Doctor of Philosophy, Vanderbilt University (2017)
Bachelor of Arts, Stanford University, PSYCH-BAH (2009)
Resolving the spatial profile of figure enhancement in human V1 through population receptive field modeling.
The Journal of neuroscience : the official journal of the Society for Neuroscience
The detection and segmentation of meaningful figures from their background is one of the primary functions of vision. While work in non-human primates has implicated early visual mechanisms in this figure-ground modulation, neuroimaging in humans has instead largely ascribed the processing of figures and objects to higher stages of the visual hierarchy. Here, we used high-field fMRI at 7 Tesla to measure BOLD responses to task-irrelevant orientation-defined figures in human early visual cortex (N = 6, four females). We employed a novel population receptive field (pRF) mapping-based approach to resolve the spatial profiles of two constituent mechanisms of figure-ground modulation: a local boundary response, and a further enhancement spanning the full extent of the figure region that is driven by global differences in features. Reconstructing the distinct spatial profiles of these effects reveals that figure enhancement modulates responses in human early visual cortex in a manner consistent with a mechanism of automatic, contextually-driven feedback from higher visual areas.Significance Statement:A core function of the visual system is to parse complex 2D input into meaningful figures. We do so constantly and seamlessly, both by processing information about visible edges and by analyzing large-scale differences between figures and background. While influential neurophysiology work has characterized an intriguing mechanism that enhances V1 responses to perceptual figures, we have a poor understanding of how the early visual system contributes to figure-ground processing in humans. Here, we use advanced computational analysis methods and high-field human fMRI data to resolve the distinct spatial profiles of local edge and global figure enhancement in the early visual system (V1 and LGN); the latter is distinct and consistent a mechanism of automatic, stimulus-driven feedback from higher-level visual areas.
View details for DOI 10.1523/JNEUROSCI.2377-19.2020
View details for PubMedID 32139585
Figure-Ground Modulation in the Human Lateral Geniculate Nucleus Is Distinguishable from Top-Down Attention.
Current biology : CB
Nearly all of the information that reaches the primary visual cortex (V1) of the brain passes from the retina through the lateral geniculate nucleus (LGN) of the thalamus. Although the LGN's role in relaying feedforward signals from the retina to the cortex is well understood [1, 2], the functional role of the extensive feedback it receives from the cortex has remained elusive [3-6]. Here, we investigated whether corticothalamic feedback may contribute to perceptual processing in the LGN in a manner that is distinct from top-down effects of attention [7-10]. We used high-resolution fMRI at 7 Tesla to simultaneously measure responses to orientation-defined figures in the human LGN and V1. We found robust enhancement of perceptual figures throughout the early visual system, which could be distinguished from the effects of covert spatial attention [11-13]. In a secondexperiment, we demonstrated that figure enhancement occurred in the LGN even when the figure and surrounding background were presented dichoptically (i.e., to different eyes). As binocular integration primarily occurs in V1 [14,15], these results implicate a mechanism of automatic, contextually sensitive feedback from binocular visual cortex underlying figure-ground modulation in the LGN. Our findings elucidate the functional mechanisms of this core function of the visual system [16-18], which allows people to segment and detect meaningful figures in complex visual environments. The involvement of the LGN in this rich, contextually informed visual processing-despite showing minimal feedforward selectivity for visual features [19, 20]-underscores the role of recurrent processing at the earliest stages of visual processing.
View details for DOI 10.1016/j.cub.2019.04.068
View details for PubMedID 31178323
Functionally defined white matter reveals segregated pathways in human ventral temporal cortex associated with category-specific processing.
2015; 85 (1): 216-227
It is unknown if the white-matter properties associated with specific visual networks selectively affect category-specific processing. In a novel protocol we combined measurements of white-matter structure, functional selectivity, and behavior in the same subjects. We find two parallel white-matter pathways along the ventral temporal lobe connecting to either face-selective or place-selective regions. Diffusion properties of portions of these tracts adjacent to face- and place-selective regions of ventral temporal cortex correlate with behavioral performance for face or place processing, respectively. Strikingly, adults with developmental prosopagnosia (face blindness) express an atypical structure-behavior relationship near face-selective cortex, suggesting that white-matter atypicalities in this region may have behavioral consequences. These data suggest that examining the interplay between cortical function, anatomical connectivity, and visual behavior is integral to understanding functional networks and their role in producing visual abilities and deficits.
View details for DOI 10.1016/j.neuron.2014.12.027
View details for PubMedID 25569351
View details for PubMedCentralID PMC4287959