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George Sperling, Peng Sun; Defining and discriminating perceptual systems that extract the direction of visual motion.. Journal of Vision 2018;18(10):1061. doi: 10.1167/18.10.1061.
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© ARVO (1962-2015); The Authors (2016-present)
Different motion systems are defined by the complexity of preprocessing of visual input prior to the motion extraction computation. Motion extraction itself seems to be functionally similar, just with different parameters, for the different systems. A common view is that humans have a fast Fourier-based motion extraction system and a more complex non-Fourier system. The input to the Fourier system (here designated as the 1st-order system) is the normalized input stimulus filtered into oriented spatial frequency bands, modeled as pairs of yoked V1 simple cells in which one member of the pair represents positive scontrasts and the other, negative contrasts. The non-Fourier motion system actually comprises two different systems: A second-order system who's input is local contrast energy--essentially the local variance (absolute value) of the input to 1st-order, and a third-order system who's input is a figure-ground map or, more accurately, a salience map. Normally, the three systems combine their outputs. Because of the great complexity of early visual processing, one cannot specify exactly which visual stimuli stimulate which motion systems; however, there are sufficient constraints that this can be determined for specially designed visual stimuli. The three systems are defined by their input computation; they are distinguished in five ways: different temporal frequency tuning functions, different central-versus-peripheral sensitivity, oppositely directed motion aftereffects at the same retinal location, selective adaptation, and best, by phase dependence/independence: Two weak sinewave stimuli of the same spatial frequency, temporal frequency, orientation, and motion direction, exhibit both phase-dependent cancellation and enhancement when they are delivered to same system, but only phase-independent enhancement when delivered to different systems. Demonstrations: Ambiguous, oppositely-directed motion stimuli that produce perception of the higher-order direction in the fovea, the lower-order direction in periphery; new barber-pole and plaid-motion illusions that are explained by relative contributions of the different systems.
Meeting abstract presented at VSS 2018
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