The most convincing and unique documentation of eidetic imagery was a case study done by Charles Stromeyer in 1970. The subject of their study, a woman named "Elizabeth," was able to write out poetry in a foreign language years after seeing the original text. She was also able to project her images onto a blank canvas or over the top of other images. Moving her eyes allowed her to scan the projected image, which remained entirely stationary. Her images would break apart instead of fading away slowly.
Mozart's was able to create one symphonic composition after another almost complete and finished in my mind, so that I can survey it, like a fine picture, but he died in his thirties, still behaving like a juvenile.
Eidetic ability fades with age. One investigator guessed that fewer than one in a thousand adults had it. Most eidetic ability can't summon the eidetic image once it fades from mind, either. But there are exceptions. In 1970 Psychology Today reported on Elizabeth, a Harvard instructor. Using her right eye, she looked for several minutes at a 100 x 100 grid of apparently random dots--10,000 dots in all. The next day, using her left eye, she looked at a second grid of 100 x 100 dots. She then mentally merged this grid with the remembered one into a 3-D image that most people needed a stereoscopic viewer and both grids to see. Reportedly she could recall eidetic images of a million dots for as much as four hours.
Even eidetikers aren't seeing a truly photographic image, psychologists believe--they just have the ability to organize information with unusual efficiency.
Mnemonists, known for impressive feats of memory, enhance their native talent with tricks. One famous case was S., described by the Russian psychologist A.R. Luria. Among other things S. had an exceptional ability to retain things long after he'd originally memorized them. Once he was read the first four lines of Dante's The Divine Comedy in Italian, a language he did not understand. He was immediately able to recite the entire passage--and more impressively, he could still do so on command 15 years later, with no advance warning.
How had he done it? He associated each syllable with a mental image. The first line, Nel mezzo del cammin di nostra vita, he rendered into images this way: Nel, Nel'skaya, a ballerina; mezzo, she is together with (Russian vmeste) a man; del, there is a pack of Deli cigarettes near them; cammin, a fireplace (Russian kamin) is also close by; di, a hand is pointing toward a door (Russian dver); nos, a man has fallen and gotten his nose (Russian nos) pinched in a doorway (Russian tra); vita, the man steps over a child, a sign of life--vitalism; and so on, for 48 syllables. It's all just a mnemonic trick, right?
Eidetic imagery has been studied for over a century and many studies have been done to test its validity. Individuals capable of superior memory were tested and many were found not to possess eidetic imagery. A study done by Degroot shows that some individuals are highly skilled at organizing information- not actually reproducing the images they see. In his study, chess players were asked to reconstruct certain arrangements of pieces on a chessboard after looking at the arrangement for a brief period of time. It was found that the performance level of an expert chess player would drop to that of a novice when the pieces were arranged in a way that would never actually occur in a game. The initially high performance level of the experts was not due to eidetic imagery; they were simply able to better organize and therefore remember the information because the arrangements could be associated with pre-existing knowledge of chess. Although some write off eidetic memory as the ability to organize vast amounts of information, others have found that this ability cannot be used to explain all the cases studied.