| Popis: |
The inferotemporal cortex in primates is thought to be the primary region that subserves object recognition. The studies presented here help to elucidate the role of IT in higher visual processing by addressing three specific outstanding issues. In the first study, we sought to determine whether IT neurons respond similarly to patterns that are perceptually confused. We considered a behavioral phenomenon whereby lateral mirror images are confused more frequently than vertical mirror images. By presenting mirror images to the monkey while simultaneously recording from IT neurons, we found that neurons differentiate less effectively between lateral mirror images than between vertical mirror images. This phenomenon may underlie the perceptual confusion documented in behavioral studies. In the second study, we sought to determine whether activity in IT reflects experience-based changes in perception. We tested this by first training monkeys to discriminate shape orientation. We then recorded from IT neurons while monkeys performed an orientation discrimination task with trained orientations, and passively viewed orientations of trained and untrained shapes. We found that training to discriminate between orientations of a shape significantly increases the ability of IT neurons to discriminate between those same orientations. This neuronal selectivity correlated with the monkeys ability to discriminate orientation. These data suggest that training-induced changes in perception are supported by processes in IT. Some IT neurons respond to the onset of a visual stimulus by firing a series of bursts at a frequency of around 5 Hz. One explanation for this phenomenon is that stimuli in the visual scene compete, with alternating success, for processing resources in IT. In the third study, we tested this by examining the oscillatory activity of IT neurons in response to the presentation of multiple stimuli, a central preferred image and a peripheral non-preferred image. We observed that the onset of a central pattern in the presence of the peripheral stimulus elicited strong oscillations phase-locked to pattern-onset. Onset of the peripheral stimulus in the presence of the central pattern elicited a succession of inhibitory troughs phase-locked to stimulus-onset. These results are congruent with a model of mutual inhibition of competing neuronal populations. |
