We are able to make a saccade toward a tactile stimuli to one hand, but trajectories of many saccades curved markedly when the arms were crossed (Groh & Sparks, 2006). However, it remains unknown why some curved and others did not. We therefore examined critical factors for inducing the curved somatosensory saccades. Participants made a saccade as soon as possible from a central fixation point toward a tactile stimulus delivered to one of the two hands, and switched between arms-crossed and arms-uncrossed postures every 6 trials. Trajectories were generally straight when the arms were uncrossed, but all participants made curved saccades when the arms were crossed (12-64%). We found that the probability of curved saccades depended critically on the onset latency: the probability was less than 5% when the latency was larger than 250 ms, but the probability
increased up to 70-80% when the onset latency was 160 ms. This relationship was shared across participants. The results suggest that a touch in the arms-crossed posture was always mapped to the wrong hand in the initial phase up to 160 ms, and then remapped to the correct hand during the next
100 ms by some fundamental neural mechanisms shared across participants.