A system of detecting EEG alpha rhythms and using these to control stimulus displays is described. The detection system parameters are chosen to match the psychological and behavioral processes with the EEG index in the time domain. The feedback control system is designed to control visual and auditory displays, clock and counters, and computer sampling routines, and provide maximum flexibility in experimental design.
Two experiments with 16 normal adults of both sexes tested the hypothesis that inattention to a biofeedback display is associated with increased variability of those physiological processes that had been regulated by the biofeedback. Each experiment was a repeated-measures-on-independent-subjects-design. Dependent variables were the time durations and the mean rms power of two mutually exclusive segments of the parietal-occipital EEG: alpha and not-alpha segments. Independent variables were combination of counting tasks and instructions to look at, listen to, and count visual and auditory flashes and clicks. The durations of alpha and not-alpha segments were controlled or regulated by means of an alpha-contingent visual feedback stimulus, Attention to the feedback stimulus was challenged by instructions to count other, noncontingent stimuli. Control of alpha and not-alpha segments was least for conditions of (1) "sham" feedback, and (2) feedback with instructions to count noncontingent auditory clicks, which were presented 3/sec while the feedback visual stimuli were occurring. A new EEG test of attention and distraction was suggested.
A two-channel general-purpose EEG alpha-detection system is described, along with the associated computer hardware and software. A specific application for the study of the human orienting response using alpha-contingent visual stimulation is presented. Limitations are discussed.
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