Distinct sensitivity to spectrotemporal modulation supports brain asymmetry for speech and melody

Speech versus music in the brain To what extent does the perception of speech and music depend on different mechanisms in the human brain? What is the anatomical basis underlying this specialization? Albouy et al. created a corpus of a cappella songs that contain both speech (semantic) and music (melodic) information and degraded each stimulus selectively in either the temporal or spectral domain. Degradation of temporal information impaired speech recognition but not melody recognition, whereas degradation of spectral information impaired melody recognition but not speech recognition. Brain scanning revealed a right-left asymmetry for speech and music. Classification of speech content occurred exclusively in the left auditory cortex, whereas classification of melodic content occurred only in the right auditory cortex. Science, this issue p. 1043 A human brain imaging study reveals that low-level acoustical cues support hemispheric lateralization of speech and music perception. Does brain asymmetry for speech and music emerge from acoustical cues or from domain-specific neural networks? We selectively filtered temporal or spectral modulations in sung speech stimuli for which verbal and melodic content was crossed and balanced. Perception of speech decreased only with degradation of temporal information, whereas perception of melodies decreased only with spectral degradation. Functional magnetic resonance imaging data showed that the neural decoding of speech and melodies depends on activity patterns in left and right auditory regions, respectively. This asymmetry is supported by specific sensitivity to spectrotemporal modulation rates within each region. Finally, the effects of degradation on perception were paralleled by their effects on neural classification. Our results suggest a match between acoustical properties of communicative signals and neural specializations adapted to that purpose.