PURPOSE:The effects of metahue and metacontrast masking on the responses of the M- and P-pathways of the human visual system were investigated using temporal analysis of the multifocal flash visually evoked potential (VEP) (VERIS system). METHODS:The experiments were carried out at three achromatic luminance contrasts, 24, 70 and 96%, with three peripheral masks: a steady 65% grey mask, a grey flicker mask and an isoluminant red/green flicker mask. The stimuli were viewed monocularly and the mask and VERIS stimuli superposed with a mirror-aperture system. RESULTS/CONCLUSIONS:The masks had no significant effect on the behaviour of the M-pathway as stimulus contrast increased. The amplitude of the P-pathway was found to be approximately level at all contrasts of the stimulus and with all three masks rather than showing the expected steady increase in activity with increasing stimulus contrast.