Differentiation of speech and nonspeech processing within primary auditory cortex.
Primary auditory cortex (PAC), located in Heschl's gyrus (HG), is the earliest cortical level at which sounds are processed. Standard theories of speech perception assume that signal components are given a representation in PAC which are then matched to speech templates in auditory association cortex. An alternative holds that speech activates a specialized system in cortex that does not use the primitives of PAC. Functional magnetic resonance imaging revealed different brain activation patterns in listening to speech and nonspeech sounds across different levels of complexity. Sensitivity to speech was observed in association cortex, as expected. Further, activation in HG increased with increasing levels of complexity with added fundamentals for both nonspeech and speech stimuli, but only for nonspeech when separate sources (release bursts/fricative noises or their nonspeech analogs) were added. These results are consistent with the existence of a specialized speech system which bypasses more typical processes at the earliest cortical level.
Whalen
D H
DH
Haskins Laboratories, 300 George Street, New Haven, Connecticut 06511, USA. whalen@haskins.yale.edu
Benson
Randall R
RR
Richardson
Matthew
M
Swainson
Brook
B
Clark
Vincent P
VP
Lai
Song
S
Mencl
W Einar
WE
Fulbright
Robert K
RK
Constable
R Todd
RT
Liberman
Alvin M
AM
D000161:Acoustic Stimulation / Q000379:methods*; D001303:Auditory Cortex / Q000502:physiology*; D001307:Auditory Perception / Q000502:physiology*; D004292:Dominance, Cerebral; D017352:Echo-Planar Imaging; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D013018:Sound Spectrography; D013060:Speech