Closer Look The Geen Study

Participants in the Geen (1984) study were selected on the basis of their answers to the extraversion scale of the Eysenck Personality Inventory (the items presented in Table 7.1 in the text). Thirty high-scoring participants formed the extraverted group, and 30 low-scoring participants formed the introverted group. Participants reported to the laboratory one at a time, whereupon they were told they would be participating in an experiment on the effects of noise on learning. Each participant was given a difficult paired-associates learning task, in which they guessed which word, from a pair of words, was selected by the experimenter according to some rule, and he or she had to learn the rule. The rules were "all words referring to animals," "all words that begin with a vowel," or "all words that are names of colors." During the time they were engaged in this task, the participants were having their heart rate and skin conductance measured.

Before starting the experiment, however, the participants were told they would have to perform the learning task while listening to random bursts of noise over headphones. One-third (10 introverts and 10 extraverts) were allowed to select the level of noise that they would hear over the headphones. Participants in this choice condition listened to the noise and turned a dial to adjust the volume of the noise. They were instructed to adjust the volume control upward until the intensity was "just right" for them in terms of working on the difficult task. Participants were told that they were not allowed to choose a perfectly quiet noise setting, although two partici pants (both introverts) inquired about this possibility before the complete instructions were given.

There were two control conditions in this study. In one control condition, called the assigned-same condition, one-third of the introverts and extraverts were subjected to the noise levels selected by previous introvert or extravert participants, respectively. In the other control condition, called the assigned-other condition, the final one-third of the introverts and extraverts experienced the noise levels selected by previous extraverts and introverts, respectively. Participants in this condition had to perform under the noise level selected by the most recently run participant from the other personality group. These two control conditions make this experiment an unusually strong one.

The results concerning the choice of noise intensity were as predicted, with extraverted participants choosing significantly louder levels of noise than introverts. The noise level chosen by the extraverts averaged 72 decibels, and the noise level chosen by the introverts averaged 55 decibels. The results for heart rate and skin conductance are displayed in Figure 7.3. When working under the noise levels selected by themselves or by someone from their personality group, there were no differences between introverts and extraverts.

Personality differences are seen, however, when we look at introverts working under conditions selected by extraverts and extraverts working under conditions selected by introverts. Under these conditions, the introverts showed evidence of greater arousal, compared with the extraverts. At the introvert-selected noise level, the extraverts were least aroused—in fact, probably bored. When subjected to the noisier, extravert-selected level of loudness, the extraverts' arousal level went up, but the introverts' went up to an even higher level. What the extraverts found just right, the introverts found overarousing.

As far as performance on the learning task was concerned, the introverts assigned to the noisy, extravert-selected volume had the poorest performance. Introverts in the noisy, extravert-selected condition took an average of 9.1 trials to learn the association, but only 5.8 trials to learn it in the quieter, introvert-chosen condition. This decrease in performance was probably due to the fact that the louder noise levels overstimulated the introverts. The extraverts, on the other hand, performed quite well under the noisy conditions, averaging only 5.4 trials to learn the association. Under the quieter, introvert-selected noise levels, the extraverts performed only somewhat worse, averaging 7.3 trials to learning.

This study is important because it clearly demonstrates that the extraverts preferred more intense stimulation than did the introverts. What the extravert finds just right is overarousing to the introvert and leads to poorer performance. Similarly, what the introvert finds just right leads to decreases in arousal and performance in the extravert. The best performance for both introverts and extraverts occurs when stimulation is provided at the appropriate level of intensity for each group.

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Figure 7.3

Results from Geen's study of preferred stimulation levels in introverts and extraverts. Unconnected

dots are the Assigned-Same Conditions.

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