Abstract
We observed that two disparity — defined depth planes were perceived at a single depth when disparity alternated rapidly between two values. We investigated quantitatively how depth of the plane depended on the temporal frequency of disparity. We alternated the two disparity values between 9 Hz and 35 Hz, which is above the limit of stereomotion. We used two types of dynamic random — dot stereograms. In one stereogram, a single pattern alternated between two disparity values. In the other stereogram, we alternated two uncorrelated patterns each having one of the two disparity values. We employed a depth discrimination task between the plane with alternating disparity and a plane with constant disparity presented against a static background. The psychophysical results show that the perceived depths depend on the type of stereogram: i) temporal averaging of depth occurs in the temporally correlated stereogram; ii) depth is always close to one of the two depths values that are associated with alternated disparities of the temporally uncorrelated stereogram. We speculate that the differences are caused by the involvement of monocular coherent motion signals in stereoscopic depth perception.