THE EFFECT OF ACOUSTIC PULSE INTENSITY UPON THE ELECTRICALLY ELICITEDBLINK REFLEX AT POSITIVE AND NEGATIVE STIMULUS ONSET ASYNCHRONIES

The present study examined the effects of acoustic pulse intensity and stimulus onset asynchrony (SOA) on the electrically elicited startle reflex response. Subjects were presented with 165 startle eliciting st imuli; 15 control trials with no acoustic pulse, and 5 trials at each pulse intensity (50, 70, and 90 dB) for each SOA (-80, -60, -40, -20, 0, 20, 40, 60, 80, and 100 ms). The results demonstrated R2 magnitude facilitation at negative, simultaneous, and short positive SOAs. R2 fa cilitation was greatest in the 90 dB condition and least in the 50 dB condition. R1 facilitation at short positive SOAs was greater for more intense acoustic pulses. These data support the notion that R2 facili tation at near-zero SOAs may be the result of a combination of pulse i nduced potentiation of the electrically elicited startle response and temporal summation of the effects of electrical and acoustic stimuli a t the facial motor nucleus.