Читать книгу Lifespan Development - Tara L. Kuther - Страница 286

Evolutionary theorists explain language as having evolved as a function of natural selection. Language gave some of our early human ancestors an advantage in survival and reproduction over those who did not have language (Berwick & Chomsky, 2016; Hauser et al., 2014). Specifically, language evolved as an adaptation that fulfilled early humans’ need to communicate information that was more complex than could be conveyed by simple calls and hoots (Tamariz & Kirby, 2016). Language may have emerged with increases in the size of human communities and the corresponding complexity of social dynamics, as well as humans’ increasingly large, more sophisticated brains (Aiello & Dunbar, 1993; Turnbull & Justice, 2016).

The brain specifically is wired for language at birth. Speech sounds produce more activity in the left hemisphere of newborns’ brains, while nonspeech sounds elicit more activity in the right hemisphere (Vannasing et al., 2016). Three-month-old infants show functional neural activity in response to language that is similar but less refined, focused, and organized than that of adults (Dehaene-Lambertz, 2017). Adult language, too, is largely governed by the left hemisphere, and cortical activity in language areas increases from infancy through adulthood (Paquette et al., 2015). Two areas in the left hemisphere of the brain are vital for language and distinguish humans from other primates: Broca’s and Wernicke’s areas (Friederici, 2017). Broca’s area controls the ability to use language for expression. Damage to this area inhibits the ability to speak fluently, leading to errors in the production of language. Wernicke’s area is responsible for language comprehension. Damage to Wernicke’s area impairs the ability to understand the speech of others and sometimes affects the ability to speak coherently.

Through infant-directed speech, adults attract infants’ attention by using shorter words and sentences, higher and more varied pitch, repetition, and a slower rate. Infants prefer listening to infant-directed speech, and infant-directed speech appears cross culturally.

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Although the brain plays a crucial role in language capacities, it cannot completely account for language development. For example, recent research has identified multiple genes associated with language development that work together in an epigenetic fashion, influenced by environmental factors (Dediu & Christiansen, 2016; Fisher, 2017). In addition, experience influences the brain architecture that supports language development (Westermann, 2016). For example, we have seen that infants’ ability to detect sounds not used in their native language declines throughout the first year of life, suggesting that contextual factors—specifically, exposure to the native languag—influence older infants’ sensitivity to speech sounds (Posner, 2001; Sansavini, Bertoncini, & Giovanelli, 1997). At the same time, information processing factors largely dependent on neurological development, such as attention and memory, affect how infants comprehend and respond to social interaction and other contextual influences on language development (Perszyk & Waxman, 2018). For example, the statistical learning abilities that enable infants to see patterns and learn quickly are also associated with rapid language learning (Lany, Shoaib, Thompson, & Estes, 2018).