“The ‘facts’, under these circumstances, are established to monotony. The twins say, ‘Give us a date—any time in the last or next forty thousand years.’ You give them a date, and, almost instantly, they tell you what day of the week it would be. ‘Another date!’ they cry, and the performance is repeated. They will also tell you the date of Easter during the same period of 80,000 years. One may observe, though this is not usually mentioned in the reports, that their eyes move and fix in a peculiar way as they do this—as if they were unrolling, or scrutinising, an inner landscape, a mental calendar. They have the look of ‘seeing’, of intense visualisation, although it has been concluded that what is involved is pure calculation.
“Their memory for digits is quite remarkable—and possibly unlimited. They will repeat a number of three digits, of thirty digits, of three hundred digits, with equal ease. This too has been attributed to a ‘method’.
“But when one comes to test their ability to calculate—the typical forte of arithmetical prodigies and ‘mental calculators’—they do astonishingly badly, as badly as their IQs of sixty might lead one to think. They cannot do simple addition or subtraction with any accuracy, and cannot even comprehend what multiplication or division means. What is this: ‘calculators’ who cannot calculate, and lack even the most rudimentary powers of arithmetic?
“And yet they are called ‘calendar calculators’—and it has been inferred and accepted, on next to no grounds, that what is involved is not memory at all, but the use of an unconscious algorithm for calendar calculations. When one recollects how even Carl Freidrich Gauss, at once one of the greatest of mathematicians, and of calculators too, had the utmost difficulty in working out an algorithm for the date of Easter, it is scarcely credible that these twins, incapable of even the simplest arithmetical methods, could have inferred, worked out, and be using, such an algorithm. . . .
“. . . And if you ask them how they can hold so much in their minds—a threehundred figure digit, or the trillion events of four decades—they say, very simply, ‘We see it.’ And ‘seeing’—‘visualizing’—of extraordinary intensity, limitless range, and perfect fidelity, seems to be the key to this. . . . .
“. . . The twins live exclusively in a thoughtworld of numbers. They have no interest in the stars shining, or the hearts of men. And yet numbers for them, I believe, are not ‘just’ numbers, but significances, signifiers whose ‘significand’ is the world. . . . Numbers for them are holy, fraught with significance.”
—Oliver Sachs, The Man Who Mistook His Wife for a Hat
(New York: Summit/Simon and Schuster, 1985)
Chapter 23, “The Twins,” pp. 185223.



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