Ziel

Previous studies on sensorimotor adaptation revealed no awareness of the nature of the perturbation after adaptation to a 30° rotation of visual feedback or after adaptation to gradually introduced perturbations. However, assessment of awareness by means of questionnaires, as done in those studies, can be problematic. Thus, the present study will use the process dissociation procedure, known in the field of cognitive psychology, to measure awareness and unawareness indices. We are interested in determining whether degree of awareness depends on the magnitude of the visual rotation. We further wish to determine if it can be manipulated by providing the subjects with an explicit strategy before adaptation.

Planung

To this end, two groups of subjects (explicit and implicit) perform alternating blocks of center-out reaching movements under null and adaptation conditions. Adaptation is to 20°, 40° and 60° cursor rotations in different adaptation blocks. The order of blocks is randomized between subjects. After each adaptation block the process dissociation procedure consisting of an inclusion and an exclusion condition is conducted. During inclusion condition subjects are asked to perform the task the same way as during the adaptation block and during exclusion they are asked to refrain from using what was learned and instead perform movements as during the baseline block. We determine an awareness index by subtraction of performance during the exclusion from performance during the inclusion condition and an unawareness index from the performance during the exclusion condition.

Ergebnisse

Analysis of variance (ANOVA) of the adaptation performance reveals no significant differences between groups for the last third of each adaptation block. A further ANOVA of the awareness index with the factor Rotation Size (20°, 40°, 60°) yields significant effects of Group and of Rotation Size. Post hoc analysis shows a significant increase of awareness from 20° to 60°, but no difference between 40° and either 20° or 60°. For the unaware index statistical analysis reveals a significant effect of Rotation Size only. Contrary to the awareness index, smaller rotations produce more unaware adaptation as confirmed by post hoc analysis. Our results suggest that aware and unaware states are differentially involved during adaptation to different perturbation sizes and awareness can be manipulated by instructions. Since it has been shown that gradual, i.e. unaware, and sudden adaptation are based on different neural correlates, it is possible that distinguished neural networks are differentially involved in adaptation to varying perturbation sizes.