SELECTIVE EFFECTS OF ATTENTIONAL DIRECTION ON THE STARTLE REFLEX AT DIFFERENT STAGES OF PROCESSING

In two experiments, we assessed the effects of directed attention on t he elicitation and modification of the startle reflex. An acoustic sta rtle stimulus was preceded on some trials by a tone at stimulus onset asynchronies (SOAs) of 120 or 240 msec (Experiment 1, N = 26) and 1,20 0 or 2,400 msec (Experiment 2, N = 24). On some trials, following the offset of the startle stimulus, either a tone or a tactile stimulus wa s presented to the hand (vibration in Experiment 1, airpuff in Experim ent 2). On each of four blocks of trials, the subject was given one of the following tasks: Ignore all stimuli, or, when a particular tone p restimulus was presented (high frequency for some subjects, low freque ncy for others), judge the duration of (1) a tone following the startl e stimulus, (2) a tactile stimulus following the startle stimulus, or (3) the startle stimulus itself. The subjects were instructed to ignor e all the stimuli when the other tone prestimulus was presented. In th e startle-probe-alone conditions, attending to the tactile stimulus in creased acoustic startle reactivity (larger startle in Experiment 1, m ore probable and faster startle in Experiment 2) compared with startle in the ignore condition. Attending to the probe itself did not affect startle amplitude. Responding was similar when subjects attended to e ither the tone or the probe, suggesting that attention effects were mo dality specific, but not stimulus specific. Prestimuli at 120- and 240 -msec SOAs inhibited startle amplitude in all cases, and this inhibiti on was more pronounced when attention was directed to any stimulus tha n in the ignore condition, showing nonspecific attentional effects at short SOAs. At longer SOAs, startle reflexes were inhibited more in th e presence of nonsignal prestimuli than signal prestimuli. The increas ed startle reactivity, which occurred in both experiments when the sub jects were required to shift attention from the auditory to the tactil e modality, may have been due to greater task demands and, therefore, greater arousal in these conditions.