Abstract
Object perception by humans and other primates depends on the ventral pathway of visual cortex, which processes information about object structure, color, texture, and identity. Object information processing can be studied at the algorithmic, neural coding level using electrode recording in macaque monkeys. We have studied information processing in three successive stages of the monkey ventral pathway: area V4, PIT (posterior inferotemporal cortex), and AIT (anterior inferotemporal cortex). At all three stages, object structure is encoded in terms of parts, including boundary fragments (2D contours, 3D surfaces) and medial axis components (skeletal shape fragments). Area V4 neurons integrate information about multiple orientations to produce signals for local contour fragments. PIT neurons integrate multiple V4 inputs to produce representations of multi-fragment configurations. Even neurons in AIT, the final stage of the monkey ventral pathway, represent configurations of parts (as opposed to holistic object structure). However, at each processing stage, neural responses are critically dependent on the position of parts within the whole object. Thus, a given neuron may respond strongly to a specific contour fragment positioned near the right side of an object but not at all when it is positioned near the left. This kind of object-centered position tuning would serve an essential role by representing spatial arrangement within a distributed, parts-based coding scheme. Object-centered position sensitivity is not imposed by top-down feedback, since it is apparent in the earliest responses at lower stages, before activity begins at higher stages. Thus, while the brain encodes objects in terms of their constituent parts, the relationship of those parts to the whole object is critical at each stage of ventral pathway processing.
Meeting abstract presented at VSS 2012