Relationships between the activities of color selective neurons in the inferior temporal cortex of the monkey and color discrimination behavior

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On the basis of lesion or electrophysiological studies, it is suggested that area TE (anterior part of IT), which is the highest area in the ventral stream of visual information processing, plays an important role for information processing of color.To study whether there exists dose link between color selective responses of TE neurons and perception, we examined the correlation between monkey's color judgment and responses of color selective TE neurons. We trained a fine color discrimination task in two monkeys and recorded single neuron activities from the color-sensitive sub-region in area TE. In this task, a sample color stimulus was presented at the confer of the display, and the monkey had to make either the rightward or leftward saccade depending on the similarity of the sample color to the two target colors. Two target colors were determined based on the color selectivity of each neuron such that one target color (preferred target color) evoked stronger response than the other … More color (non-preferred target odor). Sample color in each trial was chosen from seven colors equally spaced between the target colors on the CIE-xy chromaticity diagram. First, we quantitatively compared the color discrimination abilities of neurons and the monkeys. To calculate the discrimination ability of the neuron, we computed neurometric function by ROC analysis based on the assumption that neural responses to the center color of sample color set are used as the reference for the color judgment. We then compared neural threshold based on the neurometric function and behavioral threshold based on the psychometric function as the color separation which yielded 80% correct color judgments. We found that in general neural threshold was lower than the behavioral threshold although in some neurons both are comparable. Variation of the neural threshold across the color space corresponded well with that of behavioral threshold. We then calculated the Choice Probability (CP) that is a quantitative measure of correlation between trial-to-trial fluctuation of neural responses and the monkey's color judgment. We found that CP are on average larger than 0.5 and this is consistent with the expectation that the activities of these TE neurons positively correlate with the monkey's color judgment. Finally, we found that there is little correlation between the neural threshold for color discrimination and CP. This suggests that a large population of color selective TE neurons having various color sensitivity rather than a specific subset of neurons with particularly high color sensitivity contribute to the color discrimination performance. Less