Adaptation state of the local-motion-pooling units determines the nature of the motion aftereffect to transparent motion

When observers adapt to a transparent-motion stimulus, the resulting motion aftereffect (MAE) is typically in the direction opposite to the vector average of the component directions. It has been proposed that the reason for this is that it is the adaptation state at the local-level (i.e. of the local-motion-pooling units) that determines the nature of the MAE (Vidnyanszky et al. Trends in Cognitive Sciences, 6(4), 157-161). The adapting stimuli used in these experiments typically consisted of random-dot kinematograms, with each dot being able to move over the entire viewing aperture. Here we used spatially-localised global-plaid stimuli which enabled us, over the course of adaptation, to present either one of both motion directions at each local region. A unidirectional MAE was perceived when two motion directions were presented at each location and a transparent MAE was perceived when a single direction was presented. These results support the notion that it is the adaptation state at the local-motion-pooling level that determines the nature of the MAE to transparent motion stimuli.