NS

Development Through the Lifespan - Chapter 4: Physical Development in Infancy and Toddlerhood

The First Two Years

  • Infancy (first year) through toddlerhood (second year).
  • Rapid changes in body and brain support learning, motor skills, and perceptual capacities.
  • Motor, perceptual, cognitive, and social development mutually influence one another.
    • Example: When a child walks, their hands are free to explore and interact with the physical world.

Body Growth

  • Faster growth occurs than at any other time (growth occurs in spurts).
    • Age
      • Newborn
        • Height: 20 inches long
        • Weight: 7\frac{1}{2} pounds
      • End of year 1
        • Height: 32 inches, 50% greater than at birth
        • Weight: Triples to 22 pounds
      • End of year 2
        • Height: 36 inches, 75% greater than at birth
        • Weight: Quadruples to 30 pounds

Changes in Body Proportions

  • Cephalocaudal trend:
    • "Head to tail"
    • The head develops more rapidly than the lower part of the body.
  • Proximodistal trend:
    • "Near to far"
    • Growth proceeds from the center of the body outward.

Individual and Group Differences

  • Growth norms: height and weight averages.
  • Gender and ethnic differences are apparent.
  • Individual variation due to many factors, such as nutrition.
  • Skeletal age is the best estimate of physical maturity.

Neurons and Their Connective Fibers

  • Neurons: Nerve cells that store and transmit information.
  • Synapses: Tiny gaps between neurons where fibers from different neurons come close together but do not touch.
  • Neurotransmitters: Chemicals released by neurons that send messages across the synapse.
  • Action potential.
  • Pre-synaptic ("sending") cell.
  • Post-synaptic ("receiving") cell.

Development of Neurons

  • Establish unique functions by forming synaptic connections with neighboring cells.
  • Programmed cell death: Neurons die to make space for new connective structures.
  • Stimulation is vital for the survival of neurons and the formation of new synapses.
  • Synaptic pruning: Returns seldom-stimulated neurons to an uncommitted state.

Myelination

  • Coating of neural fibers with myelin, an insulating fatty sheath.
  • Improves efficiency of message transfer.
  • Glial cells: Responsible for myelination.
    • Account for half the brain's volume.
    • Multiply rapidly in the first two years.

Measures of Brain Functioning

  • Brain-wave patterns and changes in electrical activity:
    • Electroencephalogram (EEG)
    • Event-related potentials (ERPs)
  • Brain regions and functioning: 3-D neuroimaging:
    • Functional magnetic resonance imaging (fMRI)
    • Positron emission tomography (PET)
    • Near-infrared spectroscopy (NIRS)

Cerebral Cortex and Cortical Regions

  • Cerebral cortex: Largest brain structure, surrounds the rest of the brain.
  • Cortical regions develop as capacities emerge.
    • First year: auditory and visual; body movement areas.
    • Infancy through preschool: language areas.
  • Prefrontal cortex:
    • Responsible for complex thought.
    • Functions more effectively from age 2 months on.

Lateralization of the Cerebral Cortex

  • Left hemisphere:
    • Sequential, analytic processing.
    • Verbal communication.
    • Positive emotion.
  • Right hemisphere:
    • Holistic, integrative processing.
    • Making sense of spatial information.
    • Regulating negative emotion.

Brain Plasticity

  • At birth, hemispheres have begun to specialize.
  • Highly plastic cerebral cortex during the first few years:
    • Many areas not yet committed to specific functions.
    • High capacity for learning.
    • Early experiences influence its organization.
    • If part of the cortex is damaged, other areas can take over.

Sensitive Periods in Brain Development

  • Appropriate stimulation is vital for brain growth: counteracts negative effects of a depleted environment.
  • Early, extreme sensory deprivation results in permanent brain damage and loss of functions.
  • Rushing early learning overwhelms neural circuits and impedes the brain's potential.

Sensitive Periods in Brain Development

  • Experience-expectant brain growth:
    • Occurs early and naturally.
    • Rapidly developing organization.
    • Depends on ordinary experiences "expected" by the brain for normal growth.
  • Experience-dependent brain growth:
    • Occurs throughout our lives.
    • Growth and refinement.
    • Results from specific, individual learning experiences.

Changing States of Arousal

  • The sleep-wake pattern gradually shifts to a night-day schedule, and total sleep time declines.
  • Changes influenced by:
    • Brain development.
    • Cultural beliefs and practices.
    • Parents' needs and schedule.
    • Increased melatonin secretion.
    • Attachment to caregiver.

Cultural Influences

  • Cultural Variation in Infant Sleeping Arrangements
  • Parent-infant cosleeping is the norm for 90% of the world's population.
  • Cultural values of interdependence vs. independence influence sleeping arrangements.
  • Possible benefits:
    • Helps infants sleep.
    • Breastfeeding is more convenient.
    • Cosleeping safely may protect babies at risk for SIDS: baby sleeps in a bassinette placed next to the mother's bed.
  • Risks: Cosleeping unsafely increases the risk of SIDS: baby sleeps in the same bed as parents.

Influences on Early Growth

  • Heredity
  • Nutrition
    • Breastfeeding vs. bottle-feeding
    • Risks of overfeeding
  • Malnutrition

Heredity

  • Large influence on the rate of physical growth when diet and health are adequate.
  • Also affects height and weight.
  • Catch-up growth: return to genetically influenced growth path once negative conditions are corrected.

Nutrition and Breastfeeding

  • Crucial for development in the first two years.
  • Benefits of breastfeeding:
    • Ensures nutritional completeness.
    • Provides correct fat-protein balance.
    • Helps ensure healthy physical growth.
    • Protects against disease.
    • Protects against faulty jaw and tooth development.
    • Ensures digestibility.
    • Smooths transition to solid foods.
  • Mothers in the developing world are often unaware of the benefits; they use low-grade commercial formula and ingredients.

Preventing Overweight Children

  • Breastfeed exclusively for the first six months.
  • Avoid giving foods rich in sugar, salt, and saturated fats.
  • Provide opportunities for energetic play; limit TV viewing.

Malnutrition

  • Affects 2.1 million children annually.
  • Stunts the growth of one-third of all children under 5.
  • Severely malnourished children develop dietary diseases that cause long-term damage to their brain and organs, affects learning and behavior, and disrupts development.
  • Food insecurity afflicts 19% of U.S. children, affecting physical growth and learning.

Classical Conditioning

  • Pairs a neutral stimulus with one that prompts a reflexive response.
  • Helps infants recognize which events usually occur together.
  • The environment becomes more orderly and predictable.

Operant Conditioning

  • The infant acts, or operates, on the environment.
  • Reinforcer: increases the occurrence of a response.
    • Presenting a desirable stimulus.
    • Removing an unpleasant stimulus.
  • Punishment: decreases the occurrence of a response.
    • Presenting an unpleasant stimulus.
    • Removing a desirable stimulus.

Habituation and Recovery

  • Habituation: gradual reduction in the strength of a response due to repetitive stimulation.
    • Indicators of loss of interest: decline in time spent looking at the stimulus, heart rate, respiration rate, and brain activity.
  • Recovery: a new stimulus causes responsiveness to return to a high level.
  • Used to study infant perception and cognition.

Imitation

  • Infants are born with a primitive ability to imitate.
  • Mirror neurons may provide the biological basis.
  • The ability to imitate expands greatly over the first two years.
  • Powerful means of learning and exploring the social world.

Motor Development

  • New achievements build on previous ones.
  • Gross-motor development: crawling, standing, walking.
  • Fine-motor development: reaching, grasping.
  • The rate of motor progress varies widely.

Gross- and Fine-Motor Development in the First Two Years

  • Motor Skill - Average Age Achieved
    • Grasps cube - 3 months, 3 weeks
    • Sits up alone - 7 months
    • Crawls - 7 months
    • Pulls to stand - 8 months
    • Plays pat-a-cake - 9 months, 3 weeks
    • Walks alone - 11 months, 3 weeks
    • Scribbles vigorously - 14 months
    • Jumps in place - 23 months, 2 weeks

Motor Skills as Dynamic Systems

  • Acquisition of increasingly complex systems of action.
    • Example: crawling, standing, and stepping unite into walking.
  • Each new skill is a joint product of:
    • Central nervous system development.
    • Body's movement capacities.
    • Goals the child has in mind.
    • Environmental supports for the skill.

Milestones of Reaching and Grasping

  • Prereaching
  • Ulnar grasp
  • Transferring object from hand to hand
  • Pincer grasp

Developments in Hearing

  • 4-7 months: Sense of musical phrasing
  • 6-7 months: Distinguishes musical tunes based on variations in rhythmic patterns
  • 6-8 months: "Screens out" sounds not used in native languages
  • 6-12 months: Detects sound regularities in human speech
  • 7-9 months: Begins to divide speech stream into wordlike units

Biology and Environment

  • "Tuning In" to Familiar Speech, Faces, and Music: A Sensitive Period for Culture-Specific Learning
    • Perceptual narrowing effect:
      • Perceptual sensitivity becomes attuned with age to information most often encountered
      • Example: discriminating human and monkey faces at 6 months, but only human faces at 9 months
    • Between 6 and 12 months, biologically prepared to "zero in" on socially meaningful perceptual distinctions (speech, faces, music).

Statistical Learning Capacity

  • By analyzing the speech stream for patterns, babies:
    • Acquire speech structures for which they will later learn meanings
    • Extract patterns from complex, continuous speech
  • Present in the first weeks of life
  • Extends to visual stimuli

Visual Development

  • Supported by rapid maturation of eyes and visual centers in the brain
  • Milestones:
    • 2 months: focus
    • 4 months: color vision
    • 6 months: acuity, scanning, and tracking
    • 6-7 months: depth perception

Depth Perception

  • Milestones:
    • 3-4 weeks: sensitivity to motion
    • 2-3 months: sensitivity to binocular depth
    • 5-7 months: sensitivity to pictorial depth
  • Independent movement:
    • Promotes three-dimensional understanding
    • Helps infants remember object locations and find hidden objects

Milestones in Pattern Perception

  • 2 months: Detection of detail: sensitive to contrast in complex patterns; prefers patterns with more contrast
  • 2-3 months: Improved scanning ability: explores pattern features, pausing briefly to look at each part
  • 4 months: Detects pattern organization: perceives subjective boundaries that are not really present
  • 12 months: Detects familiar objects represented by incomplete drawings

Milestones in Face Perception

  • Newborn: Prefers simplified drawings of faces with naturally arranged features, with eyes open and a direct gaze
  • 2 months: Prefers complex facial patterns to other complex stimulus arrangements, and mother's detailed facial features to another woman's
  • 3 months: Makes fine distinctions among the features of different, moderately similar faces
  • 5 months: Perceives emotional expressions as meaningful wholes
  • 7 months: Discriminates among a wider range of facial expressions (e.g., happiness, surprise, anger)

Face Perception

  • Early experience promotes perceptual narrowing with respect to gender and race:
    • As early as 3 months, prefers and more easily discriminates female faces than male (unless caregiver is male)
    • If exposed mostly to members of own race, by 3–6 months, shows own-race bias, and between 6 and 9 months, has more difficulty discriminating other-race faces
  • By age 10-11, face discrimination in children matches that of adults

Intermodal Perception

  • Capacity to perceive streams of simultaneous, multisensory input as an integrated whole
  • Amodal sensory properties: information that overlaps multiple sensory systems
    • Example: the sight and sound of a bouncing ball
  • Rapid development during the first six months supports:
    • Perceptual understanding of the physical world
    • Social and language processing

Milestones in Intermodal Perception

  • Newborn: Perceives amodal sensory properties
  • 3-5 months: Matches faces with voices on basis of lip-voice synchrony, emotional expression, and speaker's age and gender
  • 6 months: Perceives and remembers unique face-voice pairings of unfamiliar adults

Differentiation Theory

  • Infants actively seek features that remain stable amid an ever-changing environment
    • Example: analyzing the speech stream for regularities
    • Over time, detect finer and finer invariant features
  • Applies to:
    • Intermodal perception
    • Pattern perception
    • Depth perception