Perceptual Effects of Delayed Cone-Opponent Signals from an Extended Surround Network: in Memory of Daniel J. Plummer

Cone signals in the luminance or achromatic pathway were investigated by measuring how the perceptual timing of M- or L-cone-detected flicker depended on temporal frequency and chromatic adaptation. Relative timings were measured by superimposing either M- or L-cone-isolating flicker on "equichromatic" flicker (of the same wavelength as the background) and asking the observer to vary temporal contrast and phase to cancel the flicker as a function of temporal frequency. Measurements were made in four observers on up to 35 different backgrounds varying in wavelength from 410 to 658 nm and in radiance. Observers showed substantial perceptual delays or advances of L- and M-cone flicker that varied systematically with cone class, background wavelength, and radiance. Delays were largest for M-cone isolating flicker. Although the results appear complex, they can be accounted for by a surprisingly simple model in which the representations of L- and M-cone flicker are comprised of not only a fast copy of the flicker signal, but also a slow copy that is delayed by roughly 30 ms and varies in strength and sign with both background wavelength and radiance. The delays, which are too large to be accounted for by selective cone adaptation on chromatic backgrounds, must be postreceptoral. Clear evidence for the slow signals can be found in physiological measurements of horizontal and magnocellular ganglion cells, thus placing the origin of the slow signals in the retina—most likely in an extended horizontal cell network. These results suggest that under some conditions luminance-equated stimuli chosen to isolate the chromatic channels inadvertently generate slow signals in the luminance channel. Meeting abstract presented at VSS 2018