The rapid physical growth of the human infant, just described, is impressive, but intellectual growth during infancy is even more awesome. Concepts, memories, and sentences—nonexistent in newborns—are evident by age 1 and consolidated by age 2.

As you remember from Chapter 1, Piaget called cognition in the first two years sensorimotor intelligence because infants learn through their senses and motor skills. He subdivided this period into six stages (see Table 3.2).

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STAGES ONE AND TWO Stage one, called the stage of reflexes, lasts only a month. It includes senses as well as motor reflexes, the foundations of infant thought. The newborn’s reflexes evoke some brain reactions. Soon sensation leads to perception, which ushers in stage two, first acquired adaptations (also called the stage of first habits).

Here is one example. In a powerful reflex, full-term newborns suck anything that touches their lips. Their first challenge is to learn to adapt that reflex and thus suck, swallow, and suck again without spitting up too much—a major task that often takes a few days, with the mother learning how to help her baby latch, suck, and breathe.

During the first stage, in the first month, infants adapt their sucking reflex to bottles or breasts, pacifiers or fingers, each requiring specific types of tongue pushing. This adaptation signifies that infants have begun to interpret sensations; they are using their minds—some would say “thinking.”

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During stage two, which Piaget pegged from about 1 to 4 months of age, additional adaptation occurs. Infant cognition leads babies to suck in some ways for hunger, in other ways for comfort—and not to suck fuzzy blankets.

STAGES THREE AND FOUR In stages three and four, reactions are no longer confined to the infant’s body; they are an interaction between the baby and something else. During stage three (4 to 8 months), infants attempt to produce exciting experiences, making interesting sights last.

The word sights refers to more than what is seen: At this stage, babies try to continue any pleasing event. Realizing that rattles make noise, for example, they wave their arms and laugh whenever someone puts a rattle in their hand. The sight of something delightful—a favorite book, a smiling parent—can trigger active efforts for interaction.

Next comes stage four (8 months to 1 year), new adaptation and anticipation (also called the means to the end). Babies may ask for help (fussing, pointing, gesturing) to accomplish what they want. An impressive attribute of stage four is that babies work hard to achieve their goals. Babies who are 10 months old, seeing a parent putting on a coat, might drag over their own jackets to signal that they want to go along.

Stage-four babies indicate that they are hungry—and keep their mouths firmly shut if the food on the spoon is something they do not like. If the caregivers have been using sign language, among the first signs learned by 10-month-olds are “eat” and “more.” Even without parental signing, babies this age begin displaying some universal signs—pointing, pushing, and reaching up to be held.

With a combination of experience and brain maturation, babies become attuned to the goals of others, an ability much more evident at 10 months than 8 months (Brandone et al., 2014). Personal understanding begins to extend to social understanding.

OBJECT PERMANENCE Piaget thought that, at about 8 months, babies first understand the concept of object permanence—the realization that objects or people continue to exist when they are no longer in sight. As Piaget discovered, not until about 8 months do infants search for toys that have fallen from the crib, rolled under a couch, or disappeared under a blanket. Blind babies also acquire object permanence toward the end of their first year, reaching for an object that they hear nearby (Fazzi et al., 2011).

As a recent statement of this phenomenon explains:

Many parents in our typical American middle-class households have tried out Piaget’s experiment in situ: Take an adorable, drooling 7-month-old baby, show her a toy she loves to play with, then cover it with a piece of cloth right in front of her eyes. What do you observe next? The baby does not know what to do to get the toy! She looks around, oblivious to the object’s continuing existence under the cloth cover, and turns her attention to something else interesting in her environment. A few months later, the same baby will readily reach out and yank away the cloth cover to retrieve the highly desirable toy. This experiment has been done thousands of times and the phenomenon remains one of the most compelling in all of developmental psychology.

[Xu, 2013, p. 167]

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This excerpt describes Piaget’s classic experiment to measure object permanence: An adult shows an infant an interesting toy, covers it with a lightweight cloth, and observes the response. The results:

This sequence has intrigued scientists as well as parents for decades.

Renee Baillargeon devised a series of clever experiments in which objects seemed to disappear behind a screen while researchers traced babies’ eye movements and brain activity. The data reveals that long before 8 months, infants are surprised if an object vanishes (Baillargeon & DeVos, 1991; Spelke, 1993).

The conclusion that surprise (measured by infant gaze) indicates object permanence is accepted by some scientists, who believe that “infants as young as 2 and 3 months of age can represent fully hidden objects” (Cohen & Cashon, 2006, p. 224). Other scientists are not convinced (Mareschal & Kaufman, 2012).

STAGES FIVE AND SIX In their second year, infants start experimenting in thought and deed—or, rather, in the opposite sequence, deed and thought. They act first (stage five) and think later (stage six). Piaget’s stage five (ages 12 to 18 months), new means through active experimentation, builds on the accomplishments of stage four. Now goal-directed and purposeful activities become more expansive.

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Toddlers delight in squeezing all the toothpaste out of the tube, drawing on the wall, or uncovering an anthill—activities they have never seen an adult do. Piaget referred to the stage-five toddler as a “little scientist” who “experiments in order to see.” Their research method is trial and error. Their devotion to discovery is familiar to every adult scientist—and to every parent.

Finally, in the sixth stage (ages 18 to 24 months), toddlers use mental combinations, intellectual experimentation via imagination that can supersede the active experimentation of stage five. Because they combine ideas, stage-six toddlers think about consequences, hesitating a moment before yanking the cat’s tail or dropping a raw egg on the floor.

Thus, the stage-six sequence may begin with thought followed by action. Of course, the urge to explore may overtake caution: Things that are truly dangerous (cleaning fluids, swimming pools, open windows) need to be locked and gated.

The ability to combine ideas allows stage-six toddlers to pretend. For instance, they know that a doll is not a real baby, but they can strap it into a stroller and take it for a walk. At 22 months, my grandson gave me imaginary “shoe ice cream” and laughed when I pretended to eat it.

Piaget describes another stage-six intellectual accomplishment involving both thinking and memory. Deferred imitation occurs when infants copy behavior they noticed hours or even days earlier (Piaget, 1962/2013). Piaget described his daughter, Jacqueline, who observed another child

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who got into a terrible temper. He screamed as he tried to get out of a playpen and pushed it backwards, stamping his feet. J. stood watching him in amazement, never having witnessed such a scene before. The next day, she herself screamed in her playpen and tried to move it, stamping her foot lightly several times in succession.

[Piaget, 1962/2013, p. 63]

These words from Piaget illustrate his genius: He observed children carefully, noticing how they thought at each stage. However, many researchers find that Piaget underestimated the age at which various accomplishments occurred. You already saw this with object permanence; the same is true for deferred imitation.

Scientists were awed by Piaget’s recognition that babies “learn so fast and so well” (Xu & Kushnir, 2013, p. 28). For decades researchers followed Piaget’s lead, and they demonstrated that infants master cognition in much the way Piaget described.

However, as brain scans and computerized analysis of heart rate, muscle tension, gaze, and so on made it easier to study infant cognition, Piaget’s emphasis on senses and motor abilities seems to have limited his understanding of infant cognition. Piaget missed many early cognitive accomplishments, particularly in memory (Schneider, 2015).

As explained in Chapter 1, Piaget’s sweeping overview of four periods of cognition contrasts with information-processing theory, which breaks down cognition into hundreds of small steps between input and output. Computer analysis, gaze-following, and brain scans allow researchers to measure infant cognition long before the baby can demonstrate understanding.

The thinking of young infants is impressive. As one researcher summarizes, “Rather than bumbling babies, they are individuals who … can learn surprisingly fast about the patterns of nature” (Keil, 2011, p. 1023). Concepts and categories develop in infants’ brains by 6 months or earlier (Mandler & DeLoache, 2012).

MEMORY AT 3 MONTHS We focus now on one specific ability that Piaget underestimated, memory (Schneider, 2015). Within the first weeks after birth, infants recognize their caregivers by face, voice, and smell. Memory improves month by month. In one study, after 6-month-olds had had only two half-hour sessions with a novel puppet, they remembered the experience a month later—an amazing feat for babies who could not talk or even stand up (Giles & Rovee-Collier, 2011).

In studying memory, researchers realize that, instead of noticing children’s many “faults or shortcomings relative to an adult standard,” we need to appreciate that children remember what they need to remember (Bjorklund & Sellers, 2014, p. 142). Sensory and caregiver memories are apparent in the first month, motor memories by 3 months, and then, at about 9 months, more complex memories including for language (Mullally & Maguire, 2014).

No doubt memory is fragile in the first months of life and improves with age. Repeated sensations and brain maturation are required in order to process and recall whatever happens (Bauer et al., 2010). Everyone’s memory fades with time, especially if that memory was never encoded into language, never compared with similar events, never discussed with a friend. No wonder infants forget many things.

That forgetfulness led Piaget, Freud, and other early developmentalists to write about infant amnesia, the idea that people forget everything that happened to them before age 3. However, although adults do not remember what happened at age 1, that does not mean that infants have no memory. Infants remember things that happened weeks and even months ago (Mullally & Maguire, 2014), although they are unlikely to remember it decades later.

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The most dramatic proof of very early memory comes from a series of innovative experiments in which 3-month-olds learned to move a mobile by kicking their legs (Rovee-Collier, 1987, 1990). The infants lay on their backs connected to a mobile by means of a ribbon tied to one foot (see photo).

Virtually all the babies realized that kicking made the mobile move. They then kicked more vigorously and frequently, sometimes laughing at their accomplishment. So far, this is no surprise—observing self-activated movement is highly reinforcing to infants.

When infants as young as 3 months had the mobile-and-ribbon apparatus reinstalled and reconnected one week later, most started to kick immediately, proof that they remembered their previous experience. But when other 3-month-old infants were retested two weeks later, they kicked randomly. Had they forgotten? It seemed so.

But then the lead researcher Carolyn Rovee-Collier, two weeks after the initial training, allowed some infants to watch the mobile move but did not allow them to kick. The next day, when they were connected to the mobile, they kicked almost immediately.

Apparently, watching the mobile the previous day revived their faded memory. Other research similarly finds that reminders are powerful. In real life, an infant who is reminded, day after day, is likely to remember several weeks later. If Daddy plays with a 3-month-old every day and then goes on a month-long trip, the baby might grin broadly when he reappears.

OLDER INFANTS At 9 months, memory markedly improves. This may partly be the result of new motor ability, since 9-month-olds can usually crawl (Mullally & Maguire, 2014). At 12 months, more improvement is evident. One-year-olds learn from parents and strangers, from other babies and older siblings, from picture books and family photographs, from their own walking and talking (Hayne & Simcock, 2009). The dendrites of several areas of the brain grow to reflect remembered experiences.

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The crucial insight from information-processing theory is that the brain is a very active organ, changing with each day’s events. Therefore, the particulars of early experiences are critically important in determining what a child knows or does not know. Generalization becomes possible as sensations become perceptions, which become expectations (Mullally & Maguire, 2014). Every day of their young lives, infants are processing information and storing conclusions.