Is Personality Affected by Brain Activity?

The participants were randomly selected, regardless of age, sex and religion. The only pre- requisite was that they were healthy. The results were recorded and collected as part of a class experiment and show that the sample was fairly evenly divided between introverts and extroverts. They also show that there is a slight difference between the two means from the groups, but a t-test shows that this difference is of little significance. Hence our hypothesis is rejected.

Introduction This research project was carried out as part of a follow-up experiment with regards to earlier work conducted by Anthony Gale and Eysenck, both of whom researched personality and its effect on the electrical activity carried out by the brain. It has been proposed that it is the brain that determines our personality, though it is unclear to which part of the brain is responsible. According to Eysenck there are three predominant personality types- extraversion, neuroticism and psychoticism.

Pervin (1993) explained that Eysenck and Long (1986) had considerable evidence found in studies of different cultures, which supported the existence of these three dimensions. The one that we have chosen to focus on and study is that of extraversion. There are two aspects of extraversion, an individual who scores quite low on a scale of extraversion is said to be introverted (quiet) whereas someone who scores quite high is considered an extrovert (loud).

It is unclear as to which particular part of the brain is involved in personality; a lot of research has been carried out in order to narrow it down, so to speak. It has been suggested that because in introverts and extroverts are quite different in their respective demeanours (the former is quiet and the latter is more outgoing) the particular areas of the brain concerning levels of arousal may be involved.

According to Ryckman (1992) Eysenck believed in his theory that introverts are highly aroused and so are quiet, whereas extraverts are not they are under-aroused and are so more loud and outgoing. As a result of this theory research has been done to measure the levels of arousal of these two groups, and one way in which this is done is by using an electroencephalograph (EEG) to measure electrical activity originating from the occipital lobe. An EEG is typically used to investigate the brain and how it is functioning, and is a non-evasive procedure. The activity that we were most interested in was that of alpha waves. These are important in order to measure the individual’s level of arousal.

Gale has concluded from his research that there is a significant difference between introverts and extraverts levels of arousal, and therefore their levels of alpha activity, under certain conditions. Eysenck (1967) has put forward that ‘extraverts are lower aroused than introverts’ and it is from this and Gale’s conclusions that we base our hypothesis for our practical experiment. However, it is also important to note that Gale has said under certain conditions and these conditions need to be considered and met if the experiment is to be carried out correctly to obtain accurate results.

Gale has suggested the concept of intermediate stimulation, which simply means a middle level of stimulation somewhere between the high level that extraverts would thrive under and the low level that introverts would equally thrive under. Gale suggests that the intermediate stimulation condition should be one in which the participant opens and closes their eyes, or has at least one other individual present in the room with them. Gale’s argument for this condition is that neither an introverted nor an extraverted individual is trying to work against the current level of arousal. With all this previous research in mind we decided to test Eysenck’s theory under Gale’s intermediate level of stimulation using the following hypothesis: – Under a condition of intermediate stimulation (participant in a room with other people in a relaxed state with eyes closed) extroverts should show less alpha activity than introverts.


(i) Design This practical was carried out in the form of an ex-post facto study. The variables under investigation were personality and alpha activity. The independent variable was personality (extravert or introvert) and the dependent variable was alpha activity. Allocating each participant to one of two groups – introvert or extravert – by means of a personality questionnaire (EPI – Eyscnck Personality Inventory), tested personality. The participant simply answered ‘yes’ or no’ to 24 questions, and their responses indicated to what group they belonged. Both groups were tested in the same way; there was no control group or treatment group.

(ii) Participants In total there were 122 participants in this study, 62 female (50.8%) and 60 male (49.2%) Of this 63 were introverted and 59 were extraverted. The participants were recruited simply by being asked if they would mind taking part in an experiment on behalf of the first year Psychology class. The nature of the experiment was explained before the participant agreed to anything. If they agreed, then they were recruited. It was not pre-decided how many extraverts and introverts there would be – that was only discovered afterwards. The class was divided into pairs and one participant was recruited for each pair.

It is also important to note that the participants had to be healthy, as the experiment involves breathing deeply and quickly. This was the only requirement age, sex and religion were not a factor.(iii) Materials  There were a number of materials used in this experiment. Personality was determined by the Eysenck Personality Inventory (EPI, Eysenck & Eysenck, 1964). An EEG recorder was used to measure brain activity, or more specifically alpha activity. The BIOPAC system was used and a full list of necessary equipment needed is included in the BIOPAC manual, which can be found in Appendix 1. Three electrodes and leads were required for each participant, and a headband was used to help keep them in place close to the scalp. Electrode gel was also available to help remove the electrodes from the scalp if needed.

(iv) Procedure Firstly, the pairs of students carrying out the experiment had to decide between themselves who was going to be the director and who was going to he the recorder. The role of the recorder was to simply record all the data on the computer, whilst the director relayed all the instructions to the participant. After the participant ad been recruited they were taken to the testing cubicle where the experiment was being carried out. The equipment was all set up ready to begin. Details of how to set up the equipment are included and explained in the BIOPAC manual.

The participant was seated and asked to answer the EPI (a 24-question questionnaire designed to test personality. The questions were designed to find out if the participant was an introvert or an extravert and the ‘yes’ or ‘no’ answers indicated this). After the questionnaire was completed, the 3 electrodes were attached to the scalp. The black electrode lead was attached to the ear lobe; the white was attached just above the ear and the red directly above the white. (The positions are illustrated again in the BIOPAC manual). A headband was then placed over the head in order to help keep the electrodes in place, and also to keep them pressed against the scalp with a constant pressure.

As can be seen from the previous section the data that was collected does not support the hypothesis. This section will examine some reasons why the hypothesis was not correct in this case. According to previous research by Eysenck (1967) …

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