Biological Influences on Personality

1. Biological Influences on Personality

2. Major Point • Many individual differences in personality are rooted in biology • introversion vs. extraversion • impulsivity • sensation-seeking • morningness vs. eveningness • vulnerability to positive vs. negative emotions • inhibited or “high reactive” temperament among infants

3. 1. Extraversion-Introversion • arousal level • influenced both by environmental factors and ascending reticular activating system in brain • ARAS regulates level of cortical arousal • there is some optimal level of arousal

4. Brain Stem • ARAS: ascending reticular activating system

5. Eysenck’s Arousal Theory • Introverts have higher baseline levels of cortical arousal. • Seek out less stimulating environments. • Extraverts have lower baseline levels of arousal. • Seek out more stimulating environments. • Seeking out or avoiding of social situations is a strategy for maintaining optimal level of arousal.

6. Evidence • Geen (1984) • Method • Subjects were asked to choose preferred level of background noise while working on a paired-associates learning task. • subjects’ SCRs were monitored • Results • Introverts chose noise levels substantially lower than extraverts • Each group performed best (took shorter amount of time) at preferred noise level • Introverts and extraverts had just about same number of SCRs at preferred level of noise.

7. Revision of Theory • most recent evidence suggests that extraverts and introverts don’t differ in baseline levels of arousal • real difference lies in their arousability (arousal response)

8. 2. Sensitivity to Reward and Punishment • Gray (1990) • developed theory of personality based on research with animals • many differences in behavior are governed by 2 systems in brain

9. Separate Systems • BAS (behavioral activation system) • responsive to incentives (cues for reward) • regulates approach behavior • BIS (behavioral inhibition system) • responsive to cues for punishment, frustration, and uncertainty • inhibits behavior, brings about avoidance behavior

10. Gray’s Theory • People differ regarding relative sensitivity of BAS and BIS • person with reactive BIS • especially sensitive to cues of punishment, frustration, and novelty • vulnerable to unpleasant emotions (anxiety, fear, sadness) • sensitive BIS leads to anxiety, neuroticism • person with reactive BAS • especially sensitive to reward • vulnerable to positive emotions; tends to approach stimuli • sensitive BAS leads to impulsivity

11. Evidence • Typical study • impulsive subjects play game of chance • subjects are either punished for wrong response or rewarded for correct response • result: subjects learn more slowly when punished for wrong response than when rewarded for correct response

12. Evidence (continued) • Larsen & Ketelaar (1991) • asked extraverted and introverted subjects to imagine being in positive situations and neutral situations • afterwards, rated mood • found that extraverts rated mood as more positive than introverts after positive condition • no differences in neutral condition

13. 3. Sensation-Seeking • tendency to seek out thrilling and exciting activities, to take risks, and avoid boredom

14. Typical Items • I sometimes like to do things that are a little frightening (T) • A sensible person avoids activities that are dangerous (F) • I like to have new and exciting experiences and sensations, even if they are frightening, unconventional, or illegal (T) • Almost everything enjoyable is illegal or immoral (T) • I get bored seeing the same old faces (T) • I like the comfortable familiarity of everyday friends (F)

15. Evidence • high scorers include • skydivers, police officers who volunteer for riot duty, college students who volunteer for unusual studies (drugs, ESP, hypnosis) • gambling • make riskier bets • sexuality: • larger # of partners, wider variety of sex acts

16. Sensation-Seeking and MAO • MAO = monoamine oxidase • breaks down many neurotransmitters • serotonin, norepinephrine, dopamine • high sensation seekers have low levels of MAO in bloodstream • low MAO means less inhibition

17. 4. Morningness and Eveningness • preference for being active and doing important/demanding work earlier vs. later in the day • rooted in length of person’s biological circadian temperature rhythm • morningness: peak body temp (most alert) early in day • eveningness: peak body temp late in day

18. 5. Hemispheric Asymmetry and Affective Style • Background • left hemisphere is more active when person is experiencing pleasant emotions • right hemisphere is more active when person is experiencing unpleasant emotions

19. Typical Finding • Davidson et al. (1990) • Method • showed film clips designed to either amuse or disgust • videotaped subjects and recorded EEG data • Results • when participants were smiling at amusing film, had more activation in left frontal lobe • when participants were showing facial expressions of disgust at disgusting film, had more activation in right frontal lobe

20. Theory • baseline EEG asymmetry indicates vulnerability to pleasant or unpleasant emotional states • more activity in left side = positive emotions • more activity in right side = negative emotions

21. Evidence • Tomarken et al. (1990) • Method • measured EEG while subjects were resting • showed subjects either happy or disgusting/fearful films • asked subjects to rate how films made them feel • Results • found frontal asymmetry measures taken before film clip predicted subsequent emotional reaction to film • participants with right-sided activation reported more intense negative reactions to film • participants with left-sided activation reported more intense positive reactions to film

22. Evidence • EEG asymmetry is evident during infancy • study of 10-month old infants • mothers left room • some cried; some did not • criers exhibited more right-sided activation • test-retest data suggest EEG asymmetry is stable among infants and adults

23. Are you right-sided or left-sided asymmetric? • Characteristic level of right- or left-sided activation may be indicated by direction person’s eyes drift when he/she concentrates on answering a difficult question • eyes drifting toward right = left-sided activation • eyes drifting toward left = right-sided activation

24. 6. Temperament in Childhood • infants differ in activity level, mood, responsiveness, soothability, and attention span • some are irritable and cranky; others are calm and sweet-natured • some squirm and fidget; others cuddle up in adult’s arms and snuggle • some fuss and cry; others smile easily • temperament: • characteristic emotional tone of infant • disposition to respond to the environment in relatively stable, typical ways

25. Evidence • Kagan (1994, 1998) • studies temperamental styles which he calls “reactive” and “nonreactive” • about 20% of children are at one extreme or the other

26. Kagan’s research • Kagan’s research shows longitudinal stability • study of highly reactive infants • 4 mos: excitable, nervous, overreact to little things • 14 and 21 mos: wary and fearful of new things (toys that make noise, odd-looking robots) even if mom in room • 5 years: timid and uncomfortable in new situations • 7 years: show sx of anxiety (afraid of being kidnapped, need to sleep with light on)

27. Biological Basis of Inhibition • inhibited children have lower threshold for activation of limbic system circuits that produce sympathetic arousal • Sympathetic arousal of 5.5-year-olds was correlated with behavioral indices of inhibition at 21-months (.70) and 7.5 years (.64).

28. Environment and Biology in Attachment • attachment: quality of emotional bond between infants and caregiver • assess attachment via strange situation • child put in room with unfamiliar objects • stranger comes into room • mother leaves • after short period of time, mother returns

29. Attachment Categories • securely attached (62%) • explore room while mother is present • don’t seem overly fearful of stranger • although show distress when mother leaves, they display signs of comfort and pleasure when she returns • avoidant (23%) • do not appear upset by new situation • ignore mother while present, indifferent to her absence • don’t seek her comfort when she returns

30. Attachment categories (continued) • anxious/ambivalent (15%) • do not explore room and remain close to mother • get very distressed when she leaves, continue to express distress when she returns • may express anger toward mother when she returns • avoidant and anxious/ambivalent are called “insecurely attached”

31. Van den Boom’s (1989) longitudinal study • Method • Infants assessed at 10-15 days • 17% classified as irritable • observed interaction of infants and mothers (and matched nonirritable control group) 2x per month for next 6 months • at 1 year, brought children into lab for strange situation

32. Van den Boom (1989) continued • Results • Mothers of irritable infants were more likely to ignore babies and show poor soothing skills and inconsistent responses over next 6 months. • Irritable infants were more likely to be categorized as insecurely attached at 1 year. • Question • What causes poor attachment? Infants’ biology or responses of caregivers?

33. Intervention Study • Mothers of irritable babies given training • interact sensitively • soothe babies • be aware of signals • play with babies • Results • control group: 68% insecurely attached • treatment group: 28% insecurely attached

34. Summary • introversion vs. extraversion • differences in arousability • impulsivity • sensitivity to reward (BAS) • sensation-seeking • low levels of MAO

35. Summary (continued) • morningness vs. eveningness • differences in circadian temperature rhythms • vulnerability to negative vs. positive emotions • differences in hemispheric asymmetry (right = negative)

36. Summary (continued) • inhibited or “high reactive” temperament among infants • differences in SNS activation • fearful behavior throughout childhood • difficult temperament may affect quality of attachment by influencing behavior of caregivers