Evoked potentials specific to spatial patterns of luminance and colour

Abstract

The human brain generated electrical responses (EPs) to changes in the chromatic contrast of an equiluminant spatially-patterned stimulus even when the eye's longitudinal and transverse chromatic aberrations were simultaneously cancelled. Pattern EPs were strongly affected by ocular chromatic aberration. EP and subjective estimates of longitudinal chromatic aberration agreed closely. Psychophysical contrast threshold correlated with the amplitudes of EPs elicited both by monochromatic patterns of checks and by equiluminant patterns of alternately-coloured checks or bars. Restricting stimulation to the fovea may enhance the effect of intersubject variations of neuroanatomy upon EPs. Physiological signals seem to be segregated into colour channels until the first responses to contrast. The EP data suggest that there is an antagonistically-organized chromati-contrast channel in parallel with colour-coded luminance-contrast channels. EP results suggest that the human visual system handles colour information differently when colour is linked with spatial form than when colour is not linked with form.