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Jin Qian, Harold Bedell; Perceived direction of motion and depth of missing fundamental gratings. Journal of Vision 2007;7(9):816. doi: 10.1167/7.9.816.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose. The perceived directions of motion and stereoscopic depth were assessed for missing fundamental (MF) gratings, to compare the relative importance of energy and feature-matching processes. Methods. MF gratings were constructed by subtracting the fundamental Fourier component from a 1-cpd square wave. To assess motion processing, gratings were presented with successive quarter-cycle shifts for 1 s. The temporal frequency (TF) of motion was varied by changing either the duration of each frame or the inter-stimulus interval (ISI). Grating contrast ranged from 3 to 90%. If subjects reported motion in one direction, they then compared the speeds of the MF and a 3f grating, presented alone. If subjects reported transparent motion, they judged which direction of motion was faster. To assess stereo processing, pairs of counterphase flickering MF gratings were presented with a quarter-cycle disparity, or for various durations without flicker. Other procedures were analogous to the motion experiment. Results. When MF stimuli were presented with 0 ISI, subjects preferentially reported motion in the energy direction, regardless of the grating TF and contrast. As the ISI increased, subjects more often reported the direction of feature motion, particularly for high-contrast stimuli. Subjects also reported depth in the direction of MF feature disparity more frequently as the grating contrast increased, regardless of stimulus TF or duration. The perceived speed or depth of MF gratings was judged to be either greater than or equal to that of a 3f grating, when the perceived direction of motion or depth was consistent with the feature or energy directions, respectively. Conclusion. Energy computations account better for the perceived direction of motion and stereoscopic depth when stimulus contrast is low and feature matching accounts better when stimulus contrast is high. Overall, energy-based processing is more dominant in motion than in stereo processing.
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