The role of the blobs in determining the perception of drifting plaids and their motion aftereffects.

Motion aftereffects (MAEs) can be induced by adaptation to a pair of differently oriented drifting gratings whether the gratings are presented simultaneously, as a coherent plaid, or in alternation. The fact that the former MAEs were generally larger than the latter led to the suggestion that simultaneous adaptation involved higher-level extrastriate processes not involved in the alternating effects. In the past few years evidence has accumulated that the difference is in fact due to a low-level monocular process which can be termed the 'blob-tracking mechanism'. A review is presented of the evidence on MAEs induced by simultaneous and alternating adaptation, the evidence for the monocularity of the blob-tracking mechanism, the data which implicate the blob mechanism in the determination of MAE magnitude, perceived plaid drift direction, and in perceived plaid coherence.