Cortical tracking of speech in noise accounts for reading strategies in children

Abstract

Humans’ propensity to acquire literacy relates to several factors, among which, the ability to understand speech in noise (SiN). Still, the nature of the relation between reading and SiN perception abilities remains poorly understood. Here, we dissect the interplay between (i) reading abilities, (ii) classical behavioral predictors of reading (phonological awareness, phonological memory and lexical access), and (iii) electrophysiological markers of SiN perception in 99 elementary school children (26 with dyslexia). We demonstrate that cortical representation of phrasal content of SiN relates to the development of the lexical (but not sublexical) reading strategy. In contrast, classical behavioral predictors of reading abilities and the ability to benefit from visual speech to represent the syllabic content of SiN account for global reading performance (i.e., speed and accuracy of lexical and sublexical reading). Finally, we found that individuals with dyslexia properly integrate visual speech information to optimize processing of syntactic information, but not to sustain acoustic/phonemic processing. These results clarify the nature of the relation between SiN perception and reading abilities in typical and dyslexic child readers, and identified novel electrophysiological markers of emergent literacy.

Neurodevelopmental oscillatory basis of speech processing in noise

“…Each video featured 9 conditions: 1 noiseless and 8 SiN with 3 dB signal-to-noise ratio (SNR; for the motivation behind this SNR selection, see Stimuli subsection in Materials and Methods) resulting from the combination of 4 types of noises (least-energetic non-speech, most-energetic non-speech, different-gender babble and same-gender babble) with 2 visual conditions (with or without visual speech inputs). The different-and same-gender babble noises introduced informational interferences and a similar degree of energetic masking (32). Their distinction is however relevant since speech intelligibility is generally better when attended and interfering speech are uttered by differentgender talkers compared to same-gender talkers (51,52), because on average, voice fundamental frequency and vocal tract length differ between males and females (52,53).…”

“…We first evaluated with an ANOVA whether phrasal and syllabic normalized CTS (nCTS) in noise conditions depend on noise properties, hemisphere, visibility of the talker's lips and whether they evolve with age. The nCTS is a contrast between CTS in SiN and noiseless conditions (see Methods) that takes values between -1 and 1, with negative values indicating that the noise reduces CTS (32). Such contrast presents the advantage of being specific to SiN processing abilities by factoring out the global level of CTS in the noiseless condition.…”

“…The stimuli were derived from 12 audiovisual recordings of 4 native French-speaking narrators (2 females, 3 recordings per narrator) telling a story for ~6-min (mean ± SD, 6.0 ± 0.8 min) Stories consisted of children's fairy tales; for more details, see our previous report (32). In each video, the first 5 s were kept unaltered to enable participants to unambiguously identify the narrator's voice and face they were requested to attend to.…”

“…In SiN conditions, children's and adults' cortical activity preferentially tracks the attended speech rather than the global sound (4,6,10,31), suggesting that CTS is modulated by endogenous attentional components and plays a role in segregating the attended linguistic signal (5-8, 10, 12, 13). However, the fidelity of the tracking decreases with increasing noise intensity in adults and more so in children (4)(5)(6), especially when the noise is concurrent speech babble (32) as opposed to non-speech noise such as white or spectrally-matched noise. Of note, the visual speech signal (comprising the articulatory movements of a talker) boosts CTS in adults (33)(34)(35), especially in noise conditions (31,36,37), and in children, at least in babble noise conditions (32).…”

“…However, the fidelity of the tracking decreases with increasing noise intensity in adults and more so in children (4)(5)(6), especially when the noise is concurrent speech babble (32) as opposed to non-speech noise such as white or spectrally-matched noise. Of note, the visual speech signal (comprising the articulatory movements of a talker) boosts CTS in adults (33)(34)(35), especially in noise conditions (31,36,37), and in children, at least in babble noise conditions (32). Importantly, the modulations of CTS we have just outlined mirror tangible behavioral effects.…”