Differences in contingent negative variation (CNV) related to extraversion-introversion

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AND SHORTER

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1987

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COMMUNICATIONS

Differences in Contingent Negative Variation (CNV) related to Extraversion-Introversion EVGENIA G. DIWHEVA Depurtment

and

DAFINA L. PIPEROVA-DALBOKOVA

of Work Ph~iologj.. Imtrtute of Hygiene and Occupational Medico/ Ac~rrdem v, Sofirr. Bulgaria (Receiwd

2 ,Yo~emher

Health,

1981)

The inter-individual differences in CNV form and development in non-patient populations are considerable. Significant negative correlations have been reported between CNV amplitude and questionnaire scores of anxiety and depression (McCallum and Walter, 1968: Low, 1967; Knott and Irwin, 1967; Low and Swift, 1971). The findings in general show that low-anxiety subjects developed higher CNV than high-anxiety subjects. Knott and Irwin (1967) hypothesized that there IS a fixed capacity of the cerebral structures for producing negative shifts, and that high-anxiety subjects. having higher baseline negativity, reached the ceiling more quickly than the low-anxiety subjects. Eysenck’s theory of the biological basis of personahty states that individual differences in Introversion; Extraversion

are related to the differences in the resting level of cortical arousal or activation,

i.e. introverts

are

more aroused than extraverts (Eysenck. 1967). It has been reported that, compared to extraverts, introverts are more sensitive to auditory stimulation (Smith, 1968) and pain (Haslam. 1967) and have higher sedation thresholds (Sloane et al., 1965). In accordance with these data it might be supposed that introverts develop lower CNV amplitudes. This assumption derives also from the general agreement between activation theorists in postulating an inverted-U relationship between mental efficiency and arousal. The optimal level of arousal differs for mental functions varying in complexity, and it is generally assumed that the arousal required for maximal performance is higher for simple than for complex and more difficult tasks. Some preliminary data of ours have shown that the CNV paradigm is accompanied by a decrease in EEG frequency between trials. So. extraverts might possess arousal levels near to the optimal ones required for the CNV paradigm. On the other hand, introverts have also been reported to be more resistant to the decrement in vigilance performance and distraction (Carr, 1971; Keister and McLaughlin, 1972; Krupski et al.. 1971). which is associated with attention processes. Here we report an experiment in which we have examined whether extraverts develop higher CNV than introverts, and the consistency of these differences when altering the sensory modality of the CNV paradigm.

\IETHOD Subjects

Twelve right-handed Ss, 6 introverts from 22 to 28 yr and 6 extraverts from 22 to 30yr, were paid to participate in the experiment. The Ss were selected on the basis of their scores on the Eysenck Personality Inventory (EPI), Form A-with scores for introverts less than 9, and for extraverts greater than 16. The mean scores were 6.9 (SE = 0.6) for introverts and 16.8 (SE = 0.5) for extraverts. The Ss were stable according to their Neuroticism scale scores. Procedure

All Ss were tested under two experimental situations. The basic procedure was that of a constant foreperiod simple reaction time paradigm. During the first experimental situation the warning stimulus (S,) was a click (O.Ol-set duration and approx. 40 dB SPL Intensity). presented through a loudspeaker placed behind the S. The imperative stimulus (S,) was a light flash (1.55 x IO-’ Im set m -‘) located in front of the S at a distance of I.5 m. The Ss were instructed that after S, occurred they were to press a button as quickly as possible. The experimental situation included 50 trials with an interval varying randomly from 15 to 30sec. The only difference between the two situations was that during the second experimental paradigm the warning stimulus was a light flash and the imperative stimulus was a click. The two situations were separated by the instruction that the stimuli would be presented in the opposite order, and the S had to press the button after the click. The experimental procedure may be demonstrated by the following scheme: 1. First experimental

situation S, (click)aS,

2. Brief instruction 3. Second experimental

(RashtMR

(A-V paradigm)

(clicktMR

(V-A paradigm)

situation S, (flash) -S,

447

448

-

f >-

NoThS

The Ss were seated in a comfortable room with their eyes closed.

AND

chair

SHORTER

within

CO~~MCINIC.ATIONS

a sound-attenuated,

34’)

darkened

and

electrically

shlelded

Electrodes

Golden electrodes, affixed to the s’s scalp were used to record the EEG from FJ, C,, P, and C, (according to the IO/20 system). Linked mastoids served as a reference electrode. The Ss were earthed with an electrode, placed on the neck over the 7th vertebra. The electrode impedance was maintained below 5OOOR. Left sub- and supra-orbital electrodes were used to record the electrooculogram (EOG). Apparatus

The EEG and EOG were amplified by means of Hewlett-Packard amplifiers with a high-frequency cut-off filter, set at 30 Hz and time constant set at 3.5 sec. EEG, EOG and the trigger signal 500 msec before S, were recorded on magnetic tape using a seven-channel FM tape recorder HP 3955. The trials with eye movements (including eye blinks), artifacts and button presses within the inter-stimulus interval were omitted in the further analysis. Analysis

Data were digitized at a rate of 5 msec/point m epochs beginnlng 500 msec before S, and extending for 1.5sec after S2. Electrical baseline was established as the average voltage during the 500msec preceding the stimulus onset. Averaged CNV waveforms were obtained from 40 trials as well as from each 8 consecutive trials. The following measures were obtained to encompass the CNV waveform: (a) early CNV (0 wavetaverage amplitude in the period 45&550msec. after S, relative to the baseline level; (b) peak CNV-the highest amplitude of the CNV relative to the baseline level; (c) late CNV (E wavetaverage amplitude in the period 120 msec before Sz to S, relative lo the baseline; (d) peak latency-the time (from S,) to the highest amplitude. The mean values and SEs of these parameters across the Ss for the two groups within the two situations were computed. Three-way repeated measures analyses of variance (ANOVA) ivere performed on these amplitudes and latency parameters over the data from averaged curves of 8 trials (for each S 5 curves, providing totally 30 replications). When testing for main effects, the absolute values \vere used. However, when interactions were assessed the largest absolute value of a given amplitude among the four electrode sites for a given .S and paradigm, was divided into the values of that amplitude at the other three electrode sites to produce relative amplitudes. The following set of variables was used: electrode site (4 levels), Extraversion-Introversion (2 levels) and experimental paradigm (2 levels). To specify some possible differences in CNV in a given electrode site two-way repeated measures ANOVA was performed. RESL LTS

+

In all Ss CNV was already well developed in the first averaged curves, and there were no differences between extraverts and introverts in CNV formation. In the central and the vertex derivations the introverts possessed type A CNV using the Tecce (1971) classification, and extraverts showed type B CNV. The CNV waveforms are clearly seen in Fig. 1, which presents grand-mean averaged curves across all Ss for both extraverts and introverts under the two CNV paradigms. The CNV parameters for the two groups on the A-V paradigm are presented in Table 1. It can be seen that the CNV amplitudes in frontal and central derivations tend to be higher in extraverts. reaching significance for the peak CNV in CX. No consistent amplitude differences between the two groups in the parietal region or on the vertex could be found. The earlier CNV peak latency in central regions of introverts resulted in discernible CNV waveform differences. The CNV distribution over the scalp is similar in the two groups. Table 2 shows the CNV data upon the V-A paradigm. The differences related to Extraversion-Introversion described above are not so marked in this situation. Concerning the data from both paradigms, a consistent increase of the CNV in the V-A paradigm could be observed with the E wave most enhanced in the frontal derivations (Fig, 2). The three-way ANOVA yielded a significant effect of the electrode site on the 0 wave amplitude (F(3/464) = 2.88, P = 0.05) and on the peak CNV (F(3/464) = 2.43. P = 0.1).

0 waw E

WaYe

Peak Peak latency

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14

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1060*’ x4

n%l 76

li6’* _. >‘I 91i73

IO42 62

x3,** 74

The two-way

ANOVA

carried

out for each electrode

site separately

produced

the folIowIng

results:

(a) on CA derivation a slgnficant effect of the Extraversion-Introversion on the CNV peak (f(1/116) = 17.81, P = 0.001). the 0 wave amplitude (F(l/l16) = 7.32, P = 0.001). as well as on the E wave amplitude (F(lill6) = 9.36. P = 0.001 J. The interaction between the Extraversion-Introversion and the paradigm used tends towards significance with F-ratios as follows: F(l/ll6) = 3.27, P = 0.1 for the 0 wave amplitude: F(1/116) = 3.36. P = 0.1 for the E wave amplitude and F(1/116) = 2.90, P = 0.1 for the peak CNV; (b) on F, derivation the E wave amplitude and the peak CNV were significantly affected by the paradigm (F(lill6) = 4.45, P = 0.05). resp. (F(l/116) = 4.21, P = 0.05). while the Extraversion-Introversion effect and the interaction were not significant statistically. The results for the reaction time (RT) showed no significant differences between the two groups In the A-V paradigm. The mean values for extraverts and introverts are 179msec (SE = I4 msec) and 191 msec (SE = 13 msec). The V-A paradigm did not affect the RT of the extraverts--183 msec (SE = 10 msec), but the corresponding values for the introverts reached 227 msec (SE = 18 msec).

EXTRtVERTS

INTROVERTS

f-N L l

500 msec early CNV

0 CNV peak A late CNV 0 peak latency

msec 5 _&-_C-

L

-4Y

L%

Fig. 2. Increase

of CNV In the \‘-A

paladlgm

The RT values for each S, grouped in 8, according to the averaging of 8 trials, were processed using two-\\ay ANOVA. The results showed a significant effect for Extraversion-Introversion (F(1/116) = 4.12. P = 0.05) as well as of the interaction of this factor with the paradigm (F(1/116) = 4.04, P = 0.05). DISCUSSION The hypothesis was that extraverts would be near to the optimal level of the arousal potential required bl the CNV task, whereas introverts would be hyperaroused, i.e. the level of their arousal potential would be at the descending limb of the inverted-U curve. Our data show significantly higher CNV amplitudes over the central region in extraverts, especially when the warning stimulus is an auditory one. These differences between extraverts and introverts still exist when the warning stimulus is visual, but to a lesser degree, and that is why the significance of the interaction effect Extraversion-Introversion x Paradigm decreased. This finding might be explained in terms of the more arousing effect of the auditory stimulus in comparison with the visual (Gaillard. 1976). It seems that the sensory modality of the warning stimulus is an important factor \rhen distinguishing the CNV in extraverts and introverts. The elevated CNV amplitude in introverts found by Eysenck and O’Connor (1979) in a sham-smoking situation might be due to the distractive etTect produced by this additional factor. especially for extraverts. .As regards the real smoking situation the data reported by the same authors are quite similar to ours. i.e. introverts, hyperaroused by the nicotine, develop smaller CNV. The main CNV differences between extraverts and introverts in this experiment are mostly pronounced o\er the central and to some extent over thefionral regions. In the posterior regions no differences could be found. The CNV distribution over the scalp does not vary from extraverts to introverts, and could be distinguished only when contrasting the two paradigms used. In the V-A paradigm the E wave is most enhanced in the anterior recordings, and possibly that is the reason for the increase of reaction time. A trend for the latter activity to be more negative in the anterior recordings when S2 was the auditory stimulus leaves open the possibility that the E wave might express not only motor activity but also anticipation of the sensory modality of S2. This result is consistent with the view of Ritter et al. (1980) about the modality specificity of the slow negative wave. The findings in this experiment might yield a sensitive measure in researching the biological correlates of Individual differences. REFERENCES CARR D. (1971) Introversion-extraversion and vigilance performance. Proc. 79th A Corlwntion qfthe America,1 Psychologicd Association, Vol. 6, pp. 379-380. EYSENCK H. J. (1967) Tlte Biological Basis of Personality (Edited by KUGELMASS I. N.). pp. 226251. Thomas. Springfield, Illinois. EYSENCK H. J. and O’CONNOR K. P. (1979) Smoking. arousal and personality. In E/ecr,op/t!,sio/o(lical Ef/ecrs of Nicotine (Edited by REMOND A. and IZARD C.). Elsevier/North-Holland. Amsterdam. GAILLARD A. W. K. (1976) ElTect of warning signal modality on the contingent negative variation (CNV). BIoI. Psycho/. 4, 139-154. HASLAM D. R. (1967) Individual differences in pain threshold and level of arousal. Br. J. Psycho/. 58, 139-112. KEISTER E. and MCLAUGHLIN J. (1972) Vigilance performance related to extraversion-introversion and caffeine. J. exp. Res. Person. 6, 5-11. KNOTT J. R. and IRWIN D. A. (1967) Anxiety, stress and the contingent negative variation. E/ectroe,lceph. tlrrl. Neurophysiol. 22, 188. KRUPSKI A., RASKIN D. C. and BAKAN P. (1971) Physiological and personality correlates of commission errors in an auditory vigilance task. Psychophysiology 8, 304-311. Low M. D. (1967) Variations Contingentes Negatives. Compte-rendus de 1” Colloque International. Liege. (Edited by DARGENT J. and DONGIER M.). Collection Congres et Colloque de l’universite de Liege (1969) 52, 250. LOW M. D. and SWIFT S. J. (1971) The contingent negative variation and the “resting” D.C. potential of the human brain: effect of situational anxiety. Neuropsychologia 9, 203-208. MCCALLUM W. C. and WALTER W. G. (1968) The differential effects of distraction on the contingent negate\-e variation in normal subjects and psychiatric patients. Electroenceph. c/in. Neurophysiol. 24. 593 (Abstr.). RITTER W., ROTKIN L. and VAUGHAN H. G. JR (1980) The modality specificity of the slow negative wa\e. Psychophysiolog) 17, 222-227. SLOANE R. B., DAVIDSON P. 0. and PAYNE R. W. (1965) Anxiety and arousal in psychoneurotic patients. Arclts gen. Psychiat. 13, 19-23. SMITH S. L. (1968) Extraversion and sensory threshold. Psychophysiology 5, 293-299. TECCE J. J. (1971) Contingent negative variation and individual differences: a new approach in brain research. Archs gem Psychiat. 24, l-16.