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Benjamin T. Backus, Ipek Oruç; Illusory motion from nonlinear response to contrast: how much does the visual system know about its own neuronal adaptation?. Journal of Vision 2004;4(11):43. doi: 10.1167/4.11.43.
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© ARVO (1962-2015); The Authors (2016-present)
In many visual mechanisms that adapt over time, the adaptation (change in neuronal firing rates) is not strictly internal to the mechanism, but is reflected in the neural code that the mechanism uses to transmit information elsewhere. In such cases, recipients of the information must know how the code has changed over time, if they are to read it accurately. Failure to do this may account for the striking percept of illusory motion in certain repeated asymmetric patterns (or RAPs) such as Kitaoka's (2003) image, Rotating Snakes, and Fraser & Wilcox's (1979) escalator illusion. We conducted experiments in which observers matched real motion to the illusory motion in static RAPs. An early, fast component of the illusory motion can be explained by the global-motion system's failure to compensate for known nonlinearities in early responses to contrast. A second, slow component may result from failure to compensate for slower neuronal adaptations to luminance and contrast. Movies in which real luminance changed over time, to mimic the hypothetical adaptations, evoked similar percepts of motion. Thus, whereas the pattern vision system evidently compensates for changes over time in the neural code for contrast, the global motion system does not. It is plausible that the global motion system normally need not compensate, if the statistics of natural patterns are such that the spurious local motion signals generated by adaptation to natural static images balance across space.
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