Error compensation in a redundant system during 'failure' of individual motor elements

A characteristic feature of redundancy in the motor system is the ability to compensate for the failure of individual motor elements without affecting task performance. In this study, we examined the pattern and variability in error compensation between motor elements during a virtual task. Participants performed a redundant cursor control task with finger movements. In some conditions, we induced 'failure' by using a haptic glove to apply forces to constrain the motion of one of four fingers (index, middle, ring, or little). Our results showed that (i) other fingers increased their range of motion to compensate for the failure of a specific finger, with most of this compensation coming from non-adjacent fingers, and (ii) there was greater trial-to-trial variation in how the task was achieved as indexed by the higher null space variability when the middle and ring fingers were constrained. These results highlight the key role of the interdependence between motor elements in determining error compensation patterns and the variability in coordination patterns.