Language Experience Impacts Brain Activation for Spoken and Signed Language in Infancy: Insights From Unimodal and Bimodal Bilinguals

Abstract

Recent neuroimaging studies suggest that monolingual infants activate a left-lateralized frontotemporal brain network in response to spoken language, which is similar to the network involved in processing spoken and signed language in adulthood. However, it is unclear how brain activation to language is influenced by early experience in infancy. To address this question, we present functional near-infrared spectroscopy (fNIRS) data from 60 hearing infants (4 to 8 months of age): 19 monolingual infants exposed to English, 20 unimodal bilingual infants exposed to two spoken languages, and 21 bimodal bilingual infants exposed to English and British Sign Language (BSL). Across all infants, spoken language elicited activation in a bilateral brain network including the inferior frontal and posterior temporal areas, whereas sign language elicited activation in the right temporoparietal area. A significant difference in brain lateralization was observed between groups. Activation in the posterior temporal region was not lateralized in monolinguals and bimodal bilinguals, but right lateralized in response to both language modalities in unimodal bilinguals. This suggests that the experience of two spoken languages influences brain activation for sign language when experienced for the first time. Multivariate pattern analyses (MVPAs) could classify distributed patterns of activation within the left hemisphere for spoken and signed language in monolinguals (proportion correct = 0.68; p = 0.039) but not in unimodal or bimodal bilinguals. These results suggest that bilingual experience in infancy influences brain activation for language and that unimodal bilingual experience has greater impact on early brain lateralization than bimodal bilingual experience.

Group-level cortical functional connectivity patterns using fNIRS: assessing the effect of bilingualism in young infants

“… 2 – 4 , 8 , 10 Bilingualism has been only shown to modulate RSFC in adult participants thus far, 29 – 31 and evidence of differences between monolingual and bilingual infants in previous neuroimaging studies manifested during explicit language tasks only. 8 – 13 It is, therefore, a possibility that, if differences between monolinguals and bilinguals exist at this age, they might only be observable during the performance of specific linguistic tasks. Further research with monolingual and bilingual infants at different ages should also help clarify if the differences observed in adults’ functional connectivity might only emerge at a later stage in neural development.…”

“… 30 , 31 Studying RSFC in monolingual and bilingual infants can elucidate the extent to which a long-term environmental factor such as early bilingual experience might lead to specific adaptations in the intrinsic properties of different functional brain systems, while avoiding potential confounds due to task interference. Based on previous task-based studies with similar age groups 8 – 10 and considering the spatial resolution and coverage of our fNIRS setup, differences in functional connectivity are expected to emerge over brain regions overlapping the auditory and the language networks with bilinguals showing stronger interhemispheric connectivity in these networks. Tentatively, bilinguals might also show a stronger functional connectivity in networks involving frontal regions.…”

“… 9 In a cohort of 4- to 8-month-old infants, Mercure et al. 10 showed that brain activation responses to spoken and signed language showed no lateralization effects in monolingual and bimodal bilingual infants. However, unimodal bilingual infants’ brain responses were right lateralized over posterior temporal regions for both conditions.…”

Comparing different pre-processing routines for infant fNIRS data

“…A conceptually similar pre-processing approach has been employed, with variations in specific settings, in Lloyd-Fox et al (2017) ; Mercure et al (2020) and Van Der Kant et al (2020) .…”

Inferior parietal lobule is sensitive to different semantic similarity relations for concrete and abstract words

“…Recently, this analytical approach has been successfully extended to the analysis of fNIRS data (Emberson et al., 2017; Zinszer et al., 2017). In particular, MVPA has been used in fNIRS studies for different purposes, such as to discriminate children with attention‐deficit/hyperactivity disorder from healthy controls during a working memory task (Gu et al., 2018), to decode visual and auditory stimuli in infants (Emberson et al., 2017), or to classify activation patterns associated with spoken and signed language in monolinguals (Mercure et al., 2020). To date, Zinszer and colleagues’ study (2017) is the only one that investigated whether semantic representations are encoded in fNIRS neuroimaging data in a semantic task.…”