Dissociable contributions of motor-execution and action-observation to intermanual transfer

We examined the suggestion that some of the processes subserving learning through action-observation and motor-execution are different because sensory motor reafference is not available while the limb is at rest in the former condition. We confirmed the action-observation and motor-execution groups learned equally the absolute time and relative time constraints associated with a movement sequence timing task. However, data from mirror (same motor commands as those in practice) and non-mirror (same visual spatial coordinates as those in practice) intermanual transfer tests showed a clear dissociation in performance following these forms of practice. While positive transfer was exhibited by both groups in the non-mirror condition, there was a significant decrement in relative time performance in the mirror condition only after action-observation. These findings confirm that some of the processes underpinning these forms of motor learning are not somatotopic. Indeed, while motor and visual representations are developed during motor-execution, the absence of sensorimotor reafference during action-observation enables relative time to be represented in visual spatial coordinates only. These behavioural effects for intermanual transfer are discussed with reference to activity in supplementary motor area.