Spatial resolution for the detection of pattern and movement (real and apparent)

Many investigators have studied contrast threshold for pattern and movement detection by using stimuli (lines or grating) modulated in time, but actually not moving (Kulikowski, 197 1; Keesey, 1972; Kulikowski and Tolhurst, 1973). This raised the question of how the threshold for this apparent movement is related to the threshold for real movement detection, since in general there are substantial differences between these two types of perceived movement (for review see Kolers, 1972). Levinson and Sekuler (1975) have examined the relationship between contrast thresholds for the detection of movement when gratings either drifted, or were modulated sinusoidally in time (sinusoidal contrast reversal) at the same temporal rate (between 4 and 8 c/s). Using a display whose luminance was 3.4cd/m2 they found the contrast threshold for a drifting grating was half that for a grating modulated sinusoidally over a range of spatial frequencies between 0.9 and 7c/deg. This suggests that the sinusoidal contrast reversal is detected by one of its two moving components, and it can be explained mathematically. According to a trigonometric identity