EEG, heart rate and reaction time in humans: Effect of variable vs. fixed interval repetitive stimuli

Abstract

Visual motor reaction time (RT) change was measured in 12 normal adults exposed to iterative, prolonged, photic stimulation of two kinds: (a) isochronous (IS) and (b) stochastic (SS). EEG, EKG, eye and palpebral movements were continuously recorded. The mean RT for all subjects was shorter for the IS situation. Stochastic stimulation produced an increase in RT variability. A facilitation of the monitoring task performance during the first 2 min of IS stimulation was observed. It was found that monitoring task performance was positively correlated with the amount of alpha rhythm in the EEG record. A “predictive”, brief, attenuation of alpha rhythm appeared when the subject's monitoring task was maintained at a good performance level. It is assumed that this is a sign of expectancy. Deterioration of the monitoring task performance was accompanied by a decrement of the EEG photic driving response and slowing of hear rate. These results are discussed in relation to sensory habituation and to the internal appreciation of time.