Long-lasting aftereffects of prism adaptation in the monkey

The errors in tar-et-reaching that are produced C by laterally displacing v ision with wedge prisms L decrease with trials (prism adaptation). When the prisms are removed, errors in the opposite direction are observed (afteref fect). We investigated the size of the aftereffect 24 h and 72 h after a mo nk-ey had adapted to a visual displacement (30 mm). with rapid reaching mov ements. The aftereffect more than half of the size of the displacement was observed when the effect was tested immediately after the monkey had been e xposed to the displacement for 50 trials. In contrast, the aftereffect was not observed at 24 h even when the monkey had been exposed to the displacem ent for 250 trials. However, when the monkey had been exposed for 500 trial s, significant aftereffects more than half of the size of the displacement were observed at 24 h and 72 h. When both arms were adapted to opposite pri sm displacements, the long-lasting aftereffect was further shown to be spec ific for the arm used during the exposure. The results indicate that the af tereffects of prism adaptation last for at least 3 days, though more than 2 00 trials of additional repetition are required to consolidate the short-te rm effects into long-lasting ones.