Forward and backward masking with brief chromatic stimuli

Visual masking typically occurs when mask and target are separated in time by less than 100 ms, and the form of this interaction might be expected to depend on the latency of the target and mask signals. We track psychophysically the time course of signals from the two colour-opponent channels by using forward and backward masking, in which mask and target each stimulate only one colour channel. Stimuli resemble those used in the Cambridge Colour Test,1 in that spatial luminance noise is used to ensure that neither edge artifacts nor luminance differences can be used as a cue to discrimination of the stimulus against the field. Additionally, we introduce temporal luminance noise in order to ensure that our very brief chromatic modulations are not detected via the magnocellular pathway. Our data suggest that there is no large latency difference between the two chromatic channels of the early visual system, and that previous evidence for such a difference may instead reflect a difference between chromatic and achromatic pathways. © 2000 John Wiley & Sons, Inc.