Microsaccades generate visually-evoked brain activity that superimposes on event-related EEG data
University of Potsdam, Germany
Humboldt University, Germany
University of Trento, Italy
Microsaccades are tiny, involuntary movements of the eye that occur one to three times per second during fixation. Although monkey studies have shown that microsaccades correlate with spike bursts in visual areas, little attention has been given to brain-electric correlates of microsaccades in humans. Recently, Yuval-Greenberg et al. (2008) have demonstrated that microsaccades are accompanied by single sharp spikes of muscle activity in the EEG, which are sufficient to change the EEG frequency spectrum, mimicking increases in induced Gamma band power. To investigate the impact of microsaccades on EEG recordings, we simultaneously recorded fixational eye movements and EEG while subjects fixated black-and-white checkerboards or pictures of faces, and during a visual oddball task. Replicating Yuval-Greenberg et al., we found that microsaccades (0.3° in mean amplitude) were accompanied by a peri-saccadic muscle spike and, in addition, a small corneoretinal artefact. Importantly however, microsaccades in all three experiments were followed after 100-130 ms by a large visually-evoked brain potential (VEP) that was highly similar to the visually-evoked lambda waves elicited by much larger, voluntary saccades. Results therefore challenge the assumption of cognitive brain imaging studies that saccade-related brain activity is precluded by instructions to fixate, even when complied with. Instead, results indicate that microsaccadic VEPs are superimposed on most event-related EEG data. Because the probability of microsaccades varies systematically according to properties of the stimulus, task, and response (e.g. target frequency in the current oddball task), microsaccadic VEPs may present a relevant source of signal distortion for event-related EEG analyses.
10th International Conference on Cognitive Neuroscience, Bodrum, Turkey, 1 Sep - 5 Sep, 2008.
Neuroinformatics of Cognition
(2008). Microsaccades generate visually-evoked brain activity that superimposes on event-related EEG data.
Front. Hum. Neurosci.
10th International Conference on Cognitive Neuroscience.
15 Dec 2008;
15 Dec 2008.
Olaf Dimigen, University of Potsdam, Potsdam, Germany, firstname.lastname@example.org