Hearing During Infancy and Toddlerhood

Fetuses in the womb show sensitivity to sound even before birth by showing changes in brain activity, heart rate, and body movements.

Newborns' auditory acuity, or the ability to detect sounds, is nearly adult-like for human voices within typical pitch and loudness ranges.

But they are less sensitive to some high-pitched sounds, like whistles. These sounds need to be louder for newborns to hear them.

Newborns can also turn their heads at least toward the general direction of a sound.

Auditory discrimination, the ability to differentiate between sounds, also develops quickly.

By two days, infants recognize words they heard the day before, and by one month, they distinguish similar sounds like "ba" and "pa."

By two and a half to four months, infants can recognize previously heard sentences after a brief delay.

Also, at 4 months, an infant's brain shows signs of speech lateralization.

This means one side of the brain—the left hemisphere—processes speech more strongly, especially for the infant's native language.

By 18 months, toddlers can detect smaller shifts in sound location, nearly the skill level seen in adults.