The present study investigated the effects of lead
stimulus modality on modification of the acoustic startle
reflex during three reaction time tasks. In Experiment
1, participants (N = 48) were required to press
a button at the offset of one stimulus (task relevant)
and to ignore presentations of a second (task irrelevant).
Two tones that differed in pitch or two lights served as
signal stimuli. Blink startle was elicited during some
of the stimuli and during interstimulus intervals. Skin
conductance responses were larger during task-relevant
stimuli in both groups. Larger blink facilitation during
task-relevant stimuli was found only in the group presented
with auditory stimuli, whereas larger blink latency shortening
during task-relevant stimuli was found in both groups.
Experiment 2 (N = 32) used only a task-relevant
stimulus. Blink magnitude facilitation was significant
only in the group presented with tones, whereas blink latency
shortening was significant in both groups. Experiment 3
(N = 80) used a go/nogo task that required participants
to press a button if one element of a compound stimulus
ended before the second, but not if the asynchrony was
reversed. The offset asynchrony was varied between groups
as a manipulation of task difficulty. Startle magnitude
facilitation was larger during acoustic than during visual
stimuli and larger in the easy condition. The present data
indicate that startle facilitation in a reaction time task
is affected by stimulus modality and by task demands. The
effects of the task demands seem to be independent of lead
stimulus modality.