Hearing begins in the womb—pregnant women have reported feeling the fetus move in response to loud noises at 31 weeks (7 weeks before full-term delivery). Newborns are sensitive to the location, frequency, pitch, and volume of sounds. Loud sounds startle them, while rhythmic, repetitive sounds tend to soothe them. During the second month of life, they become sensitive to a wider range of sounds, reacting to a variety of medium-range sounds that can affect them differently depending on their mood. (For example, a child at this age may enjoy the sound of a vacuum cleaner when she is feeling happy and become upset by it when she is in an irritable mood.) It has been found that infants can hear higher frequencies than adults can (a fact that may be related to the adult instinct to produce "baby talk" at higher pitches than...