What makes you think the individuals in the study weren't trained in how to visualise? Do you seriously think that people trying to conduct a meaningful comparison decided to just say to the subjects just close your eyes and imagine yourself doing it, see you later. Having read several such studies the subjects are invariably coached in visualisation techniques and supported through the process of what is typically a visualisation of a relatively simple action. The results are almost always startling and demonstrate the power of the mind, but it is naieve to believe that you can get results simply and is what leads to so many people being dismissive of the subject when they try and fail to replicate the results.