Differential saccadic adaptation controlled by the target color.

Saccade adaptation is a form of motor learning that maintains saccade accuracy in response to new sensorimotor contingencies. Several studies have shown that saccade gain can be adapted separately in double-step paradigms depending on cues affecting the motor command (velocity or direction of target motion, orbital eccentricity, or vergence). However, purely visual cues such as target color and shape consistently failed to drive different gain states during saccadic adaptation. These results are consistent with the dominant view that saccade adaptation is a simple motor recalibration process. Differential adaptation controlled by purely visual properties might imply that saccade adaptation relies on general learning mechanisms in which any informative cue could be used. Here we ask whether this absence of contextual control by color may be due to the irrelevance of target color for the saccadic system. We had 12 subjects making 500 saccades in a double-step paradigm to a red or a green disc target (50% of trials) stepping away from a fixation position (45 deg wrt the horizontal). During the saccade the target was displaced orthogonally to its primary step, upward and backward for the red target and downward and forward for the green target (6 subjects). Target colors were reversed in the other 6 subjects. A distractor appeared simultaneously at the mirror position wrt the original step. The distractor was red when the target was green and green otherwise. We observed a systematic control on saccade angle by target color (average saccade angle difference for the two target colors 6.7 deg, p< 0.01). No effect was found in 6 control participants in a similar paradigm but without a distractor (saccade angle difference 0.78 deg, NS). We conclude that target color can control saccade adaptation provided that color is made relevant for the saccadic system by adding a color-defined distractor. Meeting abstract presented at VSS 2015.