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University of Toronto Scarborough
Mark Schmuckler

Developmental Psychology Chapter 5 - The Child’s Growth: Brain, Body, Motor Skills, Sexual Maturation Brain Development in Infancy Segalowitz - little in theories of development that rely on some specific aspect of the developmental pattern of brain growth - prenatal period, brain grows rapidly - birth - infants brain weighs 1/4 of adult brain - 6 months - brain weights 1/2 of adult brain - cerebrum - the two connected hemispheres of the brain - cerebral cortex - the covering layer of the cerebrum that contains the cells that control specific functions, such as seeing, hearing, moving and thinking - as brain develops, front part expands to form the cerebrum which is covered by the cerebral cortex Neurons and Synapses - neurons - cell in the body’s nervous system (made of cell body, axon and dendrites) - send and receive neural impulses throughout the brain and nervous system - at birth, has most neurons - during embryonic period, neurons multiply at rapid pace - neuron proliferation - after birth, brain increases in size - existing neurons grow and connections between them proliferate - glial cells - nerve cells that support and protects neurons and serves to encase them in sheaths of myelin - neurons “always on the move” in the process of migrating to their final location - neural migration - movement of neurons within the brain that ensures that all the brain areas have a sufficient number of neural connections - absence - associated with mental disability and disorders - ex. dyslexia and schizophrenia - synapse - a specialized site of intercellular communication where information is ex- changed between nerves cells, usually by means of neurotransmitters - axon -> dendrite - synaptogenesis - forming of synapses - begins early in prenatal life - brain forms more synapses than neurons - brain programmed to create more nerve cells and more connections between cells than needed - with development, two processes reduce the number of neurons and connecting fibers Developmental Psychology Chapter 5 - The Child’s Growth: Brain, Body, Motor Skills, Sexual Maturation - when new synapses form, surrounding neurons die - neuronal death - provide more space of loci of information transmission - synaptic pruning - brain’s disposal of the axon and dendrites o a neuron that is not often stimulated - frees up space for new synaptic connections - goals of neuronal death and synaptic pruning - increase speed, efficiency, and com- plexity of transmissions between neurons and to allow room for new connections that develop - loss leads to gain Sequential Development of the Brain - early months, motor area develops most rapidly - 2 months old, motor reflexes (ex. rooting and startle response) drop out and motor cor- tex begins to oversee voluntary movement (ex. reaching, crawling) - in visual cortex, number of synapse per neuron multiplied by ~6 times within first two years Hemispheric Specialization - corpus callosum - band of nerve fibers that connects the two hemispheres of the brain - left controls right, vice versa - lateralization - process by which each half of the brain becomes specialized for the performance of certain functions - right hemi processes - visual-spatial info - damage - drawing skills deteriorate, trouble reading a map, recog- nizing friends, spatially disoriented - non-speech sounds - damage - music perception - perception of faces - emotional info - left hemi process - language processing - damage - trouble understanding what is being said to them or speaking clearly Developmental Psychology Chapter 5 - The Child’s Growth: Brain, Body, Motor Skills, Sexual Maturation - theory - both hemispheres associated in emotional expression, but left focuses on feel- ings that trigger approach to the environment, the right on feelings that cause the per- son to turn away from the environment - if brain injury early in life, can recover losses Consequences of Brain Lateralization - degree to which a newborn’s brain is lateralized in processing speech sounds has con- sequences for language ability three years later - infants whose left hemi differentiates among speech sounds and right hemi dif- ferentiates among non-speech sounds exhibits better language skills - dyslexia - difficulties experienced by some people in reading or learning to read - difficulty integrating visual and auditory information - some researchers suggest children do not show normal lateralization pattern - process information in both sides of the brain rather than primarily on the right - left hemi may become overloaded, leading to language deficit skills - handedness (left/right handed) function that is lateralized - 90% population right-handed, 90% newborns prefer to suck right thumb - suggests handedness develops in the womb - gene identified for left-handedness - some left-handed people ambidextrous - suggests brain may be less clearly lateralized The Brain’s Plasticity: Experience and Brain Development plasticity - the capacity of the brain, particularly in its developmental stages, to respond and adapt to input from the external environment - two types of experience influence brain development - touch, patterned visual input, sounds of language, affectionate expressions from caregivers and nutrition - exported in normal environments - trigger synaptic development and pruning - critical for normal brain development - interference with normal stimulation - basic abilities impaired - ex. when children have congenital cataracts, visual system is de- prived of stimulation and fails to develop properly, even when cataracts removed, adult is still blind Developmental Psychology Chapter 5 - The Child’s Growth: Brain, Body, Motor Skills, Sexual Maturation - experiences that are unique to individuals - encountered in particular families, communities and cultures - brain responds to different environments by developing synaptic connec- tions that encode specific and unique experiences - ex. children in Mozambique develop aspects of the motor cortex that correspond to the skills associated with hunting and fishing - size, structure, biochemistry of the brain can be modified by experience - Rosenzweig - placed young rats in two different environments - one enriched, one impoverished - rat in enriched environment had 4% heavier cerebral cortex - which controls higher order processes - rat in enriched environment had 6% heavier occipital region - enriched environments tend to increase complexity of neurons as measured by the number of dendrites they develop - more dendrites -> more synapses formed with other neurons -> more informa- tion - activity of key chemicals in brain especially in the cerebral cortex increases sig- nificantly - infants respond to sounds of all languages, over first year of life, become more selec- tive - respond increasingly to sounds of own language - different sets of neuronal connections become programmed to respond to par- ticular aspects of speech - infants’ brain develop “auditory maps” or templates - respond to certain auditory features - maps guide infants in recognizing their native language - exposure to music can enrich brain development - natural harmonics of music may help the brain develop a wiring diagram that promotes spatial-temporal reasoning - research demonstrates that the brain can undergo structural change based on unique experiences even in adulthood - Maguire - looked at structure of human brains with extensive navigational experience and compared these brains with a set of control subjects who did not drive taxis - posterior hippocampi (thought to be associated with spatial representations of the environment) larger in the taxi drivers than in the control - suggest remarkable degree of plasticity in response to environmental demands Developmental Psychology Chapter 5 - The Child’s Growth: Brain, Body, Motor Skills, Sexual Maturation - lack of stimulation or exposure to traumatic events can damage the brain and cause it to malfunction - in abused children - both cortex and limbic system 20-30% smaller and fewer synaps- es - PET show effects on developing brain on deprivation - reduced cortical activity to solve cognitive tasks ex. memory or face processing - advantage - allows function and biochemical studies - provides visual image corresponding to anatomy - disadvantage - requires exposure to low levels of radioactivity - provides spatial resolution better than EEG but poorer than MRI - cannot follow rapid changes - reduced connectivity or communication between regions of brain - EEG show lines that chart the summated electrical fields resulting from activity of bil- lions of neurons - advantage - detects very rapid changes in electrical activity, allowing analysis of stages of cognitive processing - disadvantage - provide poor spatial resolution of the source of electrical activity - MRI show high resolution image of brain anatomy - advantage - requires no exposure of radioactivity - provides high spatial resolution of anatomical details - provides high temporal resolution - TMS - normal function of a particular brain function can be studied by observing changes after TMS is applied to a specific location - advantage - shows which brain regions are necessary for given tasks - disadvantage - long term safety not well established Motor Development Hand Skills - newborns - “pre-reaching” - uncoordinated “swipes” - 3 months of age - directed reaching - complex and efficient pattern Developmental Psychology Chapter 5 - The Child’s Growth: Brain, Body, Motor Skills, Sexual Maturation - 5 months of age - generally succeed in reaching and grasping - involves muscle growth, postural control, control over movement of arms and hands, and variety of perceptual and motor abilities - all parts ready to work together - “putting pieces together” - consistent with dynamic systems view of development - component of dynamic systems view is - visual perception - nothing to look at, no incentive to reach - enriching environment could advance abilities to attend to objects and reach them - motor ability to grip an object - frequency and skill in gripping improves with age - infants vary grip according to size and shape - small objects - thumb and index finger - large objects - all fingers on one hand or both hands - 4 month old - rely on touch to determine grip - 8 month old - rely on vision as guide to shape hand - over first year of life begin to use objects as tools - learn gestures in social communication - 2 year old - use hand skillfully in play - 3 year old - use hand to scribble or copy vertical lines Locomotion - three phases/transitions - first - when holding baby upright and let his feet touch a flat surface, tilt body side to side, baby responds by moving legs in rhythmic stepping motion - stepping reflex disappears by the time infant is about two months old - second - reappearance of stepping movements - second half of baby’s first year - third - at 1 year of age, infants begin to walk without support - how walking develops - maturational theorist - depends on development of motor cortex Developmental Psychology Chapter 5 - The Child’s Growth: Brain, Body, Motor Skills, Sexual Maturation - cognitive theorist - response to cognitive plans or representation that are the consequence of watching other people walk - Thelen - dynamic systems theory - walking skills are determined by the interplay of a variety of emotional, perceptual, attentional, - all components must be ready - developmental context must be right before the infant can walk - newborn stepping response disappears for 10-month interval before true walking emerges because of anatomical factors - baby’s size and weight become too much of a load on emerging motor system - masks child’s stepping capability - if explanation right, 2 months - 12 months should be able to step as long as given stability and postural support necessary to stretch each leg for- wards and back while in upright position - 7 year old - acquired more complex skills of running, galloping and hopping - year and half - running well established, galloping emerges - 2 - 3 years - hopping emerges - requires balance and strength How Locomotion May Affect Other Aspects of Development - increased independence - initiate more contact - explore environment - changes way others respond to child - to prevent chaos, parents intervene with distractions or prohibitions - early walking related to increased parent-child interaction and more “testing” of wills between mothers and their children - “perception-action coupling” - understand growth of independent mobility - motor or action systems functionally interrelated to sensory or perceptual sys- tems - changes in one aspect influence the development of the other aspect - onset of locomotion can change the way babies understand their perceptual world - ex. crawling brings fear of heights and other spatial abilities - crawling babies better at finding a hidden toy after being moved through the world - deal better with changes in spatial orientation - “moving room” - room which the walls and ceiling can be moved back and forth Developmental Psychology Chapter 5 - The Child’s Growth: Brain, Body, Motor Skills, Sexual Maturation - researchers (Schmuckler) demonstrated that infants and young children use the visual input produced by a moving room to control their balance - Schmuckler - found that 3 - 6 year olds will not only sway back and forth peri- odically to visual movement but will even do so even when movement is quite fast - Bertenthal and Bai - self-produced locomotion critical for infants’ use of visual infor- mation in crawling infants - pre-crawling infants - use moving room input to control balance Role of Experience and Culture - seems that when parents or other caretakers give babies special physical attention, in- fants achieve motor milestones somewhat earlier - Zelazo - asked mothers of newborns to give their infants practice in the stepping reflex a few minutes a day - babies made more walking responses at 2 to 8 weeks of age - walked earlier than control (no practice) - practice in sitting yielded similar results - babies who were given practice for 3 minutes a day were able to sit up- right longer - Karen Adolph - collected diary records of infants’ walking activities - walking infants practiced keeping balance in an upright stance and locomotion for more than six hours a day (500-1500 walking steps an hour) - taken 9000 walking steps and travelled length of 29 football fields - limits to how far infants’ motor development can be pushed - Benson - possibility that aspects of the geographic region in which children are reared may influence motor development - looked at 400+ babies in Denver - observed that babies born between June and November took three weeks longer to achieve independent mobility than babies born between December and May - suggests infants born in the summer or fall months acquired motor skills later - winter months have more restrictive clothing, activity reducing ill- nesses and less time for free movement due to shorter days - urban environment - parents may maintain more uniform home temperature Developmental Psychology Chapter 5 - The Child’s Growth: Brain, Body, Motor Skills, Sexual Maturation Risk and Resilience - blindness delays motor development - lessens ability to explore independently - lessens ability to discover by himself the objective rules that govern things and events in the eternal world - decrease in some cognitive abilities - “joint attention” - spatial knowledge - Bigelow - examined the relation between blindness and such cognitive abilities in a number of contexts - blind, visually impaired and sighted children (3-7 years old) asked to hide them- selves, a toy, and specific parts of body from observer - found that the blind children were not as successful as hiding as the other groups - act as though they did not understand that a covering obstacle had to completely block an observer’s view - found that blind children’s understanding of the spatial layout of their own homes was not as good - blind children’s spatial knowledge based more on how one would move be- tween places, rather than the correct layout - technology can play a role in building motor capabilities for blind infants - device that produce echoes from nearby objects (echolocation) - Bower - had blind infants wear an echo-producing device for several months - found that using the echo-feedback, the babies could judge their distance from objects and even objects size and texture - reaching ability improved and able to do things more typical of sighted in- fants Physical Growth - cephalocaudal development - growth from head downwards - proximal-distal pattern - growth from internal organs to arms and legs - Galloway and Thelen - found that young infants reached for objects approximately two weeks earlier with their feet than they did with their hands - demonstrates more complex motor skills with parts of the body further away from the head (the feet) than body parts closer to the head (the hands) - height and weight - two principal measures of overall growth - nearly double their weight in first three months Developmental Psychology Chapter 5 - The Child’s Growth: Brain, Body, Motor Skills, Sexual Maturation - triple weight by end of first year - top heavy body becomes increasingly cylindrical - infant’s center of mass moves from sternum to below the belly button - fat toddlers become slender kindergarteners - growth episodic rather than continuous Do Genes Affect Height and Weight? - influenced by environmental factors - genetic factors strongly influence - identical twins twice as likely to resemble each other in weight as are fraternal twins - gender clear effect on height and weight - girls tend to be taller from 2 - 9 - 10.5 years of age, girls experience a growth spurt - 14 years of age, girls’ height plateaus - girls tend to weigh less than boys in early years - then exceed weight of boys until age 14 - boys continue to grow in height and weight continuously, then accelerate - tempo of growth - variability in timing of changes in infants’ and children’s growth Influence of Environmental Factors - when environmental conditions are favourable, individual growth curves tend to be very similar - in presence of one or more unfavorable conditions, such as inadequate nutrition or poor caregiving, growth rates can be seriously depressed - variations in growth rates attributes to differences in nationality, ethnicity and socio- economic class Nutrition - bottle vs breast-feeding - advan
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