Motion perception over long interstimulus intervals


Bex PJ, Baker CL. Motion perception over long interstimulus intervals. Perception & Psychophysics [Internet]. 1999;61 :1066–74.


Recent studies using moving arrays of textured micropatterns have suggested that motion perception can be supported by two mechanisms, one quasilinear and sensitive to the motion of luminance-defined local texture, the other nonlinear and coding motion of contrast-defined envelopes of texture (Baker & Hess, 1998; Boulton & Baker, 1993b). Here we used similar patterns to study motion perception under conditions previously shown to isolate the nonlinear mechanism (low micropattern densities and positive interstimulus intervals [{ISIs].} We measured direction discrimination for two-flash apparent motion over a much larger range of {ISIs}, and susceptibility to masking by incoherently moving "distractor" micropatterns. The results suggest that two nonlinear mechanisms can support motion perception under these conditions. One operates only for relatively short {ISIs} (less than c. 100 msec), is sensitive to small spatial displacements, and is relatively insensitive to distractor masking. The other operates over much longer {ISIs}, is insensitive to small spatial displacements, and is highly disrupted by distractor masking. These results are in line with previous studies suggesting that three mechanisms support motion perception.