Event-related potentials and saccadic reaction times: effects of fixation point offset or change |
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Authors: | A Spantekow Paul Krappmann Stefan Everling Hans Flohr |
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Institution: | (1) Brain Research Institute, University of Bremen (NW2/PF 67), P.O.B. 33 04 40, D-28334 Bremen, Germany, e-mail: spantekow@uni-bremen.de, Tel.: +49-421-2182438, Fax: +49-421-2184932, DE;(2) Department of Physiology, Queen’s University, Kingston, Ontario, K7L 3N6 Canada, CA |
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Abstract: | Previous studies have shown that saccadic reaction times (SRTs) are reduced if the initial fixation point (FP) disappears
200 ms (gap period) before a peripheral target is presented. This gap saccade task is associated with a negative cortical
potential at the end of the gap period. To determine whether the neural processes underlying this potential account for the
reduction of SRTs during gap saccade tasks, we recorded event-related potentials (ERPs) in 19 subjects performing a gap saccade
task (gap duration 200 ms), a warning saccade task (the color of the FP changed 200 ms prior to target appearance) and an
overlap task (the FP remained visible during the trial). SRTs were shortest during the gap task, longest during the overlap
task and intermediate during the warning task. The gap and warning tasks were accompanied by the same widespread negative
cortical potential with a maximum at the time of stimulus presentation. These findings indicate that the warning effect mediated
by the disappearance of the FP during gap saccade tasks is responsible for the gap negativity which was observed by several
authors. Our findings of shorter SRTs during the gap task than the warning task, however, suggest that the gap has an additional
effect that probably depends on subcortical mechanisms.
Received: 01 June 1998 / Accepted: 12 March 1999 |
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Keywords: | Eye movements Gap effect Event-related potentials Fixation Humans |
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