A TRANSPARENT MOTION AFTEREFFECT CONTINGENT ON BINOCULAR DISPARITY

Under transparent motion conditions overlapping surfaces are perceived simultaneously, each with its own direction. The motion aftereffect ( MAE) of transparent motion, however, is unidirectional and its directi on is opposite to that of a sensitivity-weighted vector sum of both in ducing vectors. Here we report a bidirectional and transparent MAE con tingent on binocular disparity. Depth (from retinal disparity) was int roduced between two patterns. A fixation dot was presented at zero dis parity, that is, located between the two adaptation patterns. After ad aptation to such a stimulus configuration testing was carried out with two stationary test patterns at the same depths as the preceding movi ng patterns. For opposite directions a clear transparent MAE was perce ived. However, if the adaptation directions were orthogonal the chance of a transparent MAE being perceived decreased substantially. This wa s subject dependent. Some subjects perceived an orthogonal transparent MAE whereas others saw the negative vector sum-an integrated MAE. In addition the behaviour of the MAE when the distance in depth between a dapting and test patterns was increased was investigated: it was found that the visibility of the MAE then decreased. Visibility is defined in this paper as: (i) the percentage of the trials in which MAEs are p erceived and (ii) the average MAE duration. Both measures decreased wi th increasing distance. The results suggest that segregation and integ ration may be mediated by direction-tuned channels that interact with disparity-tuned channels.