Home Page Science Frontiers

No. 65: Sep-Oct 1989

Issue Contents

Other pages

Other Interesting Sites











Calendar calculating by "idiot savants"

M.J.A. Howe and J. Smith have reported on an extensive study of calendar-calculating by individuals with otherwise subnormal intelligence. It is very clear that these so-called "idiot savants" use a variety of mental techniques, all rather different from rote memory, such as employed by memorizers of pi. First, we present Howe-and-Smith's abstract; then, a particularly interesting specific case.

"A number of mentally handicapped individuals are able to solve difficult calendar date problems such as specifying the day of the week for a particular date, sometimes over spans of more than 100 years. These individuals are self-taught and do not follow procedures at all similar to the usual, published, algorithms. An investigation of one individual revealed that he retained considerable information about the structure of days in particular months, probably as visual images. His skill closely depended on the extent and form of his knowledge of calendars, and his errors were often a consequence of lack of knowledge about a particular time period. Mentally retarded individuals who perform calendar date feats are often socially withdrawn and devote considerable periods of time to calendar dates. The most capable calendar-date calculators are usually individuals who have a strong interest in calendars as such."

Although some calendar calculators may use visual imagery - perhaps something like eidetic imagery - at least one calendar calculator was blind from birth.


"One of the few serious attempts that have been made to understand the mental operations underlying calendar skills is described by William Horwitz and others. They examined the abilities of a pair of mentally retarded identical male twins, both of whom performed calendar-calculating feats. During the twins' early childhood, despite severe family difficulties caused partly by the father's alcoholism, the parents, whose efforts to teach numerical and reading abilities to their sons were largely unsuccessful, were impressed by seeing one of the boys looking at a perpetual calendar in an almanac. Subsequently the parents encouraged the boys to acquire calendar skills. The feats of one twin were especially remarkable: he was reported to have had a range of at least 6000 years - beyond the range of any conventional or (socalled) perpetual calendar - although he gave incorrect answers for dates prior to 1582, owing to his ignorance of the 10-day calendar adjustment which was made at that time, when the Gregorian Calendar replaced the Julian one. As well as solving problems requesting the days of the week for specified dates, the more able twin could also answer questions asking, for instance, for those months in a given year in which the first day fell on a Friday, or the dates of specified days, such as 'The fourth Monday in February 1993?' (the 22nd)."

(Howe, Michael J.A., and Smith, Julia; "Calendar Calculating in 'Idiot Savants,' How Do They Do It?" British Journal of Psychology, 79:371, 1988.)

From Science Frontiers #65, SEP-OCT 1989. 1989-2000 William R. Corliss

Science Frontiers Sourcebook Project Reviewed in:


  • "A sourcebook of unexplained phenomena is therefore a valuable addition to a collection of scientific literature. William R. Corliss has provided this in the past with his source books of scientific anomalies in several subjects, and now he has provided it for astronomy. He has done an excellent job of collecting and editing a large amount of material, taken in part from scientific journals and in part from scientific reporting in the popular or semi-scientific press." -- "The Mysterious Universe: A Handbook of Astronomical Anomalies", reviwed by Thomas Gold, Cornell University, in Icarus, vol.41, 1980

  • "An interesting, systematic presentation of unusual weather [..] This book is recommended for a general audience" --"Corliss, William R., Tornados, Dark Days, Anomalous Precipitation, and Related Weather Phenomena, Sourcebook Project, 1983.", revieweed in Choice, September 1983
  • "..the science is necessarily somewhat speculative, but Corliss's symthesis is based on reputable sources." -- "Corliss, William R. (Compiler). Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena" reviwed by Joseph M. Moran, Univ. of Wisconsin in Science Books and Films, Sep/Oct 1983

  • "Before opening the book, I set certain standards that a volume which treads into dangerous grounds grounds like this must meet. The author scrupulously met, or even exceeded those standards. Each phenomenon is exhaustively documented, with references to scientific journals [..] and extensive quotations" -- "Book Review: The moon and planets: a catalog of astronomical anomalies", The Sourcebook Project, 1985., Corliss, W. R., Journal of the Royal Astronomical Society of Canada, Vol. 81, no. 1 (1987), p. 24., 02/1987