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Oren S Kadosh, Yoram Bonneh; Fixation-Related Potentials and Oculomotor Dynamics reveal Contrast Response and Adaptation in Free Viewing. Journal of Vision 2019;19(10):122a. doi: https://doi.org/10.1167/19.10.122a.
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© ARVO (1962-2015); The Authors (2016-present)
Background: Event Related Potentials (ERPs) and the Oculomotor Inhibition (OMI) in response to transient visual stimuli are known to be sensitive to stimulus saliency, repetition and attention. Eye movements, which were traditionally considered as artifacts in the EEG signal are now being set as the event potential onset, timed locked to saccade offset creating Fixation Related Potentials (FRPs). Here we combined EEG and eye tracking, using free viewing techniques, to simultaneously asses the brain and OMI responses to incoming visual information after eye movement occurrence. The result of this movement is assumed to be equivalent to flashed stimuli with additional parafoveal preview. Methods: Participants moved their gaze freely in 10 sec. trials over full-screen images of random orientation Gabor patches texture, differing in contrast or spatial frequency between experimental conditions (“free viewing”, exp1). In a second experiment, participants moved their gaze sequentially between four Gabor patches (“guided viewing”, exp2) to investigate adaptation over time. We computed the FRP triggered by saccades of 1–6 deg., and the microsaccade Reaction Time (RT) as the time of the first microsaccade released from inhibition following these triggers (in a 200–700ms window). Results: In exp1, the FRP for O1–O2 occipital electrodes showed monotonic increase in P1 (Lambda response) amplitudes and decrease in peak latency with stimulus saliency (higher contrast and lower spatial-frequency). Microsaccade RT showed a similar decrease with saliency, but with much longer latencies and therefore microsaccades could not have affected the P1 response at ~100ms. In exp2, preliminary FRP results indicate that the P1 magnitude decreases over time of few seconds, presumably due to contrast adaptation, and this effect appears to depend on stimulus uniformity. Conclusion: The FRP and OMI analyses are applicable tools for the study of low-level visual processing, including saliency and adaptation in free viewing.
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