Early-latency categorical speech sound representations in the left inferior frontal gyrus

Jussi Alho*, Brannon M. Green, Patrick J C May, Mikko Sams, Hannu Tiitinen, Josef P. Rauschecker, Iiro P. Jääskeläinen

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

25 Citations (Scopus)


Efficient speech perception requires the mapping of highly variable acoustic signals to distinct phonetic categories. How the brain overcomes this many-to-one mapping problem has remained unresolved. To infer the cortical location, latency, and dependency on attention of categorical speech sound representations in the human brain, we measured stimulus-specific adaptation of neuromagnetic responses to sounds from a phonetic continuum. The participants attended to the sounds while performing a non-phonetic listening task and, in a separate recording condition, ignored the sounds while watching a silent film. Neural adaptation indicative of phoneme category selectivity was found only during the attentive condition in the pars opercularis (POp) of the left inferior frontal gyrus, where the degree of selectivity correlated with the ability of the participants to categorize the phonetic stimuli. Importantly, these category-specific representations were activated at an early latency of 115-140 ms, which is compatible with the speed of perceptual phonetic categorization. Further, concurrent functional connectivity was observed between POp and posterior auditory cortical areas. These novel findings suggest that when humans attend to speech, the left POp mediates phonetic categorization through integration of auditory and motor information via the dorsal auditory stream.

Original languageEnglish
Pages (from-to)214-223
Number of pages10
Publication statusPublished - 1 Apr 2016
MoE publication typeA1 Journal article-refereed


  • Categorical perception
  • Inferior frontal gyrus
  • Magnetoencephalography
  • Speech perception
  • Stimulus-specific adaptation


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