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Sarah J Waugh, Monika A Formankiewicz, M Izzuddin Hairol; Effects of stimulus duration on foveal crowding using visual acuity letters. . Journal of Vision 2014;14(10):787. doi: 10.1167/14.10.787.
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© ARVO (1962-2015); The Authors (2016-present)
Previously we reported fixed foveal zones of contour interaction/crowding of up to 4 arcmin for luminance-modulated Cs, 12 arcmin for contrast-modulated Cs and 4 arcmin for luminance letters (Waugh et al, VSS 2012; Hairol et al, 2013; Siderov et al, 2013). These zones remain constant in extent for different target contrasts and retinal illuminances, despite a wide range of letter sizes used to generate constant isolated-letter performance. In this study, we investigate the effects of stimulus exposure duration on foveal crowding zones for letter acuity. In the periphery, crowding zones increase in size for briefly presented stimuli (Tripathy et al, 2002 and VSS2013). High contrast letters (H O T V) were presented at sizes that generated 80-90% performance level when isolated. Stimulus duration (800, 400, 200, 100, 50 and 25ms) and flanker type (box, bars and letters L A U C) were varied systematically in blocks. Within an experimental run, one of 10 flanker separations (0-10 arcmin), including the isolated condition, was randomly presented using a Method of Constant Stimuli, and performance monitored. The measured crowding function is dependent on flanker type (p<0.05) and stimulus duration (p<0.05), with the box showing weaker overall crowding. On average, at 25ms, the crowding function is shallower and broader than at longer durations. The spatial extent for which performance for a crowded letter is statistically different from an isolated letter, changes from 3-4 arcmin for longer durations (200-800ms), to 8 arcmin at the shortest duration of 25ms; with fitted (Gaussian) extents of 2.5 to 6 arcmin. Weaker crowding by the box may reflect a fast grouping process. Temporal changes in crowding at the fovea are similar to those reported in the periphery, indicating that contributions at short durations to the crowding function engage larger underlying mechanisms.
Meeting abstract presented at VSS 2014
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