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Gennady Erlikhman, Philip Kellman; Mechanisms of Spatiotemporal Boundary Formation. Journal of Vision 2015;15(12):521. doi: https://doi.org/10.1167/15.12.521.
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© ARVO (1962-2015); The Authors (2016-present)
Spatiotemporal boundary formation (SBF) is the perception of illusory boundaries, global form, and global motion from sequential transformations of sparse elements (Shipley & Kellman, 1993, 1994, 1997). SBF may involve two stages: 1) Local oriented edge fragments are recovered from small sets of transformations, and 2) These fragments connect across gaps via well-known contour interpolation processes. Progress in understanding the mechanisms of SBF has been hampered by the lack of a suitable paradigm that isolates the first stage. We created a novel display consisting of a saw-tooth pattern of dots that disappeared and reappeared sequentially. At long ISIs, perception was of a single dot moving along the saw-tooth. With shorter ISIs, however, the percept switched to that of a moving illusory bar that occluded the elements. Two experiments used converging subjective and objective methods to determine the conditions for perceiving the bar. In Experiment 1, subjects rated illusory bar clarity for various inter-element distances and ISIs. In Experiment 2, subjects chose the width of the bar seen from a set of different widths. True width was determined by calculating the width that would produce the timing of disappearances and reappearances. Subjective contour ratings in Exp. 1 predicted objective performance in Exp. 2. Under conditions that gave low clarity ratings, subjects were unable to accurately determine bar width (slope of linear fit =0.065, R2=0.518). Under conditions that supported perceived contours (ISIs ≤ 80 ms and for inter-element distances up to 1 deg) bar width was judged relatively accurately and scaled linearly with true width (slope=0.75, R2=0.997). We provide the first empirical support for local recovery of oriented edge fragments in SBF. We conjecture that this stage in SBF may engage classical motion-energy filters, which, when edge orientation is not given by oriented contrast, function in unsuspected ways as spatiotemporal edge detectors.
Meeting abstract presented at VSS 2015
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