title: Neural decoding of single vowels during covert articulation using electrocorticography.
abstract: The human brain has important abilities for manipulating phonemes, the basic building blocks of speech; these abilities represent phonological processing. Previous studies have shown change in the activation levels of broad cortical areas such as the premotor cortex, the inferior frontal gyrus, and the superior temporal gyrus during phonological processing. However, whether these areas actually convey signals to representations related to individual phonemes remains unclear. This study focused on single vowels and investigated cortical areas important for representing single vowels using electrocorticography (ECoG) during covert articulation. To identify such cortical areas, we used a neural decoding approach in which machine learning models identify vowels. A decoding model was trained on the ECoG signals from individual electrodes placed on the subjects' cortices. We then statistically evaluated whether each decoding model showed accurate identification of vowels, and we found cortical areas such as the premotor cortex and the superior temporal gyrus. These cortical areas were consistent with previous findings. On the other hand, no electrodes over Broca's area showed significant decoding accuracies. This was inconsistent with findings from a previous study showing that vowels within the phonemic sequence of words can be decoded using ECoG signals from Broca's area. Our results therefore suggest that Broca's area is involved in the processing of vowels within phonemic sequences, but not in the processing of single vowels.
authors.affiliation: Graduate School of Information Science, Nara Institute of Science and Technology Ikoma, Japan.
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Ikeda
authors.affiliation: Graduate School of Information Science, Nara Institute of Science and Technology Ikoma, Japan ; Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology Kitakyushu, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Shibata
authors.affiliation: Department of Neurosurgery, Kinki University Faculty of Medicine Sayama, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Nakano
authors.affiliation: Department of Neurosurgery, Kinki University Faculty of Medicine Sayama, Japan.
authors.forename: Rieko
authors.initials: R
authors.lastname: Okada
authors.affiliation: Department of Neurosurgery, Graduate School of Medicine, Osaka City University Osaka, Japan.
authors.forename: Naohiro
authors.initials: N
authors.lastname: Tsuyuguchi
authors.affiliation: Graduate School of Information Science, Nara Institute of Science and Technology Ikoma, Japan.
authors.forename: Kazushi
authors.initials: K
authors.lastname: Ikeda
authors.affiliation: Department of Neurosurgery, Kinki University Faculty of Medicine Sayama, Japan ; Core Research for Evolutionary Science and Technology, Japan Science and Technology Agency Kawaguchi, Japan.
authors.forename: Amami
authors.initials: A
authors.lastname: Kato
keywords: covert articulation; electrocorticography (ECoG); functional mapping; neural decoding; single vowel