Shakuntala Devi, an Indian mathematical wizard known as “the human computer”, died in Bangalore last Sunday at the age of 83. She was one of the world’s most prodigious mental calculators on record, past or present, especially remarkable for the incredible speed with which she performed mental calculations on very large numbers. In 1977, at Southern Methodist University in Dallas, she extracted the 23rd root of a 201-digit number in 50 seconds, beating a Univac computer, which took 62 seconds.

Devi obviously did not go about her calculations in the same way that most of us would do. Her amazing speed of performing huge arithmetic calculations must have depended on the “automatic encoding and retrieval” of a wealth of declarative and procedural information in long-term memory rather “controlled processing”⁽¹⁾. Devi’s skill became so automatic that she herself was unable to explain them in detail. She claimed she could not teach anyone how she performed her calculations because:

She obtained the solution through exercising different routines drawn from an immense repertoire of numerical information and strategies, and the peculiarities of the problem itself determine the elements that are drawn upon from this repertoire to achieve the solution most efficiently (Arthur R. Jensen. “Speed of Information Processing in a Calculating Prodigy“)

Mental calculators like Shakuntala Devi are people with a prodigious ability in some area of mental calculation, such as multiplying or factoring large numbers. They usually possess an uncanny calendrical skill to state the day of the week a given date falls on. Some rare mental calculators are autistic savants, with a narrow area of great skill and poor mental development in other directions, but many are people of normal mental development who have simply developed advanced calculating ability. They were in great demand in research centres such as CERN or NASA before the advent of modern electronic computers.

What produces a Shakuntala Devi remains a mystery. Some kind of motivational factor that sustains enormous and prolonged interest and practice in a particular skill probably plays a larger part in extremely exceptional performance than does psychometric g or the speed of elementary information processes. Most of the basic operations involved in Devi’s performance probably became automatized during her childhood, as usually happens with most exceptional performers and creative geniuses. Yet this uncanny capability to crunch numbers might not be so rare:

Another example akin to numerical calculation is the application of complex grammatical rules in the construction of long or involved sentences. Most people speak their native language fluently and grammatically without being conscious of following grammatical rules, or even without any formal knowledge of grammar. Yet it would take a large computer with an extraordinarily complex program to perform this feat. For a calculating prodigy such as Devi, the manipulation of numbers is apparently like a native language, whereas for most of us arithmetic calculation is at best like the foreign language we learned in school. (Arthur R. Jensen. “Speed of Information Processing in a Calculating Prodigy“)

Perhaps Devi’s ability is at everyone’s reach after all, except that we prefer (or we are forced) to invest our early childhood years carving our brains to know how to create sophisticated narratives instead of performing other equally interesting tricks.

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Arthur R. Jensen. “Speed of Information Processing in a Calculating Prodigy“, INTELLIGENCE 14, 259-274 (1990)