Effects of task difficulty on EEG measures of cerebral engagement

EEGs were recorded while subjects constructed 14 block designs of graded complexity, and also while reading and writing. Two measures of design difficulty were used: time to complete each construction and Ss' subjective ranking. For each task, average alpha power for each lead and R/L ratios (C₄/C₃, P₄/P₃) were calculated.Within-subject and group analyses both showed higher alpha power and higher R/L ratios with increasing difficulty. There were important differences between subjects: some showed significant increases in alpha power only on the left, some only on the right, some bilateral. Regardless of difficulty however, the R/L alpha ratios were significantly lower for block design than for writing, as in our previous studies.