Are critical periods critical for early
childhood education?
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The notion of a window of opportunity
opening in early childhood, and then
closing, never to open again, evoked a
powerful visual image in the mid-1990s.
It galvanized scientific and popular media
to attend to the problems of early childhood
education.
lectures notes for developmental psychology, ps241,
2004, prof catherine l harris, boston university
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Newsweek cover story in 1996
But they imply, too, that if you miss the
window you're playing with a handicap. They
offer an explanation of why the gains a toddler
makes in Head Start are often so evanescent
this intensive instruction begins too late to
fundamentally rewire the brain.
-- Newsweek, February 19, 1996
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From animal research
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Hubel and Wiesel
(1970), suturing shut the
eye of a kitten
The ducklings raised by
Konrad Lorenz
imprinted on first
moving object (recent
film, Fly Away Home)
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Understanding the programmatic
nature of early brain development
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Born with all (cortical) neurons you will
have, neurons die at furious pace in first
years of life (apoptosis: programmed cell
death)
Neurons that fire together, wire together
Identifiable waves of synaptogenesis,
followed by pruning of connections
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Neurons that don't connect, die
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What happens to animals raised in
complex environments?
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Greenough's research: rats reared in enriched
environments had more dendritic branching
"Revelation" for Caregivers: that they could
engage in activities that would influence their
child's brain development
Are the effects of complex environments “critical period”
effects?
Do we think that same kind of neural processes
underlie both kinds of effects?
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Synaptic Density: Infancy to Adulthood
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More factors that raised
awareness
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Deleterious effects of prenatal teratogens
(alcohol, cocaine), and early childhood exposure
to lead
Early childhood risk factors: poverty, nutritional
deprivation, social neglect, maternal depression,
childhood abuse, multiple risk factors neglect
(Romanian orphanages)
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Summary of Ideas from
Neuroscience
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Synaptogenesis -- in infancy the brain
forms synapses in excess of adult levels.
Critical periods -- normal development of
neural systems requires specific experiential
input at specific times.
Pruning at Puberty -- at sexual maturity
synapses are pruned back to adult levels.
Enriched environments increase synaptic
connections.
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Two Categories of Human Abilities
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Our brain underwent evolved under the pressure of
natural selection to have some abilities. basic vision,
first language learning, categorization, number sense,
time sense, deception, social relations
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Our brains didn't evolve to manifest: writing, algebra,
astronomical understanding, breeding of animals, etc.
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Environmental input necessary for these abilities are
those that the brain could expect to encounter. If they
are not present, brain development proceeds
abnormally, and critical period effects can occur.
.
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No special areas of the brain evolved
to support writing, algebra, etc.
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When these abilities develop, they generally recruit
specific areas of the brain.
BUT: Brain development depends on the exposure to the
relevant concepts.
If this experience doesn't occur, brain development is not
abnormal. Brain development is normal, because the
brain doesn't *expect* these inputs. The hypothesis here
is that critical period effects will not occur for these
"experience-dependent" activities.
All of education is about experience-dependent behavior.
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Side note: Controversial whether
these “evolved”
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second language acquisition
art, music, dance, religion, story telling
abstract "patterning" (cf. Gardner)
warfare, infanticide, genocide,
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“Critical Period” for Music?
In the brains of nine string players examined
with magnetic resonance imaging, the amount
of somatosensory cortex dedicated to the
thumb and fifth finger of the left hand -- the
fingering digits -- was significantly larger than
in nonplayers. How long the players practiced
each day did not affect the cortical map. But
… the younger the child when she took up an
instrument, the more cortex she devoted to
playing it.
-- Newsweek, February 19, 1966
14
Did not
control
for
duration
or
practice
effect
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John Bruer, Myth of the First Three Years
,1999 and other authors:
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Critical periods are the exception rather than the
rule
Adults can learn to read or can learn a new
language
Do critical periods exist for providing an
organism with a higher-quality experience?
Recent neurobiological work: life-long plasticity;
neural reorganization after brain injury
Wide variability in human performance for nonevolutionary, "higher cognition"
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Rationale for early childhood
initiatives
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What are “Sensitive periods”?
Windows for learning open at birth
The first years are foundational
Early childhood enrichment can
compensate for social deprivation
Shift attention away from critical periods to
critical experiences
Teachable moments; transitions, crises
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