Correlates of reaction time to startle

The present study was concerned with behavioral and physiological correlates of response time to high intensity, 'unexpected' auditory stimuli. Stimuli consisted of an initial 120 db startle tone followed by a series of 50 tones of 75 db and a final 120 db startle tone. Sub-jects responded by moving a control stick as rapidly as possible to the onset of each tone. Continuous recordings of heart rate and skin resistance were taken. Autonomic reactivity to the first intense stimulus was found to be positively correlated with response latency, while response time to the final intense stimulus suggests a negative relationship to autonomic levels and reactivity. The primary effect of the second high intensity tone was to significantly exaggerate pre-existing differences between individuals in their reaction time to the preceding moderate intensity stimuli. Possible relationships of this differential stress response to concepts of excitation and inhibition are briefly discussed.

Startle Reaction: Modification by Background Acoustic Stimulation

Six rats were exposed to a sequence of gunshot-like acoustical bursts during silence, during steady noise, and during pulsed noise. Assessment of their startle reactions to the bursts revealed that a background of steady noise enhanced the response, whereas a background of pulsed noise produced suppression of response. It is hypothesized that pulsed noise causes a relative refractory state in the mechanisms responsible for startle and that steady noise may enhance startle by masking uncontrolled punctiform acoustic stimuli.