Neuronal Bases of Color Categorization in Monkey Inferior Temporal Cortex

Abstract

Categorization and fine discrimination are two distinct aspects of our visual perception, both of which are clearly apparent in color vision. We can switch between these two modes of perception depending on the situation or task demands. To explore how visual cortical neurons behave in such situations, we recorded the activities of color-selective neurons in the inferior temporal (IT) cortex of two monkeys trained to perform a color categorization task, a color discrimination task and a simple fixation task. Many IT neurons changed their activity depending upon the task. A majority of neurons showed stronger responses during the categorization task. Moreover, for the population of IT neurons as a whole, signals contributing to performing the categorization task were enhanced. The task difference could be explained by the change in the response gain, indeed, the color selectivity was well conserved. These results imply that judgment of color category by color-selective IT neurons is facilitated during the categorization task and suppressed during the discrimination task as a consequence of task-dependent modulation of their activities.