Green, blue and short-wavelength-red rod hue biases are strongest and
most reliable with large, dimly-mesopic, extra-foveal stimuli but tend to
diminish when stimuli are confined to a small area of the central fovea.
This study explores how the stimulation of foveal and extra-foveal areas
interact in determining rod hue biases, and whether large stimuli are as
effective for revealing rod hue biases when foveally centered as when
eccentrically centered. We assessed rod influence by measuring wavelengths
of unique green and unique yellow (with 1-s duration, 1 log scot td
stimuli and a staircase procedure) under bleached and dark-adapted
conditions. We measured unique hues with foveally centered 2°- and
7.4°-diameter disks, a 7.4° (outer) × 2° (inner)
diameter annulus, and a 7°-eccentric, 7.4°-diameter disk. The rod
green bias (shift of unique yellow locus) was typically <10 nm and
remained fairly constant across spatial configurations, indicating no
special foveal influence. The rod blue bias (shift of unique green) varied
more among observers and spatial configurations, reaching up to 47 nm.
However, stimuli covering the fovea typically produced no rod blue bias.
Thus, the present results add differences in spatial dependence (i.e.,
foveal/extra-foveal interaction) between green and blue rod biases to
previously demonstrated differences (e.g., differences in amount of light
level dependence, in time course and in the spectral range influenced by