EEG forms waves which are connected with certain conditions of consciousness (Pinel 2009). These waves called alpha waves which described by frequency of 8-13Hz and amplitudes of 20-200. According to Gale (1999) arousal is defined operationally in terms of frequency and amplitude, high amplitude and low frequency are said to be an indication of low arousal (Gale 1999). These frequency and amplitude are delivered to the EEG from the neocortex region of the brain. High amplitude and low frequency are said to be an indication of low arousal extroverts.
This variance in careful processing in behavior has been explained by H.J Eysencks (1967) arousal theory of introversion-extraversion “A central theory in Eysencks theory of the neurophysiological basis of extraversion-introversion and neuroticism-stability in the low cortical arousal of extraverts (Eysneck 1967).
In Eysencks theory, introverts are more easily aroused than extraverts with the importance of reaching the peak level of arousal effortlessly (as cited by (Althaus, gomarus, Wijers, Mulder, Velzen, Minderaa, 2004). This increased level of arousal leads to enhanced selective attention. On the other hand extraverts pursue stimulation in order to increase their level of arousal.
When arousal is low, attention is banished and the individual becomes distracted (Posner & richle, 1994). When the task becomes more difficult the arousal level is said to increase. The introvert is prone to become over aroused which causes a drop in performing, whereas the extravert might reach the peak level of arousal which leads to better performance.
Eysencks theory is that extraverted individuals have inherited or are born with, low level of arousal of the brain stem and introverts are born with high level of arousal. Gale supports Eysencks theory however gale believes that extraverts and introverts adapt to their environments learning different methods of how to resolve levels of arousal in different stressful situations. Past studies have suggested an increase in EEG activity in introverts (Broadhurst, and Glass 1969; Young, Lader and Fenton, 1971 as cited by Tran, Craig, Mc Issac, 1999). A number of studies have reinforced Gale and Eysencks activation arousal theory that extraverts produce lower levels of alpha activity whereas introverts produce higher level cortical arousal. Gale also suggests that alpha rhythm should be more noticeable in extraverts than introverts as it is known to be stronger in relaxed states and reduced by arousal stimuli (Gale 1999).
The aim of this study is to test Eysenck’s (1967) personality theory which states that extraverts are less aroused than introverts. Eysenck’s personality questionnaire will be used to establish extravert/introvert and EEG will be used to measure alpha waves. Participants will be instructed to open and close their eyes and perform a mental arithmetic. It is hypothesized that extraverts will show increased amplitude in alpha wave activity than introverts in these conditions.
Method
Design
For the purpose of this study a within-participants design was used for the completion of the self-reporting questionnaire and recording of alpha wave activity. However, following the scoring of the questionnaire (see appendix 1) and participants were ranked as high/low on extraversion by process of median split of 6. Those who scored lower than the median split were coded 0 and those who scored higher than the median split were coded 1. Time group was recoded as 1 before 12:30 and 2 for after 12:30. MEANAMP was re-coded for the mean amplitude of both eyes closed and eyes open and AMP6 was re-coded for the mean amplitude during mental arithmetic task (see appendix 3)
Participants
Eighty-four male and female undergraduate students from the University of Ulster, School of Psychology participated in the study. All were over the age 18. We were not given exact ages of participants therefore the mean and SD for the number of males/females could not be recorded.
Materials
The Eysenck Personality Questionnaire Revised – Abbreviated (EPQR-A). Twelve out of 24 items measured extraversion and neuroticism and subscales recording sheet (see appendix). BIOPAC student laboratory software package, acquisition unit, electrode lead set, disposable vinyl electrodes and lycra swim cap. SPSS version 20 was used for statistical analysis.
Procedure
Prior to completion of the self-report questionnaire and alpha wave recording, each participant was allocated into groups (approx 5) and given specific times over a three week period for data collection. The psychology laboratory used was acceptably quiet to allow participants to mentally relax and this was enhanced by allowing participants a few minutes extra prior to the recoding sequence. Participants were positioned in a chair facing away from the computer screen. An electrode was positioned beside and above the ear lobe and the lycra swim cap was placed on the participants head to ensure pressure. The participants in each group were director, participant and recorded. Each participant had their alpha wave recorded for each section of measurement following the self-report questionnaire (mean alpha wave amplitude). Each recording time lasted 3.5 minutes during recording each participant was given instructions (see appendix 2)
Results
Eighty four male and female undergraduate’s data was entered and subsequent analysis using SPSS version 20 provided the following results. An independent samples t-test showed there was no significant difference in the overall mean amplitude of the alpha wave between participants who scored high on extroversion (M = 9.88, SD=6.18) and participants who scored low on extroversion (M = 11.08, SD = 6.55; t (81) = -.842, p = .402, two-tailed). The magnitude of the difference in the means (mean difference = 1.2, 95% CI -4.02208 to 1.63054) was very large (eta squared = 8.67).
An independent t-test was conducted to reveal a difference in mean alpha wave amplitude while performed a mental arithmetic task. There was no significant difference in the mean alpha wave amplitude while performing a mental arithmetic task between participants who scored high (M = 6.63, SD = 6.75) and participants who scored low in extraversion (M = 7.03, SD = 6.41; t (81) = -.270, p = .788, two-tailed). The magnitude of the difference in the means (mean difference = .0.4, 95% CI: -3.35 to 2.55) was very large (eta squared 8.9).
A paired-samples t-test was conducted on participants who scored low on extraversion to evaluate the difference in alpha wave amplitude scores when their eyes were open and when their eyes were closed. There was no significant difference when eyes were closed (M = 10.98, SD = 8.67) and when eyes were open (M = 8.79, SD = 6.36), t (49) = 1.75, p > .0005 (two-tailed). The mean difference in scores was 2.19 with a 95% confidence interval ranging from -.31902 to 4.71422. The eta squared statistic (0.05) indicated a moderate effect size.
Discussion
The aim of the study was to investigate that introverts are more aroused than extraverts by comparing the mean alpha amplitude between eyes closed/eyes open conditions and also comparing the mean alpha amplitude between participants who scored low and high on extraversion. According to Eysencks theory extraverts will show increased amplitude in alpha wave activity and introverts will have lower amplitude in alpha wave activity. The first hypothesis concluded that there was no significant association in the overall mean amplitude of the alpha wave between participants who scored high and low in extraversion. The second hypothesis concludes there is no significant association while performing a mental arithmetic task between participants who scored high and participants who scored low in extraversion. The last hypothesis concluded no association while performing a mental arithmetic task between participants who scored high and participants who scored low in extraversion.
The results are inconsistent with Eysencks theory. It appears that despite measures for confounding variables the data appears slightly distorted. A possible limitation is to decrease the noise level in the room whilst recording or possibly conducting the EEG recording in a sound proof room which would give more accurate measurements. For future research the age and range of the participants could be provided to determine if this affected the data collected. Furthermore, according to Gale (1983) sampling and scoring lack a sound bias and measurement for personality is unmethodical. For future research it might be a possibility allow each participant to complete a separate questionnaire from the recoding sheet, that way students may not feel that their class mates could see their scores. Overall the research was informative despite the lack of empirical data supporting Eysencks theory.
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