NEW YORK--When Daniel Tammet set the European record for pi memorization last year, memorizing 22,514 digits in just over 5 hours, he attributed the feat to his ability to see numbers as complex, 3-dimensional landscapes, complete with color, texture, and sometimes even sound. Now researchers say they've found evidence to support Tammet's claim that his enriched perception is at the heart of his knack for number memorization.
Tammet's experience with numbers is an example of synesthesia, a puzzling phenomenon in which a certain type of stimulus triggers a hallucinatory perception. Some synesthetes associate musical notes with distinct colors, for example, or foods with shapes (as in "pointy" flavored chicken) [ScienceNOW, 24 March 2005].
Tammet, a 26-year-old from Kent, United Kingdom, says he sees digits from 0 to 9 as having distinct sizes and locations in space. To test whether this aspect of his synesthesia aids his numerical memory, neuroscientists Vilayanur Ramachandran, Shai Azoulai, and Edward Hubbard at the University of California, San Diego, gave him a series of memory tests in which he had 3 minutes to memorize 100 digits and their locations in a 10 by 10 array. When the digits were all the same font size, Tammet recalled 68 correctly, compared to an average of about eight for a control group, and he remembered all 68 when tested again 3 days later. But when the researchers repeated the test using an array in which the digits varied in size to disrupt Tammet's synesthetic sizing scheme, his performance plummeted to just 16 correct on the day of the test and zero 3 days later, according to a poster presented here 10 April at a meeting of the Cognitive Neuroscience Society.
"It's an extremely interesting idea that his memory could be supported by synesthesia," says Lynn Robertson, a cognitive neuroscientist at the University of California, Berkeley. Although more work needs to be done to prove that Tammet's synesthesia does indeed account for his prodigious mathematical memory, Robertson says, the findings fit with other evidence that synesthetes can use their enriched sensory perception to boost memory.