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D. Liston, R. Krauzlis; Effects of varying visual salience on pursuit and saccade decisions. Journal of Vision 2001;1(3):226. doi: 10.1167/1.3.226.
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© ARVO (1962-2015); The Authors (2016-present)
Abstract: Purpose The constraints imposed on pursuit and saccade decisions by visual processing are difficult to determine because latency differences between the two movements provide different amounts of visual sampling time. We have limited the duration and quality of the visual input in order to make the period of visual processing identical for each system. Methods On each trial, human observers (n=2) initially fixated a central fixation cross. After a random interval, two stationary probe noise strips (0.7í ver × 40í hor) were presented above and below (░ 2.25í) the fixation cross. The contrast of one probe strip was held constant at 50% and the other was varied from 50% to 75%. After a variable interval (50 – 500 ms), the fixation cross disappeared and the probe strips were replaced by masks. The random contrast masks were the same size as the probes and appeared in the same locations, but moved horizontally in opposite directions at 14 í/s. Observers were asked to make an eye movement to and follow the stimulus initially of higher contrast. Because the masks moved horizontally and were vertically offset, subjects made a combination of pursuit and saccades on each trial. For each exposure duration, we constructed “oculometric” curves for pursuit and saccades by plotting the percent correct as a function of probe contrast. Results As probe duration increased from 50 to 150 ms, oculometric thresholds for pursuit and saccades decreased from 62.8% and 65.2%, respectively, to 56.6% and 56.8%. Thresholds remained constant for longer probe durations (200 – 500 ms). Pursuit and saccade thresholds were not statistically different from each other across the exposure durations tested. Conclusions Pursuit and saccade decisions are similarly accurate when forced to integrate visual input over the same temporal interval. This similarity suggests that the latency differences between pursuit and saccades are due to differences after initial visual processing.
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