Scanning visual images
The time needed for subjects to describe mental images corresponds to the time it would have taken them to scan an actual picture. Conclusion: internal images have special properties analogous to those external images.
Subjects were requested to memorize a series of pictures and later to imagine the one at a time. They were asked to focus on one end of the imagined picture and to identify a number of its features.
The time needed for subjects to correctly respond corresponded to the time it would have taken them to scan an actual picture.
Conclusion: internal images have special properties analogous to those external images.
Stephen Kosslyn (1973).