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William Harrison, Peter Bex; Contour perception across time and eye movements. Journal of Vision 2014;14(10):66. doi: https://doi.org/10.1167/14.10.66.
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© ARVO (1962-2015); The Authors (2016-present)
Our visual environment is replete with partially occluded objects. Despite having discontiguous edges, partially occluded objects are nonetheless often easily identified. We used Kanisza figures to investigate how such perceptual completion of contour segments is affected by changes in contour information across time and shifts of gaze. Observers were required to identify the apparent shape of illusory contours constructed from four pacmen (58ms duration) positioned at the corners of an invisible square. We varied the angle of the pacmen to produce apparently "fat" or "thin" illusory shapes, and defined an observer's identification threshold as the standard deviation of a cumulative Gaussian fit to their responses. Critically, we presented masking discs of variable durations at positions corresponding to each of the pacmen, and these discs could appear either before or after the illusory contours. Observers' thresholds increased when masks were presented immediately after the illusory contours, as per backward masking. However, when the discs preceded the illusory contours, we saw a strong and robust reduction in thresholds for even the shortest mask duration (25ms). We then tested whether this facilitation of perceptual completion depends on retinotopic brain areas. Observers executed a saccade and identified an illusory shape presented immediately after the eye movement. In one condition, we presented the disc masks prior to the saccade at a screen location corresponding to where the pacmen would appear following the saccade. Because of the intervening eye movement, these discs were retinotopically mismatched from the pacmen. Nonetheless, thresholds were lower when discs preceded the illusory contours (and saccade) compared with a condition in which no discs were presented prior to the saccade. Our data are consistent with the notion that feedback from non-retinotopic brain areas plays an important role in perceptual completion, and that this feedback can facilitate visual perception across eye movements.
Meeting abstract presented at VSS 2014
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