title: Early-latency categorical speech sound representations in the left inferior frontal gyrus.
abstract: 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.
authors.affiliation: Brain and Mind Laboratory, Department of Neuroscience and Biomedical Engineering (NBE), School of Science, Aalto University, 00076, AALTO, Espoo, Finland. Electronic address: jussi.alho@aalto.fi.
authors.forename: Jussi
authors.initials: J
authors.lastname: Alho
authors.affiliation: Laboratory of Integrated Neuroscience and Cognition, Interdisciplinary Program in Neuroscience, Georgetown University Medical Center, Washington, DC, 20057, USA.
authors.forename: Brannon M
authors.initials: BM
authors.lastname: Green
authors.affiliation: Special Laboratory Non-Invasive Brain Imaging, Leibniz Institute for Neurobiology, Brenneckestraße 6, D-39118 Magdeburg, Germany.
authors.forename: Patrick J C
authors.initials: PJC
authors.lastname: May
authors.affiliation: Brain and Mind Laboratory, Department of Neuroscience and Biomedical Engineering (NBE), School of Science, Aalto University, 00076, AALTO, Espoo, Finland.
authors.forename: Mikko
authors.initials: M
authors.lastname: Sams
authors.affiliation: Brain and Mind Laboratory, Department of Neuroscience and Biomedical Engineering (NBE), School of Science, Aalto University, 00076, AALTO, Espoo, Finland.
authors.forename: Hannu
authors.initials: H
authors.lastname: Tiitinen
authors.affiliation: Brain and Mind Laboratory, Department of Neuroscience and Biomedical Engineering (NBE), School of Science, Aalto University, 00076, AALTO, Espoo, Finland; Laboratory of Integrated Neuroscience and Cognition, Interdisciplinary Program in Neuroscience, Georgetown University Medical Center, Washington, DC, 20057, USA; Institute for Advanced Study, TUM, Munich-Garching, 80333 Munich, Germany.
authors.forename: Josef P
authors.initials: JP
authors.lastname: Rauschecker
authors.affiliation: Brain and Mind Laboratory, Department of Neuroscience and Biomedical Engineering (NBE), School of Science, Aalto University, 00076, AALTO, Espoo, Finland; MEG Core, Aalto NeuroImaging, Aalto University, 00076, AALTO, Espoo, Finland; AMI Centre, Aalto NeuroImaging, Aalto University, 00076, AALTO, Espoo, Finland. Electronic address: iiro.jaaskelainen@aalto.fi.
authors.forename: Iiro P
authors.initials: IP
authors.lastname: Jääskeläinen
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D005260:Female; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D017397:Prefrontal Cortex / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D013067:Speech Perception / Q000502:physiology*; D055815:Young Adult
keywords: Categorical perception; Inferior frontal gyrus; Magnetoencephalography; Speech perception; Stimulus-specific adaptation