Effect of stimulus perspective on perception of oscillation.

8 groups of subjects, 10 per group, had 10 trials for each of two perceptual tasks. Subjects in each group viewed a rotating trapezoid at a constant speed at equal-interval angles of tilt (0 degrees, 30 degrees, 60 degrees, 90 degrees) and two directions of stimulus tilt (toward observer and parallel to observer). It was predicted that most reports of oscillatory perception would occur for parallel tilt at 0 degree and 90 degree angles of orientation. In addition, there would be a hypothesized decrease in perceived oscillations from 0 degrees to 90 degrees when the stimulus was tilted toward the observer. Both direction of stimulus tilt and angle of orientation were significant. Post hoc comparisons yielded reliable differences from the parallel tilt and tilt toward the observer. The evidence supports the position that veridical information processing in the trapezoid oscillatory illusion is a joint function of signal-detection capability and availability of perceptual cues.