PSYB30-Chapter 6.docx

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University of Toronto Scarborough
Marc A Fournier

Chapter 6: Continuity and change in Traits: the roles of genes, environments, and time  Trait terms in everyday talk are assumptions that features of psychological individuality are stable for a while.  There are two kinds of continuity  Absolute continuity is constancy in the quantity of an attribute over time; it is never applied to the single individual it is understood in the group averages on a given trait (few things have changed for the group as a whole)  Differential continuity: consistency of individual differences within a sample of individuals over time, retention of an individual’s relative placement in a group; relative to his peers on a given dimension.  Trait dimensions are calculated with a correlation coefficient; high correlation coefficients suggest high differential continuity.  Low differential continuity means that people’s relative positions on dimension change unpredictably over time.  Absolute continuity refers to the consistency of the average score on a given trait over time, while differential continuity is the stability of individual differences in scores.  Longitudinal studies show high differential continuity in personality traits over the adult lifespan  The big five dimensions of extraversion and neuroticism show strong longitudinal consistency.  Differential continuity in trait ratings was shoed in a) self ratings over time and b) spouse ratings over time and c) ability of one rating to predict another kind of rating of the same trait over time.  Differential continuity for all five of trait clusters across intervals of time from 3 to 30 years.  Reason for instability is the error of measures.  Length of time interval between testing is another.  Extraversion shows higher differential continuity than the trait of N and higher continuity than overall average of other traits.  Another factor is the age of the participants, as people age they change less and less relative to one another.  There is a plateau for adults between the ages of 50 and 70. Childhood precursors: from temperament to traits  Differences in basic behavioural style early in life, which are under biological control, are viewed as indications of temperament.  Early in life framework  Thomas chess and birch said easy babies show positive mood.  Difficult babies show negative moods, intense emotional reactions, irregular sleeping and eating cycles.  Slow to warm up babies, have negative moods, low intensity of emotional reaction and withdraw from events and then approach them later.  Rothbart talks about six temperament dimensions: activity level, smiling and laughter, fearfulness, distress to limitations, “soothability,” and vocal activity.  Kagan Behavioural inhibition show timidity in novel events o Shy and extremely sociable children separable genetic types differences on thresholds of reactivity in the brain’s limbic system.  Inhibited children show neural activation of the right frontal lobe while uninhibited show left frontal lobe  Right frontal activity is associated with negative affectivity and the behavioural inhibition system  And positive affectivity is associated with the behavioural approach system.  Out of every 100 Caucasian newborns 20 are irritable and excitable.  By 2 75 of these are shy, and by adolescence 10 are very shy, and by adulthood 6 or 7 of them are extremely introverted.  2/3rds that lost their shyness may have been strongly influenced by environmental experiences.  Effortful control has implications for personality development; child’s active and voluntary capacity to withhold a dominant response in order to enact a subordinate response given situational demands.  High levels of effortful control are predictive of successful interpersonal functioning in childhood; important in moral development.  Girls show better effortful control than boys  There is high longitudinal consistency.  Longitudinal study called Dunedin study used 1000 individuals; well-adjusted children had appropriate levels of self-control. Under controlled were impulsive, restless. Confident children were adjusted to situations and were enthusiastic. The inhibited type was fearful. And the reserved children were timid but showed less shyness than inhibited children.  A self-report personality scale was administered to the above individuals when they were 26, most predictable were the under controlled and inhibited types; under controlled had the highest score on negative emotionality.  Under controlled had high levels of neuroticism, low levels of A and C.  Inhibited children had low levels of extraversion.  Capsi, temperament as the psychobiological core around personality; through developmental elaboration, they develop into fully articulated personality traits.  This is a process is shaped y inborn tendencies, and environmental inputs.  There are six mechanisms of developmental elaboration: 1. How children learn 2. How they construe their environments 3. How other people in the environment respond to them 4. How they compare themselves to other children 5. What kinds of environments they choose 6. And how they manipulate environments once they choose them. The origins of Traits: Genes and Environments  Genetically identical twins–MZ are similar and their behaviour patterns are concordant.  DZ twins seem to be equally discordant.  Differences or variability among people; the percentages of variability accounted for depends on characteristics of the population to begin with.  Heritability quotient is the proportion of variability in a given characteristic that is attributed to genetic differences between people.  Heritability we focus on 10% of the human genome that does vary.  Studies of twins and adopted children help to understand heritability of personality traits.  Usual design is to take MZ twins and sample DZ twins and compute correlations between the trait scores.  The heritability quotient: h = 2(rmz - dz)  Adoptive studies – share similar traits with members of their adoptive families, typically with siblings.  Evidence for heritability when correlations between trait scores of biologically related siblings exceed trait scores of nonbiologically related.  Behaviour genetics: explores influences of genetic and environmental factors accounting for variability in human behaviour. Heritability Estimates of Traits  All personality traits are at least moderately heritable.  Heritability’s for BF dimensions are in the 40-50% range, and strongest is for Openness to Experience.  Many of the smaller traits or facets that make up each of the BF also are heritable.  MZ correlations are twice as high as DZ correlations; this is truce for O, E and N.  Genetic variance should be additive.  Adoption yield lower heritability estimates; but it’s not really the case.  For some traits, identical twins seem to be more similar to each other than expected and second adoption studies suggest biological siblings are less similar to each other than expected.  Nonadditive genetic variance: combine and interact in a configural pattern, the absence of change in any one can produce qualitative or large quantitative change in the result.  Emergenesis: certain patterns of genes may give rise to particular behavioural tendencies that would not themselves be produced even in a weaker or more attenuated form, by the pieces that make up the pattern; every person is dealt a unique hand  Twins reared apart, are almost identical to MZ reared together  Growing up in the same family seems to have little impact on personality traits; traits of intimacy and love for others show family environment effects it. Loneliness shows no effect. Juvenile delinquency shows influence of family environment.  Half of the variance in personality traits can be attributed to genetics.  Trait measures contain error, which adds up to unexplainable variations; 10-20% of the variance.  Distinction between two different kinds of environmental effects; shared environment are influences that operate to make family members alike; such as class, parents’ education.  Nonshared environment are influences that operate to make members unalike.  First0born’s nonshared environment of being the oldest; while the second one struggle.  Rowe lists six categories of nonshared family effects: 1. Perinatal trauma 2. Accidental events – physical injuries to winning the raffle prize 3. Family constellation – birth order and birth spacing 4. Sibling mutual interaction – interact forming alliances of various sorts. 5. Unequal parent
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