| Our research focuses on shape representation in the ventral, object-processing pathway of primate visual system, which includes areas V1 (primary visual cortex), V2, V4, and higher levels in the inferior temporal cortex. This pathway functions to represent, interpret, store, and recall information about visual objects, and thus underlies much of our ability to recognize other individuals, interpret their facial expressions, comprehend symbolic written information, and to identify and interact appropriately with objects in the environment. These impressive feats of visual information processing imply complex neural mechanisms that far surpass any artificial systems yet devised.
The nature of these neural mechanisms remains largely unknown. We are studying how shape information is represented by large populations of cells at various stages in the ventral visual pathway. Our results show that shapes are represented in terms of their component parts such as boundary curvature, medial axis conformation, and relative position of shape components. A given cell, for example, might respond to all shapes that contain downward-pointing convex projections near the right. These tuning properties can be characterized with mathematical functions in high-dimensional shape space, which allows us to reconstruct the population representation of any given shape by combining signals from large populations of cells. In this way we can “read out” the neural code for object shape from the response rates of neurons. While most cells appear to represent 2-dimensional shape information, we have also found that some cells represent the orientation of 3-dimensional edges and lines in visual images. In the future we plan to study more complex aspects of 3-D shape representation. |
