01:830:338 Lecture Notes - Lecture 5: Reinforcement Sensitivity Theory, Behavioural Genetics, Twin Study

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Lecture 5: BIOLOGICAL UNDERPINNINGS OF PERSONALITY
Biological Underpinnings of Personality
History Hippocrates and Galen
Proposed four personality types tied to excesses of bodily humors
Choleric (irritable)
Melancholic (depressed)
Phlegmatic (calm)
Sanguine (optimistic)
Brought idea that physical properties determine personality
Heritability of Personality
How much is personality genetically inherited?
Behavioral genetics study of genetic influences on behavioral qualities (including
personality)
Behavioral Genetics
Twin studies
Monozygotic twins identical (100% shared genes)
Dizygotic twins fraternal (average 50% shared genes)
Compute correlation between sets of monozygotic twins and co-twins and
dizygotic twins and co-twins on some characteristic
Gene-environment interactions
Situations might cause one reaction in a person with one genetic makeup and a
different reaction in a person with a different genetic makeup
Different situations might cause different outcomes in person with certain
genetic makeup
Shared environment features of environment in common
Nonshared environment environmental factors that make people different
Results from Studies of Behavioral Genetics
Heritability proportion of observed variance in a group of individuals that can be
accounted for by genetic variance
Heritabilities of psychological traits
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Extraversion: .54-.60
Agreeableness: .42
Neuroticism: .48-.54
Conscientiousness: .49
Openness: .57
Conservatism: .45-.65
RWA: .50-.64
Biology of Personality
Eysenck proposed that introverts normally have higher cortical arousal than extraverts
avoid social interaction because it causes overstimulation
Evidence
Vigilance tasks
Drug effects
Lemon juice test
Reinforcement Sensitivity Theory
Reinforcement sensitivity theory behavioral approach system (BAS) and behavioral
inhibition system (BIS) reside in brain
BAS regulates approach behaviors
High BAS - motivated to seek out and achieve pleasurable goals
BIS responsive to cues for punishment, frustration, uncertainty
High BIS - wary, apprehensive
Individual differences in the strength of BAS and BIS
Validation of BAS/BIS theory
2 groups thought to be high or low on BIS
Scored very differently on measure of BIS sensitivity prostitutes much lower
on BIS
Children-inhibited and uninhibited
Inhibited children cautious about and at times fearful of new people and new
situations
Uninhibited children opposite
Anxiety to novelty
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