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Lori Bukowski, Avia Huisman, Mireya Rivera, Howard S Hock; Perceptual categorization: Dynamical vs. Judgmental boundaries. Journal of Vision 2003;3(9):784. doi: 10.1167/3.9.784.
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© ARVO (1962-2015); The Authors (2016-present)
Perceptual categorization was compared for two kinds of apparent motion stimuli. The first was a motion quartet for which pairs of elements in diagonally opposite corners of an imaginary rectangle were inter-changed during successive frames; subjects reported whether a horizontal or vertical motion pattern was perceived. The second stimulus was composed of two spatially separate, single-element motions, one along a horizontal, the other along a vertical path; subjects reported whether the horizontal or vertical path looked longer. Whether the boundaries separating these perceptual categories were dynamical or judgmental was determined by gradually increasing and gradually decreasing the aspect ratio of the stimuli (the vertical divided by the horizontal path length). For the motion quartet, hysteresis effects of similar magnitude were obtained, regardless of whether subjects reported the loss of the initially perceived pattern or a change to the alternative pattern sometime during a trial; when the initial percept was lost, the new percept was immediately gained, the bistability indicating that the boundary separating these perceptual categories was dynamical. For the stimuli with spatially separated motion paths, hysteresis was obtained when subjects reported whether there was a change from the initial percept (e.g., the horizontal motion path looked longer) to the reverse percept (the vertical motion path looked longer) sometime during a trial. However, the hysteresis effect was sharply reduced or eliminated when subjects instead reported whether the initially perceived difference in path length no longer was perceivable sometime during the trial. This difference between when the initial percept was lost and when a new percept was gained indicated that there was a range of aspect ratios for which perception of relative path length was uncertain, evidence that the boundary separating these perceptual categories was judgmental.
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