Thanks RN for your great explanation.
If I may add to that, mental imagery is using all (appropriate) senses to create or re-create an experience in the mind.
The more vivid these images, the more likely the brain will intrepret them as the real thing.
In trading (and beyond), it's most effective for rehearsing plans, events, self control/discipline, evoking desired states (confidence) and installing new habits.
i.e. a useful mental skill.
Hope this adds further clarity.
All the best.