Also known as photographic memory. Eidetic memory is the ability to remember things with absolute clarity--not just stupid things, like the symptoms of amylotrophic lateral sclerosis, the lyrics to Underworld's immensely popular song Mmm, Skyscraper, I Love You or the coefficient of drag of an airborn Holstein cow. We're talking about useful things here, such as the name of your first-grade teacher's assistant, or the chemical formula for Bryll-Creem.

Eidetic memory is the ability to recollect an image so vividly that it appears to be real. For the most part it is found only in children. Eidetic ability fades with age--one investigator guessed that fewer than one in a thousand of the children who had it, kept it into adulthood. Most eidetikers can't summon the eidetic image once it fades from mind, either. But there are exceptions.

In a basic experiment on eidetic memory, a child is told to examine but not stare fixedly at an illustration on an easel for 30 seconds. Then the illustration is removed and the kid is asked to look at the empty easel and describe what he sees. Most offer vague recollections of the image, but perhaps one in twelve can describe it in accurate detail for five minutes or more. It's not just a retinal afterimage, either. The image has normal coloration, not an afterimage's complementary colors (blue becomes orange, etc.). The descriptions are in present tense--"I see . . ."--and given without hesitation. Most striking of all, the subject's eyes move around the nonexistent scene as he describes it, as though it were actually there.

Some observers thought the testees were faking it, or at least not exhibiting anything out of the ordinary. Then someone hit on the ingenious notion of decomposing an illustration into two images, each consisting of an apparently meaningless set of lines or dots. One image would be presented for inspection, then taken away and after a few seconds replaced by the other. Those who truly had the gift could combine the two images into the original illustration--objective evidence, it would seem, that eidetic memory really exists.

Here's a little information about that one-in-a-thousand person who held onto her eidetic memory into adulthood. 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.

largely from the straight dope

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