One way to learn what a baby expects is to watch the baby's eyes. In violation-of-expectation studies, infants see two test events. One matches what they expect, and the other breaks the expectation. With the right controls, reliably longer looking at the unexpected event than the expected event is evidence that infants hold the expectation, notice the violation and are surprised by it.

Before the test events, infants may see habituation events that get them used to the test situation. Researchers set a rule for when that stage ends. In one study, habituation continued until a baby's looking time dropped by 50 percent or more on 3 trials in a row, compared with the first 3 trials, or until 9 habituation trials were done.

Reflexes are movements a baby makes without choosing to. When a baby's cheek is touched, the baby turns toward the touch and opens their mouth, which is the rooting reflex. When a baby's palm is stroked, the baby's fingers close around a finger, which is the grasp reflex. The tonic neck reflex is also called the fencing pose. When a baby's head turns to one side, the arm on that side stretches out and the other arm bends up.

A loud sound or a sudden move can make a baby stretch out their arms and legs and then pull them back in, which is the startle reflex. Doctors check a newborn's reflexes to see whether the brain and nervous system are working well. The grasp reflex lasts until a baby is about 5 to 6 months old, and then it fades away. The rooting reflex fades within the first several months of life, at about 4 to 6 months.

Babies cry to tell the people near them what they need, such as food, a hug, a clean diaper or sleep. A baby's first signs of communication come when the baby learns that a cry brings food, comfort and company. A familiar, gentle voice can calm a crying baby. Babies cry more in their first 3 months than at any other time, and crying usually gets better after that.

Newborn babies like to look at faces, and they also like black-and-white or high-contrast patterns. A newborn's eyes focus best on things about 8 to 12 inches (20 to 30 centimeters) away, about as far as a parent's face. By eight weeks, babies begin to focus more easily on the faces of the people near them.

By about 2 months many babies watch people as they move, and in the first months they start tracking moving objects with their eyes. For the first two months a baby's eyes are not well coordinated and may seem to wander or look crossed, which is usually normal. Seeing takes both the eyes and the brain. Signals travel from the eye to the brain, and a baby's brain has to learn to use what the eyes send.

The psychologist Jean Piaget found that babies of 5 to 7 months did not search for a toy hidden under a cloth, even though they could lift a cloth and grasp a toy. For several decades, researchers accepted Piaget's conclusion that young infants' mental pictures include only the objects they can directly perceive.

Babies can hear loud sounds from the start, and they may turn their head toward familiar voices. Researchers showed that newborns would change how they sucked to switch on a recording of their mother reading a nursery rhyme (DeCasper and Fifer, 1980). Newborns begin to recognize important sounds around them, such as the voice of a caregiver.

In an exposure study, mothers read a nursery rhyme out loud during pregnancy, and their babies later preferred it. That shows learning before birth affects preferences after birth.

As babies grow they begin to sort out the speech sounds that make up the words of their language. Babies learn the sounds of the language around them. By 6 months most recognize its basic sounds, and by the end of the first year they have learned a great deal about its sound structure.

Studies using artificial languages suggest that infants use statistical information in the speech stream to find where words begin and end. In a famous 1996 study, infants heard about 2 minutes of an artificial language and were then able to pick out the words in the stream of speech. Researchers showed that babies could tell the artificial words from nonwords by measuring how long the babies listened in a head-turn preference procedure.

In that artificial language the only clue to where words ended was statistics: the chance that one syllable follows another was 1.0 inside words and .33 across word boundaries. Real baby-directed speech also has higher transitional probabilities within words than across word boundaries, like the artificial language. The pattern from the experiment shows up in the speech babies hear.

Words to know

• habituation: getting used
• statistical: based on odds
• expectation: what you predict
• transitional: between-step