Antiphase flicker induces depth segregation

We examined the influence of the temporal phase of flickering stimuli on perceptual organization. When two regions of a uniform random-dot field are flickered in temporal alternation with the same flicker rate, one of the regions appears to lie in front of the other. Within the range of temporal frequencies used in the present experiments, depth perception was maximal between 5 and 31.3 Hz. Which region of the two is perceived as lying in front is different from person to person and sometimes fluctuates within the same subject, but when two regions are of different sizes, the smaller region tends to be perceived in front for longer than the larger region. The depth segregation was not due to a luminance difference, because the average temporal luminance of the regions was kept equal. Strikingly, the illusory depth segregation is perceived even between two adjacent regions whose densities of dots, sizes, shapes, and flicker rates are identical. This result suggests that a difference of temporal phase between two flickering regions is crucial for this new depth perception.