Short-term recall of nine-digit strings and the EEG.

In three exploratory studies, EEG changes were monitored while subjects performed a nine-digit recall task. Experiment 1 involved auditory presentation without practice or prior instruction. EEG characteristics measured before the task related to subsequent recall, EEG activation increased progressively during digit presentation and rehearsal, and several between- and within-subject analyses showed increased activation to be associated with poor recall performance. In Expt. 2 the digits were presented visually and subjects were given instruction and practice in an efficient rehearsal strategy. Recall performance improved but its relationship with the pre-task EEG disappeared. Activation increased with digit presentation but the relationship between the EEG and performance was complex since a within-subject analysis associated decreased activation with better performance (as in Expt. 1) while this relationship was reversed in a between-subject analysis. The results are explained both in terms of traditional findings relating activation to recall, and drive theory accounts of learning and performance. Finally, Expt. 3 demonstrated that performance was better, both in the morning (compared with the evening) and on a second testing session. There were complex time of day effects for the EEG, with lower and higher measured frequencies yielding higher voltage output in the evening and intermediate frequencies showing a reverse effect. In summarizing the data from the three experiments it is suggested that different EEG frequencies are differentially sensitive to different conditions (task specific factors, stimulus input characteristics, knowledge of success and failure, degree of task mastery and circadian variation).