Effects of learning on color-form conjunction in macaque inferior temporal neurons.

Many neurons in area TE of the macaque respond selectively to colors or forms. One problem remaining is how these neurons contribute to conjunctive perception of these features when there are many objects in their receptive fields. In order to investigate the effects of learning on neural activities for the conjunction of color and form, neurons were recorded during a visual fixation task and two go/no-go visual discrimination tasks. One discrimination task involved conjunction of color and form for successively presented colored patterns. In this task, the monkeys were required to hold two "go" stimuli in the transient memory. The other task involved associative discrimination between the form of gray patterns and the color of irregular textures when the two features were presented simultaneously at separate locations. Each of the two stimuli was neutral in the go/no-go behavior in the latter task. One third of responsive neurons showed a significant interaction of color and form in response to the colored patterns during the conjunction task. Responses of these neurons were mostly enhanced for a particular colored pattern, which was usually one of the go stimuli. The response enhancement was preserved when the go stimulus was presented with a distractor. However, this change was not seen during the associative discrimination task. During the fixation task, the neurons that showed interaction of color and form in the conjunction task were usually selective either for the forms of gray patterns or colors of irregular textures, and only a few neurons were selective for both. The results indicate that neurons in area TE can conjoin color and form actively for an object held in the working memory, suppressing illusory conjunction.