To compare the sensitivity of a variety of psychophysiological variables to stimulus intensity and attention parameters, we simultaneously recorded EEG, eyeblink, skin conductance, and heart rate responses. Twelve subjects were presented with 50-ms, abrupt onset, white noise bursts of four intensities: 65, 80, 95 and 110 dB SPL. Nineteen stimuli of each intensity were given in random order with ISIs between 12 and 17 seconds. This paradigm was repeated under three randomly ordered task conditions: simple reaction time to the noise bursts, passive sitting, and visual tracking.
Response components were evaluated by Principal Components Analysis and peak measurement. Several factors and peaks increased with intensity, including those representing P300 and the Slow Wave. Task also had marked effects on certain components. SCR amplitude decreased rapidly over time, while the amplitudes of P300 and other event-related potentials did not.
The findings do not allow the late positive event-related potential components to be classified unambiguously as orienting, defense, or startle responses. Cognitive theories of these components have little predictive power for the observed intensity effects.