Implicit motor adaptation driven by intermittent and invariant errors

Abstract

Our movements and movement outcomes are disturbed by environmental changes, leading to errors. During ongoing environmental changes, people should correct their movement using sensory feedback. However, when the changes are momentary, corrections based on sensory feedback are undesirable. Previous studies have suggested that implicit motor adaptation is takes place, despite the realization that the presented visual feedback should be ignored. Although several studies created experimental situations where participants had to continuously ignore the presented visual feedback, in daily lives, people intermittently encounter opportunities to ignore sensory feedback. In this study, by intermittently presenting visual error clamp feedback, always offset from a target by 16° counterclockwise, regardless of the actual movement in a reaching experiment, we provided intermittent opportunities to ignore the visual feedback. We found that in the trials conducted immediately after presenting the visual error clamp feedback, reaching movements shifted in the direction opposite to the feedback; a hallmark of implicit motor adaptation. Moreover, the magnitude of the shift was significantly correlated with the speed of motor adaptation to gradual changes in the environment. Correcting movement according to continuous environmental changes is essential to maintain a precise movement. Therefore, the results suggest that people, unintentionally, react to momentary environmental changes that should be ignored and the sensitivity to momentary changes is greater in people who adapt quickly to the relevant gradual environmental changes.