The effects of stimulus intensity, duration, and
risetime on the autonomic and behavioral components of
orienting, startle, and defense responses were investigated.
Six groups of 10 students were presented with 15 white
noise stimuli at either 60 or 100 dB, with controlled risetimes
of either 5 or 200 ms, and at stimulus durations of 1 or
5 s (1 s only in the case of the 60-dB groups). A dishabituation
stimulus consisting of a 1000 Hz tone was also presented.
Measures consisted of skin conductance and heart rate,
together with ratings of facial expressions and upper torso
movement obtained using video recording. Increased intensity
resulted in greater amplitudes and frequencies of electrodermal
and behavioral responses, and a change from cardiac deceleration
to acceleration. Faster risetimes elicited larger electrodermal
responses, greater frequencies of eye-blinks, head and
body movements, and larger cardiac accelerations. The effects
of duration for the 100-dB stimuli were less clear-cut.
Overall, the results are discussed in relation to the differentiation
of orienting, startle, and defense responses.