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Makoto Miyakoshi, Scott Makeig, Carolina Gracitelli, Ricardo Yuji Abe, Alberto Diniz-Filho, Saif Baig, Felipe A Medeiros; Source-resolved EEG analysis of human saccade-event related potentials. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2919.
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© ARVO (1962-2015); The Authors (2016-present)
We developed an active visual search task in which participants saccade freely across an evolving display of Gabor patches. Here we report the results from the EEG analyses of saccade-related brain/muscle potentials using independent component analysis (ICA) and independent component (IC) clustering.
Participants were 16 healthy young adults (8 female, mean 20.8 years, SD 2.8, range 18-26). Five Gabor patches were always present on a gray background (20-inch LCD monitor at 60 cm ). A sequence of 1200 patches were pseudo-randomly selected from four patch sizes and five orientations (SOA 2 sec, duration 5 sec). The task was to detect infrequent (15%) instances in which the size and orientation of the newest patch matched those of another patch that was still visible, prompting a button press. Eye-tracking data were obtained from the left eye while 205-channel, 512-Hz scalp EEG data were recorded. We studied event-related potentials (ERPs) time-locked to saccade events for the time courses of 650 localizable ICs assigned to 16 clusters.
Mean response accuracy was 92% (SD: 5%) with mean false positive rate 6% (SD: 4%). Mean reaction time was 1579 ms (SD: 235 ms). After excluding 3 frontal EOG clusters comprising 240 ICs, the major (90 ms) lambda response peak in the fixation-onset locked ERPs was dominated by 3 occipital IC clusters (100 ICs, 92% of the peak scalp map accounted for) (Figure 1). ERPs time locked to saccade onsets contained a pre-saccadic spike peaking at -12 ms. Three far frontal clusters dominated this spike (260 ICs, 95% variance accounted) (Figure 2 left). However, after removing all 5 EOG and far frontal clusters (314 ICs) and 1 temporal scalp muscle (EMG) cluster (26 ICs), 4 posterior clusters (114 ICs) contributed 82% of the remaining (positive-going) pre-saccadic spike (Figure 2 right).
ICA clustering analysis revealed multiple sources of the lambda response and pre-saccadic spikes. Posterior cortical contributions to the pre-saccadic spike might index corollary suppression of visual cortex during saccades. We plan to use this task to investigate functional vision in glaucoma patients.
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