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Biological Influences on Personality. 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

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major point
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
1 extraversion introversion
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

Brain Stem

  • ARAS: ascending reticular activating system
eysenck s arousal theory
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.
  • 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.
revision of theory
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)
2 sensitivity to reward and punishment
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
separate systems
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
gray s theory
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
  • 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
evidence continued
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
3 sensation seeking
3. Sensation-Seeking
  • tendency to seek out thrilling and exciting activities, to take risks, and avoid boredom
typical items
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)
  • 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
sensation seeking and mao
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
4 morningness and eveningness
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
5 hemispheric asymmetry and affective style
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
typical finding
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
  • 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
  • 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
  • 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
are you right sided or left sided asymmetric
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
6 temperament in childhood
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
  • Kagan (1994, 1998)
    • studies temperamental styles which he calls “reactive” and “nonreactive”
    • about 20% of children are at one extreme or the other
kagan s research
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)
biological basis of inhibition
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).
environment and biology in attachment
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
attachment categories
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
attachment categories continued
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”
van den boom s 1989 longitudinal study
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
van den boom 1989 continued
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?
intervention study
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
  • introversion vs. extraversion
    • differences in arousability
  • impulsivity
    • sensitivity to reward (BAS)
  • sensation-seeking
    • low levels of MAO
summary continued
Summary (continued)
  • morningness vs. eveningness
    • differences in circadian temperature rhythms
  • vulnerability to negative vs. positive emotions
    • differences in hemispheric asymmetry (right = negative)
summary continued36
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