Shapiro et al. (2004) introduced a new
visual effect (the induced contrast asynchrony) that demonstrates a
perceptual separation between the response to a modulated light and the
response to contrast of the light relative to background. The effect is
composed of two physically identical disks, one surrounded by a dark
annulus and the other by a light annulus. The luminance levels of both
central disks were modulated in time, producing a stimulus with
in-phase luminance modulation and antiphase contrast modulation.
Observers primarily perceived the disks to be modulating asynchronously
(i.e. they perceived the contrast), but at low temporal frequencies
could also track the luminance level. Here we document that the induced
contrast asynchrony disappears when the surrounds are achromatic and
the center lights are modulated near the equiluminant axis. Observers
viewed 1-deg-diameter disks embedded 2-deg-diameter achromatic
surrounds. The chromaticity of the disks was modulated in time (1 Hz)
along lines in an S versus Luminance cardinal color plane and an L-M
versus Luminance cardinal color plane; observers responded as to
whether the modulation appeared in phase. For all observers and both
color planes, the lights appeared in phase most frequently at angles
near the standard observer's equiluminant line and out of phase at
angles further away from that line. Observers differed in the range of
angles that produce the appearance of in-phase modulation. The results
suggest that induced contrast asynchronies may be useful as a technique
for equating luminance of disparate lights.