Early Development of Neural Speech Encoding Depends on Age but Not Native Language Status: Evidence From Lexical Tone

Abstract

We investigated the development of early-latency and long-latency brain responses to native and non-native speech to shed light on the neurophysiological underpinnings of perceptual narrowing and early language development. Specifically, we postulated a two-level process to explain the decrease in sensitivity to non-native phonemes towards the end of infancy. Neurons at the earlier stages of the ascending auditory pathway mature rapidly during infancy facilitating the encoding of both native and non-native sounds. This growth enables neurons at the later stages of the auditory pathway to assign phonological status to speech according to the infant’s native language environment. To test this hypothesis, we collected early- latency and long-latency neural responses to native and non-native lexical tones from 85 Cantoneselearning children aged between 23 days and 24 months and 16 days. As expected, a broad range of presumably subcortical early-latency neural encoding measures grew rapidly and substantially during the first two years for both native and non-native tones. By contrast, longlatency cortical electrophysiological changes occurred on a much slower scale and showed sensitivity to nativeness at around six months. Our study provided a comprehensive understanding of early language development by revealing the complementary roles of earlier and later stages of speech processing in the developing brain.

The effect of tone hyperarticulation in Cantonese infant-directed speech on toddlers’ word recognition in the second year of life

“…Therefore, the participants’ performance might be particularly influenced by their sensitivity to the suprasegmental component, that is, lexical tones. Neural research has shown that Cantonese-learning children’s tone encoding without lexical context keeps improving during the ages of our interest (Novitskiy et al, 2022); unfortunately, it cannot be determined whether their sensitivity in encoding tone variation in lexical processing develops between the two ages that we tested. For the older age group, as elaborated above, Ma et al (2017) reported that 2-year-old Mandarin-learning monolinguals showed good sensitivity to tone variation in novel word recognition as they did to vowel variation.…”

Language experience during the sensitive period narrows infants’ sensory encoding of lexical tones—Music intervention reverses it

“…These results complement existing literature on adults and older children with vastly different early experiences (e.g., linguistic background, music training background) demonstrating differences in early sensory encoding ( Wong et al, 2007 ; Kraus et al, 2014 ; Zhao and Kuhl, 2018 ), and suggest that these experiential effects may start accumulating during infancy. However, it is also important to note that the auditory system is also undergoing rapid maturation process during this period ( Anderson et al, 2015 ; Novitskiy et al, 2021 ), and it is important for future research to disentangle the interaction between maturation and speech learning at the sensory encoding stage, by implementing additional conditions including native and non-native speech as well as non-speech stimuli.…”

“…In neonates, pitch tracking quality in FFR for lexical tones was observed to be distinct between infants born in China as compared to infants born the United States ( Jeng et al, 2011 , 2013 ). In older infants, enhancement have been documented for some aspects of FFR to native speech sounds, presumably reflecting developmental maturation of the auditory system ( Anderson et al, 2015 ; Skoe et al, 2015 ; Musacchia et al, 2018 ; Novitskiy et al, 2021 ). No study that we are aware of has focused on the FFR during the sensitive period using longitudinal comparisons of infants with experimentally manipulated experiences to address this theoretical question.…”

Language experience during the sensitive period narrows infants’ sensory encoding of lexical tone----music intervention reverses it

“…These results complement existing literature on adults and older children with vastly different early experiences (e.g., linguistic background, music training background) demonstrating differences in early sensory encoding (Wong et al, 2007;Kraus et al, 2014;Zhao and Kuhl, 2018), and suggest that these experiential effects may start accumulating during infancy. However, it is also important to note that the auditory system is also undergoing rapid maturation process during this period (Anderson et al, 2015;Novitskiy et al, 2021), and it is important for future research to disentangle the interaction between maturation and speech learning at the sensory encoding stage, by implementing additional conditions including native and non-native speech as well as non-speech stimuli.…”

“…In neonates, pitch tracking quality in FFR for lexical tones was observed to be distinct between infants born in China as compared to infants born the United States (Jeng et al, 2011(Jeng et al, , 2013. In older infants, enhancement have been documented for some aspects of FFR to native speech sounds, presumably reflecting developmental maturation of the auditory system (Anderson et al, 2015;Skoe et al, 2015;Musacchia et al, 2018;Novitskiy et al, 2021). No study that we are aware of has focused on the FFR during the sensitive period using longitudinal comparisons of infants with experimentally manipulated experiences to address this theoretical question.…”