I am a Neuroscientist who likes to use psychophysics, EEG and fMRI to try and understand how the visual system works. I am originally from Denmark, but have lived and worked in the US since 2007. I received my PhD in Cognitive Neuroscience in 2013 from Dartmouth College, and since then I have been a post-doctoral scholar at Stanford University, working with Professor Tony Norcia.
My main interest is in the visual perception of form, motion and position, and how these three classes of information interact with each other. I am fascinated by the question of how the visual system disambiguates the inherently ambigious two-dimensional pattern of light that hits the retina, and how our rich meaningful and coherent three-dimensional perception of the visual scene come to be. One of the goals of my research is to understand the rules by which the visual system construct our visual experience from the sparse input, and to understand the neuronal circuits that give rise to these constructive processes.
Bachelor of Science, Unlisted School (2008)
Doctor of Philosophy, Dartmouth College (2013)
Anthony Norcia, Postdoctoral Faculty Sponsor
Motion-induced position shifts are influenced by global motion, but dominated by component motion
2015; 110: 93-99
Object motion and position have long been thought to involve largely independent visual computations. However, the motion-induced position shift (Eagleman & Sejnowski, 2007) shows that the perceived position of a briefly presented static object can be influenced by nearby moving contours. Here we combine a particularly strong example of this illusion with a bistable global motion stimulus to compare the relative effects of global and component motion on the shift in perceived position. We used a horizontally oscillating diamond (Lorenceau & Shiffrar, 1992) that produces two possible global directions (left and right when fully visible versus up and down when vertices are occluded by vertical bars) as well as the oblique component motion orthogonal to each contour. To measure the motion-induced shift we flashed a test dot on the contour as the diamond reversed direction (Cavanagh & Anstis, 2013). Although the global motion had a highly significant influence on the direction and size of the motion-induced position shift, the perceived displacement of the probe was closer to the direction of the component motion. These findings show that while global motion can clearly influence position shifts, it is the component motion that dominates in setting the position shift. This is true even though the perceived motion is in the global direction and the component motion is not consciously experienced. This suggests that perceived position is influenced by motion signals that arise earlier in time or earlier in processing compared to the stage at which the conscious experience of motion is determined.
View details for DOI 10.1016/j.visres.2015.03.003
View details for Web of Science ID 000354149100011
View details for PubMedID 25782364
The artist emerges: Visual art learning alters neural structure and function
2015; 105: 440-451
How does the brain mediate visual artistic creativity? Here we studied behavioral and neural changes in drawing and painting students compared to students who did not study art. We investigated three aspects of cognition vital to many visual artists: creative cognition, perception, and perception-to-action. We found that the art students became more creative via the reorganization of prefrontal white matter but did not find any significant changes in perceptual ability or related neural activity in the art students relative to the control group. Moreover, the art students improved in their ability to sketch human figures from observation, and multivariate patterns of cortical and cerebellar activity evoked by this drawing task became increasingly separable between art and non-art students. Our findings suggest that the emergence of visual artistic skills is supported by plasticity in neural pathways that enable creative cognition and mediate perceptuomotor integration.
View details for DOI 10.1016/j.neuroimage.2014.11.014
View details for Web of Science ID 000346050300040
View details for PubMedID 25463452
Extrastriate Visual Areas Integrate Form Features over Space and Time to Construct Representations of Stationary and Rigidly Rotating Objects.
Journal of cognitive neuroscience
When an object moves behind a bush, for example, its visible fragments are revealed at different times and locations across the visual field. Nonetheless, a whole moving object is perceived. Unlike traditional modal and amodal completion mechanisms known to support spatial form integration when all parts of a stimulus are simultaneously visible, relatively little is known about the neural substrates of the spatiotemporal form integration (STFI) processes involved in generating coherent object representations from a succession visible fragments. We use fMRI to identify brain regions involved in two mechanisms supporting the representation of stationary and rigidly rotating objects whose form features are shown in succession: STFI and position updating. STFI allows past and present form cues to be integrated over space and time into a coherent object even when the object is not visible in any given frame. STFI can occur whether or not the object is moving. Position updating allows us to perceive a moving object, whether rigidly rotating or translating, even when its form features are revealed at different times and locations in space. Our results suggest that STFI is mediated by visual regions beyond V1 and V2. Moreover, although widespread cortical activation has been observed for other motion percepts derived solely from form-based analyses [Tse, P. U. Neural correlates of transformational apparent motion. Neuroimage, 31, 766-773, 2006; Krekelberg, B., Vatakis, A., & Kourtzi, Z. Implied motion from form in the human visual cortex. Journal of Neurophysiology, 94, 4373-4386, 2005], increased responses for the position updating that lead to rigidly rotating object representations were only observed in visual areas KO and possibly hMT+, indicating that this is a distinct and highly specialized type of processing.
View details for DOI 10.1162/jocn_a_00850
View details for PubMedID 26226075
- Unconscious neural processing differs with method used to render stimuli invisible FRONTIERS IN PSYCHOLOGY 2014; 5
The global slowdown effect: Why does perceptual grouping reduce perceived speed?
ATTENTION PERCEPTION & PSYCHOPHYSICS
2014; 76 (3): 780-792
The percept of four rotating dot pairs is bistable. The "local percept" is of four pairs of dots rotating independently. The "global percept" is of two large squares translating over one another (Anstis & Kim 2011). We have previously demonstrated (Kohler, Caplovitz, & Tse 2009) that the global percept appears to move more slowly than the local percept. Here, we investigate and rule out several hypotheses for why this may be the case. First, we demonstrate that the global slowdown effect does not occur because the global percept is of larger objects than the local percept. Second, we show that the global slowdown effect is not related to rotation-specific detectors that may be more active in the local than in the global percept. Third, we find that the effect is also not due to a reduction of image elements during grouping and can occur with a stimulus very different from the one used previously. This suggests that the effect may reflect a general property of perceptual grouping. Having ruled out these possibilities, we suggest that the global slowdown effect may arise from emergent motion signals that are generated by the moving dots, which are interpreted as the ends of "barbell bars" in the local percept or the corners of the illusory squares in the global percept. Alternatively, the effect could be the result of noisy sources of motion information that arise from perceptual grouping that, in turn, increase the influence of Bayesian priors toward slow motion (Weiss, Simoncelli, & Adelson 2002).
View details for DOI 10.3758/s13414-013-0607-x
View details for Web of Science ID 000334521300013
View details for PubMedID 24448695
Pattern classification precedes region-average hemodynamic response in early visual cortex
2013; 78: 249-260
How quickly can information about the neural response to a visual stimulus be detected in the hemodynamic response measured using fMRI? Multi-voxel pattern analysis (MVPA) uses pattern classification to detect subtle stimulus-specific information from patterns of responses among voxels, including information that cannot be detected in the average response across a given brain region. Here we use MVPA in combination with rapid temporal sampling of the fMRI signal to investigate the temporal evolution of classification accuracy and its relationship to the average regional hemodynamic response. In primary visual cortex (V1) stimulus information can be detected in the pattern of voxel responses more than a second before the average hemodynamic response of V1 deviates from baseline, and classification accuracy peaks before the peak of the average hemodynamic response. Both of these effects are restricted to early visual cortex, with higher level areas showing no difference or, in some cases, the opposite temporal relationship. These results have methodological implications for fMRI studies using MVPA because they demonstrate that information can be decoded from hemodynamic activity more quickly than previously assumed.
View details for DOI 10.1016/j.neuroimage.2013.04.019
View details for Web of Science ID 000320488900025
View details for PubMedID 23587693
Effects of attention on visual experience during monocular rivalry
2013; 83: 76-81
There is a long-running debate over the extent to which volitional attention can modulate the appearance of visual stimuli. Here we use monocular rivalry between afterimages to explore the effects of attention on the contents of visual experience. In three experiments, we demonstrate that attended afterimages are seen for longer periods, on average, than unattended afterimages. This occurs both when a feature of the afterimage is attended directly and when a frame surrounding the afterimage is attended. The results of these experiments show that volitional attention can dramatically influence the contents of visual experience.
View details for DOI 10.1016/j.visres.2013.03.002
View details for Web of Science ID 000318202300009
View details for PubMedID 23499978
- Network structure and dynamics of the mental workspace Proceedings of the National Academy of Sciences 2013; 110 (40): 16277-16282
Associations between auditory pitch and visual elevation do not depend on language: Evidence from a remote population
2012; 41 (7): 854-861
Associations between auditory pitch and visual elevation are widespread in many languages, and behavioral associations have been extensively documented between height and pitch among speakers of those languages. However, it remains unclear whether perceptual correspondences between auditory pitch and visual elevation inform these linguistic associations, or merely reflect them. We probed this cross-modal mapping in members of a remote Kreung hill tribe in northeastern Cambodia who do not use spatial language to describe pitch. Participants viewed shapes rising or falling in space while hearing sounds either rising or falling in pitch, and reported on the auditory change. Associations between pitch and vertical position in the Kreung were similar to those demonstrated in populations where pitch is described in terms of spatial height. These results suggest that associations between visual elevation and auditory pitch can arise independently of language. Thus, widespread linguistic associations between pitch and elevation may reflect universally predisposed perceptual correspondences.
View details for DOI 10.1068/p7225
View details for Web of Science ID 000310184600008
View details for PubMedID 23155736
Rotational and translational motion interact independently with form
2011; 51 (23-24): 2478-2487
Do the mechanisms that underlie the perception of translational and rotational object motion show evidence of independent processing? By probing the perceived speed of translating and/or rotating objects, we find that an object's form contributes in independent ways to the processing of translational and rotational motion: In the context of translational motion, it has been shown that the more elongated an object is along its direction of motion, the faster it is perceived to translate; in the context of rotational motion, it has been shown that the sharper the maxima of curvature along an object's contour, the faster it appears to rotate. Here we demonstrate that such rotational form-motion interactions are due solely to the rotational component of combined rotational and translational motion. We conclude that the perception of rotational motion relies on form-motion interactions that are independent of the processing underlying translational motion.
View details for DOI 10.1016/j.visres.2011.10.005
View details for Web of Science ID 000297907600017
View details for PubMedID 22024049
Motion fading is driven by perceived, not actual angular velocity
2010; 50 (11): 1086-1094
After prolonged viewing of a slowly drifting or rotating pattern under strict fixation, the pattern appears to slow down and then momentarily stop. Here we examine the relationship between such 'motion fading' and perceived angular velocity. Using several different dot patterns that generate emergent virtual contours, we demonstrate that whenever there is a difference in the perceived angular velocity of two patterns of dots that are in fact rotating at the same angular velocity, there is also a difference in the time to undergo motion fading for those two patterns. Conversely, whenever two patterns show no difference in perceived angular velocity, even if in fact rotating at different angular velocities, we find no difference in the time to undergo motion fading. Thus, motion fading is driven by the perceived rather than actual angular velocity of a rotating stimulus.
View details for DOI 10.1016/j.visres.2010.03.023
View details for Web of Science ID 000278071800010
View details for PubMedID 20371254
The whole moves less than the spin of its parts
ATTENTION PERCEPTION & PSYCHOPHYSICS
2009; 71 (4): 675-679
When individually moving elements in the visual scene are perceptually grouped together into a coherently moving object, they can appear to slow down. In the present article, we show that the perceived speed of a particular global-motion percept is not dictated completely by the speed of the local moving elements. We investigated a stimulus that leads to bistable percepts, in which local and global motion may be perceived in an alternating fashion. Four rotating dot pairs, when arranged into a square-like configuration, may be perceived either locally, as independently rotating dot pairs, or globally, as two large squares translating along overlapping circular trajectories. Using a modified version of this stimulus, we found that the perceptually grouped squares appeared to move more slowly than the locally perceived rotating dot pairs, suggesting that perceived motion magnitude is computed following a global analysis of form. Supplemental demos related to this article can be downloaded from app.psychonomic-journals.org/content/supplemental.
View details for DOI 10.3758/APP.71.4.675
View details for Web of Science ID 000266258100002
View details for PubMedID 19429950
Therapeutic effects of a restraint procedure on posttraumatic place learning in fimbria-fornix transected rats
2008; 1217: 221-231
Restraint procedures have been shown to influence the neural processes in the brain (dendritic changes or changes in the expression of neurotrophines, etc.) as well as to alter the behavioural performance. While many report deleterious effects of this procedure in normal animals, there are also indications of positive effects in the context of brain injury. In order to address the issue from the perspective of functional posttraumatic recovery, we studied 6 experimental groups of rats--3 groups undergoing a fimbria-fornix transection, and 3 groups remaining neurally intact. Within the lesioned and intact groups, respectively, one group of animals was subjected to an 8-day long restraint procedure (2 h daily) that ended immediately prior to the infliction of trauma; another group was subjected to the same procedure starting immediately after the infliction of trauma; and one group was not subjected to the restraint procedure at all. After a brief period of postoperative pause, the animals were tested on their acquisition of an 8-arm radial maze based place learning task and the effects of the restraint procedure on the task acquisition were evaluated. The results show that within the neurally intact groups, the administration of this procedure had no effect at all. However, the lesioned groups that were subjected to the restraint procedure showed significantly improved acquisition of the studied task compared to the lesioned animals that did not undergo the restraint procedure. The improved task performance suggests a therapeutic effect of this manipulation on the functional recovery after a mechanical trauma.
View details for DOI 10.1016/j.brainres.2008.04.005
View details for Web of Science ID 000257636300023
View details for PubMedID 18501337