Bottom-up effects modulate saccadic latencies in well-known eye movement paradigm |
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Authors: | Saskia van Stockum Michael R. MacAskill Tim J. Anderson |
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Affiliation: | (1) Van der Veer Institute for Parkinson’s and Brain Research, Christchurch, New Zealand;(2) Department of Medicine, University of Otago, Christchurch, New Zealand;(3) Department of Neurology, Christchurch Hospital, Christchurch, New Zealand |
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Abstract: | A well-known eye movement paradigm combines saccades (fast eye movements) with a perceptual discrimination task. At a variable time after the onset of a central arrow cue indicating the target direction [the stimulus onset asynchrony (SOA)], discrimination symbols appear briefly at saccade target and non-target locations. A previous study revealed an unexpected effect of SOA on saccadic latencies: latencies were longer in trials with longer SOAs. It was suggested that this effect reflects a top-down process as observers may wait for the discrimination symbol to appear before executing saccades. However, symbol onsets may also modulate saccade latencies from the bottom-up. To clarify the origin of the SOA effect on latencies in this paradigm, we used a simplified version of the original task plus two new symbol onset conditions for comparison. The results indicate that the modulation of saccadic latencies was not due to a top-down strategy, but to a combination of two opposing bottom-up effects: the symbol onsets at the target location shortened saccade latencies, while symbol onsets at non-target locations lengthened saccade latencies. |
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