Color information is conveyed from the retina through lateral geniculate nucleus (LGN) to visual cortex. Color selectivity of neurons in LGN is well described by difference of cone inputs, whereas that in cortical visual areas is more complicated. Numerous studies investigated color selectivity in early visual stages using Derrington-Krauskopf-Lennie(DKL)color space (Derrington et al. 1984; Lennie et al, 1990). Since DKL color space is based on cone signals, cone contrast of stimulus can be kept constant. However, limitation of this color space is that color is always presented at low saturation. CIExy chromaticity diagram is typically used to measure neural response at high saturation. There are color selective neurons sharply tuned for colors with high saturation in higher cortical areas such as V4 and IT (Komatsu et al., 1992; Kotake et al., 2009).
To understand how neural representation of color is transformed through visual pathway, it is important to use common color space across areas. Since CIExy color space have richer information, it is quite useful if color tuning curve in DKL space can be estimated by responses obtained in CIExy space. Since it is not clear weather color selectivity measured in DKL space matches that in CIE color space in single neuron level, we directly examined this question in the present study.
Single neuron activities were recorded from area V4 while monkeys were performing fixation task. Color selectivity was measured using two different stimulus set in separate blocks. The first set (CIE set) consisted of 62 colors that systematically distributed in the gamut on CIExy chromaticity diagram whereas 32 colors were evenly selected on equiluminat plane in DKL color space in the second stimulus set (DKL set). To compare the selectivity in the two color spaces, DKL color tuning curve was estimated by linearly interpolating the response in the CIE set, and then correlation coefficient was computed between measured and estimated DKL color tuning curves. These two color tuning curves generally matched in most of color selective neurons (median r=0.8, N=38). This result indicates that color selectivity in DKL color space can be predicted from responses in the CIExy space.