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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.

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Figure 1: Psychophysics of categorical speech perception and speech-evoked responses during intraoperative human cortical recordings.
Figure 2: Categorical organization of neural response patterns to a speech-stimulus continuum.
Figure 3: Correlation of neurometric and psychometric category boundaries.
Figure 4: Topography of discriminative cortical sites in the pSTG underlying categorical speech perception.


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We are grateful to the four individuals who participated in this experiment and to A. Flinker for help with data acquisition. This research was supported by US National Institutes of Health grants NS21135 (R.T.K.), PO4813 (R.T.K.), F32NS061552 (E.F.C.), K99NS065120 (E.F.C.), FKZ-MK48-2009/003 (J.W.R.) and RI1511/1-3 (J.W.R.).

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E.F.C. designed the experiments, collected the data and wrote the manuscript. E.F.C. and J.W.R. analyzed the data, evaluated results and edited the manuscript. J.W.R., N.M.B. and M.S.B. helped with data collection. K.J. and R.T.K. reviewed the manuscript.

Corresponding authors

Correspondence to Edward F Chang or Jochem W Rieger.

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The authors declare no competing financial interests.

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Supplementary Figures 1–4, Supplementary Table 1 and Supplementary Results (PDF 221 kb)

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Chang, E., Rieger, J., Johnson, K. et al. Categorical speech representation in human superior temporal gyrus. Nat Neurosci 13, 1428–1432 (2010).

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