Auditory Development and the Role of Experience in Infants and Young Children

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Hearing is the primary sense for communication through language and music; as a consequence, auditory perception impacts language, cognitive and social development. The immaturity of auditory processing in young infants, coupled with a protracted period of development, indicates an extended period of experience-dependent plasticity during which the particular auditory experiences of an individual shape future auditory processing capabilities. The goal of the proposed research is to understand early auditory development and learning in three critical areas. (1) WINDOWS OF PLASTICITY AND EFFECTS OF EXPERIENCE ON THE DISCRIMINATION OF VOICES. Learning to identify and discriminate people by voice is important for cognitive and social development. Across a number of domains, including faces, phonemes and music, young infants discriminate stimuli within native or foreign categories equally well, whereas older infants and adults perform much better with native stimuli. We showed that such experience-driven perceptual narrowing also occurs for voice discrimination. Specifically, the ability of human infants to discriminate rhesus monkeys, but not humans, by voice declined between 6 and 12 months of age. Here we investigate (a) whether the effect generalizes across different species, (b) the nature of voice categories by exploring voice discrimination in languages similar or dissimilar to the native language, and (c) plasticity for learning new voice categories across childhood. This work will significantly increase our understanding of voice processing in particular, and learning and plasticity in auditory development in general. (2) THE BASIS OF SENSORY CONSONANCE PERCEPTION IN YOUNG INFANTS. The distinction between sensory consonance (notes rated by adults as sounding good together) and dissonance (unpleasant or rough) forms the basis of musical pitch structure. In previous work we showed that infants as young as 2 months age prefer consonance over dissonance. The classical theory states that dissonance arises from interactions (beating) on the basilar membrane in the ear between harmonics close in frequency. A more recent theory states that consonance arises instead from harmonicity, or the extent to which all harmonics of all tones present are integer multiple of a common fundamental frequency. Here we investigate (1) whether infants prefer sounds with less beating and sounds with greater harmonicity and (2) whether their preference for consonance is a result of a preference for no beating or for harmonicity. Because perception of consonance and dissonance are fundamental for musical pitch structure, understanding the nature of early preferences and how they are modified by experience is essential for understanding the perceptual origins of music. (3) DEVELOPMENT OF SENSITIVITY TO MUSICAL TONALITY AND EFFECTS OF EXPERIENCE. We have shown that infants and children learn the musical pitch structure of the music to which they are exposed in an orderly way, just as they learn language. This work consists largely of data from infants and older children because toddlers (2-3 years) are difficult to test (will not sit for infant procedures and cannot easily follow instructions and answer questions). However, critical development takes place during toddlerhood. We propose two methods for toddlers. In one, we examine whether toddlers choose hand puppets that dance, for example, to tonal music over those that dance to atonal music. The second method involves measuring EEG responses to violations of tonal structure. These findings will significantly increase our understanding of musical development and provide practical information, such as at what ages children benefit from what types of musical classes.