1/f -noise in human color vision : the role of S-cone signals

Abstract

We examine the functional role of S-cone signals on reaction time (RT) variability in human color vision. Stimuli were selected along red-green and blue-yellow cardinal directions and at random directions in the isoluminant plane of the color space. Trial-totrial RT variability was not statistically independent but correlated across experimental conditions, and exhibited 1/f-noise spectra with an exponent close to unity in most of the cases. Regarding contrast coding, 1/f-noise for random chromatic stimuli at isoluminance was similar to that for achromatic stimuli, thus suggesting that S-cone signals reduce variability of higher-order color mechanisms. If we regard spatial coding, the effect of Scone density in the retina on RT variability was investigated. The magnitude of 1/f-noise at 16 min of arc (S-cone free zone) was higher than at 90 min of arc in the blue-yellow channel and it was similar for the red-green one. The results suggest that S-cone signals are beneficial and they modulate 1/f-noise spectra at postreceptoral stages. The implications related to random multiplicative processes as a possible source of 1/f-noise and the optimal information processing in color vision are discussed.