Do rods influence the hue of foveal stimuli?

Abstract

To understand the generality and mechanisms of previously reported rod hue biases, we examined whether they are present for small foveal stimuli by comparing the wavelengths of the three spectral unique hues under dark-adapted and flash-bleached conditions. Rod green bias~shift of unique yellow! and rod blue bias~shift of unique green! were found for some observers with 18-diameter foveal stimuli, the size most likely to stimulate rods. Smaller stimuli~0.28 and 0.68 diameter!, which were least likely to stimulate rods, produced no large or consistent differences between dark-adapted and bleached conditions. This suggests that rod hue biases result from the local stimulation of rods by light, not from remote suppression by dark-adapted, unstimulated rods, and not from bleaching light artifacts.

Rod hue biases for foveal stimuli on CRT displays

“…On the other hand, neither the present study nor a prior study [8] shows rod red bias to be more likely for larger foveal stimuli that would be expected to stimulate more S cones. Indeed, the two present instances of small but reliable rod red bias were both for the smaller 0.5° test stimulus, which would be expected to stimulate fewer S cones than would the 2° stimulus.…”

“…This foveal rod green bias was observed in a higher proportion of observers than in prior foveal studies [7,8,10]. Likely, our testing of a larger number of observers—eight compared to three in the prior studies—provided a more precise incidence estimate and reduced the role of chance sampling distortions.…”

“…Indeed, several studies have reported not finding foveal rod hue biases (e.g., [6]). However, some evidence of rod hue biases was reported in two older studies [7,8]. Unfortunately, these studies employed few observers (three per study), tested for rod influence on only two of the four unique hues (green and yellow), and produced results that varied among individual observers.…”

How Do Things Look to the Color-Blind?

“…experiments is not straightforward it may be the case that inputs from the rods are capable of driving an extra color channel (Buck et al 2006). For reasons of space we will set these complications aside.…”

Rod hue biases produced on CRT displays

“…However, various investigators have shown that, at mesopic light levels, stimulation of rod photoreceptors can shift (bias) the perceived hue of a light that also stimulates cone photoreceptors [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. We have previously shown that rod signals influence the balance of both red-green and blue-yellow opponent hue dimensions, and that there are at least three separable rod hue biases: a green bias (rods strengthen green versus red) at longer wavelengths, a blue bias (rods strengthen blue versus yellow) at middle wavelengths, and a red bias (rods strengthen red versus green) at short wavelengths [20][21][22][23][24][25][26][27][28][29][30][31][32].…”