A ROLE FOR A LOW-LEVEL MECHANISM IN DETERMINING PLAID COHERENCE

A number of recent studies have suggested that the ''intersection of c onstraints'' model of two dimensional motion perception, put forward b y Adelson and Movshon [(1982) Nature, 300, 523-525], is incomplete. Ev idence has been mounting that there is a second two-dimensional motion sensitive mechanism which is monocular and which appears to respond d irectly to the movement of the intersections (or ''blobs'') in a two-d imensional image. The current study extends these findings by demonstr ating that the perceived coherence of a drifting plaid is largely unde r the control of a monocular mechanism. Prior exposure to a similarly drifting grating or plaid substantially raises the coherence threshold of a test plaid only if the same eye is adapted and tested. The thres hold elevation is much more modest if the test plaid is presented to t he unadapted eye, suggesting that coherence judgements are primarily b ased on the activity level of a monocular process-possibly the ''blob tracking mechanism''. The results of Expt 2 suggest the possibility th at this monocular mechanism is inhibited by binocular exposure.