Abstract
Investigations of the functional organization of human auditory cortex typically examine responses to different sound categories. An alternative approach is to characterize sounds with respect to their amount of variation in the time and frequency domains (i.e., spectral and temporal complexity). Although the vast majority of published studies examine contrasts between discrete sound categories, an alternative complexity-based taxonomy can be evaluated through meta-analysis. In a quantitative meta-analysis of 58 auditory neuroimaging studies, we examined the evidence supporting current models of functional specialization for auditory processing using grouping criteria based on either categories or spectro-temporal complexity. Consistent with current models, analyses based on typical sound categories revealed hierarchical auditory organization and left-lateralized responses to speech sounds, with high speech sensitivity in the left anterior superior temporal cortex. Classification of contrasts based on spectro-temporal complexity, on the other hand, revealed a striking within-hemisphere dissociation in which caudo-lateral temporal regions in auditory cortex showed greater sensitivity to spectral changes, while anterior superior temporal cortical areas were more sensitive to temporal variation, consistent with recent findings in animal models. The meta-analysis thus suggests that spectro-temporal acoustic complexity represents a useful alternative taxonomy to investigate the functional organization of human auditory cortex.
Highlights
We suggest that acoustic complexity might represent a valid alternative classificatory scheme to describe a novel withinhemisphere dichotomy regarding the functional organization for auditory processing in temporal cortex
Functional specialization of the auditory cortex response: acoustic complexity effects As an alternative to the classical division of auditory stimuli into typical categories like pure tones, noise, voices, and music, we explored how acoustic variations along the temporal and spectral dimensions were represented at the cortical level
Our meta-analysis demonstrates a clear withinhemisphere functional segregation related to spectral and temporal processing in human auditory cortex, consistent with the known organization of non-human primate auditory system
Summary
Characterizing responses to stimuli from typical auditory categories such as music, voices, animal, or environmental sounds have provided important information about the cortical specialization for auditory processing. Any auditory stimulus can be described with respect to its sound complexity characteristics specified with respect to changes in time and frequency This approach represents a comprehensive characterization of sounds that is not limited to specific categories. Complexity might represent an alternative organizing principle along which to represent auditory cortical response specialization In this conceptualization, a single frequency sinusoidal wave (pure tone), constant over time, can be classified as simple, and a sound containing multiple components can be classified as complex with respect to the frequency domain. Acoustic complexity is not independent of sound categories and the two classification methods explored here should not be considered as mutually exclusive
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