Abstract
Word learning is a significant milestone in language acquisition. The second year of life marks a period of dramatic advances in infants’ expressive and receptive word-processing abilities. Studies show that in adulthood, language processing is left-hemisphere dominant. However, adults learning a second language activate right-hemisphere brain functions. In infancy, acquisition of a first language involves recruitment of bilateral brain networks, and strong left-hemisphere dominance emerges by the third year. In the current study we focus on 14-month-old infants in the earliest stages of word learning using infant magnetoencephalography (MEG) brain imagining to characterize neural activity in response to familiar and unfamiliar words. Specifically, we examine the relationship between right-hemisphere brain responses and prospective measures of vocabulary growth. As expected, MEG source modeling revealed a broadly distributed network in frontal, temporal and parietal cortex that distinguished word classes between 150–900 ms after word onset. Importantly, brain activity in the right frontal cortex in response to familiar words was highly correlated with vocabulary growth at 18, 21, 24, and 27 months. Specifically, higher activation to familiar words in the 150–300 ms interval was associated with faster vocabulary growth, reflecting processing efficiency, whereas higher activation to familiar words in the 600–900 ms interval was associated with slower vocabulary growth, reflecting cognitive effort. These findings inform research and theory on the involvement of right frontal cortex in specific cognitive processes and individual differences related to attention that may play an important role in the development of left-lateralized word processing.
Highlights
Acquiring a native language appears deceptively simple
What perceptual and attentional constraints “tune” infants to the critical components of their native language, and thereby promote efficient learning? In the current study, we focus on the right hemisphere areas that control attentional capac ities and examine the role that activation in these brain areas in response to words plays in children’s initial language learning, and how these brain measures reflecting initial learning predict later language out comes in young children
As shown in the figure, these windows captured most of the magnitude differences between familiar and unfamiliar words and is consistent with measurement windows used in previous event-related potentials (ERPs) studies (Mills et al, 1997; Mills et al, 1993; Conboy and Mills, 2006)
Summary
Acquiring a native language appears deceptively simple. Infants master complex details of its phonological, lexical, and syntactic prop erties by the age of 3 years, following the same developmental path regardless of culture (for reviews, see [Kuhl et al, 2008; Saffran et al, 2006]). Research over the last several decades has provided information about how infants achieve this task (Saffran et al, 2006; Kuhl, 2010), yet our understanding about the brain mechanisms that underlie language learning is far from complete. What these studies show is that children acquire language rapidly, exploiting the statistical and distributional patterns in environmental language input to learn (Kuhl et al, 2008; Goodsitt et al, 1993; Grieser and Kuhl, 1989; Saffran et al, 1996; Maye et al, 2002; Bosseler et al, 2014; Teinonen et al, 2009) and that con straints on perceptual and learning processes related to attention, especially those elicited through social interaction (Conboy and Kuhl, 2011; Kuhl et al, 2003), are critical to this process. Understanding language development poses a major scientific challenge that requires a description of the neural circuits that underlie the eventual lefthemisphere specialization observed in most adults, and the brain mechanisms that are involved in and foster the initial phases of learning
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