fei75766_ch14_435-462.indd 453  02/06/20 01:10 PM
Chapter 14    Eysenck’s Biologically Based Factor Theory453
disease. Onesuchinteraction wasforsmoking, neuroticism, andemotional reactivity; 
thatis,highPscorers whosmoke andwhoreact tostress withanger, hostility, and
aggression increase theirriskforheart disease.
Related Research
Eysenck developed theEysenck Personality Questionnaire (EPQ) anditsoffshoots 
(Eysenck, 1959; Eysenck &Eysenck, 1964, 1968, 1975, 1993). TheEPQ hasbeen 
usedinconjunction withneurophysiological andgenetic measures toassess thebio-
logical basis ofpersonality.
The Biological Basis of Extraversion
Oneofthemajor thrusts ofEysenck’s theory isthatpersonality dimensions arenot
arbitrary creations ofculture but,rather, result from thebasic genetic andneurophysi -
ological makeup ofthehuman species. Ifthere wereabiological basis topersonality, 
twokeyassumptions should holdtrue.First, neurophysiological differences should 
existbetween people highononeendofadimension (forinstance, introversion) and
those highontheother endofthatdimension (forinstance, extraverts). Second, the
basic personality dimensions should beuniversal andnotlimited toagiven culture.
Thefirstdomain totestEysenck’s biological model ofpersonality isinneu-
rophysiology. If,asEysenck proposed, introverts havelower thresholds ofarousal 
thandoextraverts, thentheyshould bemore reactive (i.e.,sensitive) tosensory 
stimulation. Onewaytotestthisideaistopresent bothgroups withvarying intensi -
tiesofstimulation andmeasure their physiological reactivity. IfEysenck’s theory is
tobesupported, thenintroverts should bemore reactive thanextraverts. Atechnical 
point isimportant here: cortical arousal levelhasmostly been measured byEEG 
(electrical activity viathescalp). There aretwomain levels ofcortical activity while 
awake, known asalpha andbeta, respectively. Alpha isthelowest level(8–13 Hz)
ofarousal andbetaisthenextstrongest (14–35 Hz).Alpha istraditionally associ -
atedwithdrowsiness andrelaxation andbetawithalertness andwakefulness. Many 
researchers havefollowed Eysenck’s leadandusedalpha asameasure ofcortical 
arousal, whereas other researchers argue thatbetaisabetter measure ofcognitive 
activity andarousal (Küssner etal.,2016; Ray&Cole, 1985).
Over thepast30years, asubstantial amount ofresearch hasexplored cogni -
tive,behavioral, andphysiological measures ofreactivity inrelation toextraversion-
introversion (Beauducel, Brocke, &Leue, 2006; Küssner, deGroot, Hofman, &
Hillen, 2016; Mitchell &Kumari, 2016; Stelmack, 1990, 1997). Ingeneral, Eysenck’s 
assumption thatintroverts aremore reactive (have lower thresholds) thanextraverts 
hasbeen supported, withthequalification thatitisreactivity rather thanbaseline 
activity levels thatdistinguishes introverts from extraverts (Mitchell &Kumari, 2016). 
Forinstance, inarecent study, Beauducel andcolleagues (2006) predicted that
extraverts would belesscortically aroused andshow worse performance onabor-
ingandmonotonous task.Theresearchers selected students whoscored either very
loworveryhighontheEysenck Personality Questionnaire–Extraversion scale. They 
thenpresented theparticipants withaseries oftones every 3seconds for60minutes. 
Participants hadtopress abutton assoon aspossible aftertheyheard atarget tone. Final PDF to printer