The “Perceptual Wedge Hypothesis” as the basis for bilingual babies’ phonetic processing advantage: New insights from fNIRS brain imaging

Abstract

In a neuroimaging study focusing on young bilinguals, we explored the brains of bilingual and monolingual babies across two age groups (younger 4–6 months, older 10–12 months), using fNIRS in a new event-related design, as babies processed linguistic phonetic (Native English, Non-Native Hindi) and nonlinguistic Tone stimuli. We found that phonetic processing in bilingual and monolingual babies is accomplished with the same language-specific brain areas classically observed in adults, including the left superior temporal gyrus (associated with phonetic processing) and the left inferior frontal cortex (associated with the search and retrieval of information about meanings, and syntactic and phonological patterning), with intriguing developmental timing differences: left superior temporal gyrus activation was observed early and remained stably active over time, while left inferior frontal cortex showed greater increase in neural activation in older babies notably at the precise age when babies’ enter the universal first-word milestone, thus revealing a first-time focal brain correlate that may mediate a universal behavioral milestone in early human language acquisition. A difference was observed in the older bilingual babies’ resilient neural and behavioral sensitivity to Non-Native phonetic contrasts at a time when monolingual babies can no longer make such discriminations. We advance the “Perceptual Wedge Hypothesis”as one possible explanation for how exposure to greater than one language may alter neural and language processing in ways that we suggest are advantageous to language users. The brains of bilinguals and multilinguals may provide the most powerful window into the full neural “extent and variability” that our human species’ language processing brain areas could potentially achieve.

Bilingualism and increased attention to speech: Evidence from event-related potentials

“…This process seems to develop similarly for monolingually and bilingually raised children (Burns, Yoshida, Hill, & Werker, 2007), although bilingual children sometimes show inconsistent patterns of phoneme discrimination (Bosch & Sebastian-Galles, 2003) with these skills being proportional to their exposure to each of their languages (Garcia-Sierra et al, 2011). Surprisingly, this differential development of the bilingual auditory cortex has been associated with increased language processing ability rather than an impoverished one (Petitto et al, 2012).…”

Espectroscopia de luz próxima ao infravermelho e processamento sensorial auditivo em lactentes

“…The studies that used vocal sounds and other stimuli have investigated brain hemodynamic responses to evaluate the perceptual processing during the exposure to audiovisual stimuli 18 ; brain lateralization for speech sounds and non-vocal sounds (native and non-native speech, human onomatopoeia and monkey sounds) 10 ; processing of vocal and prosodic specificity 19 ; ability of the newborn to memorize words 6 ; processing for linguistic and non-linguistic sounds in bilingual and monolingual children 20 . These studies showed important results, including the usefulness of the NIRS technology as a tool to monitor the hemodynamic activity in children, an activity that was found in greater proportion in the left temporal region in response to audiovisual stimuli compared only with visual stimulus 18 ; greater lateralization in the left temporal region for the speech processing in comparison to non-vocal sounds 10 .…”

The Effect of Prenatal Auditory Enrichment on Perceptual Narrowing in Bobwhite Quail Neonates

“…The increased variability the infant experiences in the perinatal environment prolongs malleability, keeping the perceptual narrowing window "open" significantly later in development. Petitto et al, (2012) named this phenomenon the "perceptual wedge", wherein multiple languages figuratively hold open the perceptual window. Therefore, auditory enrichment not only prevents a preference from forming between the stimuli provided, but also generalizes to include differential response to novelty.…”

“…The differences in perceptual narrowing of bilingual infants may also cascade into perceptual and cognitive advantages into adulthood (Werker, 2012); if the environment maintains the broadened perceptual narrowing window through consistently providing this increased variation. Petitto et al (2012) looked at bilingual infants' brain response to non-native phoneme contrasts across age groups that typically corresponded to milestones in perceptual narrowing (4-6 and 10-12 months). Using fNIRS imaging, Petitto et al, (2012) found that bilingual infants showed neural response indicative of phoneme distinctions for a novel language much up through 10-12 months, wherein monolingual infants fail to make such a response.…”

“…Petitto et al (2012) looked at bilingual infants' brain response to non-native phoneme contrasts across age groups that typically corresponded to milestones in perceptual narrowing (4-6 and 10-12 months). Using fNIRS imaging, Petitto et al, (2012) found that bilingual infants showed neural response indicative of phoneme distinctions for a novel language much up through 10-12 months, wherein monolingual infants fail to make such a response. The authors suggest that infants that coacquire multiple first languages have altered neurological and behavioral language processing that is advantageous when confronted with novelty later in development.…”