INHIBITION OF THE HUMAN STARTLE RESPONSE IS AFFECTED BY BOTH PREPULSEINTENSITY AND ELICITING STIMULUS-INTENSITY

The present study evaluated the effects of the intensity of prepulses and eliciting stimuli on the modification of the adult human acoustic startle eyeblink. Eyeblinks were elicited by 85, 95, and 105 dB(A) noi se bursts, preceded on some trials by 60 or 70 dB(A) tones at a 120 ms stimulus onset asynchrony. Prepulse intensity was a within-subject va riable in Experiment 1 (N = 19) and a between-groups variable in Exper iment 2 (N = 38). For no-prepulse trials, as startle stimulus intensit y decreased, startle amplitude, probability, and magnitude decreased, and startle latency increased. As startle stimulus intensity decreased from 105 to 95 dB, the amount of inhibition of response amplitude and magnitude remained stable for 70 dB prepulses in Experiment I and for both 60 and 70 dB prepulses in Experiment 2, whereas inhibition of re sponse probability became more pronounced. As startle stimulus intensi ty decreased from 95 to 85 dB, prepulse inhibition of response amplitu de and magnitude lessened and inhibition of response probability becam e still more pronounced in both experiments. These data show that the inhibition of startle can be affected by eliciting stimulus intensity, and that startle response amplitude and probability are affected by s timulus intensity changes in different ways.