Interactions between blue- and red-sensitive colour mechanisms in metacontrast masking

In metacontrast masking the apparent brightness of a brief flash of light is reduced by the subsequent presentation of a second flash in an adjacent but non-overlapping region of the visual field. This study is concerned with interactions between blue- and red-sensitive colour mechanisms (Stiles' π1 and π5 mechanisms respectively) in this effect. By suitable choice of the spectral compositions and intensities of the stimulus flashes and conditioning fields, the first (test) flash and second (masking) flash are arranged so that each effectively stimulates just one of these two colour mechanisms. Elevation in test-flash threshold is measured as a function of the delay in presentation of the masking flash. It is shown that metacontrast can be obtained with each combination of test- and masking-flash stimulus and that the temporal characteristics of the effect vary with the particular combination of π mechanisms involved. It is argued that the conclusions also hold for the signals generated by the short- and long-wavelength-sensitive cones subserving the two mechanisms. © 1979.