Individual Differences in Infant Speech Segmentation: Achieving the Lexical Shift

Abstract

We report a large‐scale electrophysiological study of infant speech segmentation, in which over 100 English‐acquiring 9‐month‐olds were exposed to unfamiliar bisyllabic words embedded in sentences (e.g., He saw a wild eagle up there), after which their brain responses to either the just‐familiarized word (eagle) or a control word (coral) were recorded. When initial exposure occurs in continuous speech, as here, past studies have reported that even somewhat older infants do not reliably recognize target words, but that successful segmentation varies across children. Here, we both confirm and further uncover the nature of this variation. The segmentation response systematically varied across individuals and was related to their vocabulary development. About one‐third of the group showed a left‐frontally located relative negativity in response to familiar versus control targets, which has previously been described as a mature response. Another third showed a similarly located positive‐going reaction (a previously described immature response), and the remaining third formed an intermediate grouping that was primarily characterized by an initial response delay. A fine‐grained group‐level analysis suggested that a developmental shift to a lexical mode of processing occurs toward the end of the first year, with variation across individual infants in the exact timing of this shift.

Individual differences in lexical processing efficiency and vocabulary in toddlers: A longitudinal investigation

“…Data came from a cohort of children who are being followed as part of a larger longitudinal project that is tracking the interaction between language processing and language development from 9 months to 5 years (see Kidd, Junge, Spokes, Morrison, & Cutler, (2018)). Families were recruited from a medium-sized city in Australia.…”

“…However, young infants already have fairly detailed phonological representations. For instance, Swingley and Aslin (2002) showed that infants as young as 15 months are sensitive to initial-consonant mispronunciations of words, and recent work by Kidd, Junge, Spokes, Morrison, and Cutler (2018) showed that some 9month-old infants can rapidly create and access memories for newly presented words (for a review of early lexical knowledge, see Johnson, 2016). Thus, other forces are likely to be at play.…”

Infants Segment Words from Songs—An EEG Study

“…Word segmentation is also important in developing the language-ready brain, with word segmentation skills in infancy predicting language ability in the toddler years [6,[66][67][68][69][70], although possibly not beyond [70]. Although the group-level effects of word segmentation are not always replicated [71,72], which is a topic that we will return to in the discussion, infants' ability to segment words from continuous speech is well established (see [73] for a meta-analysis). In the present study, we ask whether songs provide one source of information in infants' input from which they could segment words and start building their lexicon.…”

“…The difference in ERP response to familiarized target and novel control words after song familiarization would index infants' ability to transfer words that are segmented from song to recognition in speech. ERP responses to familiarized compared to novel words are generally largest over left-frontal electrode sites, and can be either positive-or negative-going, with a negativity being considered a more mature response (see review and discussion by [71,83]). The polarity of infants' ERP familiarity response partly depends on stimulus difficulty, with 7-month-olds displaying positive-going responses to words embedded in speech after having negative-going responses to those same words presented in isolation [69].…”

“…The polarity of the response to stimuli of the same difficulty also changes developmentally, shifting from a positive-going response typically displayed by 6-month-olds to-7-month-olds [69,83] to a negative-going response after 8 months of age [67,79,83,88,92,93]. However, group effects in polarity are not consistently observed across studies due to large individual differences within age bands [71]. This variation between infants appears to be significant to early language development, as the negative responders have more robust neural segmentation responses across various stages of the procedure [70,93], better concurrent vocabulary size [71,93], better and faster vocabulary development into toddlerhood [67,69,93], and better general language skills [69].…”