title: Hierarchical Organization of Auditory and Motor Representations in Speech Perception: Evidence from Searchlight Similarity Analysis.
abstract: How humans extract the identity of speech sounds from highly variable acoustic signals remains unclear. Here, we use searchlight representational similarity analysis (RSA) to localize and characterize neural representations of syllables at different levels of the hierarchically organized temporo-frontal pathways for speech perception. We asked participants to listen to spoken syllables that differed considerably in their surface acoustic form by changing speaker and degrading surface acoustics using noise-vocoding and sine wave synthesis while we recorded neural responses with functional magnetic resonance imaging. We found evidence for a graded hierarchy of abstraction across the brain. At the peak of the hierarchy, neural representations in somatomotor cortex encoded syllable identity but not surface acoustic form, at the base of the hierarchy, primary auditory cortex showed the reverse. In contrast, bilateral temporal cortex exhibited an intermediate response, encoding both syllable identity and the surface acoustic form of speech. Regions of somatomotor cortex associated with encoding syllable identity in perception were also engaged when producing the same syllables in a separate session. These findings are consistent with a hierarchical account of how variable acoustic signals are transformed into abstract representations of the identity of speech sounds.
authors.affiliation: MRC Cognition and Brain Sciences Unit, Cambridge CB2 7EF, UK Institute of Cognitive Neuroscience, University College London, WC1 3AR, UK.
authors.forename: Samuel
authors.initials: S
authors.lastname: Evans
authors.affiliation: MRC Cognition and Brain Sciences Unit, Cambridge CB2 7EF, UK.
authors.forename: Matthew H
authors.initials: MH
authors.lastname: Davis
mesh_terms: D000293:Adolescent; D000328:Adult; D001309:Auditory Threshold; D003627:Data Interpretation, Statistical; D005260:Female; D005625:Frontal Lobe / Q000502:physiology*; D006801:Humans; D008297:Male; D015999:Multivariate Analysis; D009434:Neural Pathways / Q000502:physiology; D009622:Noise; D066191:Sensorimotor Cortex / Q000502:physiology*; D013060:Speech; D013067:Speech Perception / Q000502:physiology*; D013702:Temporal Lobe / Q000502:physiology*; D055815:Young Adult
keywords: fMRI; hierarchical processing; multivoxel pattern analysis; representational similarity analysis; speech perception