Laura-Ann Petitto

The morphometry of auditory cortex in the congenitally deaf measured using MRI.

The study of congenitally deaf individuals provides a unique opportunity to understand the organization and potential for reorganization of human auditory cortex. We used magnetic resonance imaging (MRI) to examine the structural organization of two auditory cortical regions, Heschls gyrus (HG) and the planum temporale (PT), in deaf and hearing subjects. The results show preservation of cortical volume in HG and PT of deaf subjects deprived of auditory input since birth. Measurements of grey and white matter, as well as the location and extent of these regions in the deaf showed complete overlap both with matched controls and with previous samples of hearing subjects. The results of the manual volume measures were supported by findings from voxel-based morphometry analyses that showed increased grey-matter density in the left motor hand area of the deaf, but no differences between the groups in any auditory cortical region. This increased cortical density in motor cortex may be related to more active use of the dominant hand in signed languages. Most importantly, expected interhemispheric asymmetries in HG and PT thought to be related to auditory language processing were preserved in these deaf subjects. These findings suggest a strong genetic component in the development and maintenance of auditory cortical asymmetries that does not depend on auditory language experience. Preservation of cortical volume in the deaf suggests plasticity in the input and output of auditory cortex that could include language-specific or more general-purpose information from other sensory modalities.

Age of first bilingual language exposure as a new window into bilingual reading development

How does age of first bilingual language exposure affect reading development in children learning to read in both of their languages? Is there a reading advantage for monolingual English children who are educated in bilingual schools? We studied children (grades 2-3, ages 7-9) in bilingual Spanish-English schools who were either from Spanish-speaking homes (new to English) or English-speaking homes (new to Spanish), as compared with English-speaking children in monolingual English schools. An early age of first bilingual language exposure had a positive effect on reading, phonological awareness, and language competence in both languages: early bilinguals (age of first exposure 0-3 years) outperformed other bilingual groups (age of first exposure 3-6 years). Remarkably, schooling in two languages afforded children from monolingual English homes an advantage in phoneme awareness skills. Early bilingual exposure is best for dual language reading development, and it may afford such a powerful positive impact on reading and language development that it may possibly ameliorate the negative effect of low SES on literacy. Further, age of first bilingual exposure provides a new tool for evaluating whether a young bilingual has a reading problem versus whether he or she is a typically-developing dual-language learner.

The perception of handshapes in American Sign Language

Despite the constantly varying stream of sensory information that surrounds us, we humans can discern the small building blocks of words that constitute language (phonetic forms) and perceive them categorically (categorical perception, CP). Decades of controversy have prevailed regarding what is at the heart of CP, with many arguing that it is due to domain-general perceptual processing and others that it is determined by the existence of domain-specific linguistic processing. What is most key: perceptual or linguistic patterns? Here, we study whether CP occurs withsoundless handshapes that are nonethelessphonetic in American Sign Language (ASL), in signers and nonsigners. Using innovative methods and analyses of identification and, crucially, discrimination tasks, we found that both groups separated the soundless handshapes into two classes perceptually but that only the ASL signers exhibited linguistic CP. These findings suggest that CP of linguistic stimuli is based on linguistic categorization, rather than on purely perceptual categorization.

New Insights Into Old Puzzles From Infants' Categorical Discrimination of Soundless Phonetic Units

For 4 decades, serious scientific debate has persisted as to whether infants remarkable capacity to detect and categorize phonetic units is derived from language-specific mechanisms or whether this capacity develops out of general perceptual mechanisms. The heart of this controversy has revolved around whether the young human brain is specialized to detect the underlying contrasting patterns in language or whether it simply processes general auditory perceptual features of sound that, over time, become utilized for language learning. This article takes a novel look at this question by using soundless phonetic units from a natural signed language as a new research tool. Research finds that 4-month-old hearing infants categorize soundless phonetic units on the basis of linguistic category membership, whereas 14-month-old infants fail to do so-thereby exhibiting the identical initial capacity and classic developmental shift in infant categorical discrimination of native and nonnative (foreign language) phonetic units in speech. These results suggest a novel testable hypothesis: Infants may begin life with the capacity to detect specific patterned units with alternating contrasts unique to natural language organization and to categorize them on the basis of linguistic category membership.

Anatomical Substrates of Visual and Auditory Miniature Second-language Learning

Longitudinal changes in brain activity during second language (L2) acquisition of a miniature finite-state grammar, named Wernickese, were identified with functional magnetic resonance imaging (fMRI). Participants learned either a visual sign language form or an auditory-verbal form to equivalent proficiency levels. Brain activity during sentence comprehension while hearing/viewing stimuli was assessed at low, medium, and high levels of proficiency in three separate fMRI sessions. Activation in the left inferior frontal gyrus (Brocas area) correlated positively with improving L2 proficiency, whereas activity in the right-hemisphere (RH) homologue was negatively correlated for both auditory and visual forms of the language. Activity in sequence learning areas including the premotor cortex and putamen also correlated with L2 proficiency. Modality-specific differences in the blood oxygenation level-dependent signal accompanying L2 acquisition were localized to the planum temporale (PT). Participants learning the auditory form exhibited decreasing reliance on bilateral PT sites across sessions. In the visual form, bilateral PT sites increased in activity between Session 1 and Session 2, then decreased in left PT activity from Session 2 to Session 3. Comparison of L2 laterality (as compared to L1 laterality) in auditory and visual groups failed to demonstrate greater RH lateralization for the visual versus auditory L2. These data establish a common role for Brocas area in language acquisition irrespective of the perceptual form of the language and suggest that L2s are processed similar to first languages even when learned after the critical period. The right frontal cortex was not preferentially recruited by visual language after accounting for phonetic/structural complexity and performance.

“One glove does not fit all” in bilingual reading acquisition: Using the age of first bilingual language exposure to understand optimal contexts for reading success

Abstract In teaching reading, educators strive to find the balance between a code-emphasis approach and a meaning-oriented literacy approach. However, little is known about how different approaches to literacy can benefit bilingual children’s early reading acquisition. To investigate the novel hypothesis that children’s age of first bilingual exposure can interact with different approaches to literacy, we tested 56 Spanish-English bilingual children (ages 7–9), with birth exposure to Spanish and either early (before age 3) or late (3–4) age of first bilingual exposure to English. The children attended reading programs identified with either phonics or whole language emphasis. Consistent with our hypothesis, differential outcomes were linked to different ages of first bilingual exposure. Early bilingual exposure to English was associated with more advanced reading abilities under whole language emphasis, while later (ages 3–4) exposure was associated with better decoding and reading abilities under phonics emphasis. The findings show that knowing the age of a child’s first bilingual language exposure, as it corresponds to different periods in child development, may contribute to an educator’s design of reading instruction that best accommodates young bilingual learners.

Bilingualism yields language-specific plasticity in left hemisphere's circuitry for learning to read in young children

&NA; How does bilingual exposure impact childrens neural circuitry for learning to read? Theories of bilingualism suggests that exposure to two languages may yield a functional and neuroanatomical adaptation to support the learning of two languages (Klein et al., 2014). To test the hypothesis that this neural adaptation may vary as a function of structural and orthographic characteristics of bilinguals two languages, we compared Spanish‐English and French‐English bilingual children, and English monolingual children, using functional Near Infrared Spectroscopy neuroimaging (fNIRS, ages 6–10, N =26). Spanish offers consistent sound‐to‐print correspondences (“phonologically transparent” or “shallow”); such correspondences are more opaque in French and even more opaque in English (which has both transparent and “phonologically opaque” or “deep” correspondences). Consistent with our hypothesis, both French‐ and Spanish‐English bilinguals showed hyperactivation in left posterior temporal regions associated with direct sound‐to‐print phonological analyses and hypoactivation in left frontal regions associated with assembled phonology analyses. Spanish, but not French, bilinguals showed a similar effect when reading Irregular words. The findings inform theories of bilingual and cross‐linguistic literacy acquisition by suggesting that structural characteristics of bilinguals two languages and their orthographies have a significant impact on childrens neuro‐cognitive architecture for learning to read. HighlightsWhat is the impact of bilingualism on childrens emergent brain bases for reading?French‐English, Spanish‐English, and English speakers read words during neuroimaging.Bilinguals showed orthography‐specific plasticity in English in left STG and IFG.