Pi master’s storied recall

World-record holder grabbed decimal tiger by the tale

As the March 14 celebration of Pi Day approaches, toast a man who figured out how to have his pi and recite it, too — beyond 60,000 decimals. All it took was intensive practice and a knack for storytelling, a new study finds.

A Chinese man who set a world’s record in 2005 by reciting 67,890 decimals of pi learned to associate number pairs with images of people and objects, scientists report in the June Cognitive Psychology. From those images, 23-year-old Chao Lu concocted stories that corresponded to blocks of 500 to 1,000 numbers, say Yi Hu of East China Normal University in Shanghai and K. Anders Ericsson of Florida State University in Tallahassee.

As Chao Lu delivered a heaping slice of pi to Guinness judges for 24 hours and four minutes, a tale containing more than 60 chapters ran through his head. “That’s up there with the Bible,” Ericsson says.

Several thousand hours of practice over seven years with an efficient memory strategy enabled Chao Lu’s achievement, says psychologist Elizabeth Valentine of Royal Holloway University of London. No special mental or memory abilities were required, in her view, although scientists disagree about the extent to which practice makes perfect (SN: 7/17/10, p. 10).

Ericsson agrees that practice and strategy were key. In a 2009 paper, he and his colleagues reported that Chao Lu had an average memory for rapidly presented number sequences. When allowed to study number lists, the pi champ converted digit pairs into words or images that he wove into stories. The previous record holder described the same strategy to Japanese researchers.

In the new investigation, Hu and Ericsson asked the pi master to describe aloud his thinking process as he memorized 100- and 300-digit lists. His recall immediately afterward ranged from 95 percent to 100 percent accurate.

Chao Lu described generating mental images for number pairs from 00 to 99, such as classroom for 94 and stones for 17. From these cues he created stories.

For lists of 15 to 75 numbers, Chao Lu reported constructing five-image stories. Fourth and fifth images took him longer to study than preceding images did, consistent with having to integrate later images into a pre-existing story line. Chao Lu took longest to retrieve initial images, which cued recall of later images.

Given 50-digit lists with repeating number pairs that interfered with his story strategy, Chao Lu used alternative tactics. His recall remained impressive.

In interviews, the ultimate pi guy said that different stories containing common image sequences became confusing once he surpassed 10,000 decimals of pi. At that point, he generated images for combinations of digit pairs. The second pair in a sequence was treated as primary. So 1514 became a key (14) shaped like a parrot (15), whereas 1415 became a parrot with a key in its mouth.

Chao Lu’s memory feat was as short-lived as it was fantastic. Five years after his pi-rotechnics, he could recall only 39 decimals for the researchers.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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