Birds and babies: Ontogeny of vocal learning

Abstract

In birds and human babies, the ontogeny of vocal learning shows striking parallels: Both are predisposed toward their species-specific signals at birth, require exposure to speciestypical vocalizations during a "sensitive period," and both are (traditionally) hypothesized to learn in two distinct phases (1).During the sensory learning phase, infants listen and learn the species-typical song or speech signal by memorizing its auditory characteristics and representing the information in the brain; in the sensorimotor learning phase, birds and babies begin to produce song or speech using auditory feedback to improve their nascent attempts to mimic the representations stored in memory (Fig. 1).Leito and Gahr (L&G, 2) challenge this classic view.The authors injected testosterone in young male zebra finches 16 d after hatching while the birds were experiencing typical social exposure.Testosterone caused the zebra finches to sing prematurely, well before control groups who did not receive testosterone began to sing.Birds who sang early also showed normal babbling and sensory learning based on spectrographic analysis of the mature songs produced by

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