Bucking Ham) Extra Version & Physiological Re Activity

8/8/2019 Bucking Ham) Extra Version & Physiological Re Activity

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Extraversion, neuroticism and the four temperaments of

antiquity: an investigation of physiological reactivity

Robert M. Buckingham *

Department of Psychology, University of Sydney, Sydney, NSW 2006 Australia

Received 7 August 2000; received in revised form 7 January 2001; accepted 9 January 2001

Abstract

The present study adopted an historical perspective, which highlighted the place of Pavlov's work on the

four classical temperaments in current theory and research on personality. Drawing on the work of Pavlov

and the later contribution of [Robinson (1996). Brain, mind, and behavior: a new perspective on human

nature. Westport, C.T.: Praeger Publishers] it was hypothesised that dierences in cerebral reactivity con-

trast the sanguine (low reactivity) and melancholic (high reactivity) temperaments. The EPQ was used to

identify four extreme groups of female subjects corresponding to the classical temperaments: ES/sanguine

(n=16), EN/choleric (n=16), IS phlegmatic (n=8) and IN/melancholic (n=16). Reactivity indices inclu-

ded P1N1 and N1P2 response components of the vertex evoked potential to three dierent tone intensitiesand three dierent light ash intensities. Using extraversion and neuroticism as between subject factors and

intensity as a repeated measures factor, separate analyses of variance for each dependent variable revealed

no signicant personality related eects. In comparison, planned contrasts between the ES and IN groups

revealed a number of signicant dierences in the auditory modality but no signicant dierences in the

visual modality. In accord with prediction, the IN group exhibited signicantly steeper auditory P1N1 and

N1P2 amplitude intensity functions than the ES group. Also in accord with prediction, the IN group

exhibited higher overall auditory P1N1 and N1P2 amplitudes, however, only the P1N1 dierence was sig-

nicant. It was argued that auditory evoked potential amplitude provides a more appropriate index of

cerebral reactivity than visual evoked potential amplitude. # 2001 Elsevier Science Ltd. All rights

reserved.

Keywords: Extraversion and neuroticism; Classical temperaments; Reactivity; AEP; VEP

1. Introduction

Pavlov's inuence on biologically oriented personality theories has been profound (e.g.

Eysenck, 1957, 1967; Gray, 1987; Mangan, 1982; Nebylitsyn, 1972; Robinson, 1996; Strelau,

0191-8869/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.P I I : S 0 1 9 1 - 8 8 6 9 ( 0 1 ) 0 00 2 0 - 4

Personality and Individual Differences 32 (2002) 225246

www.elsevier.com/locate/paid

* Tel.: +61-2-9351-5149; fax: +61-2-9351-2603.

E-mail address: [email protected]


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1983; Teplov, 1964; Zuckerman, 1994). Pavlov's (1955) extensive study of brain-behaviour rela-

tions in the dog led him to conclude that canine temperament could be classied according to the

four classical temperaments of antiquity and that these temperamental dierences related to dif-

ferences in the functional properties of brain cells located in the cerebral cortex.One basic property, central to Pavlov's work, was the strength of the nervous system. Pavlov

observed that the size of the conditioned response was typically directly proportional to the

intensity of the conditioned stimulus (i.e. the law of strength). However, it was found that for

every animal there was a maximum level of stimulation beyond which an increase in intensity

produced a reduction in response magnitude. This distortion of the usual relationship between

stimulus intensity and response magnitude was attributed to the development of a generalised

inhibition induced to protect the central nervous system from functional exhaustion. The onset of

protective inhibition came to be used by Pavlov (1957) as a key index of the strength of the ner-

vous system. Relative to a strong nervous system, a weak nervous system was thought to possess

highly reactive cortical cells, which passed into a state of protective inhibition more easily. Theweak and strong nervous systems were found to correspond to the melancholic and sanguine

temperaments, respectively.

A number of psychophysiologists have applied the Pavlovian concept of nervous system

strength to the event related potential (ERP) and in particular, the augmenting/reducing

phenomenon (e.g. Buchsbaum & Silverman, 1968; Lukas & Siegel, 1977; Zuckerman, Murtaugh,

& Siegel, 1974). In this context, the terms ``augmenting'' and ``reducing'' typically refer to chan-

ges in P1N1 (P100-N140) amplitude at the vertex to an increase in light ash intensity. To dene

augmenting and reducing styles, Buchsbaum and Silverman (1968) correlated visual evoked

potential (VEP) amplitude with the logarithm of ash intensity to identify those subjects who

displayed a positive amplitude-intensity slope (augmenters) and those subjects who displayed a

negative amplitude-intensity slope (reducers). According to Buchsbaum and Silverman, aug-menting was indicative of a strong nervous system, reducing a weak nervous system.

The methodology employed by Buchsbaum and Silverman to classify augmenting and reducing

styles has attracted some criticism. In particular, a number of researchers have provided evidence

which calls into question the assumption of linearity associated with the VEP slope measure (e.g.

Connolly & Gruzelier, 1982a; Iacono, Gabbay, & Lykken, 1982). Furthermore, Soskis and

Shagaas (1974) report that change in mean amplitude is a more reliable measure of augmenting/

reducing than slope. Several authors have also suggested that the latency ranges for peak identi-

cation suggested by Buchsbaum and Pfeerbaum (1971) are too narrow (e.g. Connolly and

Gruzelier, 1982b; Carrillo-De-La-Pen a and Barratt, 1993). Indeed, one of the main problems with

the study of the ash VEP is the large variability in waveform between individuals. As Halliday(1982) observed this makes reliable identication of the dierent peaks problematic.

1.1. Problems with a Pavlovian conceptualisation of ERP augmenting and reducing

In addition to these methodological issues, there has also been some scepticism concerning

Buchsbaum and Silverman's suggestion that the augmenting/reducing phenomenon is related to

the Pavlovian concept of nervous system strength. While strength of the nervous system was

conceived of as a generalised property (Pavlov, 1957), ERP augmenting/reducing shows poor

topographical consistency (e.g. Stenberg, Rose n, & Risberg, 1988; Stenberg, Rose n, & Risberg,

226 R.M. Buckingham / Personality and Individual Dierences 32 (2002) 225246


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1990); a lack of consistency between P1N1 and later amplitude measures such as N1P2 (Blenner,

1993; Friedman & Meares, 1979; Stenberg et al., 1988); and a lack of consistency between the

visual and auditory modalities (e.g. Blenner and Yingling, 1993; Kaskey, Salzman, Klorman, &

Pass, 1980; Raine, Mitchell, & Venables, 1981; Stenberg, et al., 1988).Robinson, Haier, Braden, and Krengel (1984), make the further observation that, for ethical

reasons, the stimulus intensities used in the augmenting/reducing literature are unlikely to result

in protective inhibition. They point out that ``Pavlov associated this phenomenon with `ultra

strong' stimulation which is why one of his most revealing techniques has not been applied in the

case of human subjects'' (p. 12). Reports that visual reducing occurs over a range of stimulus

intensities, including relatively low intensities, are not readily accounted for in terms of protective

inhibition (Buchsbaum, 1976, 1978; Connolly & Gruzelier, 1982a; Haier, Robinson, Braden &

Williams 1984; Kaskey et al., 1980; Zuckerman et al., 1974). Furthermore, some investigators

have even reported a quadratic amplitude-intensity function where amplitude is lowest at inter-

mediate stimulus intensities (e.g. Connolly and Gruzelier, 1982a).While Buchsbaum and Silverman's work has focused attention on the visual modality, stronger

evidence in favour of a Pavlovian conceptualisation of the augmenting/reducing phenomenon

comes from research into the auditory modality. As would be expected, given the maximum

stimulus intensities employed in human studies (around 100 dB), the vast majority of AEP studies

have found a positive linear amplitude-intensity relationship. (Blenner & Yingling, 1993; Bruneau,

Roux, Garreau, & Lelord, 1985; Davis & Zerlin, 1966; Kaskey et al., 1980; Khechinashvili,

Kevanishvili, & Kajaia, 1973; Mullins & Lukas 1984; Orlebeke, Kok, & Zeillemaker, 1989; Pic-

ton, Goodman, & Bryce 1970; Raine et al., 1981; Stenberg et al., 1988; Zuckerman, Simons, &

Como, 1988). A number of investigators have in fact suggested that reliable reducing trends do

not occur at all in the auditory modality (e.g. Kaskey et al., 1980; Raine et al., 1981). Raine et al.

(1981) also note that auditory evoked potential (AEP) amplitude-intensity slope scores tend to benormally distributed while VEP slope scores tend to be bimodal (Buchsbaum & Pfeerbaum,

1971) a distribution which is more consistent with an augmenting/reducing dichotomy.

While there is little evidence in favour of auditory reducing, some studies report an asymptotic

amplitude/intensity function suggestive of a protective inhibitory inuence (e.g. Khechinashvili et

al., 1973; Picton et al., 1970; Zuckerman et al., 1988). These studies also draw attention to stimulus

parameters other than intensity which, in view of Pavlov's work, will also contribute to the

amount of cortical fatigue. Pavlov (1955) came to dene strength of the nervous system in terms

of (a) the maximum response to a single application of a stimulus, and; (b) the maximum

duration of the response to repeated applications of a moderate intensity stimulus. In the ERP

paradigm, protective inhibition would most likely develop when a large number of strong inten-sity stimuli are presented at a high frequency.

A relationship between the frequency of stimulus presentation and response amplitude has

been demonstrated by a number of researchers. An ISI of at least 610 s is recommended for

eliciting both the largest auditory V-potential (Davis, Mast, Yoshie, & Zerlin, 1966; Fruhstorfer,

Soveri, & Ja rvilehto, 1970) as well as the later P3 and N3 components (Davis et al., 1966). Davis,

et al. reported that with an irregular ISI the average amplitude of the N1P2 peak was maximal at

610 s, half the maximum at 3 s, and quarter the maximum at 1 s. Similarly, Zuckerman et al.

(1988) employed two ISIs, either 2 s which is close to that employed by Buchsbaum and Silver-

man (1968) or a much longer ISI of 17 s. Zuckerman et al. (1988) report a decline in mean

R.M. Buckingham / Personality and Individual Dierences 32 (2002) 225246 227


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amplitude at 80 dB and 95 dB but only for the shorter ISI. Similarly, Picton et al. (1970) used ISIs

ranging from 0.5 to 10.5 s and report that a decline in response amplitude at the highest stimulus

intensity (100 dB) was only noticeable when stimuli where presented at intervals of 2.5 s or less.

The potential inuence of the total number of stimulus presentations on ERP amplitude hasbeen documented by Robinson (1993) who recorded EEG responses to one hundred 85 dB tones

and then computed averages for the rst 10 responses and the last 10 responses. P1N1 amplitude

of the average based on the last 10 responses was more than half that of the average based on the

rst 10 responses. While some augmenting-reducing studies have used as few as eight stimuli (e.g.

Buchsbaum & Pfeerbaum, 1971) others have employed up to a 100 or more (e.g. Khechinashvili

et al., 1973).

Also relevant in the present context is whether stimuli of dierent intensities are randomly

presented in one block or presented in dierent blocks of the same intensity. Pavlov's (1955)

research on extinction with reinforcement (a phenomenon he attributed to protective inhibition)

would suggest that randomly presenting dierent intensity stimuli in the one block is less likely toinduce protective inhibition.

1.2. Personality and ERP amplitudes

Eysenck (1967) suggested that extraversion dierences were causally related to dierences in

cortical arousability. Drawing on Gray's (1964) work, Eysenck (1981) argued that the concept of

arousability was synonymous with that of strength of the nervous system. According to this for-

mulation, extraverts have low arousability (a strong nervous system) and introverts high arousa-

bility (a weak nervous system). Eysenck's theory would, therefore, predict that over low to

moderate stimulus intensities, introverts will have steeper amplitude-intensity slopes as well as

higher mean amplitude responses than extraverts. In the event that protective inhibition were to

develop to moderate or high intensity stimuli, it would be expected that introverts will demon-strate an asymptotic amplitude-intensity function and possibly a reducing trend while extraverts

will continue to exhibit a linear amplitude-intensity function. Under such conditions the dier-

ence in mean amplitude between extraverts and introverts would be small or non-existent. If

ultra-strong stimulus intensities were permitted extraverts would exhibit higher mean amplitudes

than introverts.

In the visual modality, most researchers have found either no signicant correlation between

extraversion and VEP amplitude-intensity slope (e.g. Roger & Raine, 1984; Zuckerman et al.,

1974) or that extraverts rather than introverts have higher amplitudes and a steeper amplitude-

intensity function (Friedman & Meares, 1979; Soskis & Shagaas, 1974;. Stenberg et al., 1988,

1990). As higher VEP amplitudes in extraverts have been exhibited at relatively low intensitiesand often show topographical dierences, these ndings have been interpreted as reecting dif-

ferences in the way attentional resources are allocated (e.g. Stenberg et al., 1988, 1990) rather

than dierences in cortical reactivity.

Similar ndings have also been reported for Zuckerman's sensation seeking scales, and in par-

ticular, the social disinhibition scale, which has been found to correlate modestly with extraver-

sion (Zuckerman, 1979). High sensation seekers (extraverts?) tend to be VEP augmenters, low

sensation seekers (introverts?) tend to be VEP reducers (e.g. Blenner, 1993; von Knorring, 1981;

Lukas, 1987; Siegel & Driscoll, 1996; Siegel, Gayle, Sharma, & Driscoll, 1996; Zuckerman et al.,

1974, 1988). Furthermore, greater impulsivity (in particular, cognitive impulsivity), which is



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thought to be related to disinhibition (Barratt & Patton, 1983), has also been associated with

augmenting of the VEP (Barratt, Pritchard, Faulk, & Brandt, 1987; Carrillo-De-La-Pen a, &

Barratt, 1993). Again, the stimulus intensities employed in these studies are unlikely to invoke

protective inhibition. Instead, Zuckerman (1979) suggests that the higher VEP amplitudes of highsensation seekers at low to moderate stimulus intensities reect lower levels of background

arousal.

One discordant nding to those mentioned above is provided by Haier et al. (1984) who

reported that reducers dened by P1N1 amplitude-intensity slopes, in fact, had signicantly

higher scores on extraversion and sensation seeking than augmenters. Reducers also had

signicantly higher psychoticism scores than augmenters while no dierences were found on

neuroticism.

Unlike the visual modality, extraversion related dierences in the auditory modality are more

consistent with Eysenck's position that introverts are more arousable than extraverts. Larger

fronto-central ERP amplitudes have frequently been reported for introverts in response to mod-erate intensity stimuli (80 dB) and when stimuli of dierent intensities are randomly mixed

(Bruneau et al., 1985; Stelmack, Achorn, & Michaud, 1977; Stelmack & Michaud-Achorn, 1985).

Stelmack et al. (1977) reported that introverts exhibited larger N1P2 amplitudes than extraverts

but only for low frequency tones (500 Hz) and not for high frequency tones (8000 Hz). Stelmack

(1990) has suggested that low frequency tones are better able to dierentiate extraverts and

introverts because they elicit greater amplitude and greater subject variation. When the ISI is

short, Stelmack and Michaud-Achorn (1985) report that enhanced N1P2 amplitude in introverts

is only observed in response to the rst auditory stimulus. These authors attributed this reduction

to incomplete recovery of the neural response. In contrast, Stenberg et al. (1988) reported that

P1N1 and N1P2 mean amplitude and amplitude-intensity slope measures for AEPs were not

signicantly correlated with extraversion.A comparison between Bruneau et al.'s (1985) study and that of Stenberg et al. (1988) illus-

trates the potential relevance of stimulus parameters already discussed. Bruneau et al. (1985) used

a maximum stimulus intensity of 80 dB whereas Stenberg and associates employed a maximum

stimulus intensity of 100 dB; Bruneau et al. (1985) used a mean ISI of 5 s while Stenberg et al.

(1988) employed a shorter mean ISI of 2 s; Bruneau et al. (1985) employed only 20 stimuli in each

block whereas Stenberg et al. (1988) employed 64; in the Bruneau study, stimuli of dierent

intensities were randomly presented within the same block whereas Stenberg and associates pre-

sented blocks of the same intensity stimuli. The stimulus parameters selected by Stenberg et al.

are, on theoretical grounds, far more likely to generate protective inhibition in introverts, thereby

minimising amplitude dierences between extraverts and introverts.In addition to the study by Stenberg et al. (1988), a number of other studies have failed to nd

a signicant relationship between auditory amplitudes and the extraversion dimension. Rust

(1975) used a range of stimulus intensities with a maximum of 95 dB and found no signicant

correlation between AEP amplitude measures and E, N and P scores. Using a similar range of

intensities, Roger and Raine (1984) found no signicant correlation between EPQ extraversion

scores and AEP amplitude-intensity slopes (P1N1 and N1P2). The stimulus parameters used in

these two studies (particularly the high stimulus intensity) and the choice of amplitude-intensity

slope measures, may account for these anomalous ndings. Such an argument, however, cannot

account for Friedman and Meares' (1979) failure to dierentiate extraverts from introverts by



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amplitude-intensity slope or mean amplitude measures for either P1N1 or N1P2 over a range of

stimulus intensities with a maximum of 70 dB.

In the few studies which have considered neuroticism, there are no reported dierences in ERP

amplitude to simple visual or auditory stimulation (e.g. Haier et al., 1984; Rust, 1975; Zuckermanet al., 1974). With respect to Eysenck's dimensions, most ERP studies have investigated extra-

version related dierences in isolation from neuroticism. This practice has prevailed despite

Eysenck's (e.g. Eysenck, 1967; Eysenck & Eysenck, 1985) caution that results from extraversion

studies cannot be readily interpreted unless reference is also made to neuroticism. The inclusion

of neuroticism would seem particularly appropriate in the present context as Pavlov associated

the sanguine and melancholic temperaments with the strong and weak nervous systems, respec-

tively. Eysenck (e.g. Eysenck & Eysenck, 1985) has argued that the classical temperaments can be

identied with the four quadrants dened by extreme scores on both the E and N scales. The

sanguine temperament is associated with the extraverted and stable (ES) and the melancholic with

the introverted and neurotic (IN). The remaining two temperaments, the choleric and the phleg-matic, are associated with the extraverted neurotic (EN) and the introverted stable (IS), respec-

tively. A distinction between ES and IN individuals in terms of cortical reactivity dierences has

in fact been made by a number of contemporary personality theorists inuenced by Pavlov's

work (e.g. Robinson, 1996; Strelau, 1983).

The aim of the present study was to test Pavlov's reactivity hypothesis using both P1N1 and

N1P2 ERP amplitude measures. Despite the focus Buchsbaum and Silverman have brought to

bear on the visual modality, the literature reviewed in this section would suggest that support for

Pavlov's hypothesis is more likely to be found in the auditory modality. In order to examine this

question both auditory and visual ERP amplitude measures were investigated. The evidence

reviewed in this section would also suggest that if protective inhibition were to develop, it would

be manifest in an asymptotic amplitude-intensity function which would minimise inter-individualvariability at high stimulus intensities. Furthermore, Pavlov (1955) observed that once developed,

inhibition exhibits an apparent after-eect, which may inuence responses to subsequent

stimuli even those of a lower intensity. If protective inhibition were to develop in the ERP

paradigm, it may minimise response dierences between high and low reactive individuals over a

range of stimulus intensities including relatively low ones. Consequently, theoretically relevant

stimulus parameters such as intensity, frequency of presentation, total number of stimulus pre-

sentations and presentation order were selected to minimise the possibility of protective inhibition

developing. Under such conditions it was hypothesised that on both P1N1 and N1P2, IN (mel-

ancholic) individuals relative to ES (sanguine) individuals will have higher mean amplitude aver-

aged over intensity and a steeper increase in mean amplitude with increasing stimulus intensity.

2. Methods

2.1. Subjects

2.1.1. Subject selection

Subjects were selected from a pool of 877 University of Sydney students who were adminis-

tered the EPQ as partial fullment of the research participation option in their introductory



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psychology course. As the subject pool available to the present experiment was mainly female

and few males reached the criteria for inclusion into any one of the experimental groups, only

female respondents aged between 17 and 29 years of age were considered for this study

(n=688).Eysenck and Eysenck's (1975) adult norms were used to assign subjects to one of four groups

dened by scores of at least 1 S.D. above or below the mean on both the E (18) and N

(18) scales and 10 or less on the lie scale. When applying these criteria, few respondents

were eligible for the introverted-stable group. To increase the number of subjects in this group,

the E and N inclusion criteria was relaxed to a score of less than 10 on both scales. The revised

criteria represented a score of approximately 1 S.D. below the mean on both E and N using the

data obtained from the 688 female respondents.

Respondents eligible for the experiment were questioned about their medical history and

excluded if they reported a recent history of medication, clinical treatment for a psychological

problem, or auditory or visual impairment. They were further advised that they would berequired to abstain from caeine and nicotine for at least 1 h prior to arriving for the experiment.

Volunteering for the experiment earned further points in the research participation component of

the rst year psychology course.

2.1.2. Subject characteristics

Fifty-six subjects were classied into one of the four experimental groups described above:

extraverted stable (ES; n=16), extraverted neurotic (EN; n=16), introverted stable (IS; n=8) and

introverted neurotic (IN; n=16). The distribution of E, N, P, and L scores for experimental

subjects is presented in Table 1 along with age norms and retest scores. Retest scores were

obtained to improve the reliability of classication. Any subject whose score on retest was more

than two points outside the original selection criteria on either E or N, or who showed an L scoregreater than 10 was replaced. Only one subject (EN) failed to meet the retest criterion. By

using each subject's seven-digit student identication number for group assignment, the

experimenter was, in most cases, blind to group classication until the end of the experi-

mental session.

Table 1

Subjects' age distribution and test-retest scores on the EPQ scales by personality group

Group Test and retest (r) scores

E E(r) N N(r) P P(r) L L(r) Age

ES M 19.06 19.50 6.19 5.88 4.81 5.00 6.63 5.31 19.56

(n=16) S.D. 1.00 1.10 1.60 3.10 2.88 2.78 2.30 3.00 3.12

EN M 18.63 19.00 20.50 20.50 4.37 4.37 3.62 3.81 19.06

(n=16) S.D. 1.15 1.67 1.75 1.93 2.80 3.60 2.40 3.33 2.91

IS M 6.63 6.13 6.75 5.25 4.38 4.63 7.38 7.50 19.00

(n=8) S.D. 4.17 4.76 2.25 2.38 2.56 2.88 3.81 5.04 2.39

IN M 6.12 5.56 20.50 21.56 5.19 5.00 4.75 4.44 19.00

(n=16) S.D. 1.63 2.10 1.83 1.46 2.04 1.93 3.68 4.18 2.10



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2.2. Apparatus and test materials

2.2.1. Questionnaires

The initial EPQ screening was conducted in large teaching rooms using a computerised versionof the EPQ installed on Macintosh Quadra 605 computers. There were 12 computers in each test

room allowing for a maximum of 12 respondents to be screened at any one time. While com-

pleting the EPQ, respondents were asked to work in silence and not to interact with one another.

The EPQ software package automatically calculated E, N, P and L scores and relayed them to

a database for storage, along with the respondent's student ID number. Retest EPQ scores were

collected in the psychophysiology laboratory after the experimental session on a Macintosh

Quadra 605 computer. In this case, respondents were tested individually. The interval between

test and retest varied between 1 week and approximately 2 months.

2.2.2. Stimulus presentations2.2.2.1. Auditory stimuli. Each auditory stimulus was a 1 kHz sinusoidal wave of 50 ms duration,

including 5 ms rise/fall times. One hundred and ve auditory stimuli were used equally divided

into 35 presentations of three dierent intensities: 30 dB, 50 dB and 70 dB (A scale). Onset to

onset inter-stimulus interval (ISI) varied randomly from 8 s to 14 s with a mean of 11 s (1 ms).

The order of presentation of tones was randomised with two constraints. First, no more than three

consecutive presentations of the same intensity stimulus were permitted. Second, at any one time the

aggregate count of one stimulus intensity could not exceed by more than four the aggregate count of

either of the remaining two intensities. Dierent random sequences were generated for each subject.

All aspects of generation, delivery and randomisation of the auditory stimuli were controlled

by a Digital Equipment Corporation PDP/11 computer with a 12 bit digital to analogue con-

verter. The analogue signal was ltered through a 5-kHz low pass lter and then sent to a variableattenuator (Decade Attenuator, Model TE-111). Attenuated signals were amplied (Realistic SA-

150 integrated stereo amplier) for binaural delivery to Pioneer SE-205 headphones. A calibra-

tion level of 100 dB (A scale) was established at the headphones using a at-plate coupler

attached to a Bruel and Kjaer sound-level meter (Type 4152). The in-line attenuator was then

used to produce the required output levels. Attenuation was set manually according to specica-

tions continually displayed on the computer monitor during the experimental run.

2.2.2.2. Visual stimuli. The Digital Equipment Corporation PDP/11 computer used for the pre-

sentation of auditory stimuli was also used in the generation, randomisation and delivery of

visual stimuli. The analogue signal was used to trigger a custom-built regulated power supplywhere ash intensities were calibrated in energy (0.05, 0.1, and 0.2 J). One hundred and ve visual

stimuli were presented in total, 35 at each of three dierent intensities. ISI parameters were

identical to those used for the auditory stimuli. Energy settings were changed manually according

to specications displayed on the computer monitor. The signal was then sent to a xenon ash

encased in an Eveready box. The ash unit was mounted on a platform in the control room and

stimuli were presented to the subject through a window, which adjoined the recording chamber.

The window was completely blackened except for a small aperture 7.5 cm in diameter. Light

output was measured at the subject using a high speed PIN diode with an optical response

matched to the human eye (with a resolution of 12 ns) and a Gould D40 oscilloscope calibrated



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against a Tektronix (J6523-2 1) narrow angle luminance probe. The eect of increasing energy

output was to increase both the intensity (i) and duration (d) of the light ash (0.05 J, i=95 cd/

m2, d=110 ms; 0.1 J, i=102 cd/m2, d=125 ms; 0.2 J, i=107 cd/m2, d=150 ms).

2.2.3. Psychophysiological recording apparatus and electrode placement

2.2.3.1. Electrodes and application. The electroencephalogram (EEG) was recorded using 10-mm

diameter Ag/AgCl cup electrodes placed according to the International 10-20 system (Jasper,

1958). Recordings were made at CZ, the preferred site for ERP studies of stimulus intensity

modulation (Buchsbaum & Pfeerbaum, 1971). The scalp site was referenced to linked earlobes

with the ground electrode placed on the forehead. Electrode impedances were maintained below 3

ks. For artefact rejection, the electooculogram (EOG) was recorded using both vertical and

horizontal placements. For EOG recording electrodes impedances were kept below 5 ks.

Before each experimental session any Ag/AgCl electrode showing deterioration was re-coated

to ensure minimum polarisation. Prior to the attachment of electrodes, each electrode site wascleaned with SkinPure preparation gel and then rubbed with a diluted alcohol solution. Electro-

des were attached to the skin surface using collodion dried by a jet of compressed air. A sterile

needle was then used to ll the electrode cup with an electrolyte supplied by Lafayette Instru-

ments (Model 76621).

2.2.3.2. EEG and EOG recording. EEG and EOG ampliers were calibrated at the beginning of

each session by an independent calibration source. The same 100 mV peak-to-peak square wave

was sent to all channels via the lead box. EEG and EOG signals were amplied by Neotrace

NT114A ampliers with frequency limits of 0.250 Hz (24 dB/octave rollo) and a gain of 20 k.

The amplied signals were continuously sampled at a rate of 512 Hz by an IBM compatible

computer (486, 33 MHz) equipped with a Data Translation 2821 A/D board (12-bit resolution)and Impulse software (Stellate Systems, 1991). Before being displayed on screen, digitised values

were notch ltered (50 Hz) and multiplied by a value of 4. Data were temporarily stored on le

server for subsequent averaging along with stimulus codes. Following analysis, all data were

archived on compact disc using a Deltacom Pentium computer with CD writer.

2.3. Procedure

Each subject was tested individually in a single 3-h laboratory session. In addition to the

response measures reported in this paper, physiological recordings were also taken during rest

periods. Resting data included EEG recordings from several scalp locations as well as EDA andECG recordings. However, this resting data will be reported in a seperate paper. Time of testing

was held constant for all subjects (12:3015:30 in the afternoon). Recording equipment was cali-

brated immediately prior to the appointed testing time. Upon arrival at the laboratory, subjects

were given a brief description of the experimental procedure and were asked to give their

informed consent.

Preparation of the subject and the placement of electrodes took approximately 1 12

h. During

this period, a radio was left playing and the door to the laboratory was left open. The extra

background stimulation derived in this way was designed to reduce the tendency towards

drowsiness, as indicated by a self-report measure of sleepiness, in earlier pilot work.



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After the recording electrodes were axed, impedance levels were checked and subjects were

ushered into an adjoining recording room. The room, 22m, was electrically shielded and sound

dampened. The ambient temperature was held between 22 and 24C. The subject was seated

upright in a comfortable recliner 1 m in front of a wall dividing the recording room from thepreparation room. Built into this wall was a small aperture, at approximate eye level to the seated

subject, through which visual stimuli were presented. To reduce reection from the light ash, the

walls of the recording chamber were covered with black ceiling-to-oor curtains.

Once seated, a small pillow was placed against the subject's back just below the shoulders. The

subject was then requested to maintain their head in an upright position and to stay as still as possible.

When comfortable, the subject was connected to the physiological equipment and tted with a set of

headphones. The recording system was then checked and any necessary adjustments were made.

The subject was then given a standardised description of the procedure. Subjects were told that

they would be required to sit passively with eyes closed for two recording stages of approximately

25 min each, with a 5 min break between stages. They were informed that resting data would becollected during the rst 3 min of each recording stage and that immediately after each rest period

a ``series of low intensity light ashes/tones'' would be delivered which would last approximately

20 min. Subjects were advised that a ``tap on the door'' would indicate the onset of the stimulus

series. Further to these instructions, subjects were asked to remain ``passive and relaxed''

throughout the experiment.

The presentation order of visual and auditory stimuli was counterbalanced within each group

of subjects. During the 5-min interval between recording stages, the radio in the control room was

switched back on and electrode impedances were checked.

At the end of the second stage, auditory and visual acuity was checked by presenting ve of the

lowest intensity auditory and visual stimuli. Each subject was asked to count aloud whenever a

stimulus was presented, a task all subjects were able to complete without error. The subject wasthen taken back into the control room and electrodes were removed. Finally, the subject was

required to complete the EPQ a second time, the subject's scores being displayed on the computer

screen. The experimenter then gave a brief account of the dimensional structure of the EPQ, the

subject's own personality prole and the experimental hypotheses. Before leaving the laboratory,

the subject was asked not to discuss the experiment with fellow students.

2.4. Physiological editing, data quantication and data analysis

2.4.1. Editing and quantication

Averaged ERPs were obtained for each of the three stimulus intensities with an analysis periodextending for 1200 ms, which included a 200-ms pre-stimulus baseline. Any analysis period which

contained EOG changes exceeding 100 mV was automatically omitted from averaging.

From a possible maximum of 35 trials, the mean number of artefact-free trials used in the

calculation of an averaged waveform for each personality group was as follows: ES=31.33

(S.D.=3.12); EN=30.98 (S.D.=3.00); IS=33.33 (S.D.=1.95); IN=32.02 (S.D.=3.32).

Individual peaks in the auditory and visual ERPs were scored by a manual cursor-search pro-

gram. The baseline was set to 0 mV by calculating the average of the 200 ms pre-stimulus period.

This value was then subtracted from all other points in the averaged ERP. Latency windows for

AEP peak identication were as follows:



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P1: 60125 ms

N1: 100180 ms

P2: 170255 ms

Latency windows for VEP peak identication were:

P1: 95165 ms

N1: 140220 ms

P2: 195280 ms

Peak-to-peak amplitudes were then calculated for P1N1 and N1P2. Reliability of peak identi-

cation was assessed by having an independent observer score the three AEPs for 10 randomly

selected subjects and the three VEPs for 10 randomly selected subjects. There were only two dis-

agreements on the AEPs and one on the VEPs indicating high inter-rater reliability.

2.4.2. Analysis

Separate three-way repeated measures analyses of variance (ANOVAs) were carried out for

each dependent variable. Using extraversion and neuroticism as between subject factors, each

ANOVA employed a 22(3) design, with repeated measures on intensity. Linear and quadratic

trend analyses were used to test all intensity main eects and interactions. For each ANOVA, a

planned contrast was incorporated to test for dierences between the ES and IN groups. This

contrast was designed to test for dierences averaged over intensity on each of the four dependent

variables as well as any linear (or quadratic) interaction with intensity. As ERP data included

three levels of the repeated measures variable of intensity; the multivariate approach to repeated

measures was used.

3. Results

3.1. Three-Way ANOVAs for AEP and VEP data

The grand averaged AEP and VEP waveforms from each group at each of the three stimulus

intensities are displayed in Figs. 1 and 2, respectively. For ease of comparison, waveforms for the

ES and IN groups are displayed on the top row, while waveforms for extravertes groups (ES and

EN) are displayed in the left column and those for the introverted groups (IN and IS) are shown

in the right column. It is worth noting that the general morphology of the VEP waveforms dis-played in Fig. 2 are quite dierent to those typically reported in the literature (e.g. Halliday, 1982;

Niedermeyer & Lopes da Silva, 1982; Regan, 1989).

Results from the three-way ANOVAs for P1N1 and N1P2 amplitude measures in the auditory

(Table 2) and visual (Table 3) modalities revealed no signicant main eects for extraversion or

neuroticism. Furthermore, there were no signicant interactions between extraversion and neu-

roticism and neither extraversion, neuroticism nor the extraversionneuroticism interaction were

found to interact signicantly with intensity linear or intensity quadratic.

In the auditory modality, amplitude increased with increasing stimulus intensity, giving rise to

a signicant linear trend for both P1N1 [F(1, 52)=109.94, P< 0.001] and N1P2 [F(1, 52)=197.48,



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P< 0.001] amplitude measures. There was also a signicant quadratic component to the AEP

N1P2 amplitude-intensity function [F(1, 52)=9.48,P=0.003] attributable to an asymptotic trend

at the highest stimulus intensity.

The P1N1 and N1P2 amplitude intensity functions in the visual modality were in markedcontrast to those in the auditory modality. A signicant quadratic component was found for both

P1N1 [F(1, 52)=6.16, P=0.016] and N1P2 [F(1, 52)=15.51, P< 0.001] amplitude-intensity

functions and were attributable to the fact that both amplitude measures were smallest at the

intermediate stimulus intensity. Mean P1N1 and N1P2 amplitudes were larger at the highest sti-

mulus intensity relative to the lowest stimulus intensity. This dierence was, however, more pro-

nounced for N1P2 giving rise to a signicant linear trend [F(1, 52)=4.99, P=0.03] in addition to

the quadratic trend.

3.2. Auditory reactivity contrasts

When averaged across the three dierent stimulus intensities P1N1 amplitude was signicantly

dierent for the IN and ES groups [F(1, 52)=5.15, P=0.027]. In accord with prediction mean

P1N1 amplitude was higher in the IN group (M=13.16 mV, S.D.=6.65)) relative to the ES group

(M=9.99 mV, S.D.=4.78). There was no signicant dierence between the IN and ES groups on

N1P2 amplitude averaged across stimulus intensity [0(1,52)=3.57, P=0.065]. The mean N1P2

Fig. 1. Grand average AEP waveforms for each group, showing V-potentials to three dierent tone intensities.



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amplitude for the IN group was 19.79 mV (S.D. =12.04) while the mean for the ES group was

15.26 mV (S.D.=8.51), a dierence of 4.53 mV. Although non-signicant, this dierence is in the

hypothesised direction and is slightly larger than the mean dierence between the ES and IN

groups on P1N1 amplitude (3.17 mV).Trend analysis of P1N1 amplitude data revealed a signicant interaction between ES-IN reac-

tivity and intensity linear [F(1, 52)=4.65, P=0.036]. As can be seen from Fig. 3, relative to the

ES group the IN group showed a steeper linear increase in amplitude with increasing stimulus

intensity. The interaction between ES-IN reactivity and intensity quadratic was not signicant

[F(1, 52)=0.64, P=0.428].

The N1P2 contrasts also show a signicant interaction between ES-IN reactivity and intensity

linear [F(1, 52)=4.18, P=0.046]. Fig. 4 indicates that as with P1N1 the IN group exhibited a

signicantly steeper linear amplitude-intensity function relative to the ES group. The interaction

between ES-IN reactivity and intensity quadratic was not signicant [F(1, 52)=0.31, P=0.580].

Figs. 3 and 4 indicate that variation in mean amplitude between groups increases as stimulusintensity increases. At 70 dB, the IN group shows the highest mean amplitudes the ES group the

lowest mean amplitudes. The failure to nd a signicant main eect for extraversion or a sig-

nicant interaction between extraversion and intensity on auditory amplitude measures may be

attributed to the fact that the two remaining groups (EN and IS) exhibit similar mean amplitudes

at each stimulus intensity.

Fig. 2. Grand average VEP waveforms for each group, showing V-potentials to three dierent ash intensities.



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3.3. Visual reactivity contrasts

When averaged across stimulus intensity there was no signicant dierence between the ES and

IN groups for P1N1 [F(1, 52)=1.75, P=0.192] or N1P2 [F(1, 52) =0.05, P=0.82] amplitudes. Infact, both amplitude measures showed a non-signicant dierence in the opposite direction to

Table 2

Summary of repeated measures ANOVAs on AEP P1N1 and N1P2 amplitude dataa

Sources of variance Sum of squares d.f. Mean square F P

P1N1

Between subject

E-I 66.99 1 66.99 1.42 0.238

S-N 132.37 1 132.37 2.81 0.100

E-IS-N 99.59 1 99.59 2.12 0.152

Error 2447.55 52 47.07

Within subject

Intensity linear (L) 1957.90 1 1957.90 109.94 < 0.001***

E-IL 36.39 1 36.39 2.04 0.159

S-NL 29.98 1 29.98 1.68 0.200

E-IS-NL 4.25 1 4.25 0.24 0.627

Error 926.05 52 17.81

Intensity quad (Q) 0.19 1 0.19 0.04 0.841

E-IQ 2.91 1 2.91 0.63 0.432

S-NQ 0.22 1 0.22 0.05 0.828

E-IS-NQ 0.16 1 0.16 0.03 0.854

Error 240.85 52 4.63

N1P2

Between subject

E-I 241.24 1 241.24 1.75 0.191

S-N 156.07 1 156.07 1.13 0.292

E-IS-N 14.69 1 14.69 0.11 0.745

Error 7157.82 52 137.65

Within subject

Intensity linear (L) 9624.58 1 9624.58 197.48 < 0.001***

E-IL 80.06 1 80.06 1.64 0.206

S-NL 83.03 1 83.03 1.70 0.198

E-I

S-N

L 43.62 1 43.62 0.90 0.349Error 2534.32 52 48.74

Intensity quad (Q) 106.24 1 106.24 9.48 0.003**

E-IQ 15.72 1 15.72 1.40 0.242

S-NQ 2.57 1 2.57 0.23 0.634

E-IS-NQ 2.85 1 2.85 0.25 0.616

Error 582.87 52 11.21

a With extraversion (E-I) and neuroticim (S-N) as between subject factors in the three-way ANOVA and intensity as

the within subject factor. Linear and quadratic trend analysis were used to test all intensity related eects.

**P< 0.01.

***P< 0.001.



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that predicted, with the ES group having slightly higher P1N1 and N1P2 amplitudes than the IN

group.

For P1N1 the interaction between ES-IN reactivity and intensity linear [F(1, 52)=0.05,

P=0.821] and intensity quadratic [F(1, 52)=0.33, P=0.567] were non-signicant. Similarly, forN1P2 there was no signicant interaction between ES-IN reactivity and intensity linear [F(1,

Table 3

Summary of repeated measures ANOVAs on VEP P1N1 and N1P2 amplitude dataa

Sources of variance Sum of squares d.f. Mean square F P

P1N1

Between subject

E-I 0.04 1 0.04 < 0.01 0.979

N-S 163.58 1 163.58 2.71 0.106

E-IS-N 4.10 1 4.10 0.07 0.795

Error 3137.01 52 60.33

Within subject

Intensity linear (L) 15.41 1 15.41 2.55 0.117

E-IL 1.22 1 1.22 0.20 0.656

S-NL 0.16 1 0.16 0.03 0.873

E-IS-NL 14.10 1 14.10 2.33 0.133

Error 314.72 52 6.05

Intensity quad (Q) 92.95 1 92.95 6.16 0.016*

E-IQ 8.70 1 8.70 0.58 0.451

S-NQ 0.01 1 0.01 < 0.01 0.976

E-IS-NQ 19.27 1 19.27 1.28 0.263

Error 784.10 52 15.08

N1P2

Between subject

E-I 0.29 1 0.29 < 0.01 0.968

S-N 10.68 1 10.68 0.06 0.805

E-IS-N 10.48 1 10.48 0.06 0.807

Error 9004.67 52 173.17

Within subject

Intensity linear (L) 87.44 1 87.44 4.99 0.030*

E-IL 52.08 1 52.08 2.97 0.091

S-NL 24.09 1 24.09 1.37 0.247

E-I

S-N

L 11.17 1 11.17 0.64 0.428Error 912.06 52 17.54

Intensity quad (Q) 213.01 1 213.01 15.51 < 0.001***

E-IQ 2.80 1 2.80 0.20 0.653

S-NQ 4.51 1 4.51 0.33 0.569

E-IS-NQ 6.55 1 6.55 0.48 0.483

Error 714.21 52 13.74

a With extraversion (E-I) and neuroticim (S-N) as between subject factors in the three-way ANOVA and intensity as

the within subject factor. Linear and quadratic trend analysis were used to test all intensity related eects.

*P< 0.05.

***P< 0.001.



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52)=0.19, P=0.665] or intensity quadratic [F(1, 52) < 0.01, P=0.924]. Figs. 5 and 6 indicate

that each group exhibited a quadratic function, in which mean P1N1 and N1P2 amplitudes were

smallest at the intermediate stimulus intensity (0.10 J).

3.4. Summary

Results from the three-way ANOVAs for P1N1 and N1P2 amplitudes in the auditory and

visual modalities revealed no signicant personality related dierences. In the auditory modality

empirical support for the ES-IN reactivity hypothesis was found on three of the four planned

contrasts of interest, while the remaining non-signicant contrast showed a mean dierence in the

hypothesised direction. When amplitude was averaged across intensity P1N1 but not N1P2,

amplitude was signicantly higher for the IN group relative to the ES group. Trend analysis of

amplitude data revealed a signicant interaction between ES-IN reactivity and intensity for both

P1N1 and N1P2. In each case, the IN group exhibited a steeper linear increase in amplitude withincreasing stimulus intensity. The ES-IN reactivity contrasts for VEP amplitude measures failed

to reveal any signicant dierences on either P1N1 or N1P2 measures.

Fig. 3. AEP P1N1 amplitude for each group across three tone intensities. Vertical bars represent 1 S.E.



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and N1P2 have been reported by other investigators (e.g. Connolly & Gruzelier, 1982a) and are

not readily interpretable within a cortical reactivity framework.

Findings from the present study suggest that future research into the relationship between

personality and cortical reactivity should focus on the auditory modality rather than the visualmodality. In particular, this research needs to address the possible modulating role of protective

inhibition. In this context, a number of theoretically relevant variables were controlled for in the

present study but were not systematically investigated. In the ERP paradigm, stimulus intensity,

in addition to the frequency of stimulation and the total amount of stimulation, should con-

tribute to the amount of cortical fatigue generated.

With respect to VEP amplitudes, future research needs to be conducted to clarify the psycho-

physiological components associated with VEP amplitudes. Relative to the auditory modality, the

amplitude-intensity function in the visual modality may be inuenced more by background

arousal (Zuckerman, 1979) or attentional mechanisms (Stenberg et al., 1990). Stenberg et al.'s

research suggests that topographical dierences in VEP amplitude need to be systematicallyinvestigated in this context.

Another strategy to identifying the underlying psychophysiological components associated

with VEP amplitudes is suggested by the observation that peak-to-peak amplitude measures

confound dierent response waveforms in the ERP trace by adding them together (Connolly &

Fig. 5. VEP P1N1 amplitude for each group across three ash intensities. Vertical bars represent 1 S.E.



19/22

Gruzelier, 1982b; Hall, Rappaport, Hopkins, & Grin, 1973; Robinson, 1993). Robinson (1993)

has suggested that the use of narrow band analogue lters to decompose the frequency compo-

nents of the P1N1P2 triphasic complex may allow a better understanding of the relationship

between ERP indices and psychological variables.Two further areas for future research are suggested by the grand average auditory waveforms

displayed in Fig. 1. First, the positive deection around 300 ms at the highest stimulus intensity

(70 dB) tends to be larger in the two extraverted groups relative to the two introverted groups.

Davis et al. (1966) report a similar ``P3 amplitude'' which was largest with an ISI of at least 610 s.

It may be that a long ISI is required to elicit the extraversion dierences in P3 observed in the

grand average waveforms in the present study. Second, the IN group relative to the ES group

tended to show earlier P1 latency, almost identical N1 latency and a later P2 latency. This sug-

gests that the duration of the triphasic waveform may also be an important index for future

research. Alternatively, one could utilise both duration and amplitude by extrapolating the

baseline from P1 to P2 then integrating the area under the curve.The auditory data provide support for Pavlov's position that dierences in response magnitude

to simple stimuli contrast the sanguine (ES) and melancholic (IN) temperaments. Furthermore,

evidence from both human (e.g. Blenner & Yingling, 1993) and monkey (e.g. Pineda, Holmes, &

Foote, 1991) studies suggests that P1N1 and N1P2 response components are primarily modulated

Fig. 6. VEP N1P2 amplitude for each group across three ash intensities. Vertical bars represent 1 S.E.



20/22

at the cerebral level rather than by the non-specic mesencephalic reticular formation. To this

extent the present ndings support Pavlov's position, as well as more recent formulations (e.g.

Robinson, 1996), which attribute personality dierences between the sanguine and melancholic

temperaments to dierences in cortical reactivity.

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