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Mayberry, Rachel, I; Chen, Jen-Kai: Witcher, Pamela.: & Klein, Denise. (2011) Age of acquisition effects on the functional organization of language in the adult brain, Brain & Language, 119, 16-29.

Using functional magnetic resonance imaging (MRI), the researchers neuro-imaged deaf adults as they performed two linguistic tasks with sentences in American Sign Language: grammatical judgment and phonemic hand judgment. Participants’ age-onset of sign language acquisition ranged from birth to 14 years; length of sign language experience was substantial and did not vary in relation to age of acquisition. For both tasks, a more left lateralized pattern of activation was observed, with activity for grammatical judgment being more anterior than that observed for phonemic-hand judgment, which was more posterior by comparison. Age of acquisition was linearly and negatively related to activation levels in anterior language regions and positively related to activation levels in posterior visual regions for both tasks.

Poizner, H., Klima, E., & Bellugi, U. (1987). What the hands reveal about the brain. Cambridge, Massachusetts: MIT Press. 

This book provided ground-breaking research demonstrating that languages are processed in the left hemisphere of the brain, regardless of language modality. The researchers also describe parallels between the different forms of aphasic impairment in sign and spoken language users. They provide examples in spoken and sign languages of the two main kinds of aphasias, one located in the anterior areas of the left hemisphere and referred to as non-fluent aphasia, and the other found in the posterior regions, referred to as fluent aphasia.