Study of the neural representation of different aspects of color perception in the inferior temporal cortex and the prefrontal cortex of the monkey

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Discrimination and categorization are two different aspects of our color vision. On the one hand, we can discriminate subtle difference in color; on the other hand, we categorize similar colors into a single group such as 'red'. To study the effects of these different aspects of color vision on the color coding in the inferior temporal cortex, we recorded neuronal responses in area TE of two Japanese monkeys trained a color categorization task and a color discrimination task. In both tasks, while the monkey was gazing at the fixation spot, a test stimulus was presented on the fovea. In color categorization task, fixation point and saccade point were shown after presentation of a test stimulus. Monkeys were trained to keep fixation when reddish color was presented and to make saccade, when greenish color was presented as test. In color discrimination task, two color stimuli (discrimination stimuli) were shown simultaneously after presentation of a test color. Monkeys were trained to make saccade toward the same color as the test. In both tasks, we used eleven test colors that were arranged at equal intervals from red to green. Monkeys were also trained a simple visual fixation task. Neurons were recorded from a sub-region in area TE where neurons have strong color selectivity, but little shape selectivity. Color selective neurons recorded from this region showed color tuning which was very similar across different tasks including categorization, discrimination and simple fixation. These results suggest that TE neurons code exact color information independent of the task demand.