Making sense of language hinges upon a skill called speech perception. Was that a bat, a hat, a rat, or a fat cat that sat? Small sound changes make for large differences in interpretation. What sound differences do infants perceive? When do they first recognize their native language? How do they discover words in the stream of speech, and how do their perceptual abilities change with time and exposure to that speech? These are the questions asked by researchers who study the development of speech perception.

Thanks to their work, it is now known that infants distinguish extremely subtle acoustic distinctions and recognize their native language from birth. By their second birthday, infants are experts at finding words in the fluent stream of speech and focus ...