Effects of probability, intensity, and repeated sessions on sensitivity during orientation

The effects of the orienting response (OR) on sensory activity were investigated by examining evoked potentials from weak auditory probe stimuli during the presumed temporal course of the OR. The OR was elicited by salient foreground stimuli which varied in intensity and probability. The background probe stimuli consisted of a continual trains of auditory pips delivered at a rate of 40 pips per second. Under such conditions and evoked EEG rhythm is established at a corresponding frequency of 40 Hz. The rhythm showed a brief episode during which the latencies of response were decreased. The magnitude of the latency reduction response was larger for intense and for rare stimuli, and showed long-term decrement during the second session. It was hypothesized that the latency shift in the EEG rhythm reflect a brief period of sensitization during the OR.<>