Selective Temporal Interactions Between Processing Streams with Differential Sensitivity for Colour and Luminance Contrast

Temporal interactions between spatially separated visual stimuli were investigated in human observers. Subjects had to judge whether briefly presented targets consisted of a single or a double flash. Simultaneous presentation of unattended single or double flash distractors impaired performance if target and distractor followed different time courses, confirming previous findings. This interference occurred only when targets had high luminance contrast or were isoluminant and when distractors had high or low luminance contrast, but not when targets had low luminance contrast or when distractors were isoluminant. Low luminance contrast distractors strongly influenced high luminance contrast targets but not vice versa. These results suggest that (i) information about the precise temporal structure of stimuli is conveyed preferentially by the luminance-sensitive magnocellular system; and (ii) that this information influences judgements on the temporal patterning of signals transmitted by the colour-sensitive parvocellular system.