Abstract
Recent electrophysiological studies in primates and fMRI studies in human have indicated the existence of neurons in the visual cortex that selectively respond to hues off the cardinal axes of cone-opponent color space (intermediate colors). However, it is unclear when and how the hue selectivity develops in the early developmental stage of the visual system. In the present study, we measured hue selectivity of brain activity in infants using steady-state visual evoked potentials (SSVEPs). Infants observed the reversals of a checkerboard pattern during the measurement. Half of the tiles of checkerboard were filled with the background hue (Equal Energy White) and the rest of them were filled with a test hue. Twelve test hues were chosen from a hue circle, which had a color contrast of ∆L = 8 % and ∆S = 80 % with respect to the background color, in an equiluminant plane defined by the cone-opponent color space (Macleod & Boynton, 1979). To yield SSVEP responses, the pattern flipped at 5 Hz during a 5 seconds testing trial. The test hue changed every second along the hue circle during the measurement. Fourteen 5-6-months old infants participated in the study. The SSVEP response amplitudes in infants were assessed by a model that assumes that the responses of intermediate hues are the sum of responses of two nearby cardinal mechanisms. Our results revealed that infant’s SSVEP responses were more likely to be dominated by cone-opponent representation, in contrast to adults’ SSVEP responses in which amplitudes were significantly larger in intermediate hues (magenta and lime-green; Kaneko, Kuriki & Andersen, 2020). Meanwhile, average SSVEP amplitude showed a biased response along the red/green cardinal axis, which is also different from adults. This bias could result from the faster development of red/green cardinal mechanism (Teller, 1998).