Physical Development in Infancy and Toddlerhood (Comprehensive Study Notes)

Learning Goals

  • Goal 1: Body Growth

  • Goal 2: Brain Development and Learning Capacities

  • Goal 3: Motor Development

  • Goal 4: Perceptual Development

Body Growth

  • Infants grow rapidly over the first 2 years; weight gains are matched by increases in length. Growth is not uniform across all body parts. There are gender and ethnic differences in infant weight and length.

  • Decreasing proportions in the neonate: At birth, the head represents rac{1}{4} of the neonate’s body. By adulthood, the head is rac{1}{8} the size of the body. This is due to differential growth rates across body parts.

  • Growth pattern in infancy: faster growth than at any other time, occurring in spurts. Key data:

    • Newborn: height = 20\text{ inches} , weight = 7.5\text{ pounds}

    • End of year 1: height = 32\text{ inches}, weight = 22\text{ pounds} (growth cited as 50\%\text{ greater than birth height} in some summaries; height increases from 20 to 32 inches = 12\text{ inches}, a 60\% increase).\n - End of year 2: height = 36\text{ inches}, weight = 30\text{ pounds} (height increase from birth: 16\text{ inches}; weight quadruples from birth to 30 pounds).

  • Individual and group differences:

    • Growth norms: average height and weight by age

    • Gender and ethnic differences are apparent

    • Individual variation due to nutrition and other factors

    • Skeletal age is the best estimate of physical maturity

Nutrition and Breastfeeding

  • Breastfeeding is crucial for development in the first two years and has multiple benefits:

    • 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

  • Ethical/practical note: Mothers in the developing world are often unaware of the benefits of breastfeeding and may rely on low-grade commercial formula and ingredients.

Preventing Overweight in Children

  • Recommendations to reduce overweight risk:

    • Breastfeed exclusively for the first six months

    • Avoid foods high in sugar, salt, and saturated fats

      • Children under 2 years old should NOT be given candy/gor processed sugars and should instead be encouraged to eat whole foods such as fruits, vegetables, and whole grains.

    • Provide opportunities for energetic play; limit TV viewing

    • Babies wake up a lot more when breastfed compared to being given formula because they digest breast milk more quickly, leading to more frequent feedings.

Brain Development and Learning Capacities

  • The Nervous System and Brain: The Foundations of Development

  • Environmental influences on brain development:

    • Plasticity: the degree to which a developing structure (e.g., the brain) or behavior is modifiable due to experience

      • Neuroplasticity

    • Sensitive period (0-2 years old): a specific but limited time, usually early in life, during which the organism is particularly susceptible to environmental influences relating to some development facet

      • Genes provide basic foundation of cognitive structure but enviroment and experience can either enhance or inhibit the expression of these genetic potentials, shaping individual developmental outcomes.

Sleep Patterns

  • Sleep patterns: infancy sleep–wake cycles gradually shift toward a night–day schedule; total sleep time declines over time

  • Factors influencing sleep changes:

    • Brain development

    • Cultural beliefs and practices

    • Parents’ needs and schedules

    • Increased melatonin secretion

    • Attachment to caregiver

SIDS (Sudden Infant Death Syndrome)

  • Definition: the sudden and unexplained death of an infant between 1 month and 1 year old that remains unexplained after investigation; exact cause unknown, though risk factors exist and ways to reduce risk are known

  • Prevalence: about 2,300 babies in the United States die of SIDS each year

Classical Conditioning

  • Classical Conditioning: A type of learning where an infant learns to associate a neutral stimulus with an unconditioned stimulus that naturally triggers a reflexive response.

    • Unconditioned Stimulus (UCS): A stimulus that naturally and automatically triggers a response without any prior learning (e.g., food).

    • Unconditioned Response (UCR): The unlearned, natural reflexive response to the unconditioned stimulus (e.g., salivation at the sight of food).

    • Neutral Stimulus (NS): A stimulus that initially produces no specific response other than focusing attention (e.g., a bell).

    • Conditioned Stimulus (CS): After being repeatedly paired with the unconditioned stimulus, the neutral stimulus begins to evoke a conditioned response (e.g., the bell after being paired with food).

    • Conditioned Response (CR): The learned response to the previously neutral (now conditioned) stimulus (e.g., salivation at the sound of the bell).

    • Extinction: Extinction occurs when the conditioned stimulus (CS) is repeatedly presented without the unconditioned stimulus (UCS). For example, if a baby has learned to salivate at the sound of a bell (CS) because it was paired with food (UCS), extinction would happen if the bell is rung many times without any food being presented. Eventually, the baby would stop salivating at the sound of the bell.

    • Spontaneous Recovery: After a period of time where the conditioned stimulus is not presented, the conditioned response (CR) may spontaneously reappear when the CS is introduced again. This indicates that the learning was not completely unlearned and suggests the persistence of the associative bond between the CS and the UCS in the baby's memory.

  • Purpose: It helps infants recognize which events typically occur together in their environment, allowing them to anticipate and predict future occurrences.

  • Result: Through classical conditioning, the infant's environment becomes more orderly and predictable as they learn associations between stimuli.

  • Examples: For instance, a baby may begin to salivate (CR) when they hear the sound of a bell (CS) that has been consistently paired with the presentation of food (UCS). Initially, the bell was a neutral stimulus. Through repeated exposures, the infant learns to associate the bell with mealtime, demonstrating how their experiences shape behavioral responses even without direct instruction.

Operant Conditioning

  • Operant Conditioning: the infant acts on the environment (operant)

  • Key components:

    • Reinforcer: increases the occurrence of a response

    • Positive reinforcement: presents desirable stimulus

    • Negative reinforcement: removes an unpleasant stimulus

    • Punishment: decreases the occurrence of a response

    • Positive punishment: presents an unpleasant stimulus

    • Negative punishment: removes a desirable stimulus

    • Extinction: Extinction happens when a learned behavior is no longer reinforced. If a behavior (an operant) was previously followed by a reinforcer, and that reinforcer is no longer provided, the frequency of that behavior will decrease over time. For instance, if a baby learns that crying loudly (behavior) leads to being picked up (reinforcer), and caregivers stop picking up the baby when they cry loudly, the crying behavior will eventually extinguish.

Reinforcement and Punishment (Summary)

  • Reinforcement (increases desirable behavior):

    • Positive reinforcement: adds a stimulus

    • Negative reinforcement: removes a stimulus

  • Punishment (decreases undesirable behavior):

    • Positive punishment: adds a stimulus

    • Negative punishment: removes a stimulus

Motor Development

  • Motor development involves both gross-motor and fine-motor skills; 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 (Milestones)

  • Graspes cube: 3 months, 3 weeks

  • Sits up alone: 7 months

  • Crawls: 7 months

  • Pulls to stand: 8 months

  • Plays pat-a-cake: 9\text{ months}, 3\text{ weeks}

  • Walks alone: 11\text{ months}, 3\text{ weeks}

  • Scribbles vigorously: 14\text{ months}

  • Jumps in place: 23\text{ months}, 2\text{ weeks}

Perceptual Development

Milestones of Reaching and Grasping

  • Newborn: prereaching

  • 3–4 months: ulnar grasp

  • 4–5 months: transferring object from hand to hand

  • 9 months: 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

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

The Development of the Senses

Smell and Taste; Sensitivity to Pain and Touch

  • Infants are born with the capacity to experience pain

  • Touch is one of the most highly developed sensory systems in a newborn and one of the first to develop

  • Infants are born with a developed sense of smell and can distinguish mom’s smell if breastfeeding

  • Infants have an innate preference for sweetness

Visual Perception

  • Newborns can see up to about 20\text{ inches} away

  • By 6 months , many infants have 20/20 vision

Auditory Perception

  • Infants hear before birth and have good auditory perception after birth

  • They can differentiate their mother’s voice from other voices