Cochlear implants and the brain: The biological basis for language and cognition in infants, children, and adults with cochlear implants

Controversy abounds on the differences in language experience in the acquisition of spoken language in deaf individuals with cochlear implants (CIs).

Noteworthy is that early exposure to a signed language causes deviance to auditory language tissue development. Related claims are that young children with CIs should not receive early exposure to a signed language for fear that the tissue devoted to auditory processes will be “taken over” by signed language processing.

We ask whether early exposure to a visually signed language negatively impacts and causes neural deviance or abnormality to classic left-hemisphere spoken language tissue development in deaf individuals with early cochlear implantation, including left Inferior Frontal Gyrus (LIFG) and Superior Temporal Gyrus.

We find that early exposed deaf CI individuals showed entirely normal activation in classic LIFG. By contrast, late exposed deaf CI individuals showed greater activation in the right hemisphere. This supports the hypothesis that early sign language exposure facilitates standard language processing and does not cause neural deviance or abnormality in classic left-hemisphere language tissue.

Strong evidence of neural plasticity was not at work—auditory processes were not “taken over” by signed language processing in early sign-exposed individuals with CIs. Instead, their language tissue activity was entirely normal.

Rather than neural plasticity, findings suggest that aspects of left hemisphere language tissue thought to be “auditory” is not, but dedicated to processing particular patterns in natural language.

We conclude that early, not later, exposure to a signed language supports typical, healthy, and normal language development.