August 2009
Volume 9, Issue 8
Vision Sciences Society Annual Meeting Abstract  |   August 2009
We find before we Look: Neural signatures of target detection preceding saccades during visual search
Author Affiliations
  • An Luo
    Department of Biomedical Engineering, Columbia University
  • Lucas Parra
    Department of Biomedical Engineering, City College of New York
  • Paul Sajda
    Department of Biomedical Engineering, Columbia University
Journal of Vision August 2009, Vol.9, 1207. doi:10.1167/9.8.1207
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      An Luo, Lucas Parra, Paul Sajda; We find before we Look: Neural signatures of target detection preceding saccades during visual search. Journal of Vision 2009;9(8):1207. doi: 10.1167/9.8.1207.

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      © ARVO (1962-2015); The Authors (2016-present)

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We investigated neural correlates of target detection in the electroencephalogram (EEG) during a free viewing search task and analyzed signals locked to saccadic events. We adopted stimuli similar to ones we used previously to study target detection in serial presentations of briefly flashed images. Subjects performed the search task for multiple random scenes while we simultaneously recorded 64 channels of EEG and tracked subjects' eye position.

For each subject we identified target saccades (TS) and distractor saccades (DS). For TS, these were always saccades which were directly to the target and were followed by a correct behavioral response (button press); for DS, we used saccades in correctly responded trials having no target (these were 28% of the trials). We sampled the sets of TS and DS saccades such that they were equalized/matched for saccade direction and duration, ensuring no information in the saccade properties themselves was discriminating for their type. We aligned EEG to the saccade and used logistic repression (LR), in the space of the 64 electrodes, to identify components discriminating a TS from a DS on a single-trial basis. Specifically, LR was applied to narrow time windows (50ms) and discrimination was done for windows having varying latencies relative to the saccade. We found that there is significant discriminating activity in the EEG both before and after the saccade—average discriminability across 7 subjects was AUC=0.64, 80 ms before the saccade, and AUC=0.68, 60 ms after the saccade (p[[lt]]0.01 established using bootstrap resampling). Between these time periods we saw substantial reduction in discriminating activity (for 7 subjects, mean AUC=0.59). We conclude that that we can identify neural signatures of detection both before and after the saccade, indicating that the subject anticipates where the target is before he/she makes the last saccade to foveate and respond.

Luo, A. Parra, L. Sajda, P. (2009). We find before we Look: Neural signatures of target detection preceding saccades during visual search [Abstract]. Journal of Vision, 9(8):1207, 1207a,, doi:10.1167/9.8.1207. [CrossRef]
 This research was support by funding from DARPA

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