Language acquisition and speech rhythm patterns: an auditory neuroscience perspective

Abstract

All human infants acquire language, but their brains do not know which language/s to prepare for. This observation suggests that there are fundamental components of the speech signal that contribute to building a language system, and fundamental neural processing mechanisms that use these components, which are shared across languages. Equally, disorders of language acquisition are found across all languages, with the most prevalent being developmental language disorder (approx. 7% prevalence), where oral language comprehension and production is atypical, and developmental dyslexia (approx. 7% prevalence), where written language acquisition is atypical. Recent advances in auditory neuroscience, along with advances in modelling the speech signal from an amplitude modulation (AM, intensity or energy change) perspective, have increased our understanding of both language acquisition and these developmental disorders. Speech rhythm patterns turn out to be fundamental to both sensory and neural linguistic processing. The rhythmic routines typical of childcare in many cultures, the parental practice of singing lullabies to infants, and the ubiquitous presence of BabyTalk (infant-directed speech) all enhance the fundamental AM components that contribute to building a linguistic brain.

Atypical cortical encoding of speech identifies children with Dyslexia versus Developmental Language Disorder

“…We also demonstrate transfer-learning of EEG features for identification of children with dyslexia across different receptive speech tasks and different samples of children. Taken together, our data provide robust evidence for a temporal sampling deficit in two developmental disorders of language learning, dyslexia and DLD [10,45].…”

“…Further, we have shown that low-frequency oscillatory activity during speech listening can reliably classify children with dyslexia. These data suggest that mechanistic relationships between low frequency (i.e., delta and theta) oscillatory bands are fundamental to understanding the aetiology of dyslexia and DLD, as predicted by TS theory [10, 45]. The data also show the importance of studying children when trying to understand causal factors in developmental disorders of learning.…”

Infant low-frequency EEG cortical power, cortical tracking and phase-amplitude coupling predicts language a year later.

“…LFP centre frequencies were filtered from 2 to 8 Hz, in 1 Hz steps with a 2 Hz bandwidth, and HFA centre frequencies were filtered from 17.5 Hz to 42.5 Hz, in 5 Hz steps with a 5 Hz bandwidth before a normalised modulation index value was computed for each channel (19,42). The EEG bands were defined as delta (2-4 Hz), theta (4-8 Hz) beta (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) and gamma (30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45). The channel exhibiting the strongest nMI, within predefined phase and amplitude band groupings (delta/beta, delta/gamma, theta/beta, theta/gamma), was taken forward for further analysis.…”

“…The developmental theoretical framework encapsulated by TS theory informed Araujo et al's (27) modelling (Pre-print), and predicts that cortical tracking within specific low-frequency bands (i.e. delta, 1-4 Hz and theta, 4-8 Hz) and their interactive dynamics is central to language acquisition (4,28,29). In brief, if low-frequency cortical tracking and/or dynamic relations between frequency bands are atypical, then developmental trajectories for language may also be atypical.…”

Hierarchical amplitude modulation structures and rhythm patterns: Comparing Western musical genres, song, and nature sounds to Babytalk

“…TS theory now provides a systematic sensory/neural/cognitive framework for explaining childhood language disorders [27]. TS theory proposes that accurate sensory/neural processing of the amplitude envelope of speech is one foundation of language acquisition, and that impairments in discriminating key aspects of the envelope such as amplitude rise times at different temporal rates (which relate to speech rhythm) is one cause of developmental language disorders [28]. The amplitude envelope of any sound is the slower changes in AM (intensity or signal energy) that unfold over time.…”