Biological influences on personality
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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

  • 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

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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

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Brain Stem

  • ARAS: ascending reticular activating system

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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.

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  • 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.

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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)

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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

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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

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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

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  • 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

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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

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3. Sensation-Seeking

  • tendency to seek out thrilling and exciting activities, to take risks, and avoid boredom

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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)

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  • 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

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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

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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

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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

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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

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  • 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

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  • 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

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  • 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

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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

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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

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  • Kagan (1994, 1998)

    • studies temperamental styles which he calls “reactive” and “nonreactive”

    • about 20% of children are at one extreme or the other

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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)

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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).

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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

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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

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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”

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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

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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?

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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

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  • introversion vs. extraversion

    • differences in arousability

  • impulsivity

    • sensitivity to reward (BAS)

  • sensation-seeking

    • low levels of MAO

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Summary (continued)

  • morningness vs. eveningness

    • differences in circadian temperature rhythms

  • vulnerability to negative vs. positive emotions

    • differences in hemispheric asymmetry (right = negative)

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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