Shape distortions and Gestalt grouping inanorthoscopic perception

Abstract

When a figure moves behind a stationary narrow slit, observers often report seeing the figure as a whole, a phenomenon called slit viewing or anorthoscopic perception. Interestingly, in slit viewing, the figure is perceived compressed along the axis of motion. As with other perceptual distortions, it is unclear whether the perceptual space in the vicinity of the slit or the representation of the figure itself undergoes compression. In a psychophysical experiment, we tested these two hypotheses. We found that the percept of a stationary bar, presented within the slit, was not distorted even when at the same time a circle underwent compression by moving through the slit. This result suggests that the compression of form results from figural rather than from space compression. In support of this hypothesis, we found that when the bar was perceptually grouped with the circle, the bar appeared compressed. Our results show that, in slit viewing, the distortion occurs at a non-retinotopic level where grouped objects are jointly represented.

Non-retinotopic feature integration decreases response-locked brain activity as revealed by electrical neuroimaging

“…Thus, features presented at one retinotopic location are attributed to another one. These non-retinotopic attributions are not errors of the visual system but rather reflect systematic visual processing that maintains the identity of perceptual objects across space and time (Otto et al, 2009) and follows the rules of perceptual grouping (Aydin et al, 2008(Aydin et al, , 2009Öğmen et al, 2006;Otto et al, 2009). Similar non-retinotopic effects have been demonstrated for luminance (Shimozaki et al, 1999), color Watanabe and Nishida, 2007), shape Otto et al, 2006), size (Kawabe, 2008), and the conjunction of features (Cavanagh et al, 2008).…”

Non-retinotopic feature processing in the absence of retinotopic spatial layout and the construction of perceptual space from motion

“…This proposal has been supported by a recent study where spatial distortions in anorthoscopic perception were examined (Aydin et al, 2008). The figure moving behind the slit typically appears spatially compressed in the direction of its motion (e.g., Anstis & Atkinson, 1967; Aydin et al, 2009; Haber & Nathanson, 1968; Helmholtz, 1867/1962; McCloskey & Watkins, 1978; Morgan et al, 1982; Parks, 1965; Rock, 1981; Rock & Sigman, 1973; Zöllner, 1862). Aydin et al, (2008) showed that this spatial compression can be explained by the differences in the perceived speeds of the leading and trailing parts of the anorthoscopic figure.…”

The Geometry of Visual Perception: Retinotopic and Nonretinotopic Representations in the Human Visual System

“…A critical observation from these experiments is that, if one does not take into account the direction of motion, then the interpretation of the stimulus will be ambiguous in that mirror-symmetric images moving in opposite directions will generate identical patterns in the slit. Therefore, the direction of motion must be an essential component in building non-retinotopic representations associated with anorthoscopic perception [5],[6],[52],[57]. …”

“…While both parts appear to move faster than their veridical speed, the trailing part appears even faster than the leading part in accordance with our hypothesis. Data, replotted from [6], represent the average and the standard error of the mean across the observers.…”