fei75766_ch14_435-462.indd 454  02/06/20 01:10 PM
Part V    Biological/Evolutionary Theories454
Computers measured boththespeed (reaction time) andaccuracy ofresponses. The
taskwasmeant tobetedious andboring, anditwas.Theideaisthatextraverts will
doworse atthetonetaskbecause itissounderstimulating. Finally, theparticipants’ 
cortical activity wasmeasured viaEEG throughout theentire tonetask.Thepredic -
tions again werethatextraverts would havelower cortical arousal andwould doworse 
onthemonotonous task.Beauducel andcolleagues found support forbothofthese 
hypotheses, which support twoofthemost basic ofEysenck’s assumptions about the
biological basis ofpersonality traits.
Optimal levelofarousal isanother ofEysenck’s hypotheses thathasgenerated 
some research. Eysenck theorized thatintroverts should work bestinenvironments of
relatively lowsensory stimulation, whereas extraverts should perform bestunder condi -
tionsofrelatively highsensory stimulation (Dornic &Ekehammer, 1990). Onetestof
Eysenck’s theory wascarried outbyDobbs andcolleagues (2011), whoassessed per-
sonality andcognitive taskperformance under three sound conditions: silence, noise, 
andmusic. Based onEysenck, theypredicted thatextraverts would perform better 
thanintroverts onthenoise andmusic conditions butnotonthesilence condition. 
Dobbs etal.measured levels ofintroversion andextraversion using aself-report 
questionnaire (Eysenck Personality Inventory—EPI). They manipulated sound condi -
tions inthefollowing way:“noise” was12minutes ofeveryday sounds suchaschil-
drenplaying, anoffice atmosphere, andlaughs; “music” was13minutes ofcurrent 
popvocal music; and“silence” played nosounds. Various cognitive-intelligence test
measures wereadministered toassess cognitive performance. Oneofthese wasthe
nonverbal measure ofintelligence, known astheRaven’s Progressive Matrices testin
Preferring tobealone attimes isonewaythatintroverted people regulate theiroptimal level
ofarousal. Image Source/Getty Images
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