Neural correlates of categorical perception in learned vocal communication

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Abstract
The authors show that individual sensorimotor neurons in freely behaving swamp sparrows exhibit categorical responses to features of their songs. The neuronal response boundary predicts the categorical perceptual boundary that was measured in field studies of the same sparrow population, but not the perceptual boundary in populations that learn different song dialects. The division of continuously variable acoustic signals into discrete perceptual categories is a fundamental feature of vocal communication, including human speech. Despite the importance of categorical perception to learned vocal communication, the neural correlates underlying this phenomenon await identification. We found that individual sensorimotor neurons in freely behaving swamp sparrows expressed categorical auditory responses to changes in note duration, a learned feature of their songs, and that the neural response boundary accurately predicted the categorical perceptual boundary measured in field studies of the same sparrow population. Furthermore, swamp sparrow populations that learned different song dialects showed different categorical perceptual boundaries that were consistent with the boundary being learned. Our results extend the analysis of the neural basis of perceptual categorization into the realm of vocal communication and advance the learned vocalizations of songbirds as a model for investigating how experience shapes categorical perception and the activity of categorically responsive neurons.