Functional dissociation of the hemispheres using foveal visual input

A consistent 10 (± 2.2) msec visual field superiority in vocal RT to letters was found using both foveal and extra-foveal input (0.5°, 2° and 4° eccentricities), when typical procedures in the paradigm were modified. This consistency occurred in both the right visual field (for extreme right-handers) and left visual field (for extreme left-handers). A second experiment using a recognition memory task with manual RT also revealed concurrent opposite hemisphere superiorities for letters and geometric forms presented only 5.2–20.7' left or right of fixation. Acuity differences, directional scanning, and asymmetric cerebal activation could not account for the results. A substantial splitting of cortical connections from the innermost fovea is thereby indicated, as well as the viability of using foveal-only input in studies of cerebral functional asymmetries.