Lecture 4 - Physical, Sensory, and Perceptual Development in Infancy

Physical changes

Second-busiest period of physical change

• First year: 25cm-30cm growth &triple body weight

• Age 2 for girls and 2.5 for boys: half adult height

• Heads are proportionately much larger – have nearly full-sized brain at that age

Brain changes

Nervous system continues to rapidly develop… Midbrain and medulla are most developed at birth; cortex is least developed

Synaptic development

Synapses connect neurons…

1. Synaptogenesis

2. Synaptic pruning

Occurs across the lifespan; gets more efficient

• Denser synapses in children allows them to bounce back from brain harm more efficiently ➔ greater neuroplasticity

“Use it or lose it” – impact of environment

Synaptogenesis

The creation of synapses from the growth of dendrites and axons → Occurs rapidly in the first several years post-birth in spurts

• Ongoing synaptogenesis = psychological changes linked to physical changes in the brain across the lifespan

Synaptic pruning

Unnecessary pathways and connections are eliminated

Myelinization

Creation of sheath around individual axons to insulate them from one another electrically

• Improves their conductivity

• Sheath made of myelin

• Follows both cephalocaudal and proximodistal patterns • Why babies can move certain body parts before others

• Fastest during first two years after birth; continues through adolescence

Reflexes

Changes, or lack thereof, can be key indicators of nervous system health… Humans are born with adaptive reflexes; some will disappear in infancy or childhood while others last a lifetime

• Week or absent adaptive reflexes in newborns indicate the brain isn’t functioning as it should

• Primitive reflexes

Primitive reflexes

Controlled by medulla and midbrain; their purpose is unclear

• If primitive reflexes don’t disappear by 8 months of age, baby may have neurological problem

Sleep

Behavioural states

_______________ - States of consciousness: differing states of sleep and wakefulness

Five stages, in this order: deep sleep ➔lighter sleep ➔drowsy waking ➔ fussing ➔alert wakefulness

• After feeding, return to drowsy state and then drop into deep sleep • Cycle repeats ~ every 2 hours

• Newborns sleep up to 80% of the time

  • 8 weeks: time awake increases and circadian rhythm begins to develop

  • 6 months: sleeping ~13 hours/day, but more predictably

Crying

Behavioural states

________________ - Different cries for hunger, anger, and pain

• Crying increase in frequency over first 6 weeks then tapers off

• Cross-cultural similarity in strategies for soothing (i.e., picking up, holding, talking or singing)

• Colic babies

Hunger

Behavioural states → crying

________________ - rhythmical pattern of cry, silence, breath, cry, silence, breath; whistling sound often accompanies in-breath

Anger

Behavioural states → crying

________________ - loud and intense

Pain

Behavioural states → crying

_______________ - abrupt onset (vs. whimpering or moaning to start)

Colic

Behavioural states → crying

_______________ - intense crying more than 3 hours/day, 3+ days/week, 3 or more weeks with no apparent cause and with nothing working to stop it

Motor skill development

Requires development in the brain, bones, muscles, lungs, and heart…. development follows cephalocaudal and proximodistal patterns

• Relevant skills

  • Locomotor skills/gross motor skills

  • Non-locomotor skills

  • Manipulative skills/fine motor skills

• Wide variability in these developmental milestones across cultures

  • Implications for standardization of developmental milestones

The sequence of development itself is virtually identical for all children, regardless of sex or the presence of physical or mental anomalies

• Children with developmental challenges meet the milestones in the same sequence, just more slowly

• Infants are motivated to meet these milestones – despite the risks they present – because of perceived benefits

  • Benefits: caregiver praise, exploring further and faster, and interacting with objects in new way

Bone development

(Motor skill development)

Changes to size, number, and composition

• Changes in number and density result in improved motor coordination

• Ossification

Ossification

(Motor skill development → bone development)

_________ - Bone hardening. Occurs steadily from final weeks of prenatal development through puberty

• Necessary for motor development

Muscle development

(Motor skill development)

All muscle fibres are present at birth — Initially small with a high water to muscle ratio and a lot of fat

• Water content is comparable to an adult’s by end of first year

• Ratio of fat to muscle tissues begins decline by end of first year

  • These changes enable one-year-olds to begin walking

Lung + heart development

(Motor skill development)

Important for increasing stamina and strength in kids,

• Lungs grow quickly and become more efficient during first two years

• Heart muscles strengthen

• Together, result in greater in two-year-olds (vs. newborns)

  • Toddlers can engage in fairly substantial periods of sustained motor activity without rest

Locomotor skills

(Motor skill development)

AKA gross motor skills — enable infant to get around their environment (e.g., crawling)

Non-locomotor skills

(Motor skill development)

Improve infant’s ability to interact with objects and people around them (e.g., controlling head movement)

Manipulative skills

(Motor skill development)

AKA fine motor skills — use of hands (e.g., stacking blocks)

Female babies

Develop more quickly in some areas… they may have a slight advantage in the development of manipulative skills (e.g., self-feeding) because of quicker separation of wrist bones

Male babies

more physically active, display more of a preference for rough-and-tumble play, and show greater physical aggression by two years-old

Breastfeeding

Consensus is that it is substantially better nutritionally than bottle-feeding (i.e., formula feeding)

• Best-practice recommendation: only breastmilk until six months; partial breastfeeding until at least two years

  • Benefits: ideal nutrients, immune system development, digestion, bonding, mother’s mental health

  • Breast-fed children have lower short- and long-term risk of numerous illnesses and better cognitive function and academic achievement

Breastmilk is more gentle on a child’s digestive system too- breastfeeding also releases oxytocin in children, and signs it can reduce mother’s stress and strengthen the bond

BUT, any breastfeeding is better than none.

• Maternal lifestyle, breastfeeding practices, environmental factors and ethnicity can affect quality of milk

  • IN some cases, breastfeeding not recommended cuz of recreational and medical substances passing thru in milk

Breastfeeding → Third variable

Mothers who are older, better educated, have higher incomes, and are not single parents are more likely to initiate and maintain breast-feeding

Higher socioeconomic status is also associated with better physical health, cognitive functioning, and academic achievement

Breastfeeding is time-consuming (2hr cycle often)

Misconception that breastfeeding is always “natural” and “easy” – can actually be quite challenging

Solid foods

Healthy, full-term six-month-olds can begin to be introduced to these

• Should have a wide variety by age 1 years

  • Helps meet increasing nutritional needs

Order: iron-fortified infant single-grain cereal ➔pureed vegetables ➔fruits ➔ meat or meat substitutes

• Gradual introduction helps identify food allergies

Malnutrition

Can impair baby’s brain because of the nervous system’s rapid development— Leading cause of death for children under 5 years old

• Feeding issues

• Specific types:

  • Macronutrient malnutrition

  • Micronutrient malnutrition

  • Marasmus

  • Kwashiorkor

Marasmus

(Malnutrition)

A severe caloric deficit results in a weight that is less than 60% of what it should be at their age.

• Many infants suffer permanent neurological damage

  • Parasitic infections and chronic diarrhea are common and make marasmus difficult to treat

• Treatment: dietary supplementation with formula, intravenous feedings, treatment for parasites

Macronutrient malnutrition

(Malnutrition)

Results from a diet containing too few calories

Micronutrient malnutrition

(Malnutrition)

Deficiency of certain vitamins and/or minerals. Less common in Canada because of food fortification

• Vitamin D added to milk eliminating childhood ricket

• Iodine added to table salt eliminating goitre

• Vitamin A added to low-fat milk and butter substitutes reducing vision loss and blindness

Kwashiorkor

(Malnutrition)

Results from not enough protein. Can lead to numerous health problems including permanent brain damage

Baby healthcare

Well baby care = series of routine doctor visits — Includes physical exams, immunizations, & developmental screenings

• More frequent when babies are younger because development is more rapid

Immunizations

(Baby healthcare)

A critical component of well baby care — Infectious diseases were previously a leading cause of death in childhood that have now been nearly eradicated thanks to mass immunization

• Canadian Immunization Guide recommends that routine immunization starts at 2 months old and continues through adolescence

Respiratory illnesses

(Baby healthcare → illnesses in the first two years)

Over 50% of infants in Canada have a respiratory illness before they turn 1

• Attending daycare increases the risk by up to twice as much depending on the size

• BUT keeping babies too clean can also have negative effects as they may not develop as healthy of an immune system

Ear infections

(Baby healthcare → illnesses in the first two years)

Often caused by respiratory illness. Associated with attention disorders, language deficits, and learning disabilities

• Temporary impairment in hearing may negatively impact brain development in regions essential for language learning

  • Cuz of “use it or lose it”

Preterm infants

Born live before 37 weeks gestation. Infants born before 32 weeks gestation may not have adaptive reflexes developed enough for survival (swallowing, sucking etc..)

Higher risk for neurological, cardiovascular, respiratory, gastrointestinal, and immunologic difficulties

Higher risk for long-term motor, cognitive, visual, hearing, behavioural, and growth problems (Kangaroo care results in more rapid development of preterm babies)

• Canadian rate = ~8/100 live births

• Significantly higher for multiple birth infants; however, ~80% of preterm births are singletons

• 24 weeks gestation is considered viability week

Low-birth-weight infants

Most, but not all, are preterm. Delay in meeting developmental milestones because maturationally younger.

• If gestational age is corrected for, most timeline differences disappear

  • Gap disappears by age 2-to-3-years

Post-term infants

Infants born after 42 weeks gestation. Associated with higher risk of maternal medical complications and with fetal and newborn mortality

• Substantial decrease in post-term deliveries in Canada – 0.3% in 2014

• Decrease attributed to ultrasound dating and labour induction

Infant mortality

(In Canada)

Half occur before 4 weeks and the rest between 4 weeks and 1 year

• 2007 rate: ~5/1000 vs. 134/1000 in 1901 and 25/1000 in 1960s

• Still not great – among comparable nations, tied with UK for second highest rate (US highest)

• Lower socioeconomic status associated with higher infant morality

  • Particularly high rate among Indigenous people

Sudden infant death syndrome

A sudden and unexpected death of ostensibly healthy infant in first year of life. Cause of ~5% of infant deaths in Canada.

Causes are unclear but several factors that reduce risk have been identified:

• Placing baby on back for sleeping

• Eliminating quilts, duvets, pillows, soft toys, and crib bumpers from crib

• Avoiding laying baby on soft surfaces or on loose bedding to sleep or nap

• Having the baby sleep in a crib in same room as parent(s) for first 6 months

• Avoiding co-sleeping

• Making the home a smoke-free environment

Vision

(Sensory skills)

Newborns have poorer visual skills than older children — 5-10% of babies have some type of visual problem.

Visual assessment recommended at birth and at well baby checkups as w/o intervention, infant visual problems can lead to lifelong ones

• Colour vision = about equal to adults

• Visual acuity

• Tracking

Visual acuity

(Sensory skills → vision)

A measure of the ability of the eye to distinguish shapes and the details of objects at a given distance.

• At birth = 40x worse than average adult

• 8x worse by age 6 months

• Adult level acuity reached by 7 years

Vision tracking

(Sensory skills → vision)

Process of following a moving object with your eyes

• Inefficient at birth – can track for brief periods if target is moving slowly

• By 6-10 weeks becomes quite skillful quickly

• Necessary given limited motor skills

Hearing

(Sensory skills)

Can hear before birth but development continues up to adolescence

• Auditory acuity

• Detecting locations

Auditory acuity

(Sensory skills → hearing)

Ability to hear and distinguish sounds.

• Newborn acuity comparable to adults with the exception of high-pitched sounds

Detecting locations

(Sensory skills → hearing)

Newborns can tell the general direction; however, their range of discrimination is less than an adult’s

Smelling + tasting

(Sensory skills)

As in adults, the two are intricately related. Newborns respond differentially to all five basic flavours

• Appear to show preference for umami and sweet foods – may explain attraction to breast milk

Touch + motion

(Sensory skills)

Best-developed — Responsive to social touching – gentle touches on mouth, face, hands, soles of feet, and abdomen

• Sensitivity to temperature – increase activity in cold room

• Sensitivity to touch – becoming calmer when stroked and showing discomfort with irritants(e.g., rashes, scratchy clothes)

Study methods

(Perceptual skills)

Preference technique: baby shown two pictures/objects; time spent looking at each one measured

Habituation and dishabituation:

1. Present sight/sound/object over and over until baby stops displaying interest (habituation)

2. Present different stimulus and assess whether baby shows renewed interest (dishabituation)

Operant conditioning: use reinforcement to teach learned response to stimulus then change the stimulus

Looking

(Perceptual skills)

Visual stimulation is important for subsequent development of visual perception —Critical periods in infancy and childhood where a specific quality of visual stimulation is required for the development of normal visual perception

• Introduction of visual inputs undetectable to infants can set the foundation for development of that perceptual ability

• Sleeper effects for sensitivity to mid and high narrow-striped images, face processing, and facial identity based on spacing of certain features

First two months: visual attention guided by search for meaningful patterns; motion can also capture attention

2-3 months: attentional shift to what (vs. where) an object is

• Babies don’t have a heightened interest in faces, but do have a preference for some faces over others

• Depth perception

Depth perception

(Perceptual skills → looking)

_________________ - Ability to judge the relative distance of various objects. Can gauge through three types of information: binocular cues, pictorial information/monocular cues, and kinetic cues

• Not yet clear how early infants can judge depth, nor which types of cues they use

• Best guess: kinetic (~3 months) ➔binocular cues (~4 months) ➔ pictorial cues (~5-7 months)

Listening

(Perceptual skills)

Babies can discriminate between speech sounds as early as 1 month old

• By 6 months, can distinguish between two-syllable words

• Until ~6 months, can distinguish between all sound contrasts in any language better than adults can

• Newborns can distinguish and prefer their mother’s voice from another female voice

Intermodal perception

(Perceptual skills)

The ability to integrate information from multiple senses or to transfer information gained from one sense to another sense

• Possible as early as 1 month old; common by 6 months old

Nativist vs. Empiricist POV

(Perceptual skills)

Nativists’ POV: most perceptual abilities are innate

• Evidence for nativists’ position: many skills are present in newborns or very young infants

Empiricists’ POV: most perceptual abilities are learned

• Evidence for empiricists’ position: importance of early stimulation for long-term sensory outcomes

Nature and nurture – interaction between innate and experiential factors