Situation: The nurse works in the infant and toddler section of the pediatric ward of a provincial hospital, where a parent or grandparent stays at each child's bedside as a watcher. A mother asks what her son should be able to do now. He is 13 months old by birth date and was born at 28 weeks of gestation. Using his corrected age (take full term as 40 weeks and count 4 weeks as 1 month), which behavior reflects the MOST advanced sensorimotor substage, according to Piaget, that the nurse should expect at this time?

He was born 12 weeks (40 minus 28), or 3 months, early, so his corrected age is 13 minus 3 = 10 months, which is used until about 2 years. At 10 months the expected substage is coordination of secondary schemes (8 to 12 months), with intentional search for a hidden object. Using his chronological age of 13 months would wrongly expect tertiary circular reactions.

Corrected Age Calculation

The infant was born at 28 weeks of gestation, which is 12 weeks (40 − 28) before full term. Since 4 weeks equals 1 month, this represents 3 months of prematurity. Corrected age is therefore 13 months − 3 months = 10 months. Corrected age is used until approximately 2 years of age for developmental assessment in preterm infants.

Piaget's Sensorimotor Substages at 10 Months

At a corrected age of 10 months, the infant is expected to be in the substage of coordination of secondary circular reactions (8 to 12 months). This substage marks the emergence of true intentionality and means-end behavior. The hallmark cognitive achievement is object permanence—the understanding that objects continue to exist even when out of sight.

A 10-month-old infant who sees a toy hidden under a cup will lift the cup to retrieve it, demonstrating an intentional, goal-directed search for a hidden object. This behavior reflects the coordination of two previously separate schemes: lifting the cup (one scheme) and grasping the toy (another scheme), now combined into a single intentional act.

Why the Other Options Are Incorrect

Using the chronological age of 13 months would lead to an incorrect expectation. At 13 months, the infant would be entering the substage of tertiary circular reactions (12 to 18 months), characterized by active experimentation and novelty-seeking. However, the corrected age of 10 months places the child one substage earlier.

Behavior	Substage	Age Range	Why Not Expected at 10 Months Corrected
Rolls different balls down a slope to see which goes farthest	Tertiary circular reactions	12–18 months	Deliberate experimentation with variation is a hallmark of the next substage; requires active trial-and-error exploration
Pretends to feed a doll from an empty cup	Beginning of representational thought (early preoperational)	18–24 months	Symbolic play requires mental representation, which emerges only after the sensorimotor period ends
Bangs a spoon again and again to hear the noise it makes	Secondary circular reactions	4–8 months	Repetitive actions focused on environmental effects are characteristic of an earlier substage; lacks the intentional coordination seen at 10 months

The A-not-B Task and Object Permanence

The A-not-B task is a classic assessment of object permanence and early executive function. In this task, an infant watches an object hidden at location A, retrieves it successfully, and then watches the object hidden at location B. Infants in the coordination of secondary circular reactions substage often continue to search at location A, a phenomenon known as the A-not-B error. This error reflects the incomplete maturation of working memory and inhibitory control rather than a total absence of object permanence.

The ability to lift a cup to find a hidden toy represents the foundational object permanence skill that the A-not-B task measures, even though the infant may still make the A-not-B error when the hiding location changes. Research on A-not-B performance from 6 to 12 months shows that infants progress at different rates, with faster performance gains associated with earlier attainment of performance milestones and distinct patterns of EEG maturation ^[1]. This variability underscores that the corrected age of 10 months represents an expected developmental window, not a rigid cutoff.

Clinical and Exam Relevance

Key point! For preterm infants, always calculate corrected age before applying developmental milestones. Failure to correct for prematurity leads to overestimation of expected abilities and unnecessary concern or inappropriate expectations.

Watch out! The A-not-B error is normal at 10 months corrected age and does not indicate developmental delay. It resolves gradually as executive function and working memory mature through the second year of life ^[2].

The emergence of object permanence at this stage is supported by neurophysiological evidence. When objects move in and out of sight, infants show distinct patterns of brain activity during occlusion events, including event-related synchronization before and after occlusion and desynchronization during the occlusion itself ^[3]. This suggests that the infant brain actively tracks objects even when they are temporarily hidden, providing a neural basis for the behavioral milestone of searching for a hidden toy.

Sensory-motor experiences, including reaching, grasping, and visual tracking, shape early cognitive development through predictive processing mechanisms ^[4]. The act of lifting a cup to find a hidden toy integrates motor action with visual memory and expectation, exemplifying how sensorimotor schemes become coordinated into intentional, goal-directed behavior during this substage.