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David F. Nichols, Howard S. Hock; A dynamical account of motion and non-motion perception for radial counterphase sine gratings. Journal of Vision 2002;2(7):387. doi: 10.1167/2.7.387.
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The perception of motion and non-motion were studied for radial counterphase sine gratings. The perception of stationary “spoke” patterns predominated at low contrasts, motion and non-motion percepts were bistable at intermediate contrasts, and motion predominated at higher contrasts. Motion could be perceived at temporal frequencies too high for attentional tracking and for presentations too brief for saccadic eye movements to imbalance competing clockwise (CW) and counter-clockwise (CCW) motion directions. The imbalancing of opposing motion detectors, which is the basis for perceiving only CW or only CCW motion, is attributable instead to: 1) random fluctuations in activation, and 2) inhibitory competition between the detectors suppressing the motion direction not favored by the random fluctuations (by pushing its activation below the threshold level required for perception). In an additional experiment, prior adaptation to a low contrast drifting grating (CW or CCW) resulted in increased motion perception for the counterphase grating and decreased detection of the grating. The increase in motion detection by adaptation was attributed to the reduction of inhibitory competition. Motion detection increased more at high contrasts than low contrasts, indicating mutual inhibition increases with activation. The activation-dependence of inhibition is inconsistent with accounts attributing the absence of motion perception to the cancellation of equal and opposite motion directions. It is argued instead that when motion is not perceived, it is either because the contrast of the grating is too low, or because of competition between motion- and pattern-detectors reducing motion detector activation below threshold (as indicated by the decrease in grating detection when motion perception was increased by prior adaptation).
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