The influence of introversion/extraversion on the skin conductance response to stress and stimulus intensity

A series of studies compared skin conductance level (SCL) for introverts and extraverts during a series of tones varying in both stimulus intensity (SI) and the amount of stress preceding the tones. When a difficult paired-associate task preceded the tones, both groups were about the same for 83 dB tones but extraverts were much higher at 103 dB, introverts failing to show an increase as a function of SI. There were no differences between the two groups following a simple paired-associate task, both groups showing a similar increase with increased SI. Finally, SCL was higher for introverts than extraverts during tones preceded by a rest period, and this was especially true for the early trials and for lower SI (75 and 83 dB compared with 100 and 103 dB). Taken together, these results suggest that SCL is higher for extraverts at higher levels of arousal but that the reverse is true for lower levels of arousal. This relationship is consistent with the theory that introverts have a “weak nervous system” which develops transmarginal or protective inhibition under stress.     

Gray's three-arousal model: an empirical investigation

We evaluated the validity of Gray's and Fowles' three-arousal model in two studies of criminal offenders using a continuous motor task involving rewards and punishments. Consistent with predictions for the behavioral approach/activation system (BAS), offenders displayed significant (p<0.00001) increases in response time and heart rate (HR) from a no-incentive practice phase to a reward-only (experiment 1) and active-avoidance (experiment 2) phase. Trait impulsivity was correlated with the response time index of BAS activation in experiment 1 but not experiment 2. Consistent with predictions for the behavioral inhibition system (BIS), offenders showed a significant increase in number of skin conductance responses (SCRs) (p<0.05) from a reward-only to a mixed-incentive phase in experiment 1 and a significant increase in SC amplitude to punishment cues in both experiments. Consistent with predictions for the dynamics of the model, participants showed significant slowing of response time (p<0.0001) from reward-only (experiment 1) or active avoidance (experiment 2) to mixed-incentive phases despite showing an initial tendency toward response facilitation to the onset of the punishment cue signifying the beginning of the mixed-incentive phases. Participants also showed significant (p<0.002) decreases in HR between these phases in both studies, but this effect was only evident on trial 1. The BIS-influenced response time and HR indices were significantly (p<0.05) correlated with anxiety in experiment 1, but unexpectedly, anxiety was not correlated with SC indices of the BIS in either study. Although much of the data support the validity of the Gray/Fowles model, particular findings suggest that further refinement of this theory is indicated.