Previous work has documented that the direction of eye and hand movements can be adaptively modified using the double-step paradigm. Here we report that both motor systems adapt not only to small direction steps (5° gaze angle) but also to large ones (28° gaze angle). However, the magnitude of adaptation did not increase with step size, and the relative magnitude of adaptation therefore decreased from 67% with small steps to 15% with large steps. This decreasing efficiency of adaptation may reflect the participation of directionally selective neural circuits in double-step adaptation.

It is still unknown whether adaptation of saccades--like that of arm movements-deteriorates in the presence of a concurrent resource--demanding task, and whether it is affected by old age. We therefore compared double-step adaptation of saccade directions in young and older persons exposed to the adaptation task only (groups CY & CO), to the adaptation task and a spatially adjacent manual tracking task (AY & AO) or to the adaptation task and a spatially distant manual tracking task (DY & DO). Adaptation was similar in all groups except DO: the latter group showed no consistent adaptation and no adequate aftereffects. Tracking improved little by practice in all groups except AY, where the improvement was substantial. Our data therefore provide no evidence for an impact of old age and resource demand on saccadic adaptation, possibly because the neural substrate partly differs from that for arm adaptation. The lack of adaptation in DO probably reflects the well-known shrinkage of the functional field of view in old age.

Age related deficits of sensorimotor adaptation have been observed earlier with arm, but not with eye movements. Here we evaluate whether deficits of eye adaptation may depend on the subjects' believes about their own sensorimotor abilities. To find out, elderly subjects were primed with positive or negative age stereotypes using the scrambled-sentence task, and were then exposed to a double-step saccade adaptation task. The outcome was compared to data from an earlier study with unprimed elderly persons. We found adaptation to be stronger after positive priming than after negative or no priming, with no difference between the latter two. Aftereffects of adaptation were not modified by priming. From this we conclude that positive primes enhanced workaround strategies, but not adaptive recalibration, while negative primes failed completely, possibly because of a floor effect.