Categorical speech representation in human superior temporal gyrus.
Speech perception requires the rapid and effortless extraction of meaningful phonetic information from a highly variable acoustic signal. A powerful example of this phenomenon is categorical speech perception, in which a continuum of acoustically varying sounds is transformed into perceptually distinct phoneme categories. We found that the neural representation of speech sounds is categorically organized in the human posterior superior temporal gyrus. Using intracranial high-density cortical surface arrays, we found that listening to synthesized speech stimuli varying in small and acoustically equal steps evoked distinct and invariant cortical population response patterns that were organized by their sensitivities to critical acoustic features. Phonetic category boundaries were similar between neurometric and psychometric functions. Although speech-sound responses were distributed, spatially discrete cortical loci were found to underlie specific phonetic discrimination. Our results provide direct evidence for acoustic-to-higher order phonetic level encoding of speech sounds in human language receptive cortex.
Chang
Edward F
EF
Department of Neurological Surgery, University of California San Francisco, San Francisco, California, USA. changed@neurosurg.ucsf.edu
Rieger
Jochem W
JW
Johnson
Keith
K
Berger
Mitchel S
MS
Barbaro
Nicholas M
NM
Knight
Robert T
RT
D000161:Acoustic Stimulation; D001931:Brain Mapping; D004566:Electrodes; D004569:Electroencephalography / Q000379:methods; D004833:Epilepsy, Temporal Lobe / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009474:Neurons / Q000145:classification / Q000502:physiology; D010700:Phonetics; D011571:Psychoacoustics; D011594:Psychometrics / Q000379:methods; D011930:Reaction Time / Q000502:physiology; D013060:Speech / Q000502:physiology*; D013067:Speech Perception / Q000502:physiology*; D013223:Statistics as Topic; D013702:Temporal Lobe / Q000473:pathology / Q000503:physiopathology*