ABSTRACT

This chapter deals with the modification of startle caused by a lead stimulus presented at a lead interval of less than 1 s. This modification of startle can be affected by a variety of parameters of the lead stimulus, such as duration, intensity, and lead interval. Startle modification at short lead intervals can also be affected by the intensity of the startle stimulus itself. The modification of startle decreases as a testing session progresses, and this is due either to habituation of the inhibitory mechanism or to a decrease in control startle reactivity. In some cases, lead stimuli can facilitate the startle response at short lead intervals, usually when the lead and startle stimuli are presented in different sensory systems. Short lead interval modification of startle may serve to protect the processing of the lead stimulus from interruption, but this reflex modification also illustrates automatic sensory gating and the influences of attentional mechanisms early in stimulus processing.