Imagery task
A mental chronometry task was administered to participants to assess their motor imagery abilities. There were two randomly assigned tasks in the procedure: a forward-walking task (FW) and a backward-walking task (BW). In both tasks (each consisting of one trial), participants had first to imagine (forward and backward-walking) and then walk (forwards and backward). The corridor used in the present study was situated within a university building and it was familiar to all participants. According to the procedure used by Grealy and Shearer (At the beginning of the procedure, participants were asked to observe a target (a black leather chair) placed 30 m away from their position. We opted for a distance of 30 m, exceeding that used in other protocols (such as Decety et al., For both imagination and execution tasks, each participant was positioned on an “X” placed behind a starting line.Imagination and execution times were measured using a commercial digital stopwatch (Faviye stopwatch XL 0–13). Participants received instructions for using the stopwatch before the imagination task: they had to close their eyes, put their finger on the start button of the stopwatch, and press it as soon as they started imagining. For the execution phase, time was recorded by the experimenter. The times recorded have been measured in seconds. A few days before the test, participants were informed about MI, its use and benefits, and received minimum information about its execution. Each task was evaluated using an Isochrony Efficiency index (IE = difference between imagination and execution time). The bigger IE index accounted for the worst MI efficiency.