Disconjugate vertical memory-guided saccades to disparate targets

We studied the binocular coordination of normal memory-guided saccades and the possibility of inducing memory-based disconjugate learning. First, we r eport that normal vertical memory-guided saccades to non-disparate targets are yoked vertically in the two eyes as well as visually guided vertical sa ccades. To induce disconjugate vertical learning, at each trial we flashed a target that was disparate (i.e. 8% more elevated or more depressed for on e eye); the memory delay was 1 s. Memory-guided vertical saccades developed a vertical disconjugacy that was appropriate for the disparity of the reme mbered target. After 15 min of repetition, this vertical disconjugacy persi sted even when the target to be remembered was no longer disparate; this in dicates disconjugate vertical learning based on short-term memory. However, this was observed only for a few individual cases and its amplitude was sm all. This contrasts with prior findings on horizontal saccades associated w ith horizontal disparities. We conclude that vertical memory-based disconju gate learning is possible but very limited. Together with other studies, th is study suggests that the natural vertical conjugacy of vertical saccades relies little on rapid learning mechanisms. Rather it seems to be built-in, and this is consistent with earlier electrophysiological findings.