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David P. Crewther, Patricia M. Kiely, Sheila G. Crewther; Threshold recognition of phantom contour objects requires constant contrast velocity. Journal of Vision 2002;2(7):357. doi: https://doi.org/10.1167/2.7.357.
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© ARVO (1962-2015); The Authors (2016-present)
The process of object recognition of phantom objects — with contours defined by rapid phase contrast flicker, was investigated under conditions of abrupt and ramped onset and offset. Nine subjects with normal or corrected-to-normal vision participated. Thresholds were determined for the discrimination of a phantom letter “E” of four orientations (the letters defined by imaginary edges between a texture of lighter random dots inside the E compared with a texure of darker dots outside the E). Contrast revedsal at 58.5Hz was performed. For abrupt onset/offset, threshold was almost independent of the duration of presentation time over a 10-fold range from 34 – 340 msec (Mean 1.98% ±0.16%). However, when the onset and offset were shaped by a triangular envelope, over the same range of stimulus durations, threshold contrast varied strictly linearly with stimulus duration in all subjects (Mean correlation coefficient r2 = 0.96 ± 0.01). For the longest stimulus durations, thresholds exceeding 60% static contrast obtained. The results suggest that the transient edge of neural responses to novel stimuli is highly critical for recognition and that a quantity “contrast velocity” (rate of change of threshold contrast with duration time, Mean = 2.21 ± 0.19 /sec) be defined as a threshold measure for object recognition under gradual presentation conditions.
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