The research proposed here focuses on affective processes in the development of preverbal communication and language. I will conduct an integrated series of studies with infants and adults to test the following hypotheses: a) The expression of positive affect in mothers' and fathers' speech to infants is associated with elevated pitch and characteristic exaggerated intonation contours; b) Young infants are selectively responsive, both behaviorally and psychophysiologically, to these exaggerated pitch contours in parental speech; c) The highly modulated, affective pitch contours in parental speech serve to direct the attention of the preverbal infant to objects and events in the environment; d) Parents consistently use specific intonation patterns to convey specific affective and pragmatic messages to infants; these context-specific affective vocalizations may function as the first units of vocal meaning for the preverbal infant; e) The exaggerated, highly affective pitch contours of parental speech ultimately help the infant to associate speech sounds with their referents, facilitating lexical acquisition and language comprehension. I want to continue efforts to integrate the study of preverbal communication and language development with the study of perceptual and affective processes in infancy. Traditional conceptual boundaries have separated research in auditory and speech perception, language acquisition, emotional development, and parent-infant social interaction. An interdisciplinary approach to the ontogeny of communication, as proposed here, should help to integrate these areas. I hope to provide further support for the claim that infants early affective responsiveness to parental intonation prepares the child for the later linguistic use of intonation to parse the speech stream and understand spoken language. This continuity between the infant's processing of affective ad linguistic information in parental speech is the general hypothesis that motivates and unifies the studies proposed.