Memory, Rule, And Arithmetic In Calendar Calculation: What Can We Learn From A Proto-Savant?

Background: Recently, we proposed that calendar calculation skills could rely on a large fund of memorized date-weekday associations, in combination with some knowledge of the rules of calendars and simple arithmetic. Objectives: One prediction of the model is that it should be possible to find savants who have little knowledge of rules but have already memorized a set of date-weekday associations. Methods: We investigated calendar calculation skills in AVK, a 18 year-old autistic female with a full scale IQ of 90. Calendar calculation tests were designed to assess the patient's ability to name weekdays, and to evaluate her knowledge of calendar rules. Results: AVK was able to name weekdays in a range of 10 years with an accuracy significantly above chance. The number of correct responses was high for the current year and the year when AVK became first interested in calendars, but dropped quickly below chance for years further in the past or in the future. She had very little knowledge of the rules of calendars. She was unable to match years that are 28, 11, or 6 years apart and have the same calendar. She knew the one-year-one-day rule be failed to adjust her calculation in the case of leap years. AVK was also unable to deduce a weekday from knowing the weekday of a date of the same year but of a different month. She showed no evidence of visual memory of calendars as she was unable to match them with a year of the same structure. Conclusions: Savant skills might very well develop with practice. Elsewhere we have predicted that skills don't reach an exceptional level unless dates constitute a restricted area of interest for a significant amount of time. Memorizing date-weekday associations is probably the first step undertaken by young savants.