The effects of arithmetic task difficulty and performance level on EEG alpha asymmetry.

The effects of arithmetic task difficulty and performance level on ratio measures of parietal alpha asymmetry were evaluated. Sixteen subjects were given 14 visually presented problems varying in difficulty according to Thomas, Q. Jl exp. Psychol. 15, 173-191, 1963. When the mean latencies for these problems were compared, problem data were averaged across four distinctly different levels. As difficulty increased from low to moderate levels (levels 1 to 2 to 3), relative left-hemisphere activation significantly increased, but as difficulty increased to higher levels, alpha asymmetry tended to decrease. Changes in both hemispheres were responsible for this difficulty effect on ratio values and these changes appeared to be independent of strategy effects. When subjects were categorized according to performance (solution latency), the high performance group exhibited greater relative left hemisphere activation, more significant baseline-task asymmetry differences, and greater bilateral activation from baseline levels than the low performance group. Correlations between EEG measures and performance were generally nonsignificant, although task asymmetry was found to be related to performance latency on tasks of moderate difficulty.