fei75766_ch14_435-462.indd 455  02/06/20 01:10 PM
Chapter 14    Eysenck’s Biologically Based Factor Theory455
which there isaseries ofgeometric figures making upapattern andamissing piece. 
Thetaskistofigure outtheunderlying pattern intheshapes andtochoose themiss-
ingpiece based onone’s ideaofthepattern. Another cognitive-intelligence measure 
wastheWonderlic Personnel Test, which hasword, number, sentence, andgeometric 
figure problems ofvarying levels ofdifficulty. Finally, alesscomplex cognitive task
wasalsoadministered, namely theVerbal Reasoning Test, which consisted ofidenti -
fying antonyms, sentence completion, andchoosing grammatically correct sentences. 
Participants were118middle- andhigh-school girlsintheUnited Kingdom. 
Results ofthestudy ,ingeneral ,supported thepredictions andEysenck’s the-
ory.Extraverts performed better thanintroverts onthecognitive tasks inthenoise 
andmusic conditions butnotthesilence condition. Forexample, ontheRaven’s 
Progressive Matrix test,introverted students weredistracted inthenoise andmusic 
conditions ,whereas theextraverted students werenotaffected byeither thenoise or
themusic (seeFigure 14.7). Weshould point outthatthispattern didnotholdon
alessdemanding cognitive task(verbal reasoning) andtherefore howcomplex the
cognitive taskisseems tomatter.
Asecond source ofsupport forEysenck’s biologically based theory ofpersonal -
itycomes from behavioral genetics. Behavioral genetic research isoften based onthe
study oftwins, bothidentical andfraternal, whohavebeen raised together orapart. 
Twin studies havefound thatmost basic personality traits haveheritability estimates 
ofbetween 40%and60%(Plomin &Caspi, 1999). Inother words, anindividual’s 
genetic makeup goesabout halfway toward explaining hisorherbasic traits. For
instance, thetraitofextraversion, oroutgoingness, often correlates around 0.50for
identical twins andaround 0.20–0.25 forfraternal twins, which leads toaheritability 
estimate ofbetween 50%and60%. Likewise, between 50%and55%ofthediffer -
enceinneuroticism isduetogenetics (Bouchard &Loehlin, 2001; Caspi, Roberts, 
&Shiner, 2005; Krueger &Johnson, 2008; Plomin &Caspi, 1999). Moreover, other 
/three.tnum/zero.tnum
/two.tnum/five.tnum
/two.tnum/zero.tnum
/one.tnum/five.tnum
/one.tnum/zero.tnum
/six.tnum/eight.tnum /one.tnum/zero.tnum /one.tnum/two.tnum /one.tnum/four.tnum
Extraversion scoreRaven’ s test performance
/one.tnum/six.tnumCondition
Music
Noise
Silence
/one.tnum/eight.tnum /two.tnum/zero.tnum
FIGURE 14.7  Raven ’s Progressive Matrix Scores as a Function of Extraversion and Sound 
Conditions.
(Source: Dobbs etal.,2011; reprinted withpermission from Wiley &Sons, Inc.)Final PDF to printer