Dear Charmaine Ruble,

Thank you for very nice question. As you have stated, infants obtain their fundamental information through sensory perception and exploration of environmental stimuli. This interaction certainly contributes to learning and cognitive development.Therefore, as Lewkowicz and Arabel (2004) maintain, streams of  sensory information from multiple modalities concurrently  form a natural course of development .However, research findings on the issue have not been conclusive . I refer you to a comprehensive article by Fagan and Pisoni(2010).

Best regards,

R. Biria

You may consider looking into research on bilingualism and the cognitive and language benefits that come from learning two languages. Sign language does count as another language so looking into research on bilingualism may be a good place  to start.

Thank-you both for your helpful answers

You also can look the research in sign language of the deaf. Our research results (Radoman Nikolic) indicate that using sign language of deaf children stimulate development  of their verbal speaking language and verbal meaning .