Representation Of DKL Color Space In Macaque Early Visual Cortex

Color is a personal perception of the wavelength of light,which has a special significance for humans.Humans and macaques receive the light of long,medium,and short wavelengths through three types of retinal cone cells.Yet the representation of color at later stages of the visual system cannot be described by a simple linear combination of cone signals.It depends on processing in multiple cortical areas to transform the cone signals into perceptual colors.In the ventral visual pathway where cortical areas process color,there are color-sensitive cells preferring various hues,which cluster into functional color modules.Research has found that similar hues activated similar cortical regions in color modules.Cortical color representations are organized corresponding to a pattern of hue similarity.However,previous studies of color representations in different brain regions have used color stimuli defined in different color spaces for each study,making it hard to understand the similarities and differences of the color representations in cortical areas.To study the questions,we used intrinsic signal optical imaging to record the color responses of macaque V1,V2,and V4 simultaneously and these color visual stimuli were designed in retina cone-based color space(DKL color space).We performed color decoding by multivariate pattern analysis and measured the size and location of color response regions to examine the difference of these cortical areas in terms of the amount of color information and the spatial organization of local color representations.Using multivariate pattern analysis,we found that similar colors in color space had similar cortical representations.The color representations of V2 and V4 differentiated colors more effectively than V1.Image analysis of ISOI signals showed that V2 and V4 have larger functional color modules(hue clusters)than V1.We examined the confusion matrices and the overlap patterns of the color patches by representational similarity analysis and found that the overlap patterns of the smaller functional hue modules(hue patches)in V1 reflected less information about color representation than V2 and V4.Our results suggest that color information is gradually processed in different stages of the early visual cortex and higher visual areas of the cortex express more color information by the spatial overlap pattern of the hue patches.