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Marco Boi, Martina Poletti, Michele Rucci; Time course of spatial frequency sensitivity during natural fixation. Journal of Vision 2012;12(9):1011. doi: 10.1167/12.9.1011.
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Since the original hypothesis that analysis of a visual scene proceeds from a global, coarse scale to a more detailed and finer one (Navon 1977), many studies have examined the temporal course of visual processing. Most studies have used conditions in which stimuli are flashed while observers maintain steady fixation. During natural viewing, however, stimuli are brought into the fovea by saccades, which are then followed by microscopic (fixational) eye movements. Fixational eye movements have been shown to enhance high spatial frequencies (Rucci et al. 2007) and may therefore contribute to a coarse-to-fine processing of the scene. To investigate the dynamics of visual processing during natural fixation, we used a gaze-contingent display procedure, in which stimuli were presented following a saccade. Stimuli consisted of gratings embedded in noise, which were either briefly presented at the onset of fixation (early condition), or ramped up gradually during the course of fixation (late condition). Two different patterns of results were obtained depending on the characteristics of the stimulus. With a 1 cycles/deg grating, performance was significantly better in the early condition than in the late one. Conversely, with an 11 cycles/deg grating, performance was higher in the late condition. Our results suggest that the normal alternation between macroscopic and microscopic eye movements contribute to a coarse-to-fine dynamic of visual processing during natural fixation.
Meeting abstract presented at VSS 2012
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