Effects of perceptual processing demands on startle eyeblink modification.

Startle eyeblink modification was measured during a continuous performance test (CPT) with either clearly focused stimuli or visually degraded stimuli to measure the effects of early perceptual processing demands on startle modification. A startling noise was presented either 120, 240, or 1200 ms following target and nontarget CPT stimuli. In the degraded stimulus CPT, startle inhibition at 240 ms was greater following targets than nontargets and was as great during targets at 240 ms as at 120 ms, whereas in the clearly focused CPT, inhibition declined significantly from 120 to 240 ms. The results indicate that maximum prepulse inhibition is extended in time when the task involves discrimination of degraded visual stimuli and when early perceptual processing demands are high. At 1200 ms, targets and nontargets produced nondifferential inhibition during both CPTs, suggesting that modality-specific attention occurred equally for the two tasks.