CONTRAST SENSITIVITY OF THE MOTION SYSTEM

A number of experiments were conducted to investigate how global-motio n performance varies with luminance contrast. When all the dots in the stimulus were the same contrast, performance improved with increasing contrast up to about the 15% level (Experiment 1). Increasing the con trast beyond this level had no additional effect on performance. When the contrast of a subgroup of the dots was varied, differential effect s on performance could be obtained for contrasts up to the 80% level ( Experiment 2). These results are interpreted as indicating that the pe rformance saturation observed in Experiment 1 was due to the attainmen t of a performance ceiling at the global-motion level, and not due to contrast-response saturation of the underlying local-motion detectors. The results of earlier studies that have apparently found conflicting results (saturation vs no saturation) are discussed in light of the p resent results. Copyright (C) 1996 Elsevier Science Ltd.