September 2021
Volume 21, Issue 9
Open Access
Vision Sciences Society Annual Meeting Abstract  |   September 2021
Asynchronous visual flicker alters perceived curvature
Author Affiliations
  • Emily Cunningham
    University of Illinois at Urbana-Champaign
  • Rachel Heaton
    University of Illinois at Urbana-Champaign
  • John Hummel
    University of Illinois at Urbana-Champaign
Journal of Vision September 2021, Vol.21, 2630. doi:
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      Emily Cunningham, Rachel Heaton, John Hummel; Asynchronous visual flicker alters perceived curvature. Journal of Vision 2021;21(9):2630.

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      © ARVO (1962-2015); The Authors (2016-present)

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According to the recently described ‘curvature blindness illusion’ (Takahashi, 2017), when changes in contrast polarity are introduced at minima/maxima along a sinusoid, the resulting waveform is perceived as triangular, or ‘zigzag,’ rather than curved. In the initial report, this effect obtained only for changes in contrast polarity, which appear, when placed appropriately, to prevent integration over the contour resulting in the percept of discrete segments of zero net curvature. However, accounts of dynamic binding through temporal synchrony suggest an alternate approach to generating this illusion. Elements of a display that occur concurrently tend to be grouped more easily than those that occur asynchronously, even when visual alternation rates fall in the gamma range (e.g. Elliott & Muller, 1998; Lu et al., 2006). To the extent that temporal asynchrony facilitates segmentation, ‘curvature blindness’ may be also induced by visual flicker. Here, we investigated whether visual flicker is sufficient to induce ‘curvature blindness,’ and at which frequencies, if any, the illusion obtains. To this end, participants completed a 4AFC task in which they were presented with four distinctly segmented flickering waveforms (one of which was segmented at minima/maxima) and asked to choose the location of the ‘zigzag’ line. On experimental trials, all options were sinusoidal. On a small portion of catch trials, a triangle wave was substituted for one of the sinusoids in the display. To the extent that asynchronous visual flicker facilitates the ‘curvature blindness illusion,’ participants should label flickering curves that are segmented at maxima/minima as 'zigzag' more often than chance (25%). Across several experiments, the illusion emerged robustly at lower frequencies (between 5-20 Hz, peaking between 8-15 Hz), and decreased to chance as frequency was increased (up to 61 Hz), inconsistent with reports of induced grouping/segregation in the gamma range.


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