Action of Red-sensitive Colour Mechanism on Blue-sensitive Colour Mechanism in Visual Masking

In the visual masking effect, metacontrast, the perceived brightness, of a flash of light is reduced by the presentation of a second flash in an adjacent region of the visual field . A metacontrast masking interaction between different colour mechanisms is examined in the present study . The spectral compositions and intensities of the stimuli are chosen so that the first (test) flash preferentially stimulates the blue-sensitive colour mechanism and the second (masking) flash preferentially stimulates the red-sensitive colour mechanism . Elevation in test-flash threshold is measured as a function of delay in presentation of the masking flash and an interaction effect shown to occur at both positive and negative masking-flash delays . In a series of papers [1-4], Stiles developed a theory of colour-response mechanisms which was based on measurements with the two-colour threshold method . In these measurements it was supposed that these mechanisms operated independently of one another . Subsequent investigations by a number of authors using other stimulus conditions showed that in some cases [5-9] this independence of mechanism function is preserved, and that in other cases [10-17] it is not . This note is concerned with the effect of one colour mechanism upon another in the masking phenomenon known as metacontrast [18-20], where the perceived brightness of a flash of light (the test flash) is reduced if it is followed a short time later by a second flash (the masking flash) in an adjacent region of the visual field. Metacontrast masking depends not only on the geometry and time course of the stimuli [18-20], but also on the properties of the receptor mechanisms stimulated [21, 22] . Alpern and Rushton [5] performed a metacontrast experiment in which the test-flash threshold was determined as a function of the luminance of the masking flash, the interval between the onsets of the flashes being fixed . They showed that the red, green, and blue-sensitive mechanisms (Stiles' 7r5 , r4 and Tr i mechanisms respectively) did not interact . In similar study, however, Yellott and Wandell [15] obtained results indicating that metacontrast masking does not necessarily take place within a single 7T mechanism . In the present work a metacontrast interaction between two different colour mechanisms is shown explicitly . The test flash is made to preferentially excite the blue-sensitive Tri mechanism and the masking flash made to preferentially excite the red-sensitive 7r5 mechanism . The elevation in test-flash threshold is determined as a function of the time-lag between the onsets of the flashes . D ow nl oa de d by [ T he U ni ve rs ity o f M an ch es te r] a t 1 0: 35 2 1 Se pt em be r 20 11