Smooth pursuit eye movements and phonological processing in adults with dyslexia

The extent to which adults with dyslexia are characterized by concurrent smooth pursuit eye movement and phonological difficulties was investigated, as was the relationship between performance on these respective tasks and literacy skills. A total of 19 adults with dyslexia and 19 age- and IQ-matched controls undertook a comprehensive battery of psychometric, literacy, and phonological tests. Smooth pursuit initiation was measured quantitatively under both gap and nongap conditions. The results revealed that adults with dyslexia had longer smooth pursuit latencies; however, both groups showed a similar gap effect. Moreover, the group with dyslexia had poorer phonological skills than controls. The smooth pursuit impairments affected 37% of the group whereas the phonological difficulties-most notably phoneme deletion latency-were severe among participants with dyslexia, affecting 89% of the group. Phonological processing tasks, but not the smooth pursuit task, were strongly correlated with nonword- and word-decoding skills in the group with dyslexia. These results suggest a lower incidence of smooth pursuit problems than phonological difficulties in dyslexia, and that the latter tasks are more critical for word level decoding.