Infancy

Definition of Infancy

We all know an infant when we see one. They look like adorable little peanuts that we just want to cuddle. Have you ever wondered how the field of psychology defines infancy?

You might want your baby sister or brother to stay an adorable infant forever, but soon enough, they will pass through all the stages of childhood, adolescence, and adulthood. But, before they do that, let's look at the world of infancy in a little more depth.

Fig. 1 - Newborn baby at the hospital

Characteristics of Infancy in Psychology

Other than their likeness to an adorable peanut, there are a few other defining characteristics of infants.

Physical Characteristics

Infants have a few distinguishing physical characteristics. They are born with soft spots on their heads.

An infant has a small fontanel at the back of their head and a larger one at the front. The smaller spot will usually close over by three months. The front spot can take up to 18 months. You might also notice that an infant's head is shaped slightly differently or even comically. They may have formed a conehead as they passed through the vaginal canal or if assistive measures were taken during birth. Their heads usually round out in the first few days after birth.

After birth, the umbilical cord that connects the baby to the mother's placenta is cut and clamped. The stump will dry up and fall off the infant's belly button after about two weeks.

Some infants might have a birthmark, a patch of skin that differs in color from the rest. They may have red marks or patches on their face or neck, often referred to as angel kisses. Usually, just after birth, a baby will be covered with tiny, soft hairs called lanugo.

Infancy: Stages of Development

Animals and humans follow an inborn sequence of maturation.

When it comes to development, we all tend to follow relatively the same path. Unless our development is inhibited by illness, physical disorders, or trauma, human beings develop in an ordered sequence.

Physical Development

In the womb, a fetus develops rapidly. Nerve cells in the brain are formed at an incredible rate. All of the brain's neurons are formed by 28 weeks of gestation. All of the brain cells we will have are fully formed in infancy, but our immune systems need a little more time to develop. Our immune systems regulate our bodies. They help process our sensory experiences and regulate our sleep, breathing, heart rate, and so much more. Our immune system is important! The neural networks that our bodies need to process complicated information from one area of the body to the other are forming rapidly in infancy. This is why an infant's brain increases in size rapidly after birth. You might notice that an infant's head seems disproportionately large for its body. This is normal!

In the United States, the average weight for a newborn is around 7 to 7.5 pounds. It's normal for birth weights to fluctuate depending on family history and each baby's genetics. However, anything below 5 pounds 8 ounces is considered low birth weight.

From birth to two weeks, it's normal for babies to actually lose weight! Infants can lose an average of 5 to 10% of their body weight in those first few weeks. The majority of babies will quickly regain this weight within days to a week of losing it.

By the first month, most infants will have gained one pound. They start to establish a more regular feeding pattern and sleep slightly less than before. An infant will continue to gain around one pound per month until they reach the 6-month mark. At this time, their weight gain usually slows a bit throughout the rest of their first year. A newborn baby roughly doubles its weight by 6 months. They may come close to tripling it by their first birthday.

Fig. 2 - Infant crawling after a dog.

Motor Development

An infant's brain development enables motor development and physical coordination. Their muscles and nervous system mature, and they exhibit new skills. Here, too, their maturation follows a universal sequence. The exact timing may vary, but most infants will achieve the same milestones in roughly the same order.

By around six weeks, most babies can lift their own heads while lying on their stomachs. Around three months, most can lift their chests with their arms, like they're doing baby yoga. Between four and six months, most babies can roll over from their backs to their stomachs and sit up without support. Most infants are crawling by eight months and standing without support by ten months. By one year, they are usually taking their first steps.

Cognitive Development in Infancy

Can you remember anything from when you were four years old? How about from when you were two? Chances are, the answer is a resounding no. Even though we might not remember much from early childhood and infancy, our brains were processing and store a lot of information. In fact, infants can learn and remember things.

As newborns, we don't have the same conscious awareness that we do as adults or even as older children. Researchers measure conscious awareness by certain neural signals and brainwaves. One experiment (Dehaene, 2014; Kouider et al., 2013) demonstrated that infants exhibit the same neural response to stimuli that adults do by the time they are five months old. The researchers flashed images of faces on a screen and recorded adult brain activity as they became aware of the content of the image. In infants, the same neural response was exhibited starting at five months.

Language Development in Infancy

Even though babies are born without any language skills, they all have the capacity to learn any language. Infants can distinguish differences in speech sounds by four months. They also absorb linguistic information by reading lips. Kuhl & Meltzoff (1982) found that infants prefer watching the mouths of speakers that match the sound they are hearing.

Receptive language, or language comprehension, comes before the ability to produce and speak a language. By six months, infants recognize the names of certain objects. By seven months, they can break down sentences into individual words, even when listening to an unfamiliar language. They even recognize syllables that are frequently repeated together.

Language production, or speaking and its elements, starts with the babbling stage at four months.

Babies produce a wide variety of vowel and consonant sounds during the babbling stage. Their utterances are not indicative of their native language. In fact, you couldn't tell which language is spoken at home at all by listening to the babbling of an infant! It's not until around 10 months that babbling starts to take on the sounds of the household language.

Around 12 months, infants enter the one-word stage.

Before they even start babbling, infants know that certain words carry a specific meaning. They might know simple nouns like "bottle" or "cat." During the one-word stage, they begin to produce meaningful single-word utterances. They might exclaim, "cat!" when they want you to look at the cat.

Even if we forget languages that we were exposed to in infancy, traces of them still remain. One study found that English-speaking adults from Britain could distinguish sounds in the Hindi or Zulu they heard in infancy, while English speakers with no exposure to these languages could not (Bowers et al., 2009). The same results were found in Chinese adoptees living in Canada since the age of one (Pierce et al., 2014).