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Qin Hu, Jonathan D. Victor; A set of high-order spatiotemporal stimuli that elicit motion and reverse-phi percepts. Journal of Vision 2010;10(3):9. doi: 10.1167/10.3.9.
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© ARVO (1962-2015); The Authors (2016-present)
Detection of motion is a crucial component of visual processing. To probe the computations underlying motion perception, we created a new class of non-Fourier motion stimuli, characterized by their third- and fourth-order spatiotemporal correlations. As with other non-Fourier stimuli, they lack second-order correlations, and therefore their motion cannot be detected by standard Fourier mechanisms. Additionally, these stimuli lack pairwise spatiotemporal correlation of edges or flicker—and thus, also cannot be detected by extraction of one of these features, followed by standard motion analysis. Nevertheless, many of these stimuli produced apparent motion in human observers. The pattern of responses—i.e., which specific spatiotemporal correlations led to a percept of motion—was highly consistent across subjects. For many of these stimuli, inverting the overall contrast of the stimulus reversed the direction of apparent motion. This “reverse-phi” phenomenon challenges existing models, including models that correlate low-level features and gradient models. Our findings indicate that current knowledge of the computations underlying motion processing is as yet incomplete, and that understanding how high-order spatiotemporal correlations lead to motion percepts will illuminate the computations underlying early motion processing.
Note: Entries indicate the normalized size of the motion signal generated by a mechanism that sums luminance within the glider, applies the indicated nonlinearity, and compares the resulting signal to a glider facing in the opposite direction. Positive values mean that the net average signal is in the centroid direction, negative values means that it is opposite to the centroid direction. Zero means that no motion signal is generated.
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