The neural oscillations of speech processing and language comprehension: state of the art and emerging mechanisms

• Published in: The European journal of neuroscience 2018-10, Vol.48 (7), p.2609-2621
• Main Author: Meyer, Lars
• Format: Article
• Language: English
• Subjects: Animals; Auditory stimuli; chunking; Comprehension - physiology; Cortex; Electroencephalography - methods; Electrophysiology; entrainment; Excitability; Humans; Information processing; Language; Language Development; Linguistics; Listening comprehension; Mapping; memory; Oscillations; predictive coding; Semantics; Speech; Speech - physiology; Speech Perception - physiology
• ISSN: 0953-816X; 1460-9568
• DOI: 10.1111/ejn.13748

Neural oscillations subserve a broad range of functions in speech processing and language comprehension. On the one hand, speech contains—somewhat—repetitive trains of air pressure bursts that occur at three dominant amplitude modulation frequencies, physically marking the linguistically meaningful progressions of phonemes, syllables and intonational phrase boundaries. To these acoustic events, neural oscillations of isomorphous operating frequencies are thought to synchronise, presumably resulting in an implicit temporal alignment of periods of neural excitability to linguistically meaningful spectral information on the three low‐level linguistic description levels. On the other hand, speech is a carrier signal that codes for high‐level linguistic meaning, such as syntactic structure and semantic information—which cannot be read from stimulus acoustics, but must be acquired during language acquisition and decoded for language comprehension. Neural oscillations subserve the processing of both syntactic structure and semantic information. Here, I synthesise a mapping from each linguistic processing domain to a unique set of subserving oscillatory mechanisms—the mapping is plausible given the role ascribed to different oscillatory mechanisms in different subfunctions of cortical information processing and faithful to the underlying electrophysiology. In sum, the present article provides an accessible and extensive review of the functional mechanisms that neural oscillations subserve in speech processing and language comprehension. In speech processing, neural oscillations subserve the segmentation and identification of phonemes, syllables and intonational phrase boundaries (IPBs) by synchronization of three frequency bands to indicative acoustic cues; frequency bands couple through pairwise phase–amplitude coupling (PAC). In language comprehension, oscillations subserve the decoding of compositional and relational syntactic structure (delta‐, alpha‐ and theta‐band oscillations, respectively); in parallel, oscillations help the cumulative prediction of upcoming words and the accommodation of the interpretation by incoming words (beta and gamma bands, possibly coupled through PAC).