title: Delta, theta, beta, and gamma brain oscillations index levels of auditory sentence processing.
abstract: A growing number of studies indicate that multiple ranges of brain oscillations, especially the delta (δ, <4Hz), theta (θ, 4-8Hz), beta (β, 13-30Hz), and gamma (γ, 30-50Hz) bands, are engaged in speech and language processing. It is not clear, however, how these oscillations relate to functional processing at different linguistic hierarchical levels. Using scalp electroencephalography (EEG), the current study tested the hypothesis that phonological and the higher-level linguistic (semantic/syntactic) organizations during auditory sentence processing are indexed by distinct EEG signatures derived from the δ, θ, β, and γ oscillations. We analyzed specific EEG signatures while subjects listened to Mandarin speech stimuli in three different conditions in order to dissociate phonological and semantic/syntactic processing: (1) sentences comprising valid disyllabic words assembled in a valid syntactic structure (real-word condition); (2) utterances with morphologically valid syllables, but not constituting valid disyllabic words (pseudo-word condition); and (3) backward versions of the real-word and pseudo-word conditions. We tested four signatures: band power, EEG-acoustic entrainment (EAE), cross-frequency coupling (CFC), and inter-electrode renormalized partial directed coherence (rPDC). The results show significant effects of band power and EAE of δ and θ oscillations for phonological, rather than semantic/syntactic processing, indicating the importance of tracking δ- and θ-rate phonetic patterns during phonological analysis. We also found significant β-related effects, suggesting tracking of EEG to the acoustic stimulus (high-β EAE), memory processing (θ-low-β CFC), and auditory-motor interactions (20-Hz rPDC) during phonological analysis. For semantic/syntactic processing, we obtained a significant effect of γ power, suggesting lexical memory retrieval or processing grammatical word categories. Based on these findings, we confirm that scalp EEG signatures relevant to δ, θ, β, and γ oscillations can index phonological and semantic/syntactic organizations separately in auditory sentence processing, compatible with the view that phonological and higher-level linguistic processing engage distinct neural networks.
authors.affiliation: Language Engineering Laboratory, Department of Electronic Engineering, The Chinese University of Hong Kong, Hong Kong Special Administrative Region; Speech Research Lab, Experimental Psychology, Faculty of Brain Sciences, University College London, London, United Kingdom. Electronic address: guangting.mai.15@ucl.ac.uk.
authors.forename: Guangting
authors.initials: G
authors.lastname: Mai
authors.affiliation: Language Engineering Laboratory, Department of Electronic Engineering, The Chinese University of Hong Kong, Hong Kong Special Administrative Region; Joint Research Centre for Language and Human Complexity, Faculty of Arts, The Chinese University of Hong Kong, Hong Kong Special Administrative Region. Electronic address: jminett@ee.cuhk.edu.hk.
authors.forename: James W
authors.initials: JW
authors.lastname: Minett
authors.affiliation: Language Engineering Laboratory, Department of Electronic Engineering, The Chinese University of Hong Kong, Hong Kong Special Administrative Region; Joint Research Centre for Language and Human Complexity, Faculty of Arts, The Chinese University of Hong Kong, Hong Kong Special Administrative Region; Department of Chinese and Bilingual Studies, The Hong Kong Polytechnic University, Hong Kong Special Administrative Region.
authors.forename: William S-Y
authors.initials: WS
authors.lastname: Wang
mesh_terms: D000328:Adult; D001303:Auditory Cortex / Q000502:physiology*; D001307:Auditory Perception / Q000502:physiology*; D001683:Biological Clocks / Q000502:physiology*; D058256:Brain Waves / Q000502:physiology*; D004569:Electroencephalography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D009415:Nerve Net / Q000502:physiology*; D010700:Phonetics; D015203:Reproducibility of Results; D012660:Semantics; D012680:Sensitivity and Specificity; D055815:Young Adult
keywords: Auditory sentence; Brain oscillations; EEG; Phonological processing; Semantic processing; Syntactic processing