Task difficulty and EEG alpha asymmetry: an amplitude and frequency analysis.

The effects of mathematical, spatial and verbal task difficulty on EEG alpha amplitude and mean frequency asymmetry were investigated. Twenty right-handed subjects with no familial left-handedness (10 female, 10 male) were presented 3 levels of difficulty for each type of task. Difficulty was varied through increasing the rate of auditorily presented numerical stimuli. Also examined were EEG alpha correlates with measures of performance anxiety, subjective difficulty, loss of vigilance, confusion, the tendency to rely on a guessing strategy and performance. While increasing task difficulty led to right-parietal and posttemporal alpha acceleration for all tasks, task-dependent bilateral changes in alpha frequency were also observed. Increased mathematical task difficulty widened parietal amplitude asymmetry differences between high- and low-performance subjects, and produced performance-dependent changes in left-parietal and right-temporal alpha frequency. A curvilinear relationship between spatial-task difficulty and relative right-hemisphere alpha attenuation was found for the high-performance group only. Finally, numerous correlations were found between alpha measures and subjective and performance variables. Most of these correlations were found to be both task- and difficulty-level-specific. Task anxiety appeared to play a significant role in the determination of parietal- and temporal-lobe asymmetry.