Physical, Brain, and Motor Development

Every Registered Psychometrician board exam devotes a heavy slice of developmental psychology items to the body and the brain, because RA 10029, the Philippine Psychology Act of 2009, expects a licensed psychometrician to recognize normal growth before flagging what is atypical. Board writers love this topic because it rewards precision: name the direction of a growth principle, place a milestone in its correct month, or name the classic study that proved infants can perceive depth. Master the sequence from neuron to reflex to running toddler, and these items become reliable points.

Growth patterns: cephalocaudal and proximodistal

Body growth is not random; it follows directional principles that describe the order in which control appears. The cephalocaudal principle states that growth and motor control spread from the head downward: infants steady the head months before they command the trunk, and the trunk before the legs, which is also why a newborn's head looks disproportionately large. The proximodistal principle states that control spreads from the center of the body outward to the extremities: an infant controls the shoulder and upper arm before the wrist, and the wrist before the fine pincer grasp of the fingers. A related pattern, mass-to-specific (gross-to-fine) development, describes movement maturing from broad, undifferentiated activity, such as a newborn's whole-body flailing in excitement, into discrete, targeted movement, such as a precise reach toward one toy.

Brain development: neurons, myelination, and synaptic pruning

The brain grows through a specific cellular choreography. The basic unit is the neuron, a nerve cell with a cell body (soma), branching dendrites that receive signals, and a single axon that transmits signals onward across a gap called the synapse. At birth, the brain already holds nearly all the neurons it will ever have; what changes afterward is connectivity.

Two opposing processes drive that change. Myelination is the wrapping of axons in myelin, a fatty sheath produced by glial cells that insulates the axon and speeds neural transmission. Myelination begins prenatally and continues for years, generally following the same head-to-tail, center-to-periphery order seen in motor development, one reason sensory and motor pathways mature well ahead of higher-order association areas.

The second process runs in the opposite direction. In the first years of life the brain massively overproduces synaptic connections, a burst called synaptogenesis. Experience then decides which connections survive: those used are strengthened, and those unused are eliminated through synaptic pruning. This "use it or lose it" pattern is what makes early childhood a period of unusually high plasticity, the brain's capacity to reorganize itself in response to experience, and it explains why rich early stimulation supports development while prolonged deprivation can narrow a child's later capacities.

Gross and fine motor milestones

Motor development divides into two tracks. Gross motor skills use the large muscles for movement, such as sitting, crawling, walking, and running. Fine motor skills use the small muscles of the hands and fingers for precise actions, such as grasping, stacking, and drawing. Both obey the principles above: head and trunk control (gross) precedes fine command of the fingertips. Board items often hinge on an exact expected age, so learn the sequence, not just the general order.

Approximate age	Gross motor milestone	Fine motor milestone
2 months	Lifts head briefly when lying prone	Follows a moving object with the eyes
4-6 months	Rolls over; sits with support	Reaches for objects; transfers an object hand to hand
9 months	Crawls; pulls to stand	Uses a raking grasp; bangs objects together
12 months	Cruises along furniture; takes first independent steps	Uses a mature pincer grasp (thumb and forefinger)
18 months	Walks well; climbs stairs with help	Scribbles spontaneously; stacks 2-4 blocks
24 months	Runs; kicks a ball	Turns pages one at a time; stacks 6 or more blocks

Newborns also arrive with built-in primitive reflexes that items test directly: the rooting reflex (turning toward a touch on the cheek to find the nipple), the sucking reflex, the Moro (startle) reflex (arms fling outward then draw in, in response to a sudden loss of support or loud noise), the palmar grasping reflex, and the Babinski reflex (toes fan outward when the sole of the foot is stroked). These reflexes should fade on a predictable schedule as the cortex matures; one that persists past its expected window is itself a developmental red flag, not a sign of precocity.

Sensation and perception in infancy

Contrary to older assumptions that newborns are blank slates, infants arrive with functioning senses, though vision is the slowest to mature: a newborn's visual acuity is roughly 20/400 and sharpens quickly over the first year as the visual cortex and eye muscles develop. Two classic studies anchor this section and are near-guaranteed board material.

Robert Fantz used a preferential-looking chamber to show that even very young infants look significantly longer at patterned, complex, and face-like stimuli than at plain colored shapes, evidence of real form and face preferences from early on rather than an undifferentiated blur. His method, preferential looking, remains a standard tool for inferring what infants can discriminate, since they cannot yet report what they see in words.

Eleanor Gibson and Richard Walk designed the famous visual cliff, an apparatus with a sturdy glass surface built over a checkerboard pattern that appears to drop away on one side, creating the illusion of a deep edge. When crawling infants were placed on the "shallow" side and their mothers beckoned from across the "deep" side, most infants refused to cross, showing that depth perception is present and functional by the time an infant can crawl. Later studies using heart-rate monitoring found that even infants too young to crawl show interest, a deceleration in heart rate, when placed over the deep side, suggesting that depth perception emerges before the wary avoidance of it; the fear response appears to strengthen with crawling experience.

Researcher(s)	Method	What it showed
Robert Fantz	Preferential-looking chamber	Infants look longer at patterned and face-like stimuli, showing early form and face preference
Eleanor Gibson and Richard Walk	Visual cliff apparatus	Crawling infants avoided the "deep" side, showing functional depth perception by the crawling age

Nutrition and health across childhood

Physical and brain growth cannot outrun the fuel behind them, and Philippine board items regularly link nutrition law to developmental outcomes. The first 1,000 days, from conception to a child's second birthday, is the most nutritionally sensitive window because it coincides with the peak of brain growth and synaptogenesis described above, and deficits during it are difficult to fully reverse later. The Philippines codifies this priority in RA 11148, the First 1,000 Days Law, which mandates integrated maternal and child health and nutrition services to prevent stunting.

Distinguish the standard malnutrition indicators, since items often specify which measurement was taken: stunting is a chronic deficit in height-for-age, wasting is an acute deficit in weight-for-height, and underweight is a deficit in weight-for-age that can reflect either problem. Two severe protein-energy deficiency syndromes are also commonly paired on exams: marasmus is severe overall caloric and protein deficiency producing a wasted, wizened appearance, while kwashiorkor is a deficiency of protein specifically, with calories relatively preserved, marked by edema and a swollen abdomen.

Supporting laws round out the picture. The Milk Code (Executive Order 51) regulates marketing of breastmilk substitutes, the Rooming-In and Breastfeeding Act (RA 10028) mandates breastfeeding support in workplaces and health facilities, and the ASIN Law (RA 8172) mandates salt iodization because iodine deficiency in early life is a preventable cause of impaired cognitive development. Health workers track growth against the WHO Child Growth Standards; a child whose growth falls off its curve is flagged for failure to thrive, which can stem from an organic cause, poor nutrition, or psychosocial deprivation, a reminder that physical growth and psychological well-being are never fully separable on this exam.

Board traps and takeaways

• Cephalocaudal is head-to-tail; proximodistal is center-to-extremity. A baby holding its head up before it can sit shows cephalocaudal growth; a baby controlling the whole arm before a precise pincer grasp shows proximodistal growth.
• Synaptogenesis (overproduction of synapses) and synaptic pruning (elimination of unused ones) are opposite, sequential processes, not the same event. Myelination is separate again: it speeds transmission along existing axons rather than changing connection count.
• The visual cliff is Gibson and Walk's depth-perception study; do not credit it to Fantz, whose preferential-looking method tested pattern and face preference instead.
• A primitive reflex (rooting, Moro, palmar grasp, Babinski) that persists past its expected age is a red flag for atypical development, not a sign of advanced ability.
• Stunting (height-for-age), wasting (weight-for-height), and underweight (weight-for-age) are distinct indicators; know which measurement each term names.
• Marasmus is calorie-and-protein deficiency producing generalized wasting; kwashiorkor is a protein-specific deficiency with edema despite near-adequate calories. The swollen belly belongs to kwashiorkor, not marasmus.