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Jaap A. Beintema, Wouter Halfwerk, Richard J. A. Wezel; Less rivalry with more biological motion. Journal of Vision 2004;4(8):241. doi: https://doi.org/10.1167/4.8.241.
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An influential theory on binocular rivalry proposes that the alternation frequency increases with the stimulus strength in each eye (Levelt 1966), where stimulus strength relates to the amount of contour or luminance contrast. In that rivalry study, stimuli are simple of nature. Here, we examined rivalry between biological motion patterns, which presumably involve higher cortical structures. Each eye's fovea was presented a point-light walker that walked in place, but had opposite walking direction and contrast polarity to evoke a non-patchy alternation of percepts. We recorded the alternations in perceived polarity (black or white) as a function of walker velocity (slow, natural or fast walking speed). To see how much data was explained by local motion rivalry, we included stimuli with the same spatial extent and local motions, but of less biological nature: a motion pattern that was inverted (upsidedown walker) or scrambled (position and phase of walker's joints randomised). In a first experiment, we found that walking speed affected the alternation frequency. Specifically, with slower walking speed, the alternation frequency for rivalling normal walkers dropped below that for inverted and scrambled motion. Thus, in addition to local rivalry mechanisms, also biological motion influences the temporal characteristics of rivalry, but in a way opposite to that expected from Levelt's theory. In a second experiment, using the slow velocities only, we found that the detectability of a flash in the suppressed eye systematically decreased with less biological motion patterns. In summary, we find an increased suppression and decreased alternation duration for motion patterns that are less recognizable as human walkers. This suggests that cortical areas involved in biological motion perception play an essentially different role in binocular rivalry than lower cortical areas.
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