Lateral eye movements as an indication of hemispheric preference: an EEG validation study.

The hemispheric asymmetry model of lateral eye movements (LEM), hypothesizing a relation between a predominance of lateral gazes to one side with a predominance of activity in the hemisphere contralateral to the preferred direction of gaze, was tested in male, right-handed subjects. During presentation of cognitive tasks (verbal synonym tasks and spatial orienting tasks) the decrease in alpha-power from a reference period to each of four activation periods (anticipation, task-presentation, first LEM, answer) for 6 derivations from each hemisphere was calculated using the method of 'Event-related desynchronisation'. Evidence for the hypothesis was found only during the EEG-epoch one second before the answer. Discrimination between subjects with a predominance of left vs right eye movements (left- vs right-movers) was best at temporal (T3, T4) and central (C3, C4) sites. These results were significant for the entire alpha-band (8-12 Hz) and--even more pronounced--for the alpha-2-band (10-12 Hz). The alpha-1-band (8-10 Hz) did not produce significant differences. Comparing the two types of tasks, synonym tasks yielded results which were more congruent with the hypothesis. The results suggest that lateral eye movements indicate individual differences in hemispheric EEG-asymmetries under certain experimental conditions (task, segment of EEG-analysis, site, frequency band).