Online versus Cognitive Control: A Dividing Line between Physical Action and Motor Imagery
Recent work in our lab has shown that motor imagery is highly sensitive to tasks that interfere with executive resources, whereas physical actions are largely immune. This has been taken as support for the Motor-Cognitive model of motor imagery and in opposition to the theory of Functional Equivalence. Here, we examined another prediction of the MCM, namely that an opposite pattern of effects would be observed when the information available for online control was reduced, with physical actions being affected but motor imagery being largely resistant. This was tested in four experiments in which participants performed either physical actions or motor imagery, and in a replication in which they performed both. The experiments manipulated the quality of information available during the online control of movement through: 1) comparing movements made with or without visual feedback (Exp 1 and 1a); 2) comparing movements made using foveal vs. peripheral vision (Exp 2); and 3) comparing physical to mimed actions (Exp 3). All four experiments found evidence in favour of the Motor-Cognitive model in that manipulations of online control affected physical action much more than they affected motor imagery. These results were, however, inconsistent with a Functional Equivalence view. We discuss these results in the broader context of other theoretical views of motor imagery. Public Significance StatementMotor imagery is a vital component of elite motor skill training and has great utility as a rehabilitative tool in those suffering from brain imagery. A sophisticated understanding of motor imagery is thus critical to optimize its use in these contexts. However, presently there is a paucity of theoretical accounts of motor imagery. A currently popular view is that motor imagery is functionally equivalent to physical actions, yet this account is an oversimplification. We propose instead the Motor-Cognitive model, which incorporates the differences as well as similarities between motor imagery and physical action. Here, we tested the Motor-Cognitive model against the Functional Equivalence view in four experiments that manipulated the amount and/or quality of online visual feedback available and found clear evidence for a difference in motor imagery versus physical action. These experiments provided convincing support that motor imagery is functionally distinct from physical action. This advance in theory regarding motor imagery has important implications for its implementation as both a performance-enhancing and therapeutic tool.