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

Abstract

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.

Individual Differences in Infant Speech Segmentation: Achieving the Lexical Shift

“…Interestingly, gamma oscillations are thought to reflect the active maintenance of object representations in memory in infants (Kaufman, Csibra, & Johnson, ) and have been linked in adults to both attention (Müller, Gruber, & Keil, ; Ray, Niebur, Hsaio, Sinai, & Crone, ) and language (e.g., Pulvermüller et al., ). Specifically, the gamma range is likely to be implicated in the important early building blocks of linguistic representations—phonemic perception (Meyer, ). Clearly more than an ability to discriminate between phonemes is required to successfully segment continuous speech, which requires the infant to identify syllables and the relationships between them.…”

The power of neural oscillations to inform sentence comprehension: A linguistic perspective

“…Both alpha and delta oscillations are less well studied in sentence comprehension, but an early proposal suggested that alpha may have a task‐specific working memory function (Bastiaansen & Hagoort, ). A recent proposal makes this idea more concrete by claiming that during sentence comprehension, alpha plays a key role in the inhibition of competing or task‐irrelevant information in short‐term memory (Meyer, ). These ideas are compatible with the more general role of alpha in working memory mentioned earlier.…”

“…These ideas are compatible with the more general role of alpha in working memory mentioned earlier. Finally, Meyer () also discusses a role for delta oscillations in chunking information into phrasal units during sentence comprehension with this chunking being driven by intonational phrase boundaries early in development and with a gradual switch to reliance on internal constraints generated by developing knowledge of linguistic structure (see Meyer, , for a more comprehensive discussion of how to reconcile delta entrainment to bottom‐up information available in speech with its sensitivity to abstract syntactic structure).…”

“…Nevertheless, oscillatory analyses are still far from mainstream in psycholinguistics research, and many consider such analyses somewhat opaque. One reason for this caution on the part of psycholinguists may be that in the past this literature has been pitched from the perspective of the neural oscillations: studies have typically been grouped according to the frequency band(s) of observed oscillatory modulations, and linguistic and/or other cognitive functions have been assigned to those frequency‐specific oscillations (e.g., Bastiaansen & Hagoort, ; Lewis et al, ; Meyer, ; Weiss & Mueller, ).…”

“…Relatively recent work showing that "entrainment" between speech input and oscillatory signatures in auditory cortices is important for comprehension (e.g., Doelling, Arnal, Ghitza, & Poeppel, 2014;Luo & Poeppel, 2007;Peelle & Davis, 2012) has piqued psycholinguists' interest. The literature linking neural oscillations to comprehension at the sentence and discourse level has also been steadily gaining momentum (for review, see Meyer, 2017;Lewis, Wang, & Bastiaansen, 2015). Nevertheless, oscillatory analyses are still far from mainstream in psycholinguistics research, and many consider such analyses somewhat opaque.…”