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.     

Sociability/impulsivity and caffeine-induced arousal: Critical flicker/fusion frequency and procedural learning

The influence of sociability/impulsivity in caffeine-induced arousal effects was investigated in two separate experiments: Experiment 1 examined critical flicker/fusion frequency change scores (ΔCFFT) in 60 subjects; and Experiment 2 investigated procedural learning in 30 subjects. In the two experiments, subjects received either caffeine citrate (500 mg) or placebo. The pattern of results was consistent across both studies:(1) a strong interactive effect of sociability (as measured by the EPQ extraversion scale) by caffeine/placebo which showed that (a) subjects low in sociability showed the greatest increase in ACFFT and learned most under placebo, while the reverse was true under caffeine; (b) subjects high in sociability, showed no increase in ΔCFFT and learned least under placebo, while the reverse was true under caffeine; and (2) in neither experiment did impulsivity (as measured by the EPS impulsiveness scale) significantly interact with caffeine/placebo. The results are consistent with Eysenck's (The Biological Basis of Personality, 1967) theory of personality in suggesting that subjects low in sociability are highly arousable under low-arousal (placebo) but over-aroused under high-arousal (caffeine), with the reverse pattern of effects holding for subjects high in sociability. The implications of these data for the respective roles of sociability and impulsivity components of extraversion in arousal-mediated performance are discussed.     

Stimulus significance effects in habituation of the phasic and tonic orienting reflex

Phasic and tonic measures of electrodermal activity were examined in a simple habituation paradigm, using innocuous visual stimuli. Separate groups were used to investigate the effects of stimulus significance, as manipulated by instructions. One group had no stimulus-related task (indifferent group), while the other was asked to silently count the stimuli to report to the experimenter later (significant group). Prestimulus skin conductance levels were considered as measures of the arousal level at each stimulus presentation, and the subsequent electrodermal responses were taken as the phasic orienting reflex (OR) elicited by each stimulus. Changes in prestimulus arousal were taken as measures of the tonic OR to the experimental series. Marked group differences were found in both phasic and tonic components of the OR. Some, but not all, of the significance effects in the phasic OR were attributable to differences in arousal. The results are discussed in the context of theoretical accounts of the OR.     

Stimulus Significance Effects in Habituation of the Phasic and Tonic Orienting Reflex

Phasic and tonic measures of electrodermal activity were examined in a simple habituation paradigm, using innocuous visual stimuli. Separate groups were used to investigate the effects of stimulus significance, as manipulated by instructions. One group had no stimulus-related task (indifferent group), while the other was asked to silently count the stimuli to report to the experimenter later (significant group). Prestimulus skin conductance levels were considered as measures of the arousal level at each stimulus presentation, and the subsequent electrodermal responses were taken as the phasic orienting reflex (OR) elicited by each stimulus. Changes in prestimulus arousal were taken as measures of the tonic OR to the experimental series. Marked group differences were found in both phasic and tonic components of the OR. Some, but not all, of the significance effects in the phasic OR were attributable to differences in arousal. The results are discussed in the context of theoretical accounts of the OR.     

Electrodermal measures of attention and effort to stimulus onset and offset for intramodal and intermodal tasks.

Two experiments were designed to assess the relationship between task difficulty and arousal. Electrodermal measures of tonic and phasic arousal to four levels of task difficulty at stimulus onset and offset were studied in college students for intramodal and intermodal tasks. The students were presented for 18 trails with visual-auditory or visual-visual stimuli with either 2.0-, 0.2-, or 0.02-sec difference between stimuli onset or offset, and asked to judge which stimulus came on or went off first or merely to observe the stimuli. Both frequency and amplitude of skin conductance responses reliably differentiated the levels of task difficulty for both the intramodal and the intermodal task. None of the measures of tonic level of arousal was reliable. Electrodermal measures of phasic responses accurately reflected the task demands.     

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.     

The interactive effect of personality, time of day, and caffeine: a test of the arousal model

The personality dimension of introversion/extraversion is one of the few personality dimensions that can be reliably identified from study to study and investigator to investigator. The importance of this demension within personality theory is due both to the stability of the trait and the influential theory of H. J. Eysenck. The basic assumption in Eysenck's theory of introversion/extraversion is that the personality differences between introverts and extraverts reflect some basic difference in the resting level of cortical arousal or activation. Assuming that there is a curvilinear relationship (an inverted U) between levels of stress and performance leads to a test of this arousal theory. That is, moderate increases in stress should hinder the performance of introverts who are presumably already highly aroused. However, the same moderate increase in stress might help the performance of the presumably underaroused extraverts. Revelle, Amaral, and Turriff reported that the administration of moderate doses of caffeine hindered the performance of introverts and helped the performance of extraverts on a cognitive task similar to the verbal test of the Graduate Record Examination. Assuming that caffeine increases arousal, this interaction between introversion/extraversion and drug condition supports Eysenck's theory. This interaction was explored in a series of experiments designed to replicate, extend, and test the generality of the original finding. The interaction between personality and drug condition was replicated and extended to additional cognitive performance tasks. However, these interactions were affected by time of day and stage of practice, and the subscales of introversion/extraversion, impulsivity, and sociability, were differentially affected. In the morning of the first day, low impulsives were hindered and high impulsives helped by caffeine. This pattern reversed in the evening of the first day, and it reversed again in the evening of Day 2. We concluded that the results from the first day of testing require a revision of Eysenck's theory. Instead of a stable difference in arousal between low and high impulsives, it appeared that these groups differed in the phase of their diurnal arousal rhythms. The result is that low impulsives are more aroused in the morning and less aroused in the evening than are the high impulsives. A variety of peripheral or strategic explanations (differences in caffeine consumption, guessing strategies, distraction, etc.) for the observed performance increments and decrements were proposed and tentatively rejected. It seems probable that some fundamental change in the efficiency with which information is processes is responsible for these performance changes.     

Impulsivity, caffeine, and proofreading: a test of the Easterbrook hypothesis

Easterbrook's (1959) suggestion that arousal is inversely related to the range of cue utilization has been frequently cited as an explanation for the curvilinear relationship between arousal and performance. There is very little empirical support for this position, however. As a test of the Easterbrook hypothesis, 60 undergraduates who varied in their impulsivity level were given caffeine or placebo and then asked to proofread several passages. Estimates of sensitivity were calculated using signal detection techniques. It was predicted that high arousal would reduce sensitivity to interword errors, which require a broad range of cue utilization, but that the observed levels of arousal would not affect sensitivity to intraword errors, which require a minimal range of cue utilization. A significant crossover interaction between impulsivity and drug for interword errors indicated that caffeine increased the error detection rate of the (less aroused) more impulsive subjects but lowered the error detection rate of the (more aroused) less impulsive subjects. The results of this study support the suggestion that arousal has direct effects on the capacity for simultaneous information processing, independent of its effects on performance speed.     

Personality and multidimensional arousal: A study of two dimensions of extraversion

Recent research has provided conflicting accounts of the effects of extraversion on arousal, and of the role of arousal in effects of extraversion and impulsivity of performance. Data are presented from a study of the inter-relationships of various dimensions of extraversion, self-report arousal and physiological arousal. Subjects also performed a verbal intelligence test. A composite measure of skin conductance and heart rate was significantly positively correlated with a self-report general arousal measure. 16PF Extraversion, and two primary extraversion factors, F and H, were significantly negatively correlated with physiological arousal, and/or one dimension of self-report arousal. The relationship between extraversion and arousal was not affected by time of day. An interactive effect of time of day, F and general arousal on performance was found, but there were no significant effects of H on performance. Relationships between extraversion and arousal may be epiphenomenal to interactive effects of extraversion or impulsivity and arousal on performance.     

Extraversion, activation and the recall of prose.

Subjects were divided into four groups on the basis of their scores on the extraversion scale of the Eysenck Personality Inventory and the general activation scale of Thayer's Activation-Deactivation Adjective Check List. A prose passage was presented to subjects who then attempted to recall it under strict instructions to avoid errors. There were significant interactions between activation and extraversion for the error data, and the phrase-correct data, with moderate levels of arousal (high activation extraverts and low activation introverts) being associated with the fewest errors and the most phrases correctly recalled. It was concluded that the study showed the importance of arousal to recall performance, possibly due to the effects of arousal on retrieval processes.     

Tracking arousal state and mind wandering with pupillometry

In four experiments, the association between arousal state and different mind-wandering states was examined. Participants performed a sustained attention task while pupil responses were continuously recorded. Periodically during the task, participants were presented with thought probes to determine if they were on task or mind wandering. Across the four experiments, the results suggested that in situations that promoted on-task behaviors and focused external attention, mind wandering was associated with lowered arousal, as seen by smaller tonic pupil diameters and smaller phasic pupillary responses. However, in situations that promoted a more internal focus of attention, there were no differences between on-task states and mind wandering in tonic pupil diameter (although differences emerged for phasic pupillary responses), suggesting similar arousal levels. Furthermore, across the four experiments, mind blanking and mind wandering dissociated in terms of whether the situation promoted focused external attention or focused internal attention. These results are broadly consistent with the notion that mind wandering is a heterogeneous construct, with different forms of mind wandering being associated with different arousal states, and suggest that a combination of behavioral and pupillary measures can be used to track these various states.     

Impulsivity,neuroticism, and caffeine: Do they have additive effects on arousal?

The personality dimensions of impulsivity and neuroticism have been linked to differences in basal arousal. The hypothesis tested was whether these personality variables and caffeine have additive effects on arousal. All subjects received three paired-associate trials on each of two neutral control lists, two lists with semantically similar stimuli, and two lists with acoustically similar stimuli. Half of the subjects received caffeine and half placebo. Although significant interactions with personality and drug condition were obtained, the ordering of the conditions was inconsistent with the assumption that the arousal performance curve is single peaked. Further, S. Schwartz's (Journal of Research in Personality, 1975, 9, 217–225) hypothesis that in paired-associate learning high arousal and low arousal subjects process semantic and physical information differentially was not supported. The general issue of how to determine whether individual differences in performance are caused by differences in arousal is discussed.     

Cardiac-somatic changes during a simple reaction time task: A developmental study

The relationship during a simple reaction time task between heart rate and four measures of task irrelevant somatic activity was evaluated in four age groups of children, i.e., 4-, 5-, 8-, and 10-year-olds and young adults, in order to evaluate further a hypothesized coupling of cardiac and somatic activity. At all age levels, phasic decreases in both heart rate and somatic activity coincident with performance were found with the magnitude of the effect increasing with age only on three somatic measures. However, tonic levels of both heart rate and somatic activity decreased with age. Performance on the reaction task was found to be inversely related to the age-related phasic somatic effects as well as age-related tonic heart rate and somatic activity.     

A quantitative review of the relations between the “Big 3” higher order personality dimensions and antisocial behavior

In this meta-analytic review, Hans J. Eysenck’s theory of criminality (Eysenck, 1964, Eysenck, 1977) serves as a theoretical framework for examining the relations between higher order personality dimensions and antisocial behavior (ASB). The three higher order dimensions examined are referred to as extraversion/sociability, neuroticism/emotionality, and impulsivity/disinhibition (see Sher & Trull, 1994), and they are likened to Eysenck’s dimensions of extraversion (E), neuroticism (N), and psychoticism (P), respectively (Eysenck & Eysenck, 1975) and Tellegen’s dimensions of positive emotionality (PEM), negative emotionality (NEM), and constraint (reversed) (CON), respectively (Tellegen, 1982). Ninety-seven samples, from 52 published and unpublished studies, were reviewed. The results indicated that among the “Big 3” personality dimensions, impulsivity/disinhibition is most strongly related to ASB and extraversion/sociability is least strongly related to ASB. Additional variables, including age and methodological differences, were found to moderate the associations between the personality dimensions and ASB.     

Sociability/impulsivity and attenuated dopaminergic arousal: critical flicker/fusion frequency and procedural learning

Two experiments examined the interaction of sociability (Soc) and impulsivity (Imp) components of extraversion and reduced dopamine activity (by haloperidol) on critical flicker/fusion frequency change scores (ACFFT) and procedural learning. In double-blind designs, subjects received either haloperidol (5 mg) or placebo; Soc and Imp were randomly sampled. In Experiment 1, Drug × Imp, and Drug × Imp × Soc interactions were found on ΔCFFT; in Experiment 2, a drug × Soc interaction was found on procedural learning. In both experiments, introverts seemed over-aroused under placebo (putatively due to the medical context), more optimally aroused under haloperidol; for procedural learning, extraverts seemed more optimally aroused under placebo, less optimally aroused under haloperidol. These data indicate that both Soc and Imp mediate the effects of arousal; Drug × Imp effects my conceal joint effects of Soc × Imp; and that Soc shows more consistent effects than Imp. These data complement a previous study of Soc/Imp and caffeine-induced arousal (Corr, Pickering & Gray, 1995), and lend support to H. J. Eysenck's (1967) arousal model of Extraversion.     

Individual differences in circadian activity rhythm and personality

Individual differences in circadian activity rhythms were assessed in terms of peak activity time, rising time and retiring time reported every day for 84 consecutive days. A 19-item Morningness-Eveningness Questionnaire (MEQ) was found to significantly correlate with time-of-day effects on these three circadian activity measures, as well as with parental report of the S's peak activity time. Several measures of extraversion were also found to correlate significantly with the MEQ, as well as with rising and retiring time, suggesting that extraverts are evening types. However, when the differential effects of sociability and impulsivity were examined it was found that the sociability component of extraversion was most responsible for the time-of-day differences. This result diverges somewhat from previous findings that suggest impulsivity is the component responsible for time-of-day effects. This apparent contradiction is discussed in terms of arousal being a non-urinary construct, with different indices of circadian arousal allowing for differential correlates with specific personality components.     

Comparison of EPI and psychoticism scales with measures of the five-factor model of personality

The need for a comprehensive model of personality traits acceptable to the entire community of personality researches has often been acknowledged. In this article, two such models are compared. Eysenck scales measuring neuroticism, extraversion, psychoticism and lie are correlated with self-report and peer-rating measures of the five-factor model—neuroticism, extraversion, openness to experience, agreeableness and conscientiousness—in a sample of adult men and women. Findings suggest that: (1) neuroticism and extraversion factors from the two systems match well; (2) sociability and impulsivity are distinguishable traits, but both fall within the broad domain of extraversion; (3) the EPI L scale measures aspects of several substantive traits rather than a response bias; (4) openness to experience is not well-represented in the Eysenck system; and (5) psychoticism corresponds most closely to the low poles of agreeableness and conscientiousness.     

Cardiac activity in a simple reaction time task

Twenty subjects, half having high extraversion and the other half having low extraversion scores on the Eysenck Personality Inventory, performed a simple reaction time task in which the warning stimulus was a light and the imperative stimulus was a tone. Beat-by-beat analysis showed significantly different response patterns between the two groups in time of onset, magnitude, and duration of the cardiac responses. The extraversion measures were found to relate to central-nervous-system-strength types and to indicate relative strength of central inhibitory processes, as reflected by cardiac activity.     

Physiological arousal in the context of a specified anticipatory period and experimentally induced expectancy for shock

Anticipatory and reactive components of skin conductance and heart rate were assessed under different levels of shock expectancy. Sixty college males received two shock and two nonshock trials of a 12-light count-up where shock occurred at the eighth light. Expectancies were experimentally induced via 20 preliminary trials during which a red light substituted for shock. The red light appeared on 18/20, 10/20, and 2/20 preliminary trials for 90, 50, and 10% expectancy groups, respectively. Prior to each test trial, subjects estimated the likelihood of receiving shock. Major findings were that: (a) mean probability estimates corresponded closely with values provided by preliminary trials; (b) tonic skin conductance during anticipation was higher with greater expectancy for shock; (c) phasic change in skin conductance to the count-up lights was greatest in the 90% group during anticipation; and (d) reactivity at impact tended to be greater with higher anticipatory arousal. The relationship of event probability to stress was discussed with respect to length of the anticipatory periods and methods used to establish expectancies.     

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.