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In two experiments we investigated the effect of generalized orienting induced by changing the modality of the lead stimulus on the modulation of blink reflexes elicited by acoustic stimuli. In Experiment 1 (n = 32), participants were presented with acoustic or visual change stimuli after habituation training with tactile lead stimuli. In Experiment 2 (n = 64), modality of the lead stimulus (acoustic vs. visual) was crossed with experimental condition (change vs. no change). Lead stimulus change resulted in increased electrodermal orienting in both experiments. Blink latency shortening and blink magnitude facilitation increased from habituation to change trials regardless of whether the change stimulus was presented in the same or in a different modality as the reflex-eliciting stimulus. These results are not consistent with modality-specific accounts of attentional startle modulation.

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.

Two experiments examined the effects of visually presented threat and nonthreat word lead stimuli on blink modification among unselected young adults (Experiment 1, N = 35) and participants selected for low and high trait anxiety (Experiment 2, N = 60). The blink reflex was elicited by a white noise probe of 105 dB. Lead stimulus intervals of 60, 120, 240, and 2000 ms were used in both experiments. Prepulse inhibition was observed at the 240-ms interval and prepulse facilitation was observed at the 60-ms interval in both experiments. Also, greater facilitation was found in both experiments during threat words at the 60-ms interval and greater inhibition during threat words at the 240-ms interval. Experiment 2 provided some evidence that the greater facilitation during threat words than during nonthreat words at the 60-ms probe interval may be found in high trait anxious participants, but not in low trait anxious participants. The results are discussed in relation to contemporary information processing theories of anxiety.

Participants in Experiments 1 and 2 performed a discrimination and counting task to assess the effect of lead stimulus modality on attentional modification of the acoustic startle reflex. Modality of the discrimination stimuli was changed across subjects. Electrodermal responses were larger during task-relevant stimuli than during task-irrelevant stimuli in all conditions. Larger blink magnitude facilitation was found during auditory and visual task-relevant stimuli, but not for tactile stimuli. Experiment 3 used acoustic, visual, and tactile conditioned stimuli (CSs) in differential conditioning with an aversive unconditioned stimulus (US). Startle magnitude facilitation and electrodermal responses were larger during a CS that preceded the US than during a CS that was presented alone regardless of lead stimulus modality. Although not unequivocal, the present data pose problems for attentional accounts of blink modification that emphasize the importance of lead stimulus modality.

Attentional accounts of blink facilitation during Pavlovian conditioning predict enhanced reflexes if reflex and unconditional stimuli (US) are from the same modality. Emotional accounts emphasize the importance of US intensity. In Experiment 1, we crossed US modality (tone vs. shock) and intensity in a 2 x 2 between-subjects design. US intensity but not US modality affected blink facilitation. In Experiment 2, we demonstrated that the results from Experiment 1 were not due to the motor task requirements employed. In Experiment 3, we used a within-subjects design to investigate the effects of US modality and intensity. Contrary to predictions derived from an attentional account, blink facilitation was larger during conditional stimuli that preceded shock than during those that preceded tones. The present results are not consistent with an attentional account of blink facilitation during Pavlovian conditioning in humans.

Emotional accounts of startle modulation predict that startle is facilitated if elicited during aversive foreground stimuli. Attentional accounts hold that startle is enhanced if startle-eliciting stimulus and foreground stimulus are in the same modality. Visual and acoustic foreground stimuli and acoustic startle probes were employed in aversive differential conditioning and in a stimulus discrimination task. Differential conditioning was evident in electrodermal responses and blink latency shortening in both modalities, but effects on magnitude facilitation were found only for visual stimuli. In the discrimination task, skin conductance responses, blink latency shortening, and blink magnitude facilitation were larger during to-be-attended stimuli regardless of stimulus modality. The present results support the notion that attention and emotion can affect blink startle modulation during foreground stimuli.

Although task-irrelevant events elicit smaller skin conductance responses (SCRs) than do task-relevant events, secondary task probe reaction time (RT) is often slower during the former. Three experiments (N = 48 in each) examined the effects of task demands, instructions, and stimulus discriminability on this dissociation effect. SCRs were larger to task-relevant stimuli in all experiments regardless of experimental manipulation. Subjects in Experiment 1 counted either all tones of one pitch (high/low group) or longer-than-usual tones of one pitch (longer group). There was more RT slowing during task-irrelevant tones at a 250-ms probe position in the high/low group and at a 150-ms probe position in the longer group. Experiment 2 employed differential Pavlovian conditioning in which the offset of task-relevant stimuli (CS+) coincided with the onset of a shock stimulus. Half the subjects were told which stimulus would be followed by shock (information group), whereas the others received no information (no-information group). Increased RT slowing during CS- was restricted to the no-information group. Experiment 3 employed visual conditioned stimuli that were easy or difficult to discriminate. RT slowing at 4,000 ms was greater during CS+, whereas there was a tendency for more RT slowing during CS- at 150 ms. There was no effect for CS discriminability. The results suggest that during both simple discrimination and during Pavlovian conditioning, task-irrelevant stimuli are more actively processed than task-relevant stimuli within the first 250 ms of stimulus presentation.

Previous research has indicated that an intermodality change trial presented after a habituation series elicits larger orienting responses than does the first stimulus of that series. Experiment 1 (N = 48) investigated whether this effect was still present if the change stimulus was not novel but was presented once prior to the habituation series. Two groups of subjects were presented with a series of 24 tones or vibrotactile stimuli. Trial 25 was an intermodality change test trial for half of the subjects in each group (change), whereas the remaining subjects received an additional habituation stimulus (no change). Prior to the habituation trials, each subject was exposed once to the test stimulus used in the change condition. Although response magnitude on the test trial was larger in the change condition than in the no-change condition, test trial response magnitude did not exceed that on the first trial of the habituation series. In Experiment 2 (N = 84), one group was preexposed to the test stimulus, another was preexposed to an experimentally irrelevant stimulus, and a third received no stimulus prior to habituation training. Test trial response magnitude was larger than responses to the first stimulus of habituation in the change group that was not exposed to a stimulus prior to habituation but not in the preexposed groups. Preexposure to a stimulus prior to habituation training abolished the intermodality change effect even when the test stimulus was novel. The present results pose problems for noncomparator theories of habituation and support the notion that anticipatory processes are important in orienting and habituation.