fei75766_ch14_435-462.indd 446  02/06/20 01:10 PM
Part V    Biological/Evolutionary Theories446
arousal thandointroverts, theyhavehigher sensory thresholds andthuslesser reac-
tions tosensory stimulation. Introverts, conversely, arecharacterized byahigher level
ofarousal, andasaresult ofalower sensory threshold, theyexperience greater reac-
tions tosensory stimulation. Tomaintain anoptimal levelofstimulation, introverts, 
withtheircongenitally lowsensory threshold, avoid situations thatwillcause toomuch 
excitement. Hence, introverts shun suchactivities aswildsocial events, downhill skiing, 
skydiving, competitive sports, leading afraternity orsorority, orplaying practical jokes.
Conversely, because extraverts haveahabitually lowlevelofcortical arousal, they
needahighlevelofsensory stimulation tomaintain anoptimal levelofstimulation. 
Therefore, extraverts participate more often inexciting andstimulating activities. They 
mayenjoy suchactivities asmountain climbing, gambling, driving fastcars,drinking 
alcohol, andsmoking marijuana. Inaddition, Eysenck (1976) hypothesized thatextra -
verts, asopposed tointroverts, willengage insexual intercourse earlier, more frequently, 
withawider range ofpartners, inagreater number ofpositions, withalarger variety 
ofsexual behaviors, andwillindulge inlonger precoital loveplay.Because extraverts 
havealower levelofcortical arousal, however, theybecome more quickly accustomed 
tostrong stimuli (sexual orotherwise) andrespond lessandlesstothesame stimuli, 
whereas introverts arelesslikely tobecome bored anduninterested inroutine activities 
carried onwiththesame people.
Inshort, Eysenck wasarguing thatpeople seekout,prefer, andperform best
inenvironments thatmatch theirnatural arousal levels. Introverts seekoutandper-
form bestinquiet environments withrelatively lowlevels ofstimulation andarousal, 
whereas extraverts dothesame inlouder environments withrelatively highlevels of
stimulation andarousal. InFigure 14.3, weseeaversion ofafigure drawn byEysenck 
todepict thisrelationship. Hedonic tonerefers tothesubjective feeling oftheperson 
inthesituation, either positive ornegative. 
FIGURE 14.3  The Relationship Between Arousal Levels, Introversion–Extraversion, and 
Performing and Feeling Best (Hedonic Tone).
Extraverts perform bestinrelatively highlevels ofarousal andintroverts inrelatively lowlevels arousal 
(adapted from Eysenck, 1982, p.17).Hedonic
tonePositive
Arousal potentialLow HighExtraverts
Introverts
NegativeOptimal levels
of response
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