The ability to hear and understand speech.

Speech perception, the process by which we employ cognitive, motor, and sensory processes to hear and understand speech, is a product of innate preparation ("nature") and sensitivity to experience ("nurture") as demonstrated in infants' abilities to perceive speech. Studies of infants from birth have shown that they respond to speech signals in a special way, suggesting a strong innate component to language. Other research has shown the strong effect of environment on language acquisition by proving that the language an infant listens to during the first year of life enables the child to begin producing a distinct set of sounds (babbling) specific to the language spoken by its parents.

Since the 1950s, great strides have been made in research on the acoustics of speech (i.e., how sound is produced by the human vocal tract). It has been demonstrated...