Effects of attention, activation and stimulus regularity on short-term 'habituation' of the averaged evoked response.

Three studies are reported in which the effects of direction of attention, level of activation and regularity of stimulation on the rate of amplitude decrement over time of the auditory evoked vertex responses in humans were examined. Short-term, stimulus-by-stimulus changes were assessed by averaging across trains each of 10 click stimuli. The effect of directing attentions towards the stimuli was to enhance the N1 - P2 component, but usually only under conditions of high activation and with irregular stimulus presentation. Habituation rate was hardly affected by the experimental manipulations. The most clear-cut relationship between psychological influences and the AER was that between level of activation and the P2 - N2 component.