title: Hierarchical organization of human auditory cortex: evidence from acoustic invariance in the response to intelligible speech.
abstract: Hierarchical organization of human auditory cortex has been inferred from functional imaging observations that core regions respond to simple stimuli (tones) whereas downstream regions are selectively responsive to more complex stimuli (band-pass noise, speech). It is assumed that core regions code low-level features, which are combined at higher levels in the auditory system to yield more abstract neural codes. However, this hypothesis has not been critically evaluated in the auditory domain. We assessed sensitivity to acoustic variation within intelligible versus unintelligible speech using functional magnetic resonance imaging and a multivariate pattern analysis. Core auditory regions on the dorsal plane of the superior temporal gyrus exhibited high levels of sensitivity to acoustic features, whereas downstream auditory regions in both anterior superior temporal sulcus and posterior superior temporal sulcus (pSTS) bilaterally showed greater sensitivity to whether speech was intelligible or not and less sensitivity to acoustic variation (acoustic invariance). Acoustic invariance was most pronounced in more pSTS regions of both hemispheres, which we argue support phonological level representations. This finding provides direct evidence for a hierarchical organization of human auditory cortex and clarifies the cortical pathways supporting the processing of intelligible speech.
authors.affiliation: Center for Cognitive Neuroscience and Department of Cognitive Sciences, University of California, Irvine, CA 92697, USA.
authors.forename: Kayoko
authors.initials: K
authors.lastname: Okada
authors.forename: Feng
authors.initials: F
authors.lastname: Rong
authors.forename: Jon
authors.initials: J
authors.lastname: Venezia
authors.forename: William
authors.initials: W
authors.lastname: Matchin
authors.forename: I-Hui
authors.initials: IH
authors.lastname: Hsieh
authors.forename: Kourosh
authors.initials: K
authors.lastname: Saberi
authors.forename: John T
authors.initials: JT
authors.lastname: Serences
authors.forename: Gregory
authors.initials: G
authors.lastname: Hickok
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000162:Acoustics; D000293:Adolescent; D000328:Adult; D001303:Auditory Cortex / Q000098:blood supply / Q000502:physiology*; D001931:Brain Mapping; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D013067:Speech Perception / Q000502:physiology*; D018709:Statistics, Nonparametric; D055815:Young Adult
chemical_list: D010100:Oxygen