Abstract
Accurate reaching toward a visual target is disturbed after the visual field is displaced by prisms, but recovers with practice. When the prisms are removed, errors in the opposite direction are observed (after-effect). We previously reported in monkeys that the after-effect disappeared in 24 hours after a repetition of 250 trials, but remained as large for 72 hours after 500 trials. In the present study, we examined if a gradual increase of visual displacement (Exp 1) and/or a break of one hour (Exp 2) would establish long-lasting after-effects with a smaller number of trials. In Exp 1, we increased displacement from 0 to 15 D in 100 trials, and had the monkey continue the task with the 15 D displacement for additional 100, 200 and 400 trials. Twenty-four hours later, we found significant after-effects in the large-number condition (100+400 trials; p<0.001), but not in the small-number condition (100+100 trials; p>0.05). The results show that the gradual increase did not consolidate after-effects. In Exp 2, we gradually increased the visual displacement in 100 trials and had the monkey continue the task for another 100 trial-block. Then in one condition the monkey took a break of one hour before completing another 100 trial-block with prisms. In the other, the monkey took no rest. With the one-hour rest, we found significant aftereffects (p<0.001) in all five experiments but only in three of five without the rest. The aftereffects were significantly larger in the break condition (p < 0.05). The results suggest that a kind of consolidation process is triggered during the break between the two 100-trial exposure blocks. [J Physiol Sci. 2008;58 Suppl:S191]
