Saccadic adaptation in visually normal individuals using saccadic endpoint variability from amblyopia.

Purpose: Saccadic adaptation is affected by the spatial variability of the adapting error signal. Recently, we have shown that saccadic adaptation is reduced in anisometropic amblyopia, possibly impacted by spatially imprecise saccades. Here, we tested this idea by quantifying the saccadic endpoint variability difference between people with anisometropic amblyopia and visually normal individuals. We then applied this difference to the second target step distribution during saccadic adaptation in visually normal people to test whether their performance diminished to a similar extent as participants with amblyopia.

Methods: Ten visually normal adults performed a double-step adaptation task (±19°, followed by 4° back-steps) with the nondominant eye under two conditions: "consistent error," using a constant back-step; and "variable error," using a variable (σdiff) back-step determined by subtracting the saccadic endpoint variability in controls from that in anisometropic amblyopia during amblyopic/nondominant eye viewing. Percentage change in saccadic gains, percentage retention, and adaptation time constants were analyzed.

Results: Percentage change in saccadic gains decreased significantly during the variable error condition (50% ± 10%) compared to the consistent error condition (69% ± 9%; P = 0.0008). Percentage retention and time constants did not differ between conditions. The adaptation magnitude during the variable error condition was comparable to the previous percentage adaptation in people with anisometropic amblyopia during the consistent error condition with amblyopic eye viewing.

Conclusions: Our findings indicate that adding exogenous spatial noise to the adapting step consistent with the saccadic endpoint variability difference between amblyopic and visually normal groups is sufficient to reduce saccadic adaptation in healthy individuals.