The neurobiology of rhyme judgment by deaf and hearing adults: an ERP study

We used electrophysiology to determine the time course and distribution of neural activation during an English word rhyme task in hearing and congenitally deaf adults. Behavioral performance by hearing participants was at ceiling and their ERP data replicated two robust effects repeatedly observed in the literature. First, a sustained negativity, termed the contingent negative variation, was elicited following the first stimulus word. This negativity was asymmetric, being more negative over the left than right sites. The second effect we replicated in hearing participants was an enhanced negativity (N450) to nonrhyming second stimulus words. This was largest over medial, parietal regions of the right hemisphere. Accuracy on the rhyme task by the deaf group as a whole was above chance level, yet significantly poorer than hearing participants. We examined only ERP data from deaf participants who performed the task above chance level (n = 9). We observed indications of subtle differences in ERP responses between deaf and hearing groups. However, overall the patterns in the deaf group were very similar to that in the hearing group. Deaf participants, just as hearing participants, showed greater negativity to nonrhyming than rhyming words. Furthermore the onset latency of this effect was the same as that observed in hearing participants. Overall, the neural processes supporting explicit phonological judgments are very similar in deaf and hearing people, despite differences in the modality of spoken language experience. This supports the suggestion that phonological processing is to a large degree amodal or supramodal.