5.7.2: Early Experience Shapes Brain Development- The Case of Language Input

The Case of Language Input

The first two years of life are marked by dramatic gains in language acquisition. The MacArthur-Bates Communicative Development Inventories (CDIs) are measurements of language development derived from caregiver reports. Figure \(\PageIndex{1}\) displays CDI data on the growth of expressive language abilities for toddlers between sixteen to thirty months of age. CDI percentile scores place individual children in relation to a large norming sample. Unfortunately, the original norming data for the American English CDI forms (Fenson et al., 2007) are not representative of the educational, racial, and ethnic distributions of the U.S. population. A norming sample that is biased toward more educated and otherwise advantaged families results in norms that are too high, and therefore, may over-classify late talkers. To address this limitation, new CDI norms have been drawn that represent a sample distribution that more closely resembles the demographic makeup in the U.S. (Marchman, Dale, & Fenson, 2023). As illustrated in Figure \(\PageIndex{1}\), the new norms generally show lower scores, especially for children who fall below the 90th percentile and who are older than 24 months of age. ^{[1] [2]}

Figure \(\PageIndex{1}\): y-axis is labeled "Words Produced" and ranges from 0 to 700 words. The x-axis is labeled "Age in months" and ranges from 16 to 30 months. Several lines on the graph, each representing different percentiles (10th, 25th, 50th, 75th, and 90th) in the vocabulary growth of children. Each line is associated with a percentile rank indicating the relative position of a child's vocabulary size compared to a normative sample of children. The lines slope upward, showing an increase in the number of words produced as children get older. The 50th percentile line, typically considered the median, is solid and thicker than the others. The lines for the 10th and 25th percentiles are below the 50th percentile, suggesting fewer words produced, while the lines for the 75th and 90th percentiles are above, indicating a greater number of words produced. The graph is a visual representation of the data from the study by Marchman et al., 2023, illustrating the typical vocabulary development in children from 16 to 30 months old. The trend is an overall increase in the number of words produced with age, and the different percentile lines show the variation in language acquisition among children.
Development Inventory: Words and Sentences form from Fenson et al. (2007; gray lines) and Marchman et al. (2023; dark lines). ^[3]

The large language growth illustrated in Figure \(\PageIndex{1}\) are supported in part by how much and the manner in which caregivers speak to children (Hart & Risley, 1995, Huttenlocher et al., 1991, Huttenlocher et al., 2010, Swanson et al., 2019, Zimmerman et al., 2009). Recent studies have emphasized that the quality of the language environment (e.g., vocabulary diversity, narrative language, joint attention, fluency, grammatical complexity, wh- question usage) is pivotal for supporting children’s productive language development (Hirsh-Pasek et al., 2015; Rowe, 2012; Vernon‐Feagans, Bratsch‐Hines, Reynolds, & Willoughby, 2019). ^[4]

One aspect of caregiver speech quality that has received attention is conversational turn taking between caregivers and infants (Ferjan Ramírez, Hippe, & Kuhl, 2021; Romeo et al., 2018a; Romeo et al., 2018b; Swanson et al., 2019; Tamis-LeMonda, Kuchirko, & Song, 2014). These back-and-forth communicative interchanges are thought to optimally support early language acquisition because they are time-sensitive (e.g., the caregiver responds quickly to an infant’s vocalizations) and often responsive (e.g., the caregiver talks about what the child is looking at).  ^[5]

In a randomized controlled study, when caregivers and children engaged in more turn-taking, it led to greater cortical thickening in the brain (Romeo et al., 2021). The link between turn-taking and brain development can even be seen in early infancy. When caregivers and infants engage in more conversational turns, as early as six months of age, infants show greater white matter myelination later, at two years of age (Huber et al., 2023). Additional research suggests that more frequent conversational turn-taking between infants and their caregivers results in greater functional connectivity in language-related brain networks (such as the auditory cortex and bilateral superior temporal gyrus) (King et al., 2021).

Definition: Auditory cortex

Part of the temporal lobe that primarily processes auditory information

Infant vocalizations, infant-directed speech input, and caregiver-infant conversational turns at fourteen months correlated with estimates of myelin density within the left arcuate fasciculus at twenty-six months and caregiver-infant conversational turns specifically, correlated with the left superior longitudinal fasciculus myelination at twenty-six months (Weiss et al., 2022). Figure \(\PageIndex{1}\) shows the left arcuate fasciculus white matter pathway and Figure \(\PageIndex{1}\) shows the left superior longitudinal fasciculus white matter pathway. ^[6]

Definition: Myelin

A fatty substance that makes the transmission of electrochemical signals more efficient

Definition: Infant-directed speech

A special form of language caregivers use with young children, typically characterized by a slow, melodic, high-pitched, and exaggerated cadence

Definition: Arcuate fasciculus

A white matter pathway involved in language and reading development

Figure \(\PageIndex{1}\): The left arcuate fasciculus white matter pathway through the center of the brain. ^[7]

Figure \(\PageIndex{1}\): The left superior longitudinal fasciculus white matter pathway in the upper front quadrant of the brain. ^[8]

 

The left arcuate fasciculus and the left superior longitudinal fasciculus are both involved in language and reading development. Measurements of the left arcuate fasciculus and the superior longitudinal fasciculus obtained shortly after birth have been shown to correlate with receptive and expressive language skills at two years of age (Girault et al., 2019; Salvan et al., 2017; Sket et al., 2019). Longitudinal studies that measured brain structure in children from the pre-reading stage throughout reading development demonstrate that throughout development the left arcuate fasciculus relates to phonological awareness skills that are essential for reading acquisition (Lebel & Beaulieu, 2009; Saygin et al., 2013; Van Der Auwera et al., 2021; Yeatman et al., 2011). ^[9]

Figure \(\PageIndex{1}\): Caregiver and infant engaging in a turn-taking interaction. ^[10]

 

This neuroscience research corroborates previous behavioral research linking greater caregiver language exposure and turn-taking to stronger developmental abilities. When caregivers engaged in more infant-directed speech and turn-taking during everyday interactions, toddlers showed greater myelination in important language-related white matter tracts (Fibla et al., 2023). Additionally, the literacy environments created for infants are related to their white matter development. Environments with more books and caregivers who engage in more shared reading were both related to greater white matter development (Turesky et al., 2022).

Language Deprivation in Deaf Children

Experiences of deaf children, born to hearing parents, who are not exposed to a fully-accessible language early in childhood presents an interesting look at how cases of language deprivation can negatively impact brain development. Unlike the extreme and rare social deprivation cases examined in the Bucharest project, language deprivation for deaf children is much more common and continues today. Language deprivation in deaf children persists partly because over 90-95% of deaf children are born to hearing parents who do not know sign language (Mitchell & Karchmer, 2004; 2005). Even with state-of-the-art hearing technology and language interventions, the majority of deaf children, for a variety of reasons, do not reach age-expected spoken language proficiency milestones (Ching et al., 2017; Dettman et al., 2016, 2021; Gagnon, Eskridge, Brown, & Park, 2021; Ganek, Robbins, & Niparko, 2012; Geers et al., 2017; Niparko et al., 2010; Peterson, Pisoni, & Miyamoto, 2010; Sosa & Bunta, 2019; Szagun & Schramm, 2016; Wie, 2010; Yoshinaga-Itano, Sedey, Wiggin, & Mason, 2018). ^[11]

Language deprivation in deaf children has life-long consequences for cognitive, social, linguistic, and mental health (Cheng, Roth, Halgren, & Mayberry, 2019; Corina, Hafer, & Welch, 2014; Corina et al., 2020; Glickman & Hall, 2018; Hall, Hall, & Caselli, 2019; Henner, Caldwell-Harris, Novogrodsky, & Hoffmeister, 2016; Holcomb, Dostal, & Wolbers, 2023; Kushalnagar et al., 2020; Lieberman, Borovsky, Hatrak, & Mayberry, 2015; Mayberry & Eichen, 1991). Language deprivation in deaf children also has long-term consequences for brain development (Cheng et al., 2023). Figure \(\PageIndex{1}\) presents a data visualization of how early language deprivation is related to brain development. At the top of the figure are the two brain hemispheres with color showing the areas of interest: blue is for the somatomotor brain regions and red is for the language-related regions. The left chart shows the negative correlation between cortical volume (left and right hemispheres) and age of sign language exposure: the greater the language deprivation (later sign language exposure), the less cortical volume. The chart on the right shows the negative correlation between cortical thickness (left and right hemispheres) and age of sign language exposure: the greater the language deprivation (later sign language exposure), the less cortical thickness. These effects were not found in Deaf native signers exposed to sign language from birth.

Figure \(\PageIndex{1}\): Age of sign language exposure effects on cortical volume and cortical thickness. Accessible table of data in image.^[12]

​​Unlike deaf children born and raised in hearing families, Deaf children born into deaf families acquire a sign language natively as their first language, and their language acquisition follows the same time course as spoken language, from manual babbling to first signs to two-word utterances and syntactic development (Lillo-Martin & Henner, 2021). ^[13]

To help prevent the negative consequences of language deprivation, caregivers can provide deaf infants and toddlers with a fully-accessible language, such as a sign language (along with a spoken language, if desired) (Humphries et al., 2022). When deaf children with hearing parents are exposed to sign language from an early age, they show age-appropriate language development similar to the pattern and rate of growth of Deaf native signing children (Allen & Morere, 2020; Berger et al., 2023; Caselli, Pyers & Lieberman, 2021; Pontecorvo et al., 2023).

Attributions:

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• ^[1]  Estrada et al., (2023). Language exposure during infancy is negatively associated with white matter microstructure in the arcuate fasciculus. Developmental Cognitive Neuroscience, 61, 101240. CC by 4.0
• ^[2] Marchman & Dale (2023). The MacArthur-Bates Communicative Development Inventories: updates from the CDI Advisory Board. Frontiers in Psychology, 14, 1170303. CC-BY
• ^[3] Image adapted from Marchman & Dale (2023). The MacArthur-Bates Communicative Development Inventories: Updates from the CDI Advisory Board. Frontiers in Psychology, 14, 1170303. CC-BY
• ^[4] Estrada et al., (2023). Language exposure during infancy is negatively associated with white matter microstructure in the arcuate fasciculus. Developmental Cognitive Neuroscience, 61, 101240. CC by 4.0
• ^[5]  Estrada et al., (2023). Language exposure during infancy is negatively associated with white matter microstructure in the arcuate fasciculus. Developmental Cognitive Neuroscience, 61, 101240. CC by 4.0
• ^[6]  Weiss et al., (2022). Language input in late infancy scaffolds emergent literacy skills and predicts reading related white matter development. Frontiers in Human Neuroscience, 16, 922552. CC-BY
• ^[7] Image from Weiss et al., (2022). Language input in late infancy scaffolds emergent literacy skills and predicts reading related white matter development. Frontiers in Human Neuroscience, 16, 922552. CC-BY
• ^[8] Image from Weiss et al., (2022). Language input in late infancy scaffolds emergent literacy skills and predicts reading related white matter development. Frontiers in Human Neuroscience, 16, 922552. CC-BY
• ^[9] Weiss et al., (2022). Language input in late infancy scaffolds emergent literacy skills and predicts reading related white matter development. Frontiers in Human Neuroscience, 16, 922552. CC-BY
• ^[10] Image from John Marfe Bitoon is on Unsplash.
• ^[11] Pontecorvo et al., (2023). Learning a sign language does not hinder acquisition of a spoken language. Journal of Speech, Language, and Hearing Research, 66(4), 1291-1308. CC-BY-NC-SA
• ^[12] Image from Cheng et al., (2023). Restricted language access during childhood affects adult brain structure in selective language regions. Proceedings of the National Academy of Sciences, 120(7), e2215423120. CC-BY-4.0
• ^[13]  Emmorey (2023). Ten things you should know about sign languages. Current Directions in Psychological Science, 09637214231173071. CC-BY-NC