title: Categorical discrimination of human body parts by magnetoencephalography.
abstract: Humans recognize body parts in categories. Previous studies have shown that responses in the fusiform body area (FBA) and extrastriate body area (EBA) are evoked by the perception of the human body, when presented either as whole or as isolated parts. These responses occur approximately 190 ms after body images are visualized. The extent to which body-sensitive responses show specificity for different body part categories remains to be largely clarified. We used a decoding method to quantify neural responses associated with the perception of different categories of body parts. Nine subjects underwent measurements of their brain activities by magnetoencephalography (MEG) while viewing 14 images of feet, hands, mouths, and objects. We decoded categories of the presented images from the MEG signals using a support vector machine (SVM) and calculated their accuracy by 10-fold cross-validation. For each subject, a response that appeared to be a body-sensitive response was observed and the MEG signals corresponding to the three types of body categories were classified based on the signals in the occipitotemporal cortex. The accuracy in decoding body-part categories (with a peak at approximately 48%) was above chance (33.3%) and significantly higher than that for random categories. According to the time course and location, the responses are suggested to be body-sensitive and to include information regarding the body-part category. Finally, this non-invasive method can decode category information of a visual object with high temporal and spatial resolution and this result may have a significant impact in the field of brain-machine interface research.
authors.affiliation: Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine Suita, Japan.
authors.forename: Misaki
authors.initials: M
authors.lastname: Nakamura
authors.affiliation: Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine Suita, Japan ; Department of Neurosurgery, Osaka University Graduate School of Medicine Suita, Japan ; Department of Neuroinformatics, ATR Computational Neuroscience Laboratories Kyoto, Japan ; Japan Science and Technology Agency, Precursory Research for Embryonic Science and Technology Osaka, Japan.
authors.forename: Takufumi
authors.initials: T
authors.lastname: Yanagisawa
authors.affiliation: Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine Suita, Japan.
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Okamura
authors.affiliation: Department of Neurosurgery, Osaka University Graduate School of Medicine Suita, Japan ; Department of Neuroinformatics, ATR Computational Neuroscience Laboratories Kyoto, Japan ; Graduate School of Information Science, Nara Institute of Science and Technology Ikoma, Japan.
authors.forename: Ryohei
authors.initials: R
authors.lastname: Fukuma
authors.affiliation: Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine Suita, Japan ; Department of Neurosurgery, Osaka University Graduate School of Medicine Suita, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Hirata
authors.affiliation: Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine Suita, Japan.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Araki
authors.affiliation: Department of Neuroinformatics, ATR Computational Neuroscience Laboratories Kyoto, Japan ; Graduate School of Information Science, Nara Institute of Science and Technology Ikoma, Japan ; Graduate School of Informatics, Kyoto University Kyoto, Japan.
authors.forename: Yukiyasu
authors.initials: Y
authors.lastname: Kamitani
authors.affiliation: Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine Suita, Japan.
authors.forename: Shiro
authors.initials: S
authors.lastname: Yorifuji
keywords: body perception; categorization; decoding; magnetoencephalography; visual cortex