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Cheng Qiu, Shikha Saggi, Cheryl Olman, Daniel Kersten; Ellipses look like polygons with fast repeated presentation. Journal of Vision 2015;15(12):529. doi: https://doi.org/10.1167/15.12.529.
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We observed that fast-paced peripheral presentations of ellipses (including circles) with slightly varying size and position result in their apparent change in shape. When observers (N=12) were asked to sketch the perceived shapes, they all portrayed perception of a closed form consisting of a discrete set of vertices connected by straight edges. To explore the time-course of this effect, observers were asked to press a response key when they saw the distortion first begin to appear. The trial ended when a response was received or after a minute of presentation (subjects were instructed not to respond if no distortion was observed). We found that: (1) The time to see the distortion decreases with increasing eccentricity; (2) A larger percentage change in width and/or height between frames decreases the response time (especially at small eccentricities), but an excessively large change increases the response time and reduces the perceived effect; (3) A small translational jittering of the ellipse center does not affect the response time; however, a larger location shift largely eliminates the shape distortion; (4) Over a flashing frequency range between 2 and 20 Hz, the response time decreases up to about 8 Hz. We also found that the effect persists when a temporal gap (i.e. a 100ms blank frame) is inserted between stimulus frames. This effect may be due to an interaction between two processes: fast phase adaptation to local curvature (locally adapted to convex curves make subsequent ones less curved or even straight) together with global shape integration. When observers viewed non-closed curves (e.g. partial ellipses) the perceived distortion was attenuated, suggesting the importance of global continuity contributing to the effect.
Meeting abstract presented at VSS 2015
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