuits and regional cell populations implicated in higher human cognitive function and in many psychiatric disorders are not present in lower mammalian brains, while these analogous areas are replicated in NHP brains. Indeed, neuropsychiatric disorders represent a tremendous health and economic burden globally. The emerging field of genetically modified NHP models has the potential to transform our study of higher brain function and dramatically facilitate the development of effective treatment for human brain disorders. In this paper, we discuss the importance of developing such models, the infrastructure and training needed to maximize the impact of such models, and ethical standards required for using these models.

  View details for DOI 10.1073/pnas.2006515117

  View details for PubMedID 32817435

• Remote, brain region-specific control of choice behavior with ultrasonic waves. Science advances Kubanek, J. n., Brown, J. n., Ye, P. n., Pauly, K. B., Moore, T. n., Newsome, W. n. 2020; 6 (21): eaaz4193

  Abstract

  The ability to modulate neural activity in specific brain circuits remotely and systematically could revolutionize studies of brain function and treatments of brain disorders. Sound waves of high frequencies (ultrasound) have shown promise in this respect, combining the ability to modulate neuronal activity with sharp spatial focus. Here, we show that the approach can have potent effects on choice behavior. Brief, low-intensity ultrasound pulses delivered noninvasively into specific brain regions of macaque monkeys influenced their decisions regarding which target to choose. The effects were substantial, leading to around a 2:1 bias in choices compared to the default balanced proportion. The effect presence and polarity was controlled by the specific target region. These results represent a critical step towards the ability to influence choice behavior noninvasively, enabling systematic investigations and treatments of brain circuits underlying disorders of choice.

  View details for DOI 10.1126/sciadv.aaz4193

  View details for PubMedID 32671207

  View details for PubMedCentralID PMC7314556

• Deviation from the matching law reflects an optimal strategy involving learning over multiple timescales NATURE COMMUNICATIONS Iigaya, K., Ahmadian, Y., Sugrue, L. P., Corrado, G. S., Loewenstein, Y., Newsome, W. T., Fusi, S. 2019; 10

  View details for DOI 10.1038/s41467-019-09388-3

  View details for Web of Science ID 000462857700006

• Task representations in neural networks trained to perform many cognitive tasks. Nature neuroscience Yang, G. R., Joglekar, M. R., Song, H. F., Newsome, W. T., Wang, X. 2019

  Abstract

  The brain has the ability to flexibly perform many tasks, but the underlying mechanism cannot be elucidated in traditional experimental and modeling studies designed for one task at a time. Here, we trained single network models to perform 20 cognitive tasks that depend on working memory, decision making, categorization, and inhibitory control. We found that after training, recurrent units can develop into clusters that are functionally specialized for different cognitive processes, and we introduce a simple yet effective measure to quantify relationships between single-unit neural representations of tasks. Learning often gives rise to compositionality of task representations, a critical feature for cognitive flexibility, whereby one task can be performed by recombining instructions for other tasks. Finally, networks developed mixed task selectivity similar to recorded prefrontal neurons after learning multiple tasks sequentially with a continual-learning technique. This work provides a computational platform to investigate neural representations of many cognitive tasks.

  View details for PubMedID 30643294

• Deviation from the matching law reflects an optimal strategy involving learning over multiple timescales. Nature communications Iigaya, K., Ahmadian, Y., Sugrue, L. P., Corrado, G. S., Loewenstein, Y., Newsome, W. T., Fusi, S. 2019; 10 (1): 1466

  Abstract

  Behavior deviating from our normative expectations often appears irrational. For example, even though behavior following the so-called matching law can maximize reward in a stationary foraging task, actual behavior commonly deviates from matching. Such behavioral deviations are interpreted as a failure of the subject; however, here we instead suggest that they reflect an adaptive strategy, suitable for uncertain, non-stationary environments. To prove it, we analyzed the behavior of primates that perform a dynamic foraging task. In such nonstationary environment, learning on both fast and slow timescales is beneficial: fast learning allows the animal to react to sudden changes, at the price of large fluctuations (variance) in the estimates of task relevant variables. Slow learning reduces the fluctuations but costs a bias that causes systematic behavioral deviations. Our behavioral analysis shows that the animals solved this bias-variance tradeoff by combining learning on both fast and slow timescales, suggesting that learning on multiple timescales can be a biologically plausible mechanism for optimizing decisions under uncertainty.

  View details for PubMedID 30931937

• Laminar differences in decision-related neural activity in dorsal premotor cortex NATURE COMMUNICATIONS Chandrasekaran, C., Peixoto, D., Newsome, W. T., Shenoy, K. V. 2017; 8: 614

  Abstract

  Dorsal premotor cortex is implicated in somatomotor decisions. However, we do not understand the temporal patterns and laminar organization of decision-related firing rates in dorsal premotor cortex. We recorded neurons from dorsal premotor cortex of monkeys performing a visual discrimination task with reaches as the behavioral report. We show that these neurons can be organized along a bidirectional visuomotor continuum based on task-related firing rates. "Increased" neurons at one end of the continuum increased their firing rates ~150 ms after stimulus onset and these firing rates covaried systematically with choice, stimulus difficulty, and reaction time-characteristics of a candidate decision variable. "Decreased" neurons at the other end of the continuum reduced their firing rate after stimulus onset, while "perimovement" neurons at the center of the continuum responded only ~150 ms before movement initiation. These neurons did not show decision variable-like characteristics. "Increased" neurons were more prevalent in superficial layers of dorsal premotor cortex; deeper layers contained more "decreased" and "perimovement" neurons. These results suggest a laminar organization for decision-related responses in dorsal premotor cortex.Dorsal premotor cortex (PMd) is thought to be involved in making somatomotor decisions. Chandrasekaran et al. investigated the temporal response dynamics of PMd neurons across cortical layers and show stronger and earlier decision-related responses in the superficial layers and more action execution-related signals in the deeper layers.

  View details for PubMedID 28931803

• THE CRITICAL ROLE OF NONHUMAN PRIMATES IN MEDICAL RESEARCH. Pathogens & immunity Friedman, H., Ator, N., Haigwood, N., Newsome, W., Allan, J. S., Golos, T. G., Kordower, J. H., Shade, R. E., Goldberg, M. E., Bailey, M. R., Bianchi, P. 2017; 2 (3): 352-365

  View details for DOI 10.20411/pai.v2i3.186

  View details for PubMedID 29034361

  View details for PubMedCentralID PMC5636196

• Orbitofrontal Cortex Value Signals Depend on Fixation Location during Free Viewing NEURON McGinty, V. B., Rangel, A., Newsome, W. T. 2016; 90 (6): 1299-1311

  Abstract

  In the natural world, monkeys and humans judge the economic value of numerous competing stimuli by moving their gaze from one object to another, in a rapid series of eye movements. This suggests that the primate brain processes value serially, and that value-coding neurons may be modulated by changes in gaze. To test this hypothesis, we presented monkeys with value-associated visual cues and took the unusual step of allowing unrestricted free viewing while we recorded neurons in the orbitofrontal cortex (OFC). By leveraging natural gaze patterns, we found that a large proportion of OFC cells encode gaze location and, that in some cells, value coding is amplified when subjects fixate near the cue. These findings provide the first cellular-level mechanism for previously documented behavioral effects of gaze on valuation and suggest a major role for gaze in neural mechanisms of valuation and decision-making under ecologically realistic conditions.

  View details for DOI 10.1016/j.neuron.2016.04.045

  View details for Web of Science ID 000378527600017

  View details for PubMedID 27263972

  View details for PubMedCentralID PMC4911340

• Comment on "Single-trial spike trains in parietal cortex reveal discrete steps during decision-making". Science Shadlen, M. N., Kiani, R., Newsome, W. T., Gold, J. I., Wolpert, D. M., Zylberberg, A., Ditterich, J., de Lafuente, V., Yang, T., Roitman, J. 2016; 351 (6280): 1406-?

  Abstract

  Latimeret al (Reports, 10 July 2015, p. 184) claim that during perceptual decision formation, parietal neurons undergo one-time, discrete steps in firing rate instead of gradual changes that represent the accumulation of evidence. However, that conclusion rests on unsubstantiated assumptions about the time window of evidence accumulation, and their stepping model cannot explain existing data as effectively as evidence-accumulation models.

  View details for DOI 10.1126/science.aad3242

  View details for PubMedID 27013723

• Comment on "Single-trial spike trains in parietal cortex reveal discrete steps during decision-making" SCIENCE Shadlen, M. N., Kiani, R., Newsome, W. T., Gold, J. I., Wolpert, D. M., Zylberberg, A., Ditterich, J., de Lafuente, V., Yang, T., Roitman, J. 2016; 351 (6280)

  View details for DOI 10.1126/science.aad3242

  View details for Web of Science ID 000372756200034

• The BRAIN Initiative: developing technology to catalyse neuroscience discovery PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES Jorgenson, L. A., Newsome, W. T., Anderson, D. J., Bargmann, C. I., Brown, E. N., Deisseroth, K., Donoghue, J. P., Hudson, K. L., Ling, G. S., MacLeish, P. R., Marder, E., Normann, R. A., Sanes, J. R., Schnitzer, M. J., Sejnowski, T. J., Tank, D. W., Tsien, R. Y., Ugurbil, K., Wingfield, J. C. 2015; 370 (1668): 8-19

  Abstract

  The evolution of the field of neuroscience has been propelled by the advent of novel technological capabilities, and the pace at which these capabilities are being developed has accelerated dramatically in the past decade. Capitalizing on this momentum, the United States launched the Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative to develop and apply new tools and technologies for revolutionizing our understanding of the brain. In this article, we review the scientific vision for this initiative set forth by the National Institutes of Health and discuss its implications for the future of neuroscience research. Particular emphasis is given to its potential impact on the mapping and study of neural circuits, and how this knowledge will transform our understanding of the complexity of the human brain and its diverse array of behaviours, perceptions, thoughts and emotions.

  View details for DOI 10.1098/rstb.2014.0164

  View details for Web of Science ID 000354071400002

  View details for PubMedID 25823863

  View details for PubMedCentralID PMC4387507

• Natural Grouping of Neural Responses Reveals Spatially Segregated Clusters in Prearcuate Cortex NEURON Kiani, R., Cueva, C. J., Reppas, J. B., Peixoto, D., Ryu, S. I., Newsome, W. T. 2015; 85 (6): 1359-1373

  Abstract

  A fundamental challenge in studying the frontal lobe is to parcellate this cortex into "natural" functional modules despite the absence of topographic maps, which are so helpful in primary sensory areas. Here we show that unsupervised clustering algorithms, applied to 96-channel array recordings from prearcuate gyrus, reveal spatially segregated subnetworks that remain stable across behavioral contexts. Looking for natural groupings of neurons based on response similarities, we discovered that the recorded area includes at least two spatially segregated subnetworks that differentially represent behavioral choice and reaction time. Importantly, these subnetworks are detectable during different behavioral states and, surprisingly, are defined better by "common noise" than task-evoked responses. Our parcellation process works well on "spontaneous" neural activity, and thus bears strong resemblance to the identification of "resting-state" networks in fMRI data sets. Our results demonstrate a powerful new tool for identifying cortical subnetworks by objective classification of simultaneously recorded electrophysiological activity.

  View details for DOI 10.1016/j.neuron.2015.02.014

  View details for Web of Science ID 000351319000020

  View details for PubMedID 25728571

  View details for PubMedCentralID PMC4366683

• Effects of Cortical Microstimulation on Confidence in a Perceptual Decision NEURON Fetsch, C. R., Kiani, R., Newsome, W. T., Shadlen, M. N. 2014; 83 (4): 797-804

  Abstract

  Decisions are often associated with a degree of certainty, or confidence-an estimate of the probability that the chosen option will be correct. Recent neurophysiological results suggest that the central processing of evidence leading to a perceptual decision also establishes a level of confidence. Here we provide a causal test of this hypothesis by electrically stimulating areas of the visual cortex involved in motion perception. Monkeys discriminated the direction of motion in a noisy display and were sometimes allowed to opt out of the direction choice if their confidence was low. Microstimulation did not reduce overall confidence in the decision but instead altered confidence in a manner that mimicked a change in visual motion, plus a small increase in sensory noise. The results suggest that the same sensory neural signals support choice, reaction time, and confidence in a decision and that artificial manipulation of these signals preserves the quantitative relationship between accumulated evidence and confidence.

  View details for DOI 10.1016/j.neuron.2014.07.011

  View details for Web of Science ID 000340479600009

  View details for PubMedID 25123306

  View details for PubMedCentralID PMC4141901

• Dynamics of Neural Population Responses in Prefrontal Cortex Indicate Changes of Mind on Single Trials CURRENT BIOLOGY Kiani, R., Cueva, C. J., Reppas, J. B., Newsome, W. T. 2014; 24 (13): 1542-1547

  View details for DOI 10.1016/j.cub.2014.05.049

  View details for Web of Science ID 000338799800031

• Dynamics of neural population responses in prefrontal cortex indicate changes of mind on single trials. Current biology Kiani, R., Cueva, C. J., Reppas, J. B., Newsome, W. T. 2014; 24 (13): 1542-1547

  Abstract

  Decision making is a complex process in which different sources of information are combined into a decision variable (DV) that guides action [1, 2]. Neurophysiological studies have typically sought insight into the dynamics of the decision-making process and its neural mechanisms through statistical analysis of large numbers of trials from sequentially recorded single neurons or small groups of neurons [3-6]. However, detecting and analyzing the DV on individual trials has been challenging [7]. Here we show that by recording simultaneously from hundreds of units in prearcuate gyrus of macaque monkeys performing a direction discrimination task, we can predict the monkey's choices with high accuracy and decode DV dynamically as the decision unfolds on individual trials. This advance enabled us to study changes of mind (CoMs) that occasionally happen before the final commitment to a decision [8-10]. On individual trials, the decoded DV varied significantly over time and occasionally changed its sign, identifying a potential CoM. Interrogating the system by random stopping of the decision-making process during the delay period after stimulus presentation confirmed the validity of identified CoMs. Importantly, the properties of the candidate CoMs also conformed to expectations based on prior theoretical and behavioral studies [8]: they were more likely to go from an incorrect to a correct choice, they were more likely for weak and intermediate stimuli than for strong stimuli, and they were more likely earlier in the trial. We suggest that simultaneous recording of large neural populations provides a good estimate of DV and explains idiosyncratic aspects of the decision-making process that were inaccessible before.

  View details for DOI 10.1016/j.cub.2014.05.049

  View details for PubMedID 24954050

• The Brain Research Through Advancing Innovative Neurotechnologies (BRAIN) initiative and neurology. JAMA neurology Bargmann, C. I., Newsome, W. T. 2014; 71 (6): 675-676

  View details for DOI 10.1001/jamaneurol.2014.411

  View details for PubMedID 24711071

• Context-dependent computation by recurrent dynamics in prefrontal cortex. Nature Mante, V., Sussillo, D., Shenoy, K. V., Newsome, W. T. 2013; 503 (7474): 78-84

  Abstract

  Prefrontal cortex is thought to have a fundamental role in flexible, context-dependent behaviour, but the exact nature of the computations underlying this role remains largely unknown. In particular, individual prefrontal neurons often generate remarkably complex responses that defy deep understanding of their contribution to behaviour. Here we study prefrontal cortex activity in macaque monkeys trained to flexibly select and integrate noisy sensory inputs towards a choice. We find that the observed complexity and functional roles of single neurons are readily understood in the framework of a dynamical process unfolding at the level of the population. The population dynamics can be reproduced by a trained recurrent neural network, which suggests a previously unknown mechanism for selection and integration of task-relevant inputs. This mechanism indicates that selection and integration are two aspects of a single dynamical process unfolding within the same prefrontal circuits, and potentially provides a novel, general framework for understanding context-dependent computations.

  View details for DOI 10.1038/nature12742

  View details for PubMedID 24201281

• Context-dependent computation by recurrent dynamics in prefrontal cortex NATURE Mante, V., Sussillo, D., Shenoy, K. V., Newsome, W. T. 2013; 503 (7474): 78-?

  Abstract

  Prefrontal cortex is thought to have a fundamental role in flexible, context-dependent behaviour, but the exact nature of the computations underlying this role remains largely unknown. In particular, individual prefrontal neurons often generate remarkably complex responses that defy deep understanding of their contribution to behaviour. Here we study prefrontal cortex activity in macaque monkeys trained to flexibly select and integrate noisy sensory inputs towards a choice. We find that the observed complexity and functional roles of single neurons are readily understood in the framework of a dynamical process unfolding at the level of the population. The population dynamics can be reproduced by a trained recurrent neural network, which suggests a previously unknown mechanism for selection and integration of task-relevant inputs. This mechanism indicates that selection and integration are two aspects of a single dynamical process unfolding within the same prefrontal circuits, and potentially provides a novel, general framework for understanding context-dependent computations.

  View details for DOI 10.1038/nature12742

  View details for Web of Science ID 000326585600035

  View details for PubMedID 24201281

• EFFECTIVE PARAMETERS FOR ULTRASOUND-INDUCED IN VIVO NEUROSTIMULATION ULTRASOUND IN MEDICINE AND BIOLOGY King, R. L., Brown, J. R., Newsome, W. T., Pauly, K. B. 2013; 39 (2): 312-331

  Abstract

  Ultrasound-induced neurostimulation has recently gained increasing attention, but little is known about the mechanisms by which it affects neural activity or about the range of acoustic parameters and stimulation protocols that elicit responses. We have established conditions for transcranial stimulation of the nervous system in vivo, using the mouse somatomotor response. We report that (1) continuous-wave stimuli are as effective as or more effective than pulsed stimuli in eliciting responses, and responses are elicited with stimulus onset rather than stimulus offset; (2) stimulation success increases as a function of both acoustic intensity and acoustic duration; (3) interactions of intensity and duration suggest that successful stimulation results from the integration of stimulus amplitude over a time interval of 50 to 150 ms; and (4) the motor response elicited appears to be an all-or-nothing phenomenon, meaning stronger stimulus intensities and durations increase the probability of a motor response without affecting the duration or strength of the response.

  View details for DOI 10.1016/j.ultrasmedbio.2012.09.009

  View details for Web of Science ID 000313207100015

  View details for PubMedID 23219040

• Tracking the eye non-invasively: simultaneous comparison of the scleral search coil and optical tracking techniques in the macaque monkey FRONTIERS IN BEHAVIORAL NEUROSCIENCE Kimmel, D. L., Mammo, D., Newsome, W. T. 2012; 6

  Abstract

  From human perception to primate neurophysiology, monitoring eye position is critical to the study of vision, attention, oculomotor control, and behavior. Two principal techniques for the precise measurement of eye position-the long-standing sclera-embedded search coil and more recent optical tracking techniques-are in use in various laboratories, but no published study compares the performance of the two methods simultaneously in the same primates. Here we compare two popular systems-a sclera-embedded search coil from C-N-C Engineering and the EyeLink 1000 optical system from SR Research-by recording simultaneously from the same eye in the macaque monkey while the animal performed a simple oculomotor task. We found broad agreement between the two systems, particularly in positional accuracy during fixation, measurement of saccade amplitude, detection of fixational saccades, and sensitivity to subtle changes in eye position from trial to trial. Nonetheless, certain discrepancies persist, particularly elevated saccade peak velocities, post-saccadic ringing, influence of luminance change on reported position, and greater sample-to-sample variation in the optical system. Our study shows that optical performance now rivals that of the search coil, rendering optical systems appropriate for many if not most applications. This finding is consequential, especially for animal subjects, because the optical systems do not require invasive surgery for implantation and repair of search coils around the eye. Our data also allow laboratories using the optical system in human subjects to assess the strengths and limitations of the technique for their own applications.

  View details for DOI 10.3389/fnbeh.2012.00049

  View details for Web of Science ID 000308427500001

  View details for PubMedID 22912608

  View details for PubMedCentralID PMC3418577

• Dissociation of Neuronal and Psychophysical Responses to Local and Global Motion CURRENT BIOLOGY Hedges, J. H., Gartshteyn, Y., Kohn, A., Rust, N. C., Shadlen, M. N., Newsome, W. T., Movshon, J. A. 2011; 21 (23): 2023-2028

  Abstract

  Most neurons in cortical area MT (V5) are strongly direction selective, and their activity is closely associated with the perception of visual motion. These neurons have large receptive fields built by combining inputs with smaller receptive fields that respond to local motion. Humans integrate motion over large areas and can perceive what has been referred to as global motion. The large size and direction selectivity of MT receptive fields suggests that MT neurons may represent global motion. We have explored this possibility by measuring responses to a stimulus in which the directions of simultaneously presented local and global motion are independently controlled. Surprisingly, MT responses depended only on the local motion and were unaffected by the global motion. Yet, under similar conditions, human observers perceive global motion and are impaired in discriminating local motion. Although local motion perception might depend on MT signals, global motion perception depends on mechanisms qualitatively different from those in MT. Motion perception therefore does not depend on a single cortical area but reflects the action and interaction of multiple brain systems.

  View details for DOI 10.1016/j.cub.2011.10.049

  View details for Web of Science ID 000298028100031

  View details for PubMedID 22153156

• Stimulus onset quenches neural variability: a widespread cortical phenomenon NATURE NEUROSCIENCE Churchland, M. M., Yu, B. M., Cunningham, J. P., Sugrue, L. P., Cohen, M. R., Corrado, G. S., Newsome, W. T., Clark, A. M., Hosseini, P., Scott, B. B., Bradley, D. C., Smith, M. A., Kohn, A., Movshon, J. A., Armstrong, K. M., Moore, T., Chang, S. W., Snyder, L. H., Lisberger, S. G., Priebe, N. J., Finn, I. M., Ferster, D., Ryu, S. I., Santhanam, G., Sahani, M., Shenoy, K. V. 2010; 13 (3): 369-U25

  Abstract

  Neural responses are typically characterized by computing the mean firing rate, but response variability can exist across trials. Many studies have examined the effect of a stimulus on the mean response, but few have examined the effect on response variability. We measured neural variability in 13 extracellularly recorded datasets and one intracellularly recorded dataset from seven areas spanning the four cortical lobes in monkeys and cats. In every case, stimulus onset caused a decline in neural variability. This occurred even when the stimulus produced little change in mean firing rate. The variability decline was observed in membrane potential recordings, in the spiking of individual neurons and in correlated spiking variability measured with implanted 96-electrode arrays. The variability decline was observed for all stimuli tested, regardless of whether the animal was awake, behaving or anaesthetized. This widespread variability decline suggests a rather general property of cortex, that its state is stabilized by an input.

  View details for DOI 10.1038/nn.2501

  View details for Web of Science ID 000274860100020

  View details for PubMedID 20173745

  View details for PubMedCentralID PMC2828350

• Integration of Sensory and Reward Information during Perceptual Decision-Making in Lateral Intraparietal Cortex (LIP) of the Macaque Monkey PLOS ONE Rorie, A. E., Gao, J., McClelland, J. L., Newsome, W. T. 2010; 5 (2)

  Abstract

  Single neurons in cortical area LIP are known to carry information relevant to both sensory and value-based decisions that are reported by eye movements. It is not known, however, how sensory and value information are combined in LIP when individual decisions must be based on a combination of these variables. To investigate this issue, we conducted behavioral and electrophysiological experiments in rhesus monkeys during performance of a two-alternative, forced-choice discrimination of motion direction (sensory component). Monkeys reported each decision by making an eye movement to one of two visual targets associated with the two possible directions of motion. We introduced choice biases to the monkeys' decision process (value component) by randomly interleaving balanced reward conditions (equal reward value for the two choices) with unbalanced conditions (one alternative worth twice as much as the other). The monkeys' behavior, as well as that of most LIP neurons, reflected the influence of all relevant variables: the strength of the sensory information, the value of the target in the neuron's response field, and the value of the target outside the response field. Overall, detailed analysis and computer simulation reveal that our data are consistent with a two-stage drift diffusion model proposed by Diederich and Bussmeyer for the effect of payoffs in the context of sensory discrimination tasks. Initial processing of payoff information strongly influences the starting point for the accumulation of sensory evidence, while exerting little if any effect on the rate of accumulation of sensory evidence.

  View details for DOI 10.1371/journal.pone.0009308

  View details for Web of Science ID 000274923700012

  View details for PubMedID 20174574

  View details for PubMedCentralID PMC2824817

• Estimates of the Contribution of Single Neurons to Perception Depend on Timescale and Noise Correlation JOURNAL OF NEUROSCIENCE Cohen, M. R., Newsome, W. T. 2009; 29 (20): 6635-6648

  Abstract

  The sensitivity of a population of neurons, and therefore the amount of sensory information available to an animal, is limited by the sensitivity of single neurons in the population and by noise correlation between neurons. For decades, therefore, neurophysiologists have devised increasingly clever and rigorous ways to measure these critical variables (Parker and Newsome, 1998). Previous studies examining the relationship between the responses of single middle temporal (MT) neurons and direction-discrimination performance uncovered an apparent paradox. Sensitivity measurements from single neurons suggested that small numbers of neurons may account for a monkey's psychophysical performance (Britten et al., 1992), but trial-to-trial variability in activity of single MT neurons are only weakly correlated with the monkey's behavior, suggesting that the monkey's decision must be based on the responses of many neurons (Britten et al., 1996). We suggest that the resolution to this paradox lies (1) in the long stimulus duration used in the original studies, which led to an overestimate of neural sensitivity relative to psychophysical sensitivity, and (2) mistaken assumptions (because no data were available) about the level of noise correlation in MT columns with opposite preferred directions. We therefore made new physiological and psychophysical measurements in a reaction time version of the direction-discrimination task that matches neural measurements to the actual decision time of the animals. These new data, considered together with our recent data on noise correlation in MT (Cohen and Newsome, 2008), provide a substantially improved account of psychometric performance in the direction-discrimination task.

  View details for DOI 10.1523/JNEUROSCI.5179-08.2009

  View details for Web of Science ID 000266252300026

  View details for PubMedID 19458234

  View details for PubMedCentralID PMC2705937

• Can Monkeys Choose Optimally When Faced with Noisy Stimuli and Unequal Rewards? PLOS COMPUTATIONAL BIOLOGY Feng, S., Holmes, P., Rorie, A., Newsome, W. T. 2009; 5 (2)

  Abstract

  We review the leaky competing accumulator model for two-alternative forced-choice decisions with cued responses, and propose extensions to account for the influence of unequal rewards. Assuming that stimulus information is integrated until the cue to respond arrives and that firing rates of stimulus-selective neurons remain well within physiological bounds, the model reduces to an Ornstein-Uhlenbeck (OU) process that yields explicit expressions for the psychometric function that describes accuracy. From these we compute strategies that optimize the rewards expected over blocks of trials administered with mixed difficulty and reward contingencies. The psychometric function is characterized by two parameters: its midpoint slope, which quantifies a subject's ability to extract signal from noise, and its shift, which measures the bias applied to account for unequal rewards. We fit these to data from two monkeys performing the moving dots task with mixed coherences and reward schedules. We find that their behaviors averaged over multiple sessions are close to optimal, with shifts erring in the direction of smaller penalties. We propose two methods for biasing the OU process to produce such shifts.

  View details for DOI 10.1371/journal.pcbi.1000284

  View details for Web of Science ID 000263924500009

  View details for PubMedID 19214201

• Context-Dependent Changes in Functional Circuitry in Visual Area MT NEURON Cohen, M. R., Newsome, W. T. 2008; 60 (1): 162-173

  Abstract

  Animals can flexibly change their behavior in response to a particular sensory stimulus; the mapping between sensory and motor representations in the brain must therefore be flexible as well. Changes in the correlated firing of pairs of neurons may provide a metric of changes in functional circuitry during behavior. We studied dynamic changes in functional circuitry by analyzing the noise correlations of simultaneously recorded MT neurons in two behavioral contexts: one that promotes cooperative interactions between the two neurons and another that promotes competitive interactions. We found that identical visual stimuli give rise to differences in noise correlation in the two contexts, suggesting that MT neurons receive inputs of central origin whose strength changes with the task structure. The data are consistent with a mixed feature-based attentional strategy model in which the animal sometimes alternates attention between opposite directions of motion and sometimes attends to the two directions simultaneously.

  View details for DOI 10.1016/j.neuron.2008.08.007

  View details for Web of Science ID 000260237300016

  View details for PubMedID 18940596

  View details for PubMedCentralID PMC2652654

• The temporal precision of reward prediction in dopamine neurons NATURE NEUROSCIENCE Fiorillo, C. D., Newsome, W. T., Schultz, W. 2008; 11 (8): 966-973

  View details for DOI 10.1038/nn.2159

  View details for Web of Science ID 000257969100023

• The temporal precision of reward prediction in dopamine neurons. Nature neuroscience Fiorillo, C. D., Newsome, W. T., Schultz, W. 2008

  Abstract

  Midbrain dopamine neurons are activated when reward is greater than predicted, and this error signal could teach target neurons both the value of reward and when it will occur. We used the dopamine error signal to measure how the expectation of reward was distributed over time. Animals were trained with fixed-duration intervals of 1-16 s between conditioned stimulus onset and reward. In contrast to the weak responses that have been observed after short intervals (1-2 s), activations to reward increased steeply and linearly with the logarithm of the interval. Results with varied stimulus-reward intervals suggest that the neural expectation was substantial after just half an interval had elapsed. Thus, the neural expectation of reward in these experiments was not highly precise and the precision declined sharply with interval duration. The neural precision of expectation appeared to be at least qualitatively similar to the precision of anticipatory licking behavior.

  View details for DOI 10.1038/nn.2159

  View details for PubMedID 18660807

• Brain stimulation: Feeling the buzz CURRENT BIOLOGY Reppas, J. B., Newsome, W. T. 2007; 17 (10): R358-R360

  Abstract

  A recent study demonstrates that artificially generated patterns of brain activity are surprisingly easy to sense. Brain areas that differ substantially in their functional specialization are remarkably similar in their ability to support this awareness.

  View details for DOI 10.1016/j.cub.2007.03.038

  View details for Web of Science ID 000246572900012

  View details for PubMedID 17502087

• Local field potential in cortical area MT: Stimulus tuning and behavioral correlations JOURNAL OF NEUROSCIENCE Liu, J., Newsome, W. T. 2006; 26 (30): 7779-7790

  Abstract

  Low-frequency electrical signals like those that compose the local field potential (LFP) can be detected at substantial distances from their point of origin within the brain. It is thus unclear how useful the LFP might be for assessing local function, for example, on the spatial scale of cortical columns. We addressed this problem by comparing speed and direction tuning of LFPs obtained from middle temporal area MT with the tuning of multiunit (MU) activity recorded simultaneously. We found that the LFP can be well tuned for speed and direction and is highly correlated with that of MU activity, particularly for frequencies at and above the gamma band. LFP tuning is substantially poorer for lower frequencies, although tuning for direction extends to lower frequencies than does tuning for speed. Our data suggest that LFP signals at and above the gamma band reflect neural processing on the spatial scale of cortical columns, within a few hundred micrometers of the electrode tip. Consistent with this notion, we also found that frequencies at and above the gamma band measured during a speed discrimination task exhibit an effect known as "choice probability," which reveals a particularly close relationship between neural activity and behavioral choices. In the LFP, this signature of the perceptual choice comprises a shift in relative power from low-frequency bands (alpha and beta) to the gamma band. It remains to be determined how LFP choice probability, which is a temporal signature, is related to conventional choice probability effects observed in spike rates.

  View details for DOI 10.1523/JNEUROSCI.5052-05.2006

  View details for Web of Science ID 000239361200003

  View details for PubMedID 16870724

• Linear-Nonlinear-Poisson models of primate choice dynamic JOURNAL OF THE EXPERIMENTAL ANALYSIS OF BEHAVIOR Corrado, G. S., Sugrue, L. P., Seung, H. S., Newsome, W. T. 2005; 84 (3): 581-617

  Abstract

  The equilibrium phenomenon of matching behavior traditionally has been studied in stationary environments. Here we attempt to uncover the local mechanism of choice that gives rise to matching by studying behavior in a highly dynamic foraging environment. In our experiments, 2 rhesus monkeys (Macacca mulatta) foraged for juice rewards by making eye movements to one of two colored icons presented on a computer monitor, each rewarded on dynamic variable-interval schedules. Using a generalization of Wiener kernel analysis, we recover a compact mechanistic description of the impact of past reward on future choice in the form of a Linear-Nonlinear-Poisson model. We validate this model through rigorous predictive and generative testing. Compared to our earlier work with this same data set, this model proves to be a better description of choice behavior and is more tightly correlated with putative neural value signals. Refinements over previous models include hyperbolic (as opposed to exponential) temporal discounting of past rewards, and differential (as opposed to fractional) comparisons of option value. Through numerical simulation we find that within this class of strategies, the model parameters employed by animals are very close to those that maximize reward harvesting efficiency.

  View details for DOI 10.1901/jeab.2005.23-05

  View details for Web of Science ID 000235691800016

  View details for PubMedID 16596981

  View details for PubMedCentralID PMC1389782

• Choosing the greater of two goods: Neural currencies for valuation and decision making NATURE REVIEWS NEUROSCIENCE Sugrue, L. P., Corrado, G. S., Newsome, W. T. 2005; 6 (5): 363-375

  Abstract

  To make adaptive decisions, animals must evaluate the costs and benefits of available options. The nascent field of neuroeconomics has set itself the ambitious goal of understanding the brain mechanisms that are responsible for these evaluative processes. A series of recent neurophysiological studies in monkeys has begun to address this challenge using novel methods to manipulate and measure an animal's internal valuation of competing alternatives. By emphasizing the behavioural mechanisms and neural signals that mediate decision making under conditions of uncertainty, these studies might lay the foundation for an emerging neurobiology of choice behaviour.

  View details for DOI 10.1038/nrn1666

  View details for Web of Science ID 000228863100011

  View details for PubMedID 15832198

• A general mechanism for decision-making in the human brain? TRENDS IN COGNITIVE SCIENCES Rorie, A. E., Newsome, W. T. 2005; 9 (2): 41-43

  Abstract

  A new fMRI study by Heekeren and colleagues suggests that left dorsolateral prefrontal cortex (DLPFC) contains a region that integrates sensory evidence supporting perceptual decisions. DLPFC meets two criteria posited by Heekeren et al. for such a region: (1) its activity is correlated in time with the output of sensory areas of the visual cortex measured simultaneously, and (2) as expected of an integrator, its activity is greater on trials for which the sensory evidence is substantial than on trials for which the sensory evidence is weak. Complementary experiments in humans and monkeys now offer a realistic hope of elucidating decision-making networks in the primate brain.

  View details for DOI 10.1016/j.tics.2004.12.007

  View details for Web of Science ID 000227225700001

  View details for PubMedID 15668095

• Correlation between speed perception and neural activity in the middle temporal visual area JOURNAL OF NEUROSCIENCE Liu, J., Newsome, W. T. 2005; 25 (3): 711-722

  Abstract

  We conducted electrophysiological recording and microstimulation experiments to test the hypothesis that the middle temporal visual area (MT) plays a direct role in perception of the speed of moving visual stimuli. We trained rhesus monkeys on a speed discrimination task in which monkeys chose the faster speed of two moving random dot patterns presented simultaneously in spatially segregated apertures. In electrophysiological experiments, we analyzed the activity of speed-tuned MT neurons and multiunit clusters during the discrimination task. Neural activity was correlated with the monkeys' behavioral choices on a trial-to-trial basis (choice probability), and the correlation was predicted by the speed-tuning properties of each unit. In microstimulation experiments, we activated clusters of MT neurons with homogeneous speed-tuning properties during the same speed discrimination task. In one monkey, microstimulation biased speed judgments toward the preferred speed of the stimulated neurons. Together, evidence from these two experiments suggests that MT neurons play a direct role in the perception of visual speed. Comparison of psychometric and neurometric thresholds revealed that single and multineuronal signals were, on average, considerably less sensitive than were the monkeys perceptually, suggesting that signals must be pooled across neurons to account for performance.

  View details for DOI 10.1523/JNEUROSCI.4034-04.2005

  View details for Web of Science ID 000226414700021

  View details for PubMedID 15659609

• Microstimulation of the superior colliculus focuses attention witnout moving the eyes PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Muller, J. R., Philiastides, M. G., Newsome, W. T. 2005; 102 (3): 524-529

  Abstract

  The superior colliculus (SC) is part of a network of brain areas that directs saccadic eye movements, overtly shifting both gaze and attention from position to position, in space. Here, we seek direct evidence that the SC also contributes to the control of covert spatial attention, a process that focuses attention on a region of space different from the point of gaze. While requiring monkeys to keep their gaze fixed, we tested whether microstimulation of a specific location in the SC spatial map would enhance visual performance at the corresponding region of space, a diagnostic measure of covert attention. We find that microstimulation improves performance in a spatially selective manner: thresholds decrease at the location in visual space represented by the stimulated SC site, but not at a control location in the opposite hemifield. Our data provide direct evidence that the SC contributes to the control of covert spatial attention.

  View details for Web of Science ID 000226436000003

  View details for PubMedID 15601760

• Cone signal interactions in direction-selective neurons in the middle temporal visual area (MT) JOURNAL OF VISION Barberini, C. L., Cohen, M. R., Wandell, B. A., Newsome, W. T. 2005; 5 (7): 603-621

  Abstract

  Many experimental measurements support the hypothesis that the middle temporal visual area (MT) of the rhesus monkey has a central role in processing visual motion. Most of these studies were performed using luminance stimuli, leaving open the question of how color information is used during motion processing. We investigated the specific question of how S-cone signals, an important source of color information, interact with L,M-cone signals, the dominant source of luminance information. In MT, S-cone-initiated signals combine synergistically with L,M-cone (luminance) signals over most of the stimulus range, regardless of whether the stimuli are added or subtracted. A quantitative analysis of the responses to the combination of S- and L,M-cone signals shows that for a significant minority of cells, these S-cone signals are carried to MT by a color-opponent ("blue-yellow") pathway, such that in certain limited contrast ranges, a small amount of S- and L,M-cone cancellation is observed. Both S- and L,M-cone responses are direction-selective, suggesting that MT processes a wide range of motion signals, including those carried by luminance and color. To investigate this possibility further, we measured MT responses while monkeys discriminated the direction of motion of luminance and S-cone-initiated gratings. The sensitivity of single MT neurons and the correlation between trial-to-trial variations in single neuron firing and perception are similar for S- and L,M-cone stimuli, further supporting a role for MT in processing chromatic motion.

  View details for DOI 10.1167/5.7.1

  View details for Web of Science ID 000232320700001

  View details for PubMedID 16231996

• Linear-Nonlinear-Poisson models of primate choice dynamics Journal of the Experimental Analysis of Behavior GS Corrado, LP Sugrue, WT Newsome 2005; 84: 581-617
• Choosing the greater of two goods: neural currencies for valuation and decision making Nature Reviews Neuroscience LP Sugrue, GS Corrado, WT Newsome 2005; 6: 363-375
• Direction-selective visual responses in macaque superior colliculus induced by behavioral training NEUROSCIENCE LETTERS Horwitz, G. D., Batista, A. P., Newsome, W. T. 2004; 366 (3): 315-319

  Abstract

  In a previous report, we described a heretofore undetected population of neurons in the intermediate and deep layers of the monkey superior colliculus (SC) that yielded directionally selective visual responses to stimuli presented within the central 4 degrees of the visual field. We observed these neurons in three monkeys that had been extensively trained to perform a visual direction discrimination task in this region of the visual field. The task required the monkeys to report the perceived direction of motion by making a saccadic eye movement to one of two targets aligned with the two possible directions of motion. We hypothesized that these neurons reflect a learned association between visual motion direction and saccade direction formed through extensive training on the direction discrimination task. We tested this hypothesis by searching for direction-selective visual responses in two monkeys that had been trained to perform a similar motion discrimination task in which the direction of stimulus motion was dissociated from the direction of the operant saccade. Strongly directional visual responses were absent in these monkeys, consistent with the notion that extensive training can induce highly specific visual responses in a subpopulation of SC neurons.

  View details for DOI 10.1016/j.neulet.2004.05.059

  View details for Web of Science ID 000223438400019

  View details for PubMedID 15288442

• Matching behavior and the representation of value in the parietal cortex SCIENCE Sugrue, L. P., Corrado, G. S., Newsome, W. T. 2004; 304 (5678): 1782-1787

  Abstract

  Psychologists and economists have long appreciated the contribution of reward history and expectation to decision-making. Yet we know little about how specific histories of choice and reward lead to an internal representation of the "value" of possible actions. We approached this problem through an integrated application of behavioral, computational, and physiological techniques. Monkeys were placed in a dynamic foraging environment in which they had to track the changing values of alternative choices through time. In this context, the monkeys' foraging behavior provided a window into their subjective valuation. We found that a simple model based on reward history can duplicate this behavior and that neurons in the parietal cortex represent the relative value of competing actions predicted by this model.

  View details for Web of Science ID 000222089500040

  View details for PubMedID 15205529

• Representation of an abstract perceptual decision in macaque superior colliculus JOURNAL OF NEUROPHYSIOLOGY Horwitz, G. D., Batista, A. P., Newsome, W. T. 2004; 91 (5): 2281-2296

  Abstract

  We recorded from neurons in the intermediate and deep layers of the superior colliculus (SC) while monkeys performed a novel direction discrimination task. In contrast to the task we used previously, the new version required the monkey to dissociate perceptual judgments from preparation to execute specific operant saccades. The monkey discriminated between 2 opposed directions of motion in a random-dot motion stimulus and was required to maintain the decision in memory throughout a delay period before the target of the required operant saccade was revealed. We hypothesized that perceptual decisions made in this paradigm would be represented in an "abstract" or "categorical" form within the brain, probably in the frontal cortex, and that decision-related neural activity would be eliminated from spatially organized preoculomotor structures such as the SC. To our surprise, however, a small population of neurons in the intermediate and deep layers of the SC fired in a choice-specific manner early in the trial well before the monkey could plan the operant saccade. Furthermore, the representation of the decision during the delay period appeared to be spatial: the active region in the SC map corresponded to the region of space toward which the perceptually discriminated stimulus motion flowed. Electrical microstimulation experiments suggested that these decision-related SC signals were not merely related to covert saccade planning. We conclude that monkeys may employ, in part, a spatially referenced mnemonic strategy for representing perceptual decisions, even when an abstract, categorical representation might appear more likely a priori.

  View details for DOI 10.1152/jn.00872.2003

  View details for Web of Science ID 000220692300037

  View details for PubMedID 14711971

• What electrical microstimulation has revealed about the neural basis of cognition CURRENT OPINION IN NEUROBIOLOGY Cohen, M. R., Newsome, W. T. 2004; 14 (2): 169-177

  Abstract

  Neurophysiologists have shown repeatedly that neural activity in different brain structures can be correlated with specific perceptual and cognitive functions, but the causal efficacy of the observed activity has generally been a matter of conjecture. By contrast, electrical microstimulation, which allows the experimenter to manipulate the activity of small groups of neurons with spatial and temporal precision, can now be used to demonstrate causal links between neural activity and specific cognitive functions. Here, we review this growing literature, including applications to the study of attention, visual and somatosensory perception, 'read-out' mechanisms for interpreting sensory maps, and contextual effects on perception. We also discuss potential applications of microstimulation to studies of higher cognitive functions such as decision-making and subjective experience.

  View details for DOI 10.1016/j.conb.2004.03.016

  View details for Web of Science ID 000221430600006

  View details for PubMedID 15082321

• Perceptual "Read-Out" of conjoined direction and disparity maps in extrastriate area MT PLOS BIOLOGY DeAngelis, G. C., Newsome, W. T. 2004; 2 (3): 394-404

  View details for DOI 10.1371/journal.pbio.0020077

  View details for Web of Science ID 000220512000015

• Perceptual "read-out" of conjoined direction and disparity maps in extrastriate area MT PLOS Biology DeAngelis, G., WT Newsome 2004; 2: 394-404
• Matching behavior and the encoding of value in parietal cortex Science Sugrue, L., GS Corrado, WT Newsome 2004; 304: 1782-1787
• Functional organization of speed tuned neurons in visual area MT JOURNAL OF NEUROPHYSIOLOGY Liu, J., Newsome, W. T. 2003; 89 (1): 246-256

  Abstract

  We analyzed the functional organization of speed tuned neurons in extrastriate visual area MT. We sought to determine whether neurons tuned for particular speeds are clustered spatially and whether such spatial clusters are elongated normal to the cortical surface so as to form speed columns. Our data showed that MT neurons are indeed clustered according to preferred speed. Multiunit recordings were speed tuned, and the speed tuning of these signals was well correlated with the speed tuning of single neurons recorded simultaneously. To determine whether speed columns exist in MT, we compared the rates at which preferred speed changed in electrode tracks that traversed MT obliquely and normally to the cortical surface. If speed columns exist, the preferred speed should change at a faster rate during oblique electrode tracks. We found, however, that preferred speed changed at similar rates for either type of penetration. In the same data set, the rate of change of preferred direction and preferred disparity differed substantially in normal and oblique penetrations as expected from the known columnar organization of MT. Thus our results suggest that a columnar organization for speed tuned neurons does not exist in MT.

  View details for DOI 10.1152/jn.00097.2002

  View details for Web of Science ID 000180329300024

  View details for PubMedID 12522176

• Middle temporal visual area microstimulation influences veridical judgments of motion direction JOURNAL OF NEUROSCIENCE Nichols, M. J., Newsome, W. T. 2002; 22 (21): 9530-9540

  Abstract

  Microstimulation of direction columns in the middle temporal visual area (MT, or V5) provides a powerful tool for probing the relationship between cortical physiology and visual motion perception. In the current study we obtained "veridical" reports of perceived motion from rhesus monkeys by permitting a continuous range of possible responses that mapped isomorphically onto a continuous range of possible motion directions. In contrast to previous studies, therefore, the animals were freed from experimenter-imposed "categories" that typify forced choice tasks. We report three new findings: (1) MT neurons with widely disparate preferred directions can cooperate to shape direction estimates, inconsistent with a pure "winner-take-all" read-out algorithm and consistent with a distributed coding scheme like vector averaging, whereas neurons with nearly opposite preferred directions seem to compete in a manner consistent with the winner-take-all hypothesis, (2) microstimulation can influence direction estimates even when paired with the most powerful motion stimuli available, and (3) microstimulation effects can be elicited when a manual response (instead of our standard oculomotor response) is used to communicate the perceptual report.

  View details for Web of Science ID 000179031600042

  View details for PubMedID 12417677

• Target selection for saccadic eye movements: Direction-selective visual responses in the superior colliculus JOURNAL OF NEUROPHYSIOLOGY Horwitz, G. D., Newsome, W. T. 2001; 86 (5): 2527-2542

  Abstract

  We investigated the role of the superior colliculus (SC) in saccade target selection in rhesus monkeys who were trained to perform a direction-discrimination task. In this task, the monkey discriminated between opposed directions of visual motion and indicated its judgment by making a saccadic eye movement to one of two visual targets that were spatially aligned with the two possible directions of motion in the display. Thus the neural circuits that implement target selection in this task are likely to receive directionally selective visual inputs and be closely linked to the saccadic system. We therefore studied prelude neurons in the intermediate and deep layers of the SC that can discharge up to several seconds before an impending saccade, indicating a relatively high-level role in saccade planning. We used the direction-discrimination task to identify neurons whose prelude activity "predicted" the impending perceptual report several seconds before the animal actually executed the operant eye movement; these "choice predicting" cells comprised approximately 30% of the neurons we encountered in the intermediate and deep layers of the SC. Surprisingly, about half of these prelude cells yielded direction-selective responses to our motion stimulus during a passive fixation task. In general, these neurons responded to motion stimuli in many locations around the visual field including the center of gaze where the visual discriminanda were positioned during the direction-discrimination task. Preferred directions generally pointed toward the location of the movement field of the SC neuron in accordance with the sensorimotor demands of the discrimination task. Control experiments indicate that the directional responses do not simply reflect covertly planned saccades. Our results indicate that a small population of SC prelude neurons exhibits properties appropriate for linking stimulus cues to saccade target selection in the context of a visual discrimination task.

  View details for Web of Science ID 000172012800036

  View details for PubMedID 11698540

• Target selection for saccadic eye movements: Prelude activity in the superior colliculus during a direction-discrimination task JOURNAL OF NEUROPHYSIOLOGY Horwitz, G. D., Newsome, W. T. 2001; 86 (5): 2543-2558

  Abstract

  We investigated the role of the superior colliculus (SC) in saccade target selection while macaque monkeys performed a direction-discrimination task. The monkeys selected one of two possible saccade targets based on the direction of motion in a stochastic random-dot display; the difficulty of the task was varied by adjusting the strength of the motion signal in the display. One of the two saccade targets was positioned within the movement field of the SC neuron under study while the other target was positioned well outside the movement field. Approximately 30% of the neurons in the intermediate and deep layers of the SC discharged target-specific preludes of activity that "predicted" target choices well before execution of the saccadic eye movement. Across the population of neurons, the strength of the motion signal in the display influenced the intensity of this "predictive" prelude activity: SC activity signaled the impending saccade more reliably when the motion signal was strong than when it was weak. The dependence of neural activity on motion strength could not be explained by small variations in the metrics of the saccadic eye movements. Predictive activity was particularly strong in a subpopulation of neurons with directional visual responses that we have described previously. For a subset of SC neurons, therefore, prelude activity reflects the difficulty of the direction discrimination in addition to the target of the impending saccade. These results are consistent with the notion that a restricted network of SC neurons plays a role in the process of saccade target selection.

  View details for Web of Science ID 000172012800037

  View details for PubMedID 11698541

• Neural basis of a perceptual decision in the parietal cortex (area LIP) of the rhesus monkey JOURNAL OF NEUROPHYSIOLOGY Shadlen, M. N., Newsome, W. T. 2001; 86 (4): 1916-1936

  Abstract

  We recorded the activity of single neurons in the posterior parietal cortex (area LIP) of two rhesus monkeys while they discriminated the direction of motion in random-dot visual stimuli. The visual task was similar to a motion discrimination task that has been used in previous investigations of motion-sensitive regions of the extrastriate cortex. The monkeys were trained to decide whether the direction of motion was toward one of two choice targets that appeared on either side of the random-dot stimulus. At the end of the trial, the monkeys reported their direction judgment by making an eye movement to the appropriate target. We studied neurons in LIP that exhibited spatially selective persistent activity during delayed saccadic eye movement tasks. These neurons are thought to carry high-level signals appropriate for identifying salient visual targets and for guiding saccadic eye movements. We arranged the motion discrimination task so that one of the choice targets was in the LIP neuron's response field (RF) while the other target was positioned well away from the RF. During motion viewing, neurons in LIP altered their firing rate in a manner that predicted the saccadic eye movement that the monkey would make at the end of the trial. The activity thus predicted the monkey's judgment of motion direction. This predictive activity began early in the motion-viewing period and became increasingly reliable as the monkey viewed the random-dot motion. The neural activity predicted the monkey's direction judgment on both easy and difficult trials (strong and weak motion), whether or not the judgment was correct. In addition, the timing and magnitude of the response was affected by the strength of the motion signal in the stimulus. When the direction of motion was toward the RF, stronger motion led to larger neural responses earlier in the motion-viewing period. When motion was away from the RF, stronger motion led to greater suppression of ongoing activity. Thus the activity of single neurons in area LIP reflects both the direction of an impending gaze shift and the quality of the sensory information that instructs such a response. The time course of the neural response suggests that LIP accumulates sensory signals relevant to the selection of a target for an eye movement.

  View details for Web of Science ID 000171562000035

  View details for PubMedID 11600651

• Correlated firing in macaque visual area MT: Time scales and relationship to behavior JOURNAL OF NEUROSCIENCE Bair, W., Zohary, E., Newsome, W. T. 2001; 21 (5): 1676-1697

  Abstract

  We studied the simultaneous activity of pairs of neurons recorded with a single electrode in visual cortical area MT while monkeys performed a direction discrimination task. Previously, we reported the strength of interneuronal correlation of spike count on the time scale of the behavioral epoch (2 sec) and noted its potential impact on signal pooling (Zohary et al., 1994). We have now examined correlation at longer and shorter time scales and found that pair-wise cross-correlation was predominantly short term (10-100 msec). Narrow, central peaks in the spike train cross-correlograms were largely responsible for correlated spike counts on the time scale of the behavioral epoch. Longer-term (many seconds to minutes) changes in the responsiveness of single neurons were observed in auto-correlations; however, these slow changes in time were on average uncorrelated between neurons. Knowledge of the limited time scale of correlation allowed the derivation of a more efficient metric for spike count correlation based on spike timing information, and it also revealed a potential relative advantage of larger neuronal pools for shorter integration times. Finally, correlation did not depend on the presence of the visual stimulus or the behavioral choice of the animal. It varied little with stimulus condition but was stronger between neurons with similar direction tuning curves. Taken together, our results strengthen the view that common input, common stimulus selectivity, and common noise are tightly linked in functioning cortical circuits.

  View details for Web of Science ID 000167129700030

  View details for PubMedID 11222658

• A comparison of spiking statistics in motion sensing neurones of flies and monkeys Conference on Motion Vision Barberini, C. L., Horwitz, G. D., Newsome, W. T. SPRINGER-VERLAG BERLIN. 2001: 307–320

  View details for Web of Science ID 000166736400016

• Somatosensation: Touching the mind's fingers CURRENT BIOLOGY Liu, J., Newsome, W. T. 2000; 10 (16): R598-R600

  Abstract

  Whether mental operations can be reduced to the biological properties of the brain has intrigued scientists and philosophers alike for millennia. New microstimulation experiments on awake, behaving monkeys establish causality between activity of specialized cortical neurons and a controlled behavior.

  View details for Web of Science ID 000089121000010

  View details for PubMedID 10985377

• Visuo-motor control: Giving the brain a hand CURRENT BIOLOGY Batista, A. P., Newsome, W. T. 2000; 10 (4): R145-R148

  Abstract

  Sensory information is acquired in spatial coordinate systems linked to sense organs, yet movement must be executed in coordinate systems linked to motor effector organs. Neurophysiological experiments are yielding new insights into how the brain transforms coordinate systems to facilitate movement.

  View details for Web of Science ID 000088977600009

  View details for PubMedID 10704408

• The neurobiology of cognition NATURE Nichols, M. J., Newsome, W. T. 1999; 402 (6761): C35-C38

  Abstract

  Perhaps the deepest mysteries facing the natural sciences concern the higher functions of the central nervous system. Understanding how the brain gives rise to mental experiences looms as one of the central challenges for science in the new millennium.

  View details for Web of Science ID 000084014100005

  View details for PubMedID 10591223

• Color signals in human motion-selective cortex NEURON Wandell, B. A., Poirson, A. B., Newsome, W. T., Baseler, H. A., Boynton, G. M., Huk, A., Gandhi, S., Sharpes, L. T. 1999; 24 (4): 901-909

  Abstract

  The neural basis for the effects of color and contrast on perceived speed was examined using functional magnetic resonance imaging (fMRI). Responses to S cone (blue-yellow) and L + M cone (luminance) patterns were measured in area V1 and in the motion area MT+. The MT+ responses were quantitatively similar to perceptual speed judgments of color patterns but not to color detection measures. We also measured cortical motion responses in individuals lacking L and M cone function (S cone monochromats). The S cone monochromats have clear motion-responsive regions in the conventional MT+ position, and their contrast-response functions there have twice the responsivity of S cone contrast-response functions in normal controls. But, their responsivity is far lower than the normals' responsivity to luminance contrast. Thus, the powerful magnocellular input to MT+ is either weak or silent during photopic vision in S cone monochromats.

  View details for Web of Science ID 000084495300018

  View details for PubMedID 10624953

• Color signals in area MT of the macaque monkey NEURON Seidemann, E., Poirson, A. B., Wandell, B. A., Newsome, W. T. 1999; 24 (4): 911-917

  Abstract

  The relationship between the neural processing of color and motion information has been a contentious issue in visual neuroscience. We examined this relationship directly by measuring neural responses to isoluminant S cone signals in extrastriate area MT of the macaque monkey. S cone stimuli produced robust, direction-selective responses at most recording sites, indicating that color signals are present in MT. While these responses were unequivocal, S cone contrast sensitivity was, on average, 1.0-1.3 log units lower than luminance contrast sensitivity. The presence of S cone responses and the relative sensitivity of MT neurons to S cone and luminance signals agree with functional magnetic resonance imaging (fMRI) measurements in human MT+. The results are consistent with the hypothesis that color signals in MT influence behavior in speed judgment tasks.

  View details for Web of Science ID 000084495300019

  View details for PubMedID 10624954

• Motion opponency in visual cortex JOURNAL OF NEUROSCIENCE Heeger, D. J., Boynton, G. M., Demb, J. B., Seidemann, E., Newsome, W. T. 1999; 19 (16): 7162-7174

  Abstract

  Perceptual studies suggest that visual motion perception is mediated by opponent mechanisms that correspond to mutually suppressive populations of neurons sensitive to motions in opposite directions. We tested for a neuronal correlate of motion opponency using functional magnetic resonance imaging (fMRI) to measure brain activity in human visual cortex. There was strong motion opponency in a secondary visual cortical area known as the human MT complex (MT+), but there was little evidence of motion opponency in primary visual cortex. To determine whether the level of opponency in human and monkey are comparable, a variant of these experiments was performed using multiunit electrophysiological recording in areas MT and MST of the macaque monkey brain. Although there was substantial variability in the degree of opponency between recording sites, the monkey and human data were qualitatively similar on average. These results provide further evidence that: (1) direction-selective signals underly human MT+ responses, (2) neuronal signals in human MT+ support visual motion perception, (3) human MT+ is homologous to macaque monkey MT and adjacent motion sensitive brain areas, and (4) that fMRI measurements are correlated with average spiking activity.

  View details for Web of Science ID 000081900800041

  View details for PubMedID 10436069

• Sensory systems - Editorial overview CURRENT OPINION IN NEUROBIOLOGY Eatock, R. A., Newsome, W. T. 1999; 9 (4): 385-388

  View details for Web of Science ID 000082156400002

  View details for PubMedID 10448170

• Separate signals for target selection and movement specification in the superior colliculus SCIENCE Horwitz, G. D., Newsome, W. T. 1999; 284 (5417): 1158-1161

  Abstract

  At any given instant, multiple potential targets for saccades are present in the visual world, implying that a "selection process" within the brain determines the target of the next eye movement. Some superior colliculus (SC) neurons begin discharging seconds before saccade initiation, suggesting involvement in target selection or, alternatively, in postselectional saccade preparation. SC neurons were recorded in monkeys who selected saccade targets on the basis of motion direction in a visual display. Some neurons carried a direction-selective visual signal, consistent with a role in target selection in this task, whereas other SC neurons appeared to be more involved in postselection specification of saccade parameters.

  View details for Web of Science ID 000080359100034

  View details for PubMedID 10325224

• Effect of spatial attention on the responses of area MT neurons JOURNAL OF NEUROPHYSIOLOGY Seidemann, E., Newsome, W. T. 1999; 81 (4): 1783-1794

  Abstract

  This study examines the influence of spatial attention on the responses of neurons in the middle temporal visual area (MT or V5) of extrastriate cortex. Two monkeys were trained to perform a direction-discrimination task. On each trial, two apertures of random-dot stimuli appeared simultaneously at two spatially separated locations; the monkeys were required to discriminate the direction of stimulus motion at one location while ignoring the stimulus at the other location. After extensive training, we recorded the responses of MT neurons in two configurations: 1) Both apertures placed "within" the neuron's receptive field (RF) and 2) one aperture covering the RF while the other was presented at a "remote" location. For each unit we compared the responses to identical stimulus displays when the monkey was instructed to attend to one or the other aperture. The responses of MT neurons were 8.7% stronger, on average, when the monkey attended to the spatial location that contained motion in the "preferred" direction. Attentional effects were equal, on average, in the within RF and remote configurations. The attentional modulations began approximately 300 ms after stimulus onset, gradually increased throughout the trial, and peaked near stimulus offset. An analysis of the neuronal responses on error trials suggests that the monkeys failed to attend to the appropriate spatial location on these trials. The relatively weak attentional effects that we observed contrast strikingly with recent results of Treue and Maunsell, who demonstrated very strong attentional modulations (median effect >80%) in MT in a task that shares many features with ours. Our results suggest that spatial attention alone is not sufficient to induce strong attentional effects in MT even when two competing motion stimuli appear within the RF of the recorded neuron. The difference between our results and those of Treue and Maunsell suggests that the magnitude of the attentional effects in MT may depend critically on how attention is directed to a particular stimulus and on the precise demands of the task.

  View details for Web of Science ID 000079752000033

  View details for PubMedID 10200212

• Organization of disparity-selective neurons in macaque area MT JOURNAL OF NEUROSCIENCE DeAngelis, G. C., Newsome, W. T. 1999; 19 (4): 1398-1415

  Abstract

  Neurons selective for binocular disparity are found in a number of visual cortical areas in primates, but there is little evidence that any of these areas are specialized for disparity processing. We have examined the organization of disparity-selective neurons in the middle temporal visual area (MT), an area shown previously to contain an abundance of disparity-sensitive neurons. We recorded extracellularly from MT neurons at regularly spaced intervals along electrode penetrations that passed through MT either normal to the cortical surface or at a shallow oblique angle. Comparison of multiunit and single-unit recordings shows that neurons are clustered in MT according to their disparity selectivity. Across the surface of MT, disparity-selective neurons are found in discrete patches that are separated by regions of MT that exhibit poor disparity tuning. Within disparity-selective patches of MT, we typically observe a smooth progression of preferred disparities (e.g. , near to far) as our electrode travels parallel to the cortical surface. In electrode penetrations normal to the cortical surface, on the other hand, MT neurons generally have similar disparity tuning, with little variation from one recording site to the next. Thus disparity-tuned neurons are organized into cortical columns by preferred disparity, and preferred disparity is mapped systematically within larger, disparity-tuned patches of MT. Combined with other recent findings, the data suggest that MT plays an important role in stereoscopic depth perception in addition to its well known role in motion perception.

  View details for Web of Science ID 000078603500023

  View details for PubMedID 9952417

• Nonhuman Primate Models of Visually Based Cognition. ILAR journal Newsome, W. T., Stein-Aviles, J. A. 1999; 39 (2): 78-91

  View details for PubMedID 11533513

• Cortical area MT and the perception of stereoscopic depth NATURE DeAngelis, G. C., Cumming, B. G., Newsome, W. T. 1998; 394 (6694): 677-680

  Abstract

  Stereopsis is the perception of depth based on small positional differences between images formed on the two retinae (known as binocular disparity). Neurons that respond selectively to binocular disparity were first described three decades ago, and have since been observed in many visual areas of the primate brain, including V1, V2, V3, MT and MST. Although disparity-selective neurons are thought to form the neural substrate for stereopsis, the mere existence of disparity-selective neurons does not guarantee that they contribute to stereoscopic depth perception. Some disparity-selective neurons may play other roles, such as guiding vergence eye movements. Thus, the roles of different visual areas in stereopsis remain poorly defined. Here we show that visual area MT is important in stereoscopic vision: electrical stimulation of clusters of disparity-selective MT neurons can bias perceptual judgements of depth, and the bias is predictable from the disparity preference of neurons at the stimulation site. These results show that behaviourally relevant signals concerning stereoscopic depth are present in MT.

  View details for Web of Science ID 000075384200043

  View details for PubMedID 9716130

• Tuning bandwidths for near-threshold stimuli in area MT JOURNAL OF NEUROPHYSIOLOGY Britten, K. H., Newsome, W. T. 1998; 80 (2): 762-770

  Abstract

  It is not known whether psychophysical performance depends primarily on small numbers of neurons optimally tuned to specific visual stimuli, or on larger populations of neurons that vary widely in their properties. Tuning bandwidths of single cells can provide important insight into this issue, yet most bandwidth measurements have been made using suprathreshold visual stimuli, whereas psychophysical measurements are frequently obtained near threshold. We therefore examined the directional tuning of cells in the middle temporal area (MT, or V5) using perithreshold, stochastic motion stimuli that we have employed extensively in combined psychophysical and physiological studies. The strength of the motion signal (coherence) in these displays can be varied independently of its direction. For each MT neuron, we characterized the directional bandwidth by fitting Gaussian functions to directional tuning data obtained at each of several motion coherences. Directional bandwidth increased modestly as the coherence of the stimulus was reduced. We then assessed the ability of MT neurons to discriminate opposed directions of motion along six equally spaced axes of motion spanning 180 degrees. A signal detection analysis yielded neurometric functions for each axis of motion, from which neural thresholds could be extracted. Neural thresholds remained surprisingly low as the axis of motion diverged from the neuron's preferred-null axis, forming a plateau of high to medium sensitivity that extended approximately 45 degrees on either side of the preferred-null axis. We conclude that directional tuning remains broad in MT when motion signals are reduced to near-threshold values. Thus directional information is widely distributed in MT, even near the limits of psychophysical performance. These observations support models in which relatively large numbers of signals are pooled to inform psychophysical decisions.

  View details for Web of Science ID 000075383000025

  View details for PubMedID 9705467

• Temporal gating of neural signals during performance of a visual discrimination task NATURE Seidemann, E., Zohary, E., Newsome, W. T. 1998; 394 (6688): 72-75

  Abstract

  The flow of neural signals within the cerebral cortex must be subject to multiple controls as behaviour unfolds in time. In a visual discrimination task that includes a delay period, the transmission of sensory signals to circuitry that mediates memory, decision-making and motor-planning must be governed closely by 'filtering' or 'gating' mechanisms so that extraneous events occurring before, during or after presentation of the critical visual stimulus have little or no effect on the subject's behavioural responses. Here we study one such mechanism physiologically by applying electrical microstimulation to columns of directionally selective neurons in the middle temporal visual area at varying times during single trials of a direction-discrimination task. The behavioural effects of microstimulation varied strikingly according to the timing of delivery within the trial, indicating that signals produced by microstimulation may be subject to active 'gating'. Our results show several important features of this gating process: first, signal flow is modulated upwards on onset of the visual stimulus and downwards, typically with a slower time course, after stimulus offset; second, gating efficacy can be modified by behavioural training; and third, gating is implemented primarily downstream of the middle temporal visual area.

  View details for Web of Science ID 000074579600050

  View details for PubMedID 9665129

• Neurophysiology: Sensing and categorizing CURRENT BIOLOGY Horwitz, G. D., Newsome, W. T. 1998; 8 (11): R376-R378

  Abstract

  Objects differ along many stimulus dimensions, but observers typically group them into fewer 'categories' according to their potential use or behavioral relevance. New experiments in awake, behaving monkeys open a window onto the process of stimulus categorization within the central nervous system.

  View details for Web of Science ID 000073778400009

  View details for PubMedID 9635182

• The variable discharge of cortical neurons: Implications for connectivity, computation, and information coding JOURNAL OF NEUROSCIENCE Shadlen, M. N., Newsome, W. T. 1998; 18 (10): 3870-3896

  Abstract

  Cortical neurons exhibit tremendous variability in the number and temporal distribution of spikes in their discharge patterns. Furthermore, this variability appears to be conserved over large regions of the cerebral cortex, suggesting that it is neither reduced nor expanded from stage to stage within a processing pathway. To investigate the principles underlying such statistical homogeneity, we have analyzed a model of synaptic integration incorporating a highly simplified integrate and fire mechanism with decay. We analyzed a "high-input regime" in which neurons receive hundreds of excitatory synaptic inputs during each interspike interval. To produce a graded response in this regime, the neuron must balance excitation with inhibition. We find that a simple integrate and fire mechanism with balanced excitation and inhibition produces a highly variable interspike interval, consistent with experimental data. Detailed information about the temporal pattern of synaptic inputs cannot be recovered from the pattern of output spikes, and we infer that cortical neurons are unlikely to transmit information in the temporal pattern of spike discharge. Rather, we suggest that quantities are represented as rate codes in ensembles of 50-100 neurons. These column-like ensembles tolerate large fractions of common synaptic input and yet covary only weakly in their spike discharge. We find that an ensemble of 100 neurons provides a reliable estimate of rate in just one interspike interval (10-50 msec). Finally, we derived an expression for the variance of the neural spike count that leads to a stable propagation of signal and noise in networks of neurons-that is, conditions that do not impose an accumulation or diminution of noise. The solution implies that single neurons perform simple algebra resembling averaging, and that more sophisticated computations arise by virtue of the anatomical convergence of novel combinations of inputs to the cortical column from external sources.

  View details for Web of Science ID 000073484300037

  View details for PubMedID 9570816

• Sense and the single neuron: Probing the physiology of perception ANNUAL REVIEW OF NEUROSCIENCE PARKER, A. J., Newsome, W. T. 1998; 21: 227-277

  Abstract

  The newly defined field of cognitive neuroscience attempts to draw together the study of all brain mechanisms that underlie our mental life. Historically, the major sensory pathways have provided the most trustworthy insights into how the brain supports cognitive functions such as perception, attention, and short-term memory. The links between neural activity and perception, in particular, have been studied revealingly in recent decades. Here we review the striking progress in this area, giving particular emphasis to the kinds of neural events that underlie the perceptual judgments of conscious observers.

  View details for Web of Science ID 000072446400009

  View details for PubMedID 9530497

• Deciding about motion: Linking perception to action JOURNAL OF COMPARATIVE PHYSIOLOGY A-NEUROETHOLOGY SENSORY NEURAL AND BEHAVIORAL PHYSIOLOGY Newsome, W. T. 1997; 181 (1): 5-12

  View details for Web of Science ID A1997XK92600003

• The King Solomon Lectures in Neuroethology. Deciding about motion: linking perception to action. Journal of comparative physiology. A, Sensory, neural, and behavioral physiology Newsome, W. T. 1997; 181 (1): 5-12

  View details for PubMedID 9216071

• How is a sensory map read out? Effects of microstimulation in visual area MT on saccades and smooth pursuit eye movements JOURNAL OF NEUROSCIENCE Groh, J. M., Born, R. T., Newsome, W. T. 1997; 17 (11): 4312-4330

  Abstract

  To generate behavioral responses based on sensory input, motor areas of the brain must interpret, or "read out," signals from sensory maps. Our experiments tested several algorithms for how the motor systems for smooth pursuit and saccadic eye movements might extract a usable signal of target velocity from the distributed representation of velocity in the middle temporal visual area (MT or V5). Using microstimulation, we attempted to manipulate the velocity information within MT while monkeys tracked a moving visual stimulus. We examined the effects of the microstimulation on smooth pursuit and on the compensation for target velocity shown by saccadic eye movements. Microstimulation could alter both the speed and direction of the motion estimates of both types of eye movements and could also cause monkeys to generate pursuit even when the visual target was actually stationary. The pattern of alterations suggests that microstimulation can introduce an additional velocity signal into MT and that the pursuit and saccadic systems usually compute a vector average of the visually evoked and microstimulation-induced velocity signals (pursuit, 55 of 122 experiments; saccades, 70 of 122). Microstimulation effects in a few experiments were consistent with vector summation of these two signals (pursuit, 6 of 122; saccades, 2 of 122). In the remainder of the experiments, microstimulation caused either an apparent impairment in motion processing (pursuit, 47 of 122; saccades, 41 of 122) or had no effect (pursuit, 14 of 122; saccades, 9 of 122). Within individual experiments, the effects on pursuit and saccades were usually similar, but the occasional striking exception suggests that the two eye movement systems may perform motion computations somewhat independently.

  View details for Web of Science ID A1997XA05600035

  View details for PubMedID 9151748

• Visual response properties of striate cortical neurons projecting to area MT in macaque monkeys JOURNAL OF NEUROSCIENCE Movshon, J. A., Newsome, W. T. 1996; 16 (23): 7733-7741

  Abstract

  We have previously shown that some neurons in extrastriate area MT are capable of signaling the global motion of complex patterns; neurons randomly sampled from V1, on the other hand, respond only to the motion of individual oriented components. Because only a small fraction of V1 neurons projects to MT, we wished to establish the processing hierarchy more precisely by studying the properties of those neurons projecting to MT, identified by antidromic responses to electrical stimulation of MT. The neurons that project from V1 to MT were directionally selective and, like other V1 neurons, responded only to the motion of the components of complex patterns. The projection neurons were predominantly "special complex," responsive to a broad range of spatial and temporal frequencies, and sensitive to very low stimulus contrasts. The projection neurons thus comprise a homogeneous and highly specialized subset of V1 neurons, consistent with the notion that V1 acts as clearing house of basic visual measurements, distributing information appropriately to higher cortical areas for specialized analysis.

  View details for Web of Science ID A1996VY43300034

  View details for PubMedID 8922429

• Neurophysiology: Neural fingerprints of visual attention CURRENT BIOLOGY Groh, J. M., Seidemann, E., Newsome, W. T. 1996; 6 (11): 1406-1409

  Abstract

  Pronounced effects of attention have been demonstrated in a region of visual cortex previously thought to be devoid of such influences; identifying the features critical for eliciting these effects should teach us a great deal about the neural underpinnings of visual attention.

  View details for Web of Science ID A1996VT11900020

  View details for PubMedID 8939585

• Visual attention: Spotlights, highlights and visual awareness CURRENT BIOLOGY Newsome, W. T. 1996; 6 (4): 357-360

  View details for Web of Science ID A1996UH68400008

  View details for PubMedID 8723331

• A computational analysis of the relationship between neuronal and behavioral responses to visual motion JOURNAL OF NEUROSCIENCE Shadlen, M. N., Britten, K. H., Newsome, W. T., Movshon, J. A. 1996; 16 (4): 1486-1510

  Abstract

  We have documented previously a close relationship between neuronal activity in the middle temporal visual area (MT or V5) and behavioral judgments of motion (Newsome et al., 1989; Salzman et al., 1990; Britten et al., 1992; Britten et al., 1996). We have now used numerical simulations to try to understand how neural signals in area MT support psychophysical decisions. We developed a model that pools neuronal responses drawn from our physiological data set and compares average responses in different pools to produce psychophysical decisions. The structure of the model allows us to assess the relationship between "neuronal" input signals and simulated psychophysical performance using the same methods we have applied to real experimental data. We sought to reconcile three experimental observations: psychophysical performance (threshold sensitivity to motion stimuli embedded in noise), a trial-by-trial covariation between the neural response and the monkey's choices, and a modest correlation between pairs of MT neurons in their variable responses to identical visual stimuli. Our results can be most accurately simulated if psychophysical decisions are based on pools of at least 100 weakly correlated sensory neurons. The neurons composing the pools must include a broader range of sensitivities than we encountered in our MT recordings, presumably because of the inclusion of neurons whose optimal stimulus is different from the one being discriminated. Central sources of noise degrade the signal-to-noise ratio of the pooled signal, but this degradation is relatively small compared with the noise typically carried by single cortical neurons. This suggests that our monkeys base near-threshold psychophysical judgments on signals carried by populations of weakly interacting neurons; these populations include many neurons that are not tuned optimally for the particular stimuli being discriminated.

  View details for Web of Science ID A1996TV54100021

  View details for PubMedID 8778300

• Motion perception: Seeing and deciding Colloquium on Vision - From Photon to Perception Shadlen, M. N., Newsome, W. T. NATL ACAD SCIENCES. 1996: 628–33

  Abstract

  The primate visual system offers unprecedented opportunities for investigating the neural basis of cognition. Even the simplest visual discrimination task requires processing of sensory signals, formation of a decision, and orchestration of a motor response. With our extensive knowledge of the primate visual and oculomotor systems as a base, it is now possible to investigate the neural basis of simple visual decisions that link sensation to action. Here we describe an initial study of neural responses in the lateral intraparietal area (LIP) of the cerebral cortex while alert monkeys discriminated the direction of motion in a visual display. A subset of LIP neurons carried high-level signals that may comprise a neural correlate of the decision process in our task. These signals are neither sensory nor motor in the strictest sense; rather they appear to reflect integration of sensory signals toward a decision appropriate for guiding movement. If this ultimately proves to be the case, several fascinating issues in cognitive neuroscience will be brought under rigorous physiological scrutiny.

  View details for Web of Science ID A1996TR32600017

  View details for PubMedID 8570606

• A relationship between behavioral choice and the visual responses of neurons in macaque MT VISUAL NEUROSCIENCE Britten, K. H., Newsome, W. T., Shadlen, M. N., Celebrini, S., Movshon, J. A. 1996; 13 (1): 87-100

  Abstract

  We have previously documented the exquisite motion sensitivity of neurons in extrastriate area MT by studying the relationship between their responses and the direction and strength of visual motion signals delivered to their receptive fields. These results suggested that MT neurons might provide the signals supporting behavioral choice in visual discrimination tasks. To approach this question from another direction, we have now studied the relationship between the discharge of MT neurons and behavioral choice, independently of the effects of visual stimulation. We found that trial-to-trial variability in neuronal signals was correlated with the choices the monkey made. Therefore, when a directionally selective neuron in area MT fires more vigorously, the monkey is more likely to make a decision in favor of the preferred direction of the cell. The magnitude of the relationship was modest, on average, but was highly significant across a sample of 299 cells from four monkeys. The relationship was present for all stimuli (including those without a net motion signal), and for all but the weakest responses. The relationship was reduced or eliminated when the demands of the task were changed so that the directional signal carried by the cell was less informative. The relationship was evident within 50 ms of response onset, and persisted throughout the stimulus presentation. On average, neurons that were more sensitive to weak motion signals had a stronger relationship to behavior than those that were less sensitive. These observations are consistent with the idea that neuronal signals in MT are used by the monkey to determine the direction of stimulus motion. The modest relationship between behavioral choice and the discharge of any one neuron, and the prevalence of the relationship across the population, make it likely that signals from many neurons are pooled to form the data on which behavioral choices are based.

  View details for Web of Science ID A1996TN93200009

  View details for PubMedID 8730992

• MICROSTIMULATION OF EXTRASTRIATE AREA MST INFLUENCES PERFORMANCE ON A DIRECTION DISCRIMINATION TASK JOURNAL OF NEUROPHYSIOLOGY Celebrini, S., Newsome, W. T. 1995; 73 (2): 437-448

  Abstract

  1. Evidence from single-unit recordings suggests that neurons in the medial superior temporal visual area (MST) carry directional signals that influence psychophysical judgements of motion direction. We tested this hypothesis by electrically stimulating clusters of directionally selective neurons in MST (the dorsomedial subdivision, primarily) while rhesus monkeys performed a two-alternative, forced-choice direction discrimination task. 2. We performed forty-six microstimulation experiments on two rhesus monkeys. The visual stimuli were dynamic random dot patterns in which the strength of a coherent motion signal could be varied continuously about psychophysical threshold. The monkeys were rewarded for reporting correctly the direction of the coherent motion signal. Microstimulation was applied on half the trials, selected randomly, and the psychophysical data were analyzed to determine whether stimulation of MST neurons influenced the monkeys' choices. 3. Microstimulation influenced the monkeys' performance in a statistically significant manner in 67% of the experiments. In all but one of the significant experiments, microstimulation biased the monkeys' choices toward the direction of motion encoded by MST neurons at the stimulation site. Microstimulation had little effect on the slopes of the psychometric functions, suggesting that the stimulation-induced neural activity resembled a relatively pure motion "signal" rather than "noise." 4. Microstimulation exerted strong effects on the monkeys' behavior only when the visual stimulus was located within the multiunit receptive field measured at the stimulation site. This kind of spatial specificity has also been observed in the middle temporal visual area (MT), but receptive fields in MST are typically much larger than those in MT. Thus MST microstimulation effects are characterized by a coarser spatial scale: stimulation of a single site in MST can influence judgements over a much larger portion of the visual field than equivalent stimulation in MT. 5. Microstimulation was often most effective when visual stimuli were placed within a particularly responsive subregion of the receptive field (a "hot spot"). 6. The results show that MST neurons, like MT neurons, can strongly influence performance on a direction discrimination task. Whether MT and MST influence the decision process in parallel or in series remains to be determined.

  View details for Web of Science ID A1995QU21500002

  View details for PubMedID 7760110

• On neural codes and perception J. Cogn. Neurosci. Newsome, W. 1995; 7: 95-100
• ON NEURAL CODES AND PERCEPTION JOURNAL OF COGNITIVE NEUROSCIENCE Newsome, W. T. 1995; 7 (1): 95-100

  Abstract

  Abstract Bill Newsome is a professor in the Department of Neurobiology at the Stanford University School of Medicine. He received his B.S. in physics from Stetson University in 1974 and his Ph.D. in biology from Caltech in 1980. Following postdoctoral work at MH, he served on the faculty at SUNY Stony Brook before joining the Stanford faculty in 1988. His research has focused on the neural mechanisms underlying visual perception and visually guided behavior. Bill was a corecipient of the Rank Prize in optoelectronics in 1992, and received the Minerva Foundation's Golden Brain Award in the same year. This fall he received the Spencer Award, granted yearly by the College of Physicians and Surgeons at Columbia University for highly original contributions to research in neurobiology. In addition, he won the Kaiser Award for excellence in preclinical teaching granted annually by the Stanford School of Medicine.

  View details for Web of Science ID A1995QF59000007

  View details for PubMedID 23961756

• Noise, neural codes and cortical organization. Current opinion in neurobiology Shadlen, M. N., Newsome, W. T. 1994; 4 (4): 569-579

  Abstract

  Cortical circuitry must facilitate information transfer in accordance with a neural code. In this article we examine two candidate neural codes: information is represented in the spike rate of neurons, or information is represented in the precise timing of individual spikes. These codes can be distinguished by examining the physiological basis of the highly irregular interspike intervals typically observed in cerebral cortex. Recent advances in our understanding of cortical microcircuitry suggest that the timing of neuronal spikes conveys little, if any, information. The cortex is likely to propagate a noisy rate code through redundant, patchy interconnections.

  View details for PubMedID 7812147

• CORRELATED NEURONAL DISCHARGE RATE AND ITS IMPLICATIONS FOR PSYCHOPHYSICAL PERFORMANCE NATURE Zohary, E., Shadlen, M. N., Newsome, W. T. 1994; 370 (6485): 140-143

  Abstract

  Single neurons can signal subtle changes in the sensory environment with surprising fidelity, often matching the perceptual sensitivity of trained psychophysical observers. This similarity poses an intriguing puzzle: why is psychophysical sensitivity not greater than that of single neurons? Pooling responses across neurons should average out noise in the activity of single cells, leading to substantially improved psychophysical performance. If, however, noise is correlated among these neurons, the beneficial effects of pooling would be diminished. To assess correlation within a pool, the responses of pairs of neurons were recorded simultaneously during repeated stimulus presentations. We report here that the observed covariation in spike count was relatively weak, the correlation coefficient averaging 0.12. A theoretical analysis revealed, however, that weak correlation can limit substantially the signalling capacity of the pool. In addition, theory suggests a relationship between neuronal responses and psychophysical decisions which may prove useful for identifying cell populations underlying specific perceptual capacities.

  View details for Web of Science ID A1994NW80400057

  View details for PubMedID 8022482

• NEURONAL AND PSYCHOPHYSICAL SENSITIVITY TO MOTION SIGNALS IN EXTRASTRIATE AREA MST OF THE MACAQUE MONKEY JOURNAL OF NEUROSCIENCE Celebrini, S., Newsome, W. T. 1994; 14 (7): 4109-4124

  Abstract

  We recorded the responses of single neurons in extrastriate area MST while rhesus monkeys discriminated the direction of motion in a set of stochastic visual displays. By varying systematically the strength of a coherent motion signal within the visual display, we were able to measure simultaneously the monkeys' psychophysical thresholds for direction discrimination and the responses of single neurons to the same motion signals. Neuronal thresholds for reliably signaling the direction of motion in the visual display were calculated from the measured responses using a method based in signal detection theory. Neurons in MST were exquisitely sensitive to motion signals in the display, having thresholds for discriminating the direction of coherent motion that were, on average, equal to the psychophysical thresholds of the monkeys. For many MST neurons, the intensity of the response was correlated with the monkey's psychophysical judgements for repeated presentations of a given near-threshold stimulus; the monkey tended to choose the preferred direction of the neuron under study when that neuron responded more strongly to the stimulus. In both of these respects, MST neurons were indistinguishable from neurons in extrastriate area MT, a major source of afferent input to MST. In a second set of experiments, we found that both of these results held true in the face of pronounced manipulations of the visual stimulus. Severe reductions in stimulus size and speed, for example, compromised neuronal and psychophysical sensitivities by similar amounts so that the average neuronal and psychophysical thresholds remained approximately equal. In addition, the trial-to-trial covariation of neuronal response and perceptual decision was unaffected by our stimulus manipulations. Thus, MST neurons carry signals appropriate for supporting psychophysical performance on our task over an impressively wide range of stimulus configurations.

  View details for Web of Science ID A1994NZ62000010

  View details for PubMedID 8027765

• POWER SPECTRUM ANALYSIS OF BURSTING CELLS IN AREA MT IN THE BEHAVING MONKEY JOURNAL OF NEUROSCIENCE Bair, W., Koch, C., Newsome, W., Britten, K. 1994; 14 (5): 2870-2892

  Abstract

  It is widely held that visual cortical neurons encode information primarily in their mean firing rates. Some proposals, however, emphasize the information potentially available in the temporal structure of spike trains (Optican and Richmond, 1987; Bialek et al., 1991), in particular with respect to stimulus-related synchronized oscillations in the 30-70 Hz range (Eckhorn et al., 1988; Gray et al., 1989; Kreiter and Singer, 1992) as well as via bursting cells (Cattaneo et al., 1981a; Bonds, 1992). We investigate the temporal fine structure of spike trains recorded in extrastriate area MT of the trained macaque monkey, a region that plays a major role in processing motion information. The data were recorded while the monkey performed a near-threshold direction discrimination task so that both physiological and psychophysical data could be obtained on the same set of trials (Britten et al., 1992). We identify bursting cells and quantify their properties, in particular in relation to the behavior of the animal. We compute the power spectrum and the distribution of interspike intervals (ISIs) associated with individual spike trains from 212 cells, averaging these quantities across similar trials. (1) About 33% of the cells have a relatively flat power spectrum with a dip at low temporal frequencies. We analytically derive the power spectrum of a Poisson process with refractory period and show that it matches the observed spectrum of these cells. (2) About 62% of the cells have a peak in the 20-60 Hz frequency band. In about 10% of all cells, this peak is at least twice the height of its base. The presence of such a peak strongly correlates with a tendency of the cell to respond in bursts, that is, two to four spikes within 2-8 msec. For 93% of cells, the shape of the power spectrum did not change dramatically with stimulus conditions. (3) Both the ISI distribution and the power spectrum of the vast majority of bursting cells are compatible with the notion that these cells fire Poisson-distributed bursts, with a burst-related refractory period. Thus, for our stimulus conditions, no explicitly oscillating neuronal process is required to yield a peak in the power spectrum. (4) We found no statistically significant relationship between the peak in the power spectrum and psychophysical measures of the monkeys' performance on the direction discrimination task.(ABSTRACT TRUNCATED AT 400 WORDS)

  View details for Web of Science ID A1994NK23600035

  View details for PubMedID 8182445

• NEURAL MECHANISMS FOR FORMING A PERCEPTUAL DECISION SCIENCE SALZMAN, C. D., Newsome, W. T. 1994; 264 (5156): 231-237

  Abstract

  Cognitive and behavioral responses to environmental stimuli depend on an evaluation of sensory signals within the cerebral cortex. The mechanism by which this occurs in a specific visual task was investigated with a combination of physiological and psychophysical techniques. Rhesus monkeys discriminated among eight possible directions of motion while directional signals were manipulated in visual area MT. One directional signal was generated by a visual stimulus and a second signal was introduced by electrically stimulating neurons that encoded a specific direction of motion. The decisions made by the monkeys in response to the two signals allowed a distinction to be made between two possible mechanisms for interpreting directional signals in MT. The monkeys tended to cast decisions in favor of one or the other signal, indicating that the signals exerted independent effects on performance and that an interactive mechanism such as vector averaging of the two signals was not operative. Thus, the data suggest a mechanism in which monkeys chose the direction encoded by the largest signal in the representation of motion direction, a "winner-take-all" decision process.

  View details for Web of Science ID A1994NE41000028

  View details for PubMedID 8146653

• NEURONAL PLASTICITY THAT UNDERLIES IMPROVEMENT IN PERCEPTUAL PERFORMANCE SCIENCE Zohary, E., Celebrini, S., Britten, K. H., Newsome, W. T. 1994; 263 (5151): 1289-1292

  Abstract

  The electrophysiological properties of sensory neurons in the adult cortex are not immutable but can change in response to alterations of sensory input caused by manipulation of afferent pathways in the nervous system or by manipulation of the sensory environment. Such plasticity creates great potential for flexible processing of sensory information, but the actual effects of neuronal plasticity on perceptual performance are poorly understood. The link between neuronal plasticity and performance was explored here by recording the responses of directionally selective neurons in the visual cortex while rhesus monkeys practiced a familiar task involving discrimination of motion direction. Each animal experienced a short-term improvement in perceptual sensitivity during daily experiments; sensitivity increased by an average of 19 percent over a few hundred trials. The increase in perceptual sensitivity was accompanied by a short-term improvement in neuronal sensitivity that mirrored the perceptual effect both in magnitude and in time course, which suggests that improved psychophysical performance can result directly from increased neuronal sensitivity within a sensory pathway.

  View details for Web of Science ID A1994MY57000040

  View details for PubMedID 8122114

• RESPONSES OF NEURONS IN MACAQUE MT TO STOCHASTIC MOTION SIGNALS VISUAL NEUROSCIENCE Britten, K. H., Shadlen, M. N., Newsome, W. T., Movshon, J. A. 1993; 10 (6): 1157-1169

  Abstract

  Dynamic random-dot stimuli have been widely used to explore central mechanisms of motion processing. We have measured the responses of neurons in area MT of the alert monkey while we varied the strength and direction of the motion signal in such displays. The strength of motion is controlled by the proportion of spatiotemporally correlated dots, which we term the correlation of the stimulus. For many MT cells, responses varied approximately linearly with stimulus correlation. When they occurred, nonlinearities were equally likely to be either positively or negatively accelerated. We also explored the relationship between response magnitude and response variance for these cells and found, in general agreement with other investigators, that this relationship conforms to a power law with an exponent slightly greater than 1. The variance of the cells' discharge is little influenced by the trial-to-trial fluctuations inherent in our stochastic display, and is therefore likely to be of neural origin. Linear responses to these stochastic motion stimuli are predicted by simple, low-level motion models incorporating sensors having relatively broad spatial and temporal frequency tuning.

  View details for Web of Science ID A1993MD85800019

  View details for PubMedID 8257671

• MICROSTIMULATION IN VISUAL AREA MT - EFFECTS OF VARYING PULSE AMPLITUDE AND FREQUENCY JOURNAL OF NEUROSCIENCE MURASUGI, C. M., SALZMAN, C. D., Newsome, W. T. 1993; 13 (4): 1719-1729

  Abstract

  We have previously shown that perceptual judgements of motion direction are based in part on the activity of direction selective neurons in extrastriate visual area MT (Salzman et al., 1990, 1992). In those experiments, we applied low-amplitude microstimulation pulses (10 microA, 200 Hz) to clusters of MT neurons whose preferred directions were similar. The effect of microstimulation was to bias the monkeys' choices on a direction discrimination task toward the preferred direction of neurons at the stimulation site. The results suggest that microstimulation generated a directionally specific cortical signal by activating selectively neurons near the electrode tip. To test this notion more directly, we have now examined the behavioral effects of varying current amplitude, current frequency, and electrode position. In the majority of experiments, the directional bias in the monkeys' choices was reduced or eliminated as current amplitude increased to 80 microA. In addition, 80 microA stimulating pulses frequently impaired overall performance as measured by the percentage of correct responses. This decrement in performance indicated that 80 microA pulses introduced "noise" into the neural circuitry encoding motion direction, presumably by increasing current spread to activate a larger population of neurons representing all directions of motion. In contrast, increasing current frequency to 500 Hz (10 microA pulses) preserved the directional specificity of microstimulation effects. The precise position of the stimulating electrode also influenced the magnitude of microstimulation effects; in some cases, differences in position on the order of 100 microns determined whether an experiment yielded a very large effect or no effect at all. Thus, directionally specific activation of cortical circuitry within MT can be disrupted by increases in current spread or by small changes in electrode position. These observations suggest that the effects of low-amplitude microstimulation depend upon direct activation of a well-localized population of neurons.

  View details for Web of Science ID A1993KV71100035

  View details for PubMedID 8463847

• THE NEURONAL BASIS OF MOTION PERCEPTION CIBA FOUNDATION SYMPOSIA Newsome, W. T., SALZMAN, C. D. 1993; 174: 217-246

  Abstract

  The central nervous system of humans supports a range of cognitive functions that contribute to conscious mental states. The neural systems underlying several of these cognitive functions, including perception, memory, planning and action, are proving susceptible to experimental analysis in lower primate species such as rhesus monkeys. In particular, recent investigations have generated striking new insights concerning the neural mechanisms that mediate visual perception. We briefly review the functional organization of the primate visual pathways and describe new experiments that demonstrate a causal link between neural activity in one of these pathways and a specific aspect of perceptual performance. The experiments illustrate an incisive method for linking perceptual abilities to their neural substrates. This approach may prove applicable to the analysis of other cognitive functions as well.

  View details for Web of Science ID A1993KR02700011

  View details for PubMedID 8319509

• MICROSTIMULATION OF VISUAL AREA MT - EFFECTS ON CHOICE BEHAVIOR IN THE ABSENCE OF MOVING VISUAL-STIMULI International Symposium on Brain Mechanisms of Perception and Memory: From Neuron to Behavior MURASUGI, C. M., SALZMAN, C. D., Newsome, W. T. OXFORD UNIV PRESS. 1993: 200–215

  View details for Web of Science ID A1993BA75C00012

• THE NEURONAL BASIS OF MOTION PERCEPTION SYMP ON EXPERIMENTAL AND THEORETICAL STUDIES OF CONSCIOUSNESS Newsome, W. T., SALZMAN, C. D. JOHN WILEY & SONS LTD. 1993: 217–246

  View details for Web of Science ID A1993BX68M00011

• THE ANALYSIS OF VISUAL-MOTION - A COMPARISON OF NEURONAL AND PSYCHOPHYSICAL PERFORMANCE JOURNAL OF NEUROSCIENCE Britten, K. H., Shadlen, M. N., Newsome, W. T., Movshon, J. A. 1992; 12 (12): 4745-4765

  Abstract

  We compared the ability of psychophysical observers and single cortical neurons to discriminate weak motion signals in a stochastic visual display. All data were obtained from rhesus monkeys trained to perform a direction discrimination task near psychophysical threshold. The conditions for such a comparison were ideal in that both psychophysical and physiological data were obtained in the same animals, on the same sets of trials, and using the same visual display. In addition, the psychophysical task was tailored in each experiment to the physiological properties of the neuron under study; the visual display was matched to each neuron's preference for size, speed, and direction of motion. Under these conditions, the sensitivity of most MT neurons was very similar to the psychophysical sensitivity of the animal observers. In fact, the responses of single neurons typically provided a satisfactory account of both absolute psychophysical threshold and the shape of the psychometric function relating performance to the strength of the motion signal. Thus, psychophysical decisions in our task are likely to be based upon a relatively small number of neural signals. These signals could be carried by a small number of neurons if the responses of the pooled neurons are statistically independent. Alternatively, the signals may be carried by a much larger pool of neurons if their responses are partially intercorrelated.

  View details for Web of Science ID A1992KC84000016

  View details for PubMedID 1464765

• MICROSTIMULATION IN VISUAL AREA MT - EFFECTS ON DIRECTION DISCRIMINATION PERFORMANCE JOURNAL OF NEUROSCIENCE SALZMAN, C. D., MURASUGI, C. M., Britten, K. H., Newsome, W. T. 1992; 12 (6): 2331-2355

  Abstract

  Physiological and behavioral evidence suggests that the activity of direction selective neurons in visual cortex underlies the perception of moving visual stimuli. We tested this hypothesis by measuring the effects of cortical microstimulation on perceptual judgements of motion direction. To accomplish this, rhesus monkeys were trained to discriminate the direction of motion in a near-threshold, stochastic motion display. For each experiment, we positioned a microelectrode in the middle of a cluster of neurons that shared a common preferred direction of motion. The psychophysical task was then adjusted so that the visual display was presented directly over the neurons' receptive field. The monkeys were required to discriminate between motion shown either in the direction preferred by the neurons or in the opposite direction. On half the trials of an experiment, we applied electrical microstimulation while monkeys viewed the motion display. We hypothesized that enhancing the neurons' discharge rate would introduce a directionally specific signal into the cortex and thereby influence the monkeys' choices on the discrimination task. We compared the monkeys' performance on "stimulated" and "nonstimulated" trials in 139 experiments; all trials within an experiment were presented in random order. Statistically significant effects of microstimulation were obtained in 89 experiments. In 86 of the 89 experiments with significant effects (97%), the monkeys indicated that motion was in the neurons' preferred direction more frequently on stimulated trials than on nonstimulated trials. The data demonstrate a functional link between the activity of direction selective neurons and perceptual judgements of motion direction.

  View details for Web of Science ID A1992HY15600031

  View details for PubMedID 1607944

• EFFECTS OF INFEROTEMPORAL CORTEX LESIONS ON FORM-FROM-MOTION DISCRIMINATION IN MONKEYS EXPERIMENTAL BRAIN RESEARCH Britten, K. H., Newsome, W. T., Saunders, R. C. 1992; 88 (2): 292-302

  Abstract

  The inferotemporal cortex of primates plays a prominent role in the learning and retention of visual form discriminations. In this experiment we investigated the role of inferotemporal (IT) cortex in the discrimination of two-dimensional forms defined by motion cues. Six monkeys were trained to a criterion level of performance on two form-from-motion problems. Three of these animals received complete bilateral lesions of IT cortex, while the other three served as unoperated controls. All animals were then retrained to criterion to evaluate the effects of IT lesions on the retention of form-from-motion learning. Compared with the control group, the lesion group was significantly impaired on both problems. Following retention testing, we trained both groups of monkeys on two new form-from-motion problems to investigate the effects of IT lesions on acquisition rates for new learning. The lesion group performed well on the new problems; the learning rates of the operated and control groups were not significantly different. When forms were defined by luminance cues, monkeys with IT lesions, like those in previous studies, were impaired both for retention and for acquisition. These findings indicate that the anterograde effects of IT lesions on learning new form discriminations are less severe for forms defined by motion cues than for forms defined by luminance cues. However, the retrograde effects of IT lesions on retention are severe for forms defined by either cue.

  View details for Web of Science ID A1992HF51100006

  View details for PubMedID 1577103

• CORTICAL MICROSTIMULATION INFLUENCES PERCEPTUAL JUDGMENTS OF MOTION DIRECTION NATURE SALZMAN, C. D., Britten, K. H., Newsome, W. T. 1990; 346 (6280): 174-177

  Abstract

  Neurons in the visual cortex respond selectively to perceptually salient features of the visual scene, such as the direction and speed of moving objects, the orientation of local contours, or the colour or relative depth of a visual pattern. It is commonly assumed that the brain constructs its percept of the visual scene from information encoded in the selective responses of such neurons. We have now tested this hypothesis directly by measuring the effect on psychophysical performance of modifying the firing rates of physiologically characterized neurons. We required rhesus monkeys to report the direction of motion in a visual display while we electrically stimulated clusters of directionally selective neurons in the middle temporal visual area (MT, or V5), an extrastriate area that plays a prominent role in the analysis of visual motion information. Microstimulation biased the animals' judgements towards the direction of motion encoded by the stimulated neurons. This result indicates that physiological properties measured at the neuronal level can be causally related to a specific aspect of perceptual performance.

  View details for Web of Science ID A1990DN42400061

  View details for PubMedID 2366872

• NEURONAL MECHANISMS OF MOTION PERCEPTION COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY Newsome, W. T., Britten, K. H., SALZMAN, C. D., Movshon, J. A. 1990; 55: 697-705

  View details for Web of Science ID A1990HB91800064

  View details for PubMedID 2132847

• NEURONAL CORRELATES OF A PERCEPTUAL DECISION NATURE Newsome, W. T., Britten, K. H., Movshon, J. A. 1989; 341 (6237): 52-54

  Abstract

  The relationship between neuronal activity and psychophysical judgement has long been of interest to students of sensory processing. Previous analyses of this problem have compared the performance of human or animal observers in detection or discrimination tasks with the signals carried by individual neurons, but have been hampered because neuronal and perceptual data were not obtained at the same time and under the same conditions. We have now measured the performance of monkeys and of visual cortical neurons while the animals performed a psychophysical task well matched to the properties of the neurons under study. Here we report that the reliability and sensitivity of most neurons on this task equalled or exceeded that of the monkeys. We therefore suggest that under our conditions, psychophysical judgements could be based on the activity of a relatively small number of neurons.

  View details for Web of Science ID A1989AN95800053

  View details for PubMedID 2770878

• SINGLE NEURONS AND THE PERCEPTION OF VISUAL-MOTION 2ND RETINA RESEARCH FOUNDATION SYMP ON NEURAL MECHANISMS OF VISUAL PERCEPTION Newsome, W. T., Britten, K. H., Movshon, J. A., Shadlen, M. PORTFOLIO PUBLISHING CO INC. 1989: 171–198

  View details for Web of Science ID A1989BP98M00008

• PROBING VISUAL CORTICAL FUNCTION WITH DISCRETE CHEMICAL LESIONS TRENDS IN NEUROSCIENCES Newsome, W. T., Wurtz, R. H. 1988; 11 (9): 394-400

  View details for Web of Science ID A1988P641300008

  View details for PubMedID 2469205