Auditory-neurophysiological responses to speech during early childhood: Effects of background noise

Abstract

Early childhood is a critical period of auditory learning, during which children are constantly mapping sounds to meaning. But learning rarely occurs under ideal listening conditions—children are forced to listen against a relentless din. This background noise degrades the neural coding of these critical sounds, in turn interfering with auditory learning. Despite the importance of robust and reliable auditory processing during early childhood, little is known about the neurophysiology underlying speech processing in children so young. To better understand the physiological constraints these adverse listening scenarios impose on speech sound coding during early childhood, auditory-neurophysiological responses were elicited to a consonant-vowel syllable in quiet and background noise in a cohort of typically-developing preschoolers (ages 3–5 yr). Overall, responses were degraded in noise: they were smaller, less stable across trials, slower, and there was poorer coding of spectral content and the temporal envelope. These effects were exacerbated in response to the consonant transition relative to the vowel, suggesting that the neural coding of spectrotemporally-dynamic speech features is more tenuous in noise than the coding of static features—even in children this young. Neural coding of speech temporal fine structure, however, was more resilient to the addition of background noise than coding of temporal envelope information. Taken together, these results demonstrate that noise places a neurophysiological constraint on speech processing during early childhood by causing a breakdown in neural processing of speech acoustics. These results may explain why some listeners have inordinate difficulties understanding speech in noise. Speech-elicited auditory-neurophysiological responses offer objective insight into listening skills during early childhood by reflecting the integrity of neural coding in quiet and noise; this paper documents typical response properties in this age group. These normative metrics may be useful clinically to evaluate auditory processing difficulties during early childhood.

Relative contribution of envelope and fine structure to the subcortical encoding of noise-degraded speech

“…However, it remains possible that stimuli with more dynamically changing F0 than those used here would have produced stronger noise-related changes in pitch coding. 23 In speech perception, F0 provides a correlate of voice pitch, a robust cue for stream segregation, and identifying the number of sources in complex auditory scenes. 24 Lower susceptibility of FFR F0 to noise is consistent with the notion that pitch remains a robust cue for segregating target speech from a sound mixture despite substantial signal degradation.…”

Unraveling the Biology of Auditory Learning: A Cognitive–Sensorimotor–Reward Framework

“…In this regard, the ability to recognize speech in noise may reflect overall brain health. FFR properties are linked to these listening challenges, suggesting that it may be an approach to uncover individual differences in listening abilities and their responses to intervention [96–100], thereby providing a biological indication of brain health. FFR is agnostic to a subject's age and species: the same protocols have been used as early as infancy [101], across the lifespan [102], and in animal models [103], providing granularity and uniformity to the study of sound processing.…”

Neural encoding of voice pitch and formant structure at birth as revealed by frequency-following responses

“…The potential of the FFR as a biomarker for auditory deficits and their relation to literacy skills has thus been proposed 11 , 15 , 37 – 41 . However, most developmental studies on the FFR targeted babies of several months of age (e.g., 42 – 44 ), toddlers, infants or years-old children (e.g., 37 , 40 , 44 – 49 ), with only a few published reports on newborns 8 – 13 , 50 . Thus, knowledge about the expected speech perceptual skills in newborns, who are more vulnerable than older age groups to hearing damage 3 , 15 , may aid the early detection of language impairments and guide appropriate interventions benefitting from the massive neural plasticity during the first years of life 47 , 51 – 54 .…”