Explicit and implicit components of visuo-motor adaptation: An analysis of individual differences.

Adaptation to visuo-motor rotations embraces implicit and explicit components. We contrast this two-component model with a three-component model by means of an individual-differences approach. Adaptive changes were tested under four conditions: (1) closed-loop test, presence of the rotation cued (initial adaptive shift), (2) open-loop test, presence of the rotation cued (adaptive shift), (3) open-loop test, absence of the rotation cued (after-effect), (4) test of explicit knowledge (explicit shift). After-effects and explicit shifts were uncorrelated. After regression on after-effects and explicit shifts, the residuals of the initial adaptive shifts and the adaptive shifts remained correlated, suggesting an additional implicit component of adaptation found only in the cued presence of the visuo-motor rotation. The two implicit components are consistent with the distinction between a change of the body schema giving rise to after-effects, and the development of an internal model of a tool that is applied only when the transformation is present.