Dorsal stream associations with orthographic and phonological processing.

Several studies have indicated a key role for dorsal stream processing in lexical decoding. To examine this relationship further, performance on orthographic and phonological reading tests was compared with both steady-state visual evoked potentials and a putative behavioral measure of dorsal stream processing, coherent motion detection. Frequency analysis of the visual evoked potential data showed power at the second harmonic to be largely confined to dorsal stream regions, and significantly correlated with motion detection thresholds. Regression analyses showed that orthographic processing was significantly associated with the second harmonic power. Although consistent with previous reports, there remains a question as to why the orthographic visual evoked potential power relationship did not extend to include the coherent motion detection measures.