Patricia J. Dall

The effect of warning stimulus modality on blink startle modification in reaction time tasks

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.

Effects of stimulus modality and task condition on blink startle modification and on electrodermal responses

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.

The effects of unconditional stimulus valence and conditioning paradigm on verbal, skeleto-motor, and autonomic indices of human Pavlovian conditioning

The effects of unconditional stimulus (US) valence (aversive electro-tactile stimulus vs. non-aversive imperative stimulus of a RT task) and conditioning paradigm (delay vs. trace) on affective learning as indexed by verbal ratings of conditional stimulus (CS) pleasantness and blink startle modulation and on relational learning as indexed by electrodermal responses were investigated. Affective learning was not affected by the conditioning paradigm; however, electrodermal responses and blink latency shortening indicated delayed learning in the trace procedure. Changes in rated CS pleasantness were found with the aversive US, but not with the non-aversive US. Differential conditioning as indexed by electrodermal responses and startle modulation was found regardless of US valence. The finding of significant differential blink modulation and electrodermal responding in the absence of a change in rated CS pleasantness as a result of conditioning with a non-aversive US was replicated in a second experiment. These results seem to indicate that startle modulation during conditioning is mediated by the arousal level of the anticipated US, rather than by the valence of the CS.

Effects of miscuing on Pavlovian conditioned responding and on probe reaction time.

Two experiments examined the effect of the miscuing of an unconditioned stimulus on Pavlovian conditioned responding. In Experiment 1 (N = 32), subjects received 12 CS+-US and 12 CS- presentations followed, in the experimental group, by a CS--US pairing (miscuing) on Trial 25 and a CS+-US pairing on Trial 26. For the control group, Trial 25 consisted of a CS--alone presentation and Trial 26 consisted of a CS+-US pairing. Visual stimuli (geometric shapes) of 8-s duration served as CSs, and a 1-s burst of white noise (100 dBA) was used as the US. Both electrodermal activity and a continuous measure of US expectancy were obtained. Expectancy of the US was significantly lower in the experimental group than in the control on the CS+-US trial which followed miscuing, whereas electrodermal responses to the US were significantly larger. However, first- and second-interval responses during CS+ on this trial were not influenced by miscuing. Experiment 2 (N = 64) employed the same stimuli and procedures as used in Experiment 1, but the dependent measure was reaction time to a probe stimulus presented either early (300 ms) or late (7500 ms) during some CSs+ and some CSs-. During the acquisition phase, probe reaction time was slower during CS+ than during CS- regardless of probe position. Moreover, reaction time to probes presented during CS+ on the trial which followed miscuing was slower in the experimental group than in the control irrespective of probe position. Although not all findings were as predicted, the present results suggest that a CS-US pairing disrupted the association between CS+ and the US. This effect of US miscuing is difficult to interpret within the framework of current theories of Pavlovian conditioning.

The effects of change in lead stimulus modality on the modulation of acoustic blink startle

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.

Assessing the Effects of Attention and Emotion on Startle Eyeblink Modulation

Two experiments were conducted to assess simultaneously the effects of attentional and emotional processes on startle eyeblink modulation. In each experiment, participants were presented with a pleasant and an unpleasant picture. Half the participants were asked to attend to the pleasant picture and to ignore the unpleasant picture, whereas the reverse was the case for the other participants. Startle probes were presented at 3500 and 4500 ins after stimulus onset in Experiment I and at 250, 750, and 4450 ms after stimulus onset and 950 ms after stimulus offset in Experiment 2. Attentional processing affected startle eyeblink modulation and electrodermal responses in both experiments, However, effects of picture valence on startle eyeblink modulation were found only in Experiment 2. The results confirm the utility of startle eyeblink modulation as an index of attentional and emotional processing. They also illustrate that procedural characteristics, such as the nature of the lead intervals and how attention and emotion are operationalized, can determine whether emotional or attentional processes will be reflected in startle eyeblink.

Effects of intermodality change and number of training trials on electrodermal orienting and on the allocation of processing resources

The present experiments examined the hypothesis that the electrodermal orienting response elicited by and the processing resources allocated to an intermodality change stimulus will vary as a function of the amount of pre-change habituation training. Experiment 1 (N = 64) employed a 2 x 2 design in which subjects received either 6 or 24 training trials followed by either an intermodality change trial or a further trial with the training stimulus. Skin conductance responses were measured throughout. Training and test stimuli (visual and vibrotactile) were counterbalanced within groups. Intermodality change elicited larger responses than did no-change, and in the 24-trial condition, test trial responses were larger than those on trial 1 of the habituation series. Experiment 2 (N = 64) employed the same design and procedure except that reaction time to auditory probes presented 300 ms following the onset of some stimuli and during some of the intertrial intervals was also measured. The results indicated that in the 24-trial condition, but not in the 6-trial condition, probe reaction time on the test trial was slower in the Change group than in the No Change group. Probe reaction time on the test trial did not exceed reaction time on the first trial of habituation. The results are consistent with the view that development of a stimulus expectancy is one important factor in producing the intermodality change effect.

Blink reflexes as a measure of generalised orienting

Measures of autonomic activity have long been the indices of choice in western research on orienting and habituation. Recent research, however, has suggested blink reflexes as a measure of attentional processes that occur during generalised and localised orienting. Two experiments assessed whether generalised orienting affects blink reflex modulation and whether effects of orienting are mediated by stimulus modality. Attention to a lead stimulus is said to enhance blink reflexes if lead and reflex stimuli are presented in the same sensory modality, but is said to reduce blink reflexes if the stimuli are presented in different modalities. Lead stimuli used in previous studies, however, differed in interest and in valence, which renders the interpretation of results difficult. The present experiments used neutral lead stimuli in a stimulus change procedure to avoid potential confounds. In Experiment 1 (n = 32), participants were presented during habituation training with 43 lead stimuli (4 s), 40 of which were tactile. Acoustic or visual change stimuli were presented on trials 25, 33, and 43. In Experiment 2 (n - 64), modality of the lead stimulus (acoustic vs. visual) was crossed with experimental condition (Change vs. No Change). Blink eliciting noise bursts were presented during inter-trial intervals and at lead intervals of 2.5 and 3.5 s during some habituation and all change stimuli. Lead stimulus change resulted in increased electrodermal orienting in both experiments. The extent of blink latency shortening and of blink magnitude facilitation increased from habituation to change trials regardless of whether the change stimulus was presented in the same modality as was the reflex eliciting stimulus. These results are not consistent with findings from previous research that employed interesting and dull lead stimuli and indicate that effects of generalised orienting on reflex modification are not stimulus modality specific.

Mobility, extraversion, and neuroticism

Mobility, a property of Pavlovian higher nervous activity, was measured using an induction task. Negative induction, following presentation of an excitatory stimulus, is an index of mobility of excitation and positive induction, following presentation of an inhibitory stimulus is an index of mobility of inhibition. Mobility scores from 27 male and 37 female first-year psychology students, age 17 to 42 years were related to extraversion and neuroticism derived from Eysenck’s Personality Inventory (Form A). Mobility of excitation and mobility of inhibition were found to be unrelated. Individual differences in the magnitude and latency of induction indicate that individuals can be typed according to low, medium, or high mobility of either nervous process. No relationship was found between neuroticism and mobility, and no relationship was found between extraversion and mobility of excitation. However, a significant negative relationship was found between extraversion and mobility of inhibition, providing a link between Pavlovian properties of the nervous system and Eysenck’s personality dimension of extraversion.