Dichoptic saccadic adaptation
43.325, Monday, 19-May, 8:30 am - 12:30 pm, Jacaranda Hall
Guido Maiello1,2, William J. Harrison1, Peter J. Bex1; 1Schepens Eye Research Institute, Department of Ophthalmology, Harvard Medical School, 2UCL Institute of Ophthalmology, University College London
In order to maintain accurate control of eye movements, the oculomotor system rapidly adapts to visual error based on foveal feedback. The short term plasticity of the saccadic system can be tested using intrasaccadic target displacements which induce visual motor error. The saccadic system rapidly adjusts to the perceived error by modifying the amplitude of saccadic eye movements. We tested in four participants whether it is possible to induce disconjugate saccadic adaptation by presenting intrasaccadic displacement to only one eye. We presented stimuli dichoptically using a stereo shutter-glass system. At the beginning of each trial, subjects fixated a central binocular fixation target. After a delay, the target was displaced by 10 degrees. During the preadaptation and postadaptation phases, the target was presented in the same location to both eyes without intrasaccadic displacement. In the adaptation phase, the target for the eye moving in the temporal direction was displaced one degree outward during the saccade. This induced uncrossed disparity which required divergent eye movements and induced a stereoscopic percept. We found that, in the preadaptation phase, the eye moving in the nasal direction systematically undershot the target by a greater distance than the eye moving in the temporal direction. These errors required subsequent vergence movements to correctly fixate the target. In the adaptation phase, the saccade amplitude changed for both eyes. However, the eye in which the intrasaccadic target displacement occurred had a greater change in amplitude, and this was the case for both leftward and rightward eye movements. During the postadaptation phase, saccade amplitudes returned to baseline within just a few trials, but the data suggest that the adapted eye takes longer to return to baseline. Therefore, we found evidence of both conjugate and disconjugate changes in saccadic adaptation, which supports the possibility of dissociable spatial maps for each eye.