This talk about synesthesia, memory for texts, and blindfold chess suggests to me that posters do not have a very clear sense of the truly incredible nature of the feat “Elizabeth” is supposed to have achieved. She is supposed to have seen the emergent 3-D shape in a Julesz random dot stereogram through her eidetic memory. Such a stereogram consists of one frame with many (hundreds or thousands) of dots randomly scattered, and a second frame that is identical except that the dots (or a proportion of them) in a certain area are shifted very slightly to one side. If one examines these frames side by side it is very hard, to see any difference whatsoever between them (if you know there is a difference, and scrutinize individual clumps of dots very carefully, you may be able to find differences, but to a quick glance or even along stare they will seem indistinguishable). However, if you view the two frames through a stereoscope, an optical device that presents one frame to one eye and the other to the other (like one of those View-Master toys), the area where the dots are shifted stands out vividly in depth, either in front of or behind the rest of the area.
There are other ways of “fusing” the two frames to see the 3-D effect. When I was at Caltech I was lucky enough to see a public demonstration of random dot stereograms by Bela Julesz (the inventor of the random dot stereogram) himself, using superimposed frames with differently colored dots and the 2-colored 3-D glasses they use for movies like Spy Kids 3-D. It was really quite impressive to see: great 3-D shapes jutting out fall into the hall from what, without the glasses, was a meaningless and quite flat jumble of color. It is also supposed to be possible to “fuse” two side-by-side frames by crossing ones eyes, but I have never been able to make this work very well, and it hurts! “Elizabeth” however, is supposed to have viewed one frame and then seen the 3-D effect by superimposing her memory image on the other frame viewed later. If you look at the images of random dot stereograms I have linked below, you will understand just what a sensational feat of memory this would be, which explains, of course, both why the original report got such attention, and why the hoax story is so plausible.
Some examples of random dot stereograms from around the web:
http://www.cquest.utoronto.ca/psych/psy280f/ch7/rds.html
http://www.fangtu.com/vlab/rds.html
http://www.owlnet.rice.edu/~psyc351/Images/JuleszRDS.jpg
Incidentally, even if one accepts that “Elizabeth’s” memory could be up to the task it is still not clear why that would enable her to see the 3-D effect. Superimposing the two frames is not the same as presenting them to different eyes. If you print one frame on a transparency and superimpose it over the other you will not see the 3-D.
Also, the claims about "Elizabeth run completely counter to the implications of the recent experiments demonstrating “change blindness”. These experiments have shown that people’s immediate memory for the details (even quite major, salient details) of pictures is very much poorer than most people would imagine. Quite large and seemingly obvious changes in a picture (e.g., two people’s heads being switched onto each others bodies) will often go completely unnoticed, even while you are looking right at it, provided that (i) the change is not in the central feature of interest, and (ii) the change occurs at the same moment as the viewer moves their eyes, or while the picture momentarily flickers, or a few random “mud splashes” are momentarily superimposed on it, or during some other brief interruption of normal vision. The effects can be quite shocking, when you eventually realize what an “obvious” change you have missed.
There is a good brief introductory description of change blindness here (from the Nature Encyclopedia of Cognitive Science), and some great demonstrations here. Provided you view the versions with the mudsplashes, flicker, or whatever, before you view the version without, you probably have to view them quite a few times before you see what has changed, and you will then wonder how you could have missed something so obvious. Change blindness is itself a very surprising phenomenon to most people, but unlike the alleged abilities of “Elizabeth,” the effect is easily reproducible, and works with just about anyone.
Nigel J.T. Thomas
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