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Sara Spotorno, Anna Montagnini; Investigating task-dependent and stimulus-driven mechanisms of fixational saccades when detecting or discriminating a stimulus . Journal of Vision 2014;14(10):116. doi: 10.1167/14.10.116.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies have indicated that fixational saccades are influenced by the spatial frequency content of the stimulus (Simoncini et al., 2012), enhance processing of stimuli of high spatial frequency (Rucci et al., 2007) and may be modulated in order to improve performance in high-acuity tasks (Ko et al., 2010). We further investigated the adaptive nature of fixational saccades in human observers in two classical psychophysical tasks with a two-interval forced choice paradigm. The first task required detection of a vertical or tilted grating characterised by one of three spatial frequencies, one of four contrasts and embedded in pink or white noise (with high or low contrast). The second task required frequency discrimination between two high-contrast tilted gratings in high-contrast or low-contrast pink noise. Findings revealed that the pattern of fixational saccades was participant-specific. Saccadic amplitude varied slightly between frequencies, but was similar between tasks and display types (gratings with noise vs. noise-only in the detection task, reference vs. test in the discrimination task). However, in both tasks, smaller amplitude and fewer saccades were found in low-noise than in high-noise displays. This effect was enhanced when detecting low-contrast gratings. In the detection task saccadic amplitude was also reduced with high-contrast gratings compared to low-contrast gratings, but only with high-noise. These findings indicate that saccadic amplitude was inversely correlated with the degree of stimulus visibility. Grating orientation did not affect saccade direction in either task. Moreover, no consistent differences in saccade amplitude and saccade number were observed depending on performance accuracy. Overall, our results challenge the idea that fixational saccades can generally be modulated adaptively by either task-dependent mechanisms or by stimulus-driven mechanisms related to the frequency spectrum of the stimulus. They suggest instead that idiosyncratic factors, task context and stimulus visibility can have an importance that has been previously underestimated.
Meeting abstract presented at VSS 2014
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