High loads induce differences between actual and imagined movement duration

Abstract

Actual and imagined action may be governed by common information and neural processes. This hypothesis has found strong support from a range of chronometric studies showing that it takes the same amount of time to actually move and to imagine moving. However, exceptions have been observed when actual and imagined movements were made under conditions of inertial loading: sometimes the equivalency of actual and imagined movement durations (MDs) has been preserved, and other times it has been disrupted. The purpose of the current study was to test the hypothesis that the appearance and magnitude of actual-imagined MD differences in those studies was dependent on the level of load relative to the maximum loading capacity of the involved effector system [the maximum voluntary load (MVL)]. The experiment required 12 young, healthy humans to actually produce, and to imagine producing, single degree of freedom index finger movements under a range of loads (0, 5, 10, 20, 40, and 80% MVL). As predicted, statistically significant actual-imagined MD differences were absent at lower loads (0-20% MVL), but differences appeared and increased in magnitude with further increases in %MVL (40 and 80% MVL). That pattern of results may relate to the common, everyday experience individuals have in interacting with loads. Participants are likely to have extensive experience interacting with very low loads, but not high loads. It follows that the control of low inertial loads should be governed by complete central representations of action, while representations should be less complete for high loads. A consequence may be increases in the uncertainty of predicting motor output with increases in load. Compensation for the increased uncertainty may appear as increases in the MD values selected during both the preparation and imagery of action--according to a speed-uncertainty trade-off. Then, during actual action, MD may be reduced if movement-related feedback indicates that a faster movement would succeed.

Motor imagery of locomotion with an additional load: actual load experience does not affect differences between physical and mental durations

“…On the one hand, the congruency of body conditions during MI obviously did not reveal any impact on mental durations at all. On the other hand, and rather surprisingly, this experimental manipulation did not modulate the difference between actual and mental durations in the AL conditions, which per se can be explained by the arguments of and Slifkin (2008). In summary, we argue that a supposable suppression of somatosensory and vestibular feedback eventually related to limitations of working memory capacity might account for the present findings on the mental chronometry of walking with an additional load.…”

“…It is then concluded that this discrepancy will be interpreted as an elongation of the walking duration and, accordingly, as a slowing down of the respective imagined walking movements. Another interpretation of this effect also relying on problems with generating an effective efference copy for the purpose of MI has been proposed by Slifkin (2008). Here, the problem is not to generate an image of a movement with an additional load per se, but to generate an image of an own movement with an additional load that lies outside of previous experience.…”

“…They certainly call for a closer examination in light of the fundamentally strong relation usually found between actual and mental durations, and the fact that effort and physiological conditions appear to be well represented in MI (Courtine et al 2004;Decety et al 1993;Guillot et al 2005). In this context, a study relying on different load conditions showed a dissociation between actual and imagery durations and disproportionately long mental durations only for heavier loads (Slifkin 2008). …”

“…It has been argued that a deviation of mental durations from actual durations for movements with a high load reflects a lack of experience with these specific load conditions in everyday contexts (Slifkin 2008). Another important contextual variable influencing mental durations of movements with an additional load is the degree of somatosensory perception of the additional load during imagery.…”

Motor imagery effectiveness for mirror reversed movements

“…In a pre-experimental session with an independent group of participants, we checked that movement times were not too rapid or too long, but generally ranged between 7 s and 15 s in each experimental condition, though the subjects were asked to perform the task as fast as possible. This time window was preselected to determine the speed of the cursor, as rapid and long movements were frequently found to be respectively overand underestimated during MI, whereas movements lasting between 7 s and 15 s were more frequently imagined in real-time (e.g., Guillot & Collet, 2005;Slifkin, 2008).…”