Early and late VEPs for reading stimuli are altered by common binocular misalignments

Effects of mild binocular anomalies on early and late evoked response complexes to word stimuli were examined in visual evoked potentials (VEPs) recorded over occipital cortex, Wernicke's area, and its right side homolog in university students with (fixation disparity group) and without (normal group) fixation disparity. Stimuli were monocularly or binocularly viewed words of a paragraph presented individually for 100 ms, one per second, and a binocular control condition without linguistic content. An early complex (P125-N170) recorded at Oz and a late complex (N170-late P) recorded from the temporoparietal placements were analyzed. The early complex was not influenced by linguistic content. Binocular stimuli generally resulted in larger early and late VEP amplitudes than did monocular stimuli except that the fixation disparity group had no binocular amplitude enhancement at Oz. Left hemisphere amplitude was greater than right for all conditions, more so for words than for nonlinguistic stimuli. For words, the left hemisphere advantage was significant only for the normal group. Relationships between basic visual processing and language processing in relation to early and late complexes are considered from several perspectives.