Motion of contrast envelopes: peace and noise

We examined the effect of changing the composition of the carrier on the pe rception of motion in a drifting contrast envelope. Human observers were re quired to discriminate the direction of motion of contrast modulations of a n underlying carrier as a function of temporal frequency and scaled (carrie r) contrast. The carriers were modulations of both color and luminance, def ined within a cardinal color space. Random-noise carriers had either binary luminance profiles or flat (gray-scale-white) or 1/f (pink) spectral power functions. Independent variables investigated were the envelope spatial fr equency and temporal-drift frequency and the fundamental spatial frequency, color, and temporal-update frequency of the carrier. The results show that observers were able to discriminate correctly the direction of envelope mo tion for binary-noise carriers at both high (16 Hz) and low (2 Hz) temporal -drift frequencies. Changing the carrier format from binary noise to a flat (gray-scale) or 1/f amplitude profile reduced discrimination performance s lightly but only in the high-temporal-frequency condition. Manipulation of the fundamental frequency of the carrier elicited no change in performance at the low temporal frequencies but produced ambiguous or reversed motion a t the higher temporal frequencies as soon as the fundamental frequency was higher than the envelope modulation frequency. We found that envelope motio n detection was sensitive to the structure of the carrier. (C) 2001 Optical Society of America.