low on this dimension, they get more pleasure out of rewards and more en-
joyment out of simply anticipating that rewards are coming. Individualswith an active BAS also experience more anger and frustration when they
fall short of reaching their anticipated pleasure. People with a highly active
BIS tend to be more apprehensive than others. They approach new situa-
tions warily, are on the constant lookout for signs of danger, and are quick
to retreat from a situation that they sense might lead to problems. Not
surprisingly, they also are more likely to experience anxiety than peoplelow on this dimension.
Just how these two hypothetical systems are related to extraversion and
neuroticism remains a matter of debate (Smillie, Pickering, & Jackson, 2006).But most researchers see a connection between the BAS and extraversion and
between the BIS and neuroticism. That is, people with a highly active BAS
are similar to those scoring high in extraversion, and those with a highlyactive BIS are similar to people scoring high in neuroticism. Scales designed
to measure BAS and BIS do correlate with scales measuring extraversion and
neuroticism, respectively, but the correlation is far from perfect (Jackson,2009). Thus, although the concepts are related, they probably are not the
same thing.
Nonetheless, when looked at in these terms, we can think of extraverts as
more aware of and more attracted to situations that promise rewards. Whenextraverts encounter an opportunity to have a good time, they are motivated
to approach the object of their desire. As a result, extraverts are more impul-
sive than introverts and are more likely to find themselves in the middle of a
party or riding on a roller coaster. One implication of this description is that
extraverts aren ’t necessarily attracted to all social situations, but only to those
that are likely to be enjoyable (Lucas, Diener, Grob, Suh, & Shao, 2000).
One team of researchers found that extraverts actually preferred nonsocial
situations, such as going for a walk alone, more than introverts did ifthey
thought the experience would be pleasant (Lucas & Diener, 2001).
A Biological Basis for Personality
Eysenck (1990) pointed to three arguments when making the case that indi-
vidual differences in personality are based in biology. First, he noted the
consistency of extraversion –introversion over time. Participants in one study
found scores on measures of extraversion –introversion remained fairly consis-
tent over a span of 45 years (Conley, 1984, 1985). Of course, this finding
alone does not establish that extraversion –introversion is determined through
biology. It is possible that people remain in similar environments throughout
their lives or throughout the time period in which this personality trait is
developed.
Second, Eysenck pointed to the results of cross-cultural research. He
argued that researchers find the same three dimensions of personality —
extraversion –introversion, neuroticism, and psychoticism —in research con-
ducted in many different countries with different cultural backgrounds and
histories (Barrett & Eysenck, 1984; Lynn & Martin, 1995). Moreover,
Eysenck argued that the three “superfactors ”not only appear in his research“Heritability is not a
fixed number. Once
you realize what ’s
inherited, there ’s a lot
you can do about it. ”
Hans EysenckHans Eysenck ’s Theory of Personality 227