Somatosensory, Vestibular, Taste, and Hearing Development in Infants

Somatosensory system

Multiple senses including touch, pressure, kinesthesia (body position), temperature, and pain.

Touch development in utero

First trimester - lips/nose (5½ wks), chin/eyelids/arms (9 wks), legs (10 wks), whole body (12 wks).

Importance of touch at birth

It's critical for survival and brain development - helps with bonding, feeding, and exploration.

Maturation of the somatosensory system

Axons/myelination continue into the first year, maps become adult-like around 6 yrs.

Oral touch development

Oral touch develops first; babies can discriminate shapes/textures with their mouths before hands.

Key experiments in somatosensory development

Infants mouthed pacifiers → later looked longer at matching visual pacifier (tactile-visual match).

Nature vs. nurture in somatosensory development

Genes set the base map, but experience fine-tunes sensory pathways (plasticity).

Developmental importance of touch

Influences cognitive, emotional, immune, and stress systems (e.g., Harlow's monkeys, rat pups).

Vestibular system

Balance, orientation, and movement awareness via the vestibular apparatus (semicircular canals + vestibular sacs).

Formation of the vestibular system

From the otocyst (5 wks). Canals form by 7 wks, hair cells by 15 wks, and it functions by 5 months.

Early development of the vestibular system

To help the fetus prepare for birth movement and survival outside the womb.

Moro reflex

Arms fling out when falling (appears prenatally, gone by 4-5 months).

Asymmetrical neck reflex

Head turn → same-side arm/leg extend (gone by 8 months).

Doll's eye reflex

Eyes move opposite to head turn.

Nystagmus

Eye movement adapting to constant rotation.

Importance of bouncing or rocking for babies

Vestibular stimulation is soothing and supports motor + emotional development.

Developmental deficits linked to vestibular system

Deficits linked to motor delays, attention, learning disabilities, autism. Stimulation strengthens neural systems.

Taste bud development

Begin 8 weeks in utero, mature by end of 1st trimester. By 3rd trimester, fetus shows taste reactions.

Taste detection in newborns

Sweet, sour, bitter (not salt until ~4 months). Attracted to sweet.

Role of amniotic fluid in taste

Fetuses experience flavors from maternal diet (e.g., garlic studies show preference after birth).

Difference between flavor and taste

Taste = chemical cues via tongue receptors. Flavor = taste + smell (odor contribution).

Breast milk and taste development

Contains antibodies, enzymes, nutrients (taurine, lipids) → boosts cognition + health.

Importance of sweet taste

Evolutionary preference: sweet = safe, high energy. Also has pain-reducing effect (sucrose analgesia).

Exposure and taste preferences

Yes - repeated exposures reduce neophobia (fear of new foods).

Auditory system formation

3 wks: neurons appear; 5-10 wks: cochlea coils; 11 wks: fully coiled; 24 wks: pathways myelinate.

Fetal hearing capabilities

By 23-25 wks, respond to sounds (low-pitch, loud). By 34-36 wks, can discriminate tones and speech.

Newborn hearing preferences

Low-pitch, complex sounds (speech, music) more than high pitch or pure tones.

Motherese

High-pitched, exaggerated speech helps babies process language + supports bonding.

Hearing development milestones

3 months: detect high pitches. 6 months: better sound localization. By 2 yrs: pathways myelinated. Hearing in noise improves by 10 yrs.

Importance of hearing for development

Foundation for language, cognition, and emotional development. Loss impacts speech learning.

Risks to hearing development

Prenatal infections, toxins, loud NICUs, middle ear infections, low birth weight.