PSYC 332 Chapter Notes - Chapter 4: Jerome Kagan, Susan Cain, Amygdala

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10 Feb 2016
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Quiet by Susan Cain
Psyc 332
Chapter 4: Is Temperament Destiny?
Part Two: Your Biology, Your Self?
The author starts with an anecdote about how incredibly nervous she was to make a seminar
speech to a big media company
o But eventually she overcame her fear of public speeches
Dr. Jerome Kagan, a developmental psychologist at Harvard, studied the emotional and cognitive
development of children
o In a longitudinal study with 500 four-month-old infants, he predicted that he'd be able to
tell which babies would turn out to be introverts and which ones would turn out to be
extroverts based on 45 minutes of observations
o The infants were exposed to popping balloons, tape-recorded voices, alcohol cotton swabs
and reacted differently to the stimuli
o 20% of them cried and flailed their arms and legs in response - those were the "high-
reactive" infants
o 40% of them stayed quiet and placid - they were "low-reactive"
o The remaining 40% was in the middle of the two extremes
o He then did a follow-up on the children at the age of 2, 4, 7, and 11 where they would
undergo more series of tests - the parents were also interviewed
o The high-reactive infants were introverts and the low-reactive infants were extroverts, just
as Kagan had predicted
High-reactive = serious, careful
Low-reactive = relaxed, confident
Temperament: "inborn, biologically based behavioural and emotional patterns that are observable
in infancy and early childhood"
Personality: "complex brew that emerges after cultural influence and personal experience are
thrown into the mix"
Kagan believes that certain properties of the nervous system when afflicted by stimuli are
controlled by the amygdala
o The amygdala is part of the limbic system
o It acts as the brain's emotional switchboard - it receives information from the senses then
signals the rest of the brain and the nervous system on how to respond
Kagan believed that infants born with an excitable amygdala would react strongly to unfamiliar
objects and they would grow up to be more vigilant when meeting new people - these were the
introverts
o The opposite would happen with extroverts - they had a less excitable amygdala
The more reactive the amygdala, the higher the heart rate, the more dilated the eyes, and the
tighter the vocal cords when encountering new stimuli
High-reactive children also tend to pay more alert attention to people and things
o They think and feel more deeply, i.e. they experience more guilt
Introversion/extroversion has some genetic basis
o They are 40-50% heritable
Kagan's theory doesn't apply to all introverts. Susan Cain claims that her mother did not find her
highly reactive at all
At an interview, Kagan states that every behaviour has more than one cause
o Although public-speaking phobia is more likely in introverts than in extroverts, it has many
different causes such as early childhood setbacks
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