Motor Equivalence in Motor Awareness

Motor awareness (MA) describes the level of conscious access we have to the details of our movements and as such is critical to the feeling of control we maintain over our actions (sense of agency). Although our movements rely on specific sensorimotor transformations as well as distinct reference frames for the active body part, or effector, numerous studies report spatiotemporal thresholds of MA that are comparable across different effectors and tasks as well as supramodal. However, this has not been tested directly and there is currently no direct empirical support for effector-independent MA nor a description of a potentially shared underlying mechanisms. We therefore designed a goal-directed reaching paradigm that participants performed once with their upper-limbs, using a joystick, and once with their full body, by leaning and thereby displacing their center-of-mass. We assessed both MA and corrective movements for sensorimotor mismatches by providing either veridical feedback or introducing random spatial deviations. We hypothesized that changes in motor compensation and awareness, across effectors, with and without a concurrent cognitive load, would follow the same pattern of behavior if they relied on a shared underlying mechanism. Our results lend support for such an effector-independent mechanism, as we observed that MA was comparable across effectors: i) in un-deviated control trials with and without cognitive load, ii) in converging trials where the direction of the deviation corresponded to the direction of the target location, and iii) based on strongly correlated psychometric MA thresholds across effectors. At the same time, data from diverging trials, where the direction of the deviation opposed the direction of the target location, indicate that in case of conflicting information and increased kinematic task demands MA draws on effector-specific sensorimotor information, corresponding to performance differences between hand and full body movements observed in baseline blind-reaching versus visually guided reaching. Overall, our findings provide a direct link between low-level sensorimotor transformations and abstract motor representations and their role in MA, consolidating a gap in conceptual frameworks of the sense of agency.