An investigation of calendar calculating by an idiot savant.

Three mechanisms (eidetic imagery, high-speed calculation, and substitute compensation for normal learning) were investigated and rejected as possible explanations for the calendar-calculating ability of a particular idiot savant. Reaction times for calendar calculations indicated that he used neither an idiosyncratic nor a calendar-based system. Rote memory and a special ability to concentrate for extended periods of time were postulated to explain this individual's performance.