The PEN model is
comprised of three personality dimensions based on psychophysiology: Psychoticism,
Extraversion, and Neuroticism. As dimensions of temperament, the three
dimensions are related to Basic Emotions.
A competing model of personality structure is the Five-Factor Model.
Biological Dimensions of
The PEN model, proposed
and advocated by Eysenck as the overarching paradigm of personality psychology,
has two main aspects: descriptive and causal. The descriptive aspect of
the model is a hierarchical taxonomy based on factor analysis. At the top
of the hierarchy are the superfactors of Psychoticism, Extraversion,
and Neuroticism (PEN). These superfactors are comprised of factor analyses
of lower-order factors such as sociability and positive affect (components
of Extraversion). These factors are comprised of factor analyses of low-order
habits such as liking to study with a group of people (a component
of sociability). These habits are comprised of factor analyses of lower-order
behaviors such as studying for the personality midterm with a group
Two important principles
of personality research that are incorporated into the PEN model are aggregation
and the state-trait distinction. The principle of aggregation is
that measures will have higher reliability if they are comprised of many
items. For example, Extraversion is comprised of many different factors,
habits, and behaviors, and therefore should have good reliability. The
state-trait distinction is also built into the PEN model. At the
top level, the superfactors of P, E, and N are traits that are very stable
across time and situation. At the bottom level, the behavior of studying
for the midterm with a group of people is a state that could vary widely,
for example, with the availability of study partners. While states are
very changeable, traits are very stable.
Eysenck believes that
the five-factor model
is a hodge-podge of factors and superfactors. The five-factor model and
the PEN model both include Extraversion and Neuroticism at the highest
level. However, the superfactor of Psychoticism is made up of the lower-level
factors of (dis-) agreeableness and (non-) conscientiousness. Moreover,
the big five include "intellect" (self- or peer rated) at the top level.
Eysenck thinks of this as simply a bad way of measuring intelligence,
which is a cognitive ability that would be better reflected in I.Q. tests
than in self-reports on adjective questionnaires.
One factor that was
originally subsumed under the superfactor of Extraversion in the Eysenck
Personality Inventory (EPI) is impulsivity.
Later, when the dimension of Psychoticism was added, impulsivity was moved
from Extraversion to Psychoticism in the Eysenck Personality Questionnaire
(EPQ). Some investigators, such as Gray and Revelle,
believe impulsivity is uniquely important, and that its removal from the
Extraversion superfactor is a bad idea.
The PEN model is biologically based. Extraversion is based on cortical
arousal. Arousal can be measured by skin conductance, brain waves, or
sweating. While theoretically introverts are chronically overaroused and
jittery, theoretically extraverts are chronically underaroused and bored.
The theory presupposes that there is an optimal level of arousal, and that
performance deteriorates as one becomes more or less aroused than this optimal
level. The finding that arousal is related to performance as an inverted
U-shaped curve is called the Yerkes-Dodson Law.
Extraversion is related
to social interest and positive affect. Some investigators have proposed
that social interest causes positive affect, since the best of times are
usually those spent with other people. However, Diener and Larsen (1993)
have found that this hypothesis is incorrect. Another alternative is that
positive affect causes social interest, since being very enthusiastic
and fun loving may make people want to go out and be with other people.
This hypothesis has not yet been studied. Yet another possibility is that
a third factor causes both positive affect and social interest. Dopamine
responsivity, which makes people highly sensitive to reward, may be the
factor responsible for both positive affect and social interest.
Neuroticism is based on activation thresholds in the
sympathetic nervous system or visceral brain. This is the part of the brain
that is responsible for the fight-or-flight response in the face of danger.
Activation can be measured by heart rate, blood pressure, cold hands, sweating,
and muscular tension (especially in the forehead). Neurotic people, who
have a low activation threshold, experience negative affect (fight-or-flight)
in the face of very minor stressors--i.e., they are easily upset. Emotionally
stable people, who have a high activation threshold, experience negative
affect only in the face of very major stressors--i.e., they are calm under
It is interesting
to note that measures of activation are not highly correlated. That is,
people differ in which responses are influenced by stress--some sweat,
others get headaches. This is called individual response specificity.
It is also interesting to note that stressors differ in the responses
they elicit. This is called stimulus response specificity.
Psychoticism is associated not only with the liability to
have a psychotic episode (or break with reality), but also with aggression.
While less research has been done on Psychoticism than on Extraversion and
Neuroticism, the research that has been done has indicated that Psychoticism
too has a biological basis: increased testosterone levels.
In order to draw causal
conclusions, researchers on the PEN model have not been content to use
only correlational research methods such as factor analysis, but have
gone further and used experimental research methods. These methods have
been used not only on humans, but also on non-human animals such as rats.
(Isn't it interesting that Eysenck believes even rats have personality--with
the same three dimensions as humans?!)