Left middle frontal gyrus represents color categories but not metric differences in color; evidence from fMRI adaptation.

摘要

The network of brain areas that support color vision has been known for some time. However, the areas of the brain that code color categorically have not yet been reliably identified. We used fMRI adaptation to identify neuronal populations that represent color categories irrespective of metric differences in color. FMRI adaption is a decrease in BOLD response due to repetitions of a stimulus that is represented by a population of neurons. Square stimuli were centrally presented on a calibrated MRI screen, and the color of the square changed pseudo-randomly 6 times between 2 colors within a 9.6 second block. The 2 colors were either from the same or different categories (e.g., a??blue 1 and blue 2a?? or a??blue 1 and green 1a??), and the difference in CIE hue angle was varied so that there were small (26.37?°) or medium (52.74?°) or large (79.11?°) chromatic differences. Participants were engaged in a target detection task that was unrelated to the color of the squares (task required detecting a luminance change in one of the squares; targets appeared in 12.5% of blocks). Despite the fact that color was irrelevant to the task, fMRI adaption for color category was present in the middle frontal gyrus in the left hemisphere. Specifically, BOLD response was reduced for repetitions of colors from the same category relative to colors from different categories. Importantly, fMRI adaptation in this region was not modulated by the size of the color difference. The results indicate that neurons in the left middle frontal gyrus represent color categorically regardless of metric color differences. These findings extend our understanding of how the brain processes color, and also have implications for understanding the metric and categorical coding of visual information more broadly.