An infant at birth is a very different organism from a 12-month-old as regards to both brain and behavior. Thus, infancy is a particularly informative time to study behaviors that may reflect the underlying development of the brain, precisely because many changes occur over a short period of time. It is possible to follow the development of diverse abilities prospectively, from their earliest appearance, and consider what impact experience, both social and perceptual, might have on their emergence. Given the rapid course of brain development during the first years of life, the onset and timing of such abilities may suggest particular neurological substrates. Language is a particularly fascinating emergent ability that has been of enduring research interest. Even after many years of study, however, the neural substrate and fundamental processes that support language acquisition are not fully delineated. For example, scientists have not yet deciphered the mechanisms by which the temporally complex acoustic signals of speech are encoded in the auditory cortex and interpreted with the rich complexity of language-all within the time constraints of ongoing speech.