Extraversion and electrodermal activity: arousability and the inverted-U

The Eysenck hypothesis that extraverts are less aroused or more inhibited than introverts has been subjected to a number of tests in the psychophysiological literature. Research to date suggests the need to clearly differentiate between tests of overall group differences in arousal or inhibition and studies of the differential reactions of the two groups to arousal manipulations. Psychophysiological studies of overall arousal differences in our laboratories and elsewhere have yielded somewhat inconsistent results for SCL, nonspecific response frequency, trials-to-criterion habituation and initial response amplitude, though dishabituation results are consistent with the expectation of higher amplitudes in introverts. Far more consistent are findings testing the inverted-U hypothesis, which suggests that introverts reach a point of optimal arousal at lower levels of stimulus input than do extraverts and hence should show earlier asymptotes and decrements in arousal measures. Using stimulus intensity and caffeine to manipulate arousal, we have found supportive results for SCL and several phasic measures, including the initial, test, and dishabituation responses. Overall, findings suggest that the two personality groups differ more clearly in arousability than in overall arousal level and that this difference is most consistent when conditions induce a rapid breakdown of inhibition and increase in arousal. Further research is needed to better understand the conditional relationship of extraversion to arousability, and arousal-manipulation paradigms would appear to be a fruitful initial approach to carrying out the needed research.     

Habituation and dishabituation of the electrodermal orienting reflex in relation to extraversion and neuroticism

Orienting reflex (OR) habituation and dishabituation may be influenced by individual difference variables, including Eysenck's Extraversion (E) and Neuroticism (N) dimensions. Ninety subjects formed nine groups based on the crossover of high, medium, and low E and N. Each subject received, at each of two auditory stimulus intensities, two blocks of tone presentations. The last standard stimulus trial was followed by a novel stimulus and four repetitions of the standard stimulus. Using square root SCR, extraverts showed smaller initial response amplitudes than introverts at the low intensity of stimulation, while the reverse was true at high intensity. E and N were unrelated to SCR habituation rate. However, extraverts showed no dishabituation, while introverts did dishabituate.     

Extraversion and neuroticism in orienting reflex dishabituation

The present study examined the effects of extraversion (E) and neuroticism (N) as individual difference dimensions and of stimulus intensity on electrodermal orienting response habituation, test response, and dishabituation. Subjects were 162 college students selected from a screening sample of 860 as representing extreme groups of high, medium, and low E crossing with high, medium, and low N. Subjects in all nine resulting groups were habituated to criterion on auditory stimuli of 60, 80, and 100 db. A novel (test) stimulus and a dishabituating standard stimulus followed criteron habituation at each intensity. Results indicated that response amplitude for initial, test, and dishabituation responses was a direct function and that habituation rate (trials-to-criterion) was an inverse function of stimulus intensity. Extraverts habituated more rapidly than introverts at high intensity and gave smaller test and dishabituation responses. Some results differed when regression coefficients defined habituation rate and when first stimulus intensities alone were examined. Correlations among initial, test, and dishabituation responses and between each of these and the two measures of habituation rate are also reported. Results were interpreted as partially supportive of Eysenck's theory.     

Extraversion, attention, and habituation of the auditory evoked response

Short-term changes in the auditory evoked response to low-frequency tones (0.5 kHz, 80 dB) were examined for independent groups of introverts and extraverts under attend and ignore conditions. Introverts displayed greater N1-P2 amplitude than extraverts to the first stimulus in a four-stimulus train. The N1-P2 amplitude differences between introverts and extraverts could not be attributed to differences between the groups in either habituation or attention processes. Overall, the effect is indicative of the introverts' enhanced sensitivity to physical stimulation.     

Electrodermal activity and extraversion: Caffeine,preparatory signal and stimulus intensity effects

The Eysenck hypothesis that introverts are more and extraverts less cortically aroused has been supported by the results of most electrodermal studies, though there is some inconsistency in the literature. Further tests of the hypothesis can be carried out using arousal-manipulation paradigms. Some studies have used caffeine or stimulus intensity to increase arousal, as was also the case in the present study. The latter, however, also introduced a preparatory signal, which may be expected under certain conditions, to reduce responses to the stimulus which follows it. Extraverts and introverts were randomly assigned to receive low, medium or high doses of caffeine or a placebo. Each S then heard two sets of tones with the tones in one set preceded by a preparatory signal. Results showed that the preparatory signal reduced phasic amplitudes only at the highest levels of stimulus intensity. Introverts had higher overall SCLs and response magnitudes. In addition, the preparatory signal had little effect on extraverts, but reversed dosage-related response patterns in introverts. Results were supportive of the basic Eysenck arousal hypothesis and also showed that the arousal difference leads to attentional variability between the two groups.     

Attention and personality in augmenting/reducing of visual evoked potentials

Earlier research has shown that extraverts tend to increase their visual evoked potential amplitudes with increasing light intensity (augmenting), while introverts reach their maximum amplitude at lower intensities (reducing). The evoked response has normally been measured from association areas of the brain (at the vertex). The present study measured VEP amplitudes over visual cortex and at the vertex, using four light intensities in two conditions, where attention was either directed towards the light stimuli, or away from them by a concurrent auditory task. Forty subjects were classified as extraverts or introverts based on the Eysenck Personality Inventory. The results show that attention interacted significantly with extraversion. Introverts exhibited a narrower focus of attention, while higher amplitudes and amplitude-intensity functions when attending to the light flashes and lower when distracted. Extraverts showed smaller differences between conditions, indicating a more evenly distributed attention. Higher arousal in introverts is the probable cause of their narrower focus of attention. There were marked differences in the distribution of activity between vertex and occipital cortex. Introverts showed relatively stronger occipital responses and extraverts stronger vertex responses across all intensities and in both conditions. The predisposition for mainly perceptual responses to aversive stimuli in introverts, and for general alerting and motor preparatory responses in extraverts, are interpreted as supportive of Brebner and Cooper's hypothesis that introverts are ‘geared to inspect’ and extraverts are ‘geared to respond’.     

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.     

Extraversion and reactions to cognitive inconsistency

Two studies are reported which test the hypothesis that extraverts are more tolerant of cognitive inconsistency than are introverts. The first study tested this prediction in the context of Heider's balance model. While degree of extraversion did not moderate reactions to imbalance, extraverts did show less aversion to interpersonal disagreement than introverts. When coupled with other recently published data this suggests that extraverts find arousing social situations less aversive than introverts. In support of the main hypothesis, the second experiment showed that extraverts changed their attitudes less than introverts as a result of writing an essay which was counter to their own attitude under conditions where they had high perceived freedom of choice.     

Memory scanning,introversion-extraversion,and levels of processing

Individual differences in information processing were studied in the form of the hypothesis that arousal, as indexed by a personality measure of introversion-extraversion, affects the speed with which certain kinds of processing are completed. The Sternberg paradigm was used, and the results suggested that introverts and extraverts scanned for physical features equally rapidly, but that introverts were slower than extraverts at scanning for the semantic features of category membership. There was limited support for the hypothesis that introverts, thought to be more aroused than extraverts, are less able to engage in shared or parallel processing. It was concluded that information processing in introverts and extraverts may differ qualitatively as well as quantitatively.     

Effects of noise on sensitivity of introverts and extraverts to signals in a vigilance task

Forty Ss, previously classified as introverts or extraverts on the basis of scores on the Eysenck Personality Inventory, performed a visual vigilance task while being stimulated with noise at an intensity level of either 65 or 85 dB. Introverts given noise of 65 dB intensity showed an improvement in detection rate across trials, whereas introverts given noise of 85 dB intensity showed a decline in detection rate. Extraverts responded to noise of 65 dB intensity with a slight decrease in detection rate, but showed an improvement in detection over trials when noise of 85 dB intensity was given. When noise of the lower intensity was given, introverts showed greater sensitivity to signals than extraverts. When noise of the higher intensity was given, introverts and extraverts were equal in sensitivity. The results are discussed in terms of a hypothesized relationship between stimulation and arousal, with E-I as a moderator variable.     

Extraversion and the orienting reaction habituation rate to visual stimuli

Eysenck's (1967) proposal that introversion is characterized by increased levels of activity in the cortico-reticular loop was treated in a series of experiments which compared high, middle, and low extraversion groups on the basis of OR habituation rate to visual stimulation. Generally, introverts were observed to have longer OR habituation rates to chromatic and word stimulation than extraverts as evidenced by cardiac, electrodermal, and vasomotor indices of habituation rate, a result which endorses Eysenck's hypothesis. Results are also discussed from the standpoint of individual differences in autonomic response.     

Personality and the topography of the conditioned eyelid response

One-hundred and four women were tested on an eyelid conditioning paradigm in a 2 x 2 x 2 factorial design where two levels of US intensity (1 vs 3 p.s.i.) were balanced against two rest pause interpolations (after 25 and after 50 trials), and the presence or absence of a warning stimulus prior to CS-US presentation. Subjects were later classified as high, low or intermediate extraverts on the basis of a personality questionnaire. A very detailed analysis of conditioned responses was carried out, using both simple and composite measures including work-ratio, utility-ratio, CR frequency, peak latency, peak amplitude, response area and effective response area, degree of avoidance amplitude and latency, etc. Major findings related to similar effects of high intensity US vs low intensity US, and introversion vs extraversion; introverts react as if they were responding to more intense stimuli than extraverts. This finding cuts across other parameter variables, and supports Eysenck's formulation of personality-conditioning relationships in terms of higher cortical arousal in introverts as compared with extraverts.     

Differences in the transmission of sensory input into motor output between introverts and extraverts: Behavioral and psychophysiological analyses

The present study was designed to investigate extraversion-related individual differences in the speed of transmission of sensory input into motor output. In a sample of 16 introverted and 16 extraverted female volunteers, event-related potentials, lateralized readiness potentials (LRPs), and electromyogram (EMG) were recorded as participants performed a visual choice reaction time task. As additional behavioral indicators of performance, measures of reaction time (RT) and response dynamics were obtained. Although extraversion-related differences were found neither for behavioral measures nor for the N1 and P3 components of the evoked potential, introverts showed a reliably shorter latency in stimulus-locked LRP than extraverts. This latter finding supports the notion of faster stimulus analysis in introverts compared to extraverts. Furthermore, there was no indication of extraversion-related individual differences in speed of response organization and response execution as indicated by response-locked LRP and EMG latencies, respectively. However, a significantly higher EMG amplitude observed with introverts pointed to a less accurately adjusted motor output system of introverts compared to extraverts.     

认知操作、认知方式与外倾性人格特质的关系

对28名外倾被试和28名内倾被试进行实验性认知测试,以考察认知操作、认知方式与外倾性人格特质的关系。结果表明,内外倾被试在含有社会认知操作、非社会认知操作的认知任务的测试总分上没有差异,而在社会认知一非社会认知方式的评价分数上存在显著差异。外倾被试更多地倾向于社会认知型认知方式,内倾被试更多地倾向于非社会认知型认知方式。研究结果支持了外倾性与智力关系的假设：外倾性与社会认知一非社会认知的认知方式存在相关关系,而与认知操作测试总分无关。     

Biological Bases of Extraversion Psychophysiological Evidence

There is a good deal of evidence, particularly from electrodermal and electrocortical recording procedures, that introverts exhibit greater reactivity to sensory stimulation than extraverts. There is little evidence that introverts and extraverts differ in base level of arousal in neutral conditions, and there is no clear evidence that their differences in sensitivity to stimulation are determined by differences in attentional state. Faster auditory brainstem evoked response latencies observed for introverts implicate differences in peripheral sensory processes that are not determined by mechanisms in the reticular system as proposed in the arousal hypothesis. There is also evidence that individual differences in the expression of motor activity between introverts and extraverts involve differences in motoneuronal excitability.     

Dishabituation and spontaneous recovery of the electrodermal orienting response: Effects of extraversion,impulsivity, sociability,and caffeine

The relationship between extraversion and psychophysiological indices of arousal is not yet fully understood. The present study attempted to further clarify this relationship by using caffeine to systematically manipulate arousal. Subjects pretested on the Eysenck Personality Inventory were given caffeine or a placebo, then underwent habituation, dishabituation, and spontaneous recovery of the electrodermal OR. Separate analyses examined the main and interactive effects of extraversion, impulsivity, and sociability with caffeine. Several tonic and phasic measures showed group reversal effects, with introverts having higher tonic levels and larger phasic responses under placebo conditions and extraverts having larger phasic responses and higher tonic levels under caffeine. Although both tonic and phasic responses were differentially affected, the group reversal effects occurred at different points in time on tonic than they did on phasic measures relative to the theoretical buildup of inhibition. The findings for impulsivity were quite consistent with those for extraversion, and both sets of results were generally supportive of the Eysenck hypothesis.     

Individual differences in components of slow cortical potentials: implications for models of information processing

Individual differences in the effects of pharmacological and behavioural manipulations on slow cortical potentials (SCP), may reflect personality differences in type of informational control under attentional stress. Two experiments were conducted to examine SCP component differences in extraverts and introverts under different attentional tasks and with and without nicotine smoking ‘stressor’ conditions. In an initial experiment a decrease in late negativity for introverts and an increase in late negativity for extraverts suggested that smoking enhanced introverts' stimulus set and extraverts' motor set. In a second experiment, personality differences in SCP were examined again, but within a signal-detection paradigm, which allows separate assessment of the contribution of sensory sensitivity and response bias factors to performance. Smoking increased sensitivity in both personality groups, but response bias (caution) increased in introverts only. Extraverts showed an increase in central negativity during smoking whilst introverts showed a decrease in negativity and a decrease in positive wave components. The results are explained in terms of a motor model of attentional control whereby smoking regulates inhibitory controlled actions in introverts, but activates general motor processes for extraverts.     

Study habits and Eysenck's theory of extraversion-introversion

Predictions derived from Eysenck's theory of personality were tested in two samples by relating extraversion scores to library study locations, frequency of study breaks, and self-report of factors which influence study location. The predicted main effects for study location were found, with extraverts occupying locations that provided greater external stimulation. Positive correlations were consistently found between extraversion and preferred level of noise, preferred level of socializing opportunities, and rated importance of socializing opportunities. The prediction that extraverts would take more frequent study breaks was supported in Sample 1 but not replicated in Sample 2. The data are interpreted as providing direct support for Eysenck's theory of behavioral differences and mixed indirect support for his theory of neurological differences between introverts and extraverts.     

Stimulus- or response-induced excitation. A comparison of the behavior of introverts and extraverts

The tendency to inspect visual material (slides) rather than to respond by pressing a key in an attempt to move on to the next slide, was compared among introverts and extraverts. As predicted from Brebner and Cooper (1974): (1) extraverts inspected the stimuli for a shorter time before making their first response, (2) extraverts made more responses at a faster rate than introverts did, and (3) extraverts produced a significantly higher proportion of runs of accelerating responses.     

Extraversion and task performance: A fresh look through the workload history lens

This study manipulated workload levels and used a technique examining workload history to test Eysenck’s (1967) theory of extraversion. Participants consisted of 71 undergraduates who had been selected from a larger pool that had completed the Eysenck Personality Inventory. Participants performed an auditory vigilance task while percent correct data were recorded. A repeated measures ANOVA was conducted and results indicated that extraverts and introverts respond differently to a sudden decrease in workload level. Specifically, a sudden decrease in workload level resulted in an immediate significant decrement in correct responses for extraverts while the decrement for introverts was minimal. Limitations were discussed and implications for future research were addressed.