Disconjugate adaptation of saccades: contribution of binocular and monocular mechanisms

We studied the effects of prism-induced disparity on static and intrasaccad ic alignment in six normal human subjects. A ten diopter base-out prism, ca lling for convergence, was placed in front of the central field of the righ t eye, so that at the center the eye viewed through the prism; at left and right, outside the prism. During 15 min of training, subjects made repetiti ve saccades solely in the right field of vision (C-R-C sequence). This para digm required relative divergence for centrifugal (C-R) saccades and relati ve convergence for centripetal (R-C) saccades, as well as increase of the a mplitude for all saccades made by the right eye. We found that during train ing, all subjects incorporated the necessary change in alignment into the s accades. After training the resultant intrasaccadic disconjugacy persisted when tested during monocular viewing, indicating that motor learning had oc curred. Subjects demonstrated increased divergence for C-R and increased co nvergence for R-C saccades, in accordance with the change acquired during a daptation to the prism. In addition, five subjects developed increased dive rgence for C-L saccades, for which they did not train. Smaller and less con sistent divergence was also observed for L-C saccades. Changes in intrasacc adic alignment were accompanied by changes in the relative Velocities of th e two eyes' saccades and slowing of the peak velocities in both eyes during training. Static alignment showed a general tendency toward convergence th at did not parallel the changes in the intrasaccadic alignment, suggesting that saccade adaptation is system-specific. The pattern of transfer of the intrasaccadic disconjugacy to saccades in the untrained field and the chang es in the relative speeds of the two eyes cannot be explained by monocular adjustment of the saccades. Our results indicate that both a binocular mech anism - saccade-vergence interaction and monocular adaptation contribute to disconjugate adaptation of saccades. (C) 1998 Elsevier Science Ltd. All ri ghts reserved.