Inferior temporal mechanisms for invariant object recognition.

The specific size and retinal location of an object are readily perceived, yet recognition of an object's identity is hardly affected by transformations of its size or location. To explore how such stimulus transformations are treated by known mechanisms for visual short-term memory in inferior temporal (IT) cortex, IT cells were recorded in monkeys performing a delayed matching-to-sample task. The stimuli were pictures of complex objects, and the monkeys ignored differences in size and 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 assessed 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 nonetheless preferred stimuli of a given size or location. In the mnemonic domain, the responses of many cells were modulated according to whether the test stimulus matched the sample held in memory, and these memory effects were invariant over the relative sizes and locations of the stimuli. Thus, IT neuronal populations may mediate not only the recognition and memory of object identity, which are invariant over size and location, but also the perception of the transformations themselves.