Neuroplasticity of Spatial Working Memory in Signed Language Processing

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DESCRIPTION (provided by applicant): Signers, when compared to nonsigners, have demonstrated enhanced visuo-spatial processes such as facial discrimination, mental rotation, and spatial maintenance following the learning of a signed language (Bettger, Emmorey, McCullough, & Bellugi, 1997; Emmorey, 2002; Wilson, Bettger, Niculae, & Klima, 1997). The processing of signed, as compared to spoken, language makes unique demands on visuo-spatial cognition because many of the processes involved in everyday sign discourse map onto the known properties of spatial working memory (SWM). As a consequence, exposure to sign language appears to produce unique adaptations to SWM functioning. This adaptive effect has been observed to extend to nonnative signers (Keehner & Gathercole, 2006) but little remains known about the neural foundations of such behavioral outcomes. It is not clear if there is a CP--a hypothesized time frame within which young human brains optimally learn language (Au, Knightly, Jun, & Oh, 2002; Lennenberg, 1967; Newport, 1990; Penfield & Roberts, 1959)-- for learning a signed language. But, we know that early exposure to two languages produces positive, robust impact on neurocognitive development, even possibly prolonging the CP (Jasinska & Petitto, 2013; Kovelman, et al., 2008; Petitto & Kovelman, 2003; Petitto, et. al., 2012). Furthermore, children exposed to two languages during the CP have shown working memory advantage, specifically enhanced executive control in nonverbal tasks (e.g. stroop and simon) (Bialystok, 1999). The bilingual advantage was not found in American Sign Language (ASL)-English bilinguals (Emmorey, Pyers, & Bialystok, 2008), but it might be because the administered nonverbal tasks (directional flanker) in the study didn't tap cognitive functions that are essential for sign language processing such as SWM. Here we ask, whether the timing of sign language acquisition yield changes in the neural resources facilitating SWM. Specifically, we will investigate whether there is a critical period fo the SWM maintenance enhancement found in other studies; and whether there is a critical period for SWM executive inhibition. By studying a spatial syntax based language like ASL, a unique window, that would not be possible with spoken language, is gained into the structural and functional plasticity of the human brain. Furthermore, this study will provide advancement to scientific debate about the nature of brain plasticity and learning across the human lifespan. Furthermore, if we discover that learning a signed language is possible after the critical period, then it may be possible to reverse the CP in adult learners.