VERs in normal and disabled adult readers.

The purposes of this study were to assess the visual evoked response (VER) technique in localizing the reading process and to explore VER differences between normal and disabled readers. VERs recorded from O1, O2, P3, and P4, all referenced to linked mastoids, were obtained from 9 normal and 9 carefully selected disabled adult readers under two test conditions: a series of non-patterned flashes of light viewed passively and a series of common three-letter words containing a target word. Peak-to-peak amplitude for P100-N140 and N140-P200, and amplitude from baseline for P200 and the late positive component (LPC) were obtained. The data were examined for hemispheric, parietal-occipital, and group differences. The main findings were: 1) increased amplitude for P200 and the LPC on the left side for word stimuli only, 2) increased LPC amplitude on the parietal leads compared to occipital for flash and word stimuli with greater increase for words, and 3) a larger difference between words and flash on the left parietal electrode for normals compared to disabled on the P200 and LPC measures.