INFERIOR TEMPORAL MECHANISMS FOR INVARIANT OBJECT RECOGNITION

The specific size and retinal location of an object are readily percei ved, yet recognition of an object's identity is hardly affected by tra nsformations of its size or location. To explore how such stimulus tra nsformations are treated by known mechanisms for visual short-term mem ory in inferior temporal (IT) cortex, IT cells were recorded in monkey s performing a delayed matching-to-sample task. The stimuli were pictu res of complex objects, and the monkeys ignored differences in size an d retinal location when matching the test items to the sample held in memory. The sensory information communicated by cells was assessed in their responses to the sample stimuli, and mnemonic information was as sessed in their responses to the test stimuli. In the sensory domain, the ordering of relative stimulus preferences for nearly all cells was invariant over changes in size or location; however, some cells nonet heless preferred stimuli of a given size or location. In the mnemonic domain, the responses of many cells were modulated according to whethe r the test stimulus matched the sample held in memory, and these memor y effects were invariant over the relative sizes and locations of the stimuli. Thus, IT neuronal populations may mediate not only the recogn ition and memory of object identity, which are invariant over size and location, but also the perception of the transformations themselves.