Modification of the acoustic startle reflex by a tactile prepulse: the effects of stimulus onset asynchrony and prepulse intensity.

Abstract

ABSTRACTThe present experiments were designed to assess the effects of a tactile prepulse on the acoustic startle response in human adults. Acoustic startle stimuli were presented via loudspeaker, and tactile prepulse stimuli were presented by a vibrator contactor on the thenar eminence of the right band. In Experiment 1 stimulus intensity was 20dB above each individual subject's psychophysical tactile threshold and stimulus onset asynchrony (lead time) was 50, 100, 200. or 300 ms, with a control condition in which no prepulse was presented. In Experiment 2, the same stimuli were used, except that tactile prepulse intensity was varied (−4, 0, 4, 8, 12, and 20 dB above each subject's psychophysical threshold), and lead time was constant at 200 ms. Reflex eyeblink responses were assessed from integrated periorbital etectromyographic (EMG) activity. Compared to responding in the control condition (no prepulse), a prepulse at a 50‐ms lead time facilitated responding by increasing response amplitude and decreasing latency. At a lead time of 100 ms, the amplitude increase was no longer found, but the latency decrease was still apparent, as was a decrease in response probability. At lead times of 200 and 300 ms, responding was inhibited, as shown by‐decreased response amplitude and probability. At a lead time of 200 ms. tactile prepulses as low as 8dB above threshold caused a reduction in response amplitude, but no effects of prepulse intensity on response probability or latency were found. The prepulse intensity and lead time effects shown in the present study demonstrate that the presentation of a brief, near‐threshold tactile prepulse can either facilitate or inhibit an acoustically‐elicited startle response, depending upon the temporal relationship between the two stimuli. Also, the different measures of the startle response reflect this modification in different ways.