Poster Session A, Saturday, March 23, 1:30 pm - 3:30 pm, Pacific Concourse
Preserved shape sensitivity in the dorsal pathway of a visual agnosia patient
Erez Freud1, Marlene Behrmann2; 1York University, Toronto, ON, Canada, 2Carnegie Mellon University, Pittsburgh, PA, USA
Shape processing is a cornerstone for various perceptual behaviours such as object recognition, face perception and orthographic processing. For decades, these perceptual behaviours were considered to be and investigated as the product of one visual pathway- i.e. the ventral pathway. In contrast, the dorsal visual pathway was assumed to support the visuomotor control of objects. Importantly, however, recent research has revealed novel evidence for a contribution of the dorsal pathway to shape processing. An obvious outstanding question, then, is whether dorsal shape processing mechanisms are dissociable from computations carried out by the ventral pathway. To address this issue, we utilized a parametric scrambling manipulation that has been used successfully in healthy individuals (Freud, Culham, Plaut & Behrmann, 2017; eLife) to map the large-scale organization of shape processing mechanisms in a patient with object agnosia. As expected, neural indices of shape sensitivity along the ventral pathway were remarkably altered in the patient, particularly in regions proximal and anterior to the location of the injury. In contrast, shape sensitivity along the dorsal pathway was preserved and followed a similar topographical organization to that observed in controls. These findings were corroborated when the experiment was repeated two-years after the initial scans were acquired. Together, these findings challenge the binary segregation between the two visual pathways and suggest that the dorsal pathway derives shape representations, that might contribute to perception, independently of the ventral pathway.
Topic Area: PERCEPTION & ACTION: Vision