EEG AMPLITUDE CHANGES DURING DIFFERENT COGNITIVE PROCESSES INVOLVING SIMILAR STIMULI AND RESPONSES

In order to investigate the effects on electroencephalographic (EEG) amplitude of cognitive processes, as distinct from direct effects of sensory stimulation and motor response, subjects were given three different tasks in which the stimuli were always similar sets of spoken numbers and the responses were always written numbers. In response to 61 regularly occurring, randomly ordered, single‐digit numbers, seven S s wrote, on successive trials, (1) the sum of every 4 consecutive numbers, (2) every fourth number, and (3) every “7” and “9” heard. Since the physical stimuli were the same and the movements of response were similar for the three tasks, intertask pattern differences in EEG alpha and beta amplitude would presumably be due to differences in the cognitive processes required in the tasks. No differences due to cognitive factors were found. All short‐term variations in both alpha and beta appeared related to widespread effects of response and preparation for response. Preresponse effects seemed related to motor set which was distinguished from attentional factors. The results suggest the necessity for a greater emphasis on motor effects in EEG studies.