Reports of individuals who, despite having severe intellectual impairments, nevertheless show remarkable skills in a particular area, can be traced back centuries. In 1887 Langdon Down1 was the first to coin the term ‘idiot savant’ in his description of 10 individuals who exhibited outstanding abilities in specific areas but whose level of general ability was so poor that they were unable to live independently. Savant skills typically tend to fall within a fairly circumscribed range viz: mathematical skills (calendrical calculations, lightning arithmetic, and prime number calculations), music (especially the ability to re-play complex sequences after only one exposure), art (complex scenes with accurate perspective either created or replicated following a single brief viewing), and memory for dates, places, routes, or facts. Although savant abilities have been identified in a wide range of neurological and neurodevelopmental disorders they are most frequently reported in individuals with autism or autism spectrum disorder.2 Calendrical calculation (i.e. the ability of individuals with autism or other severe intellectual impairments to name, almost instantly, the day of the week of past or future dates) has long been a particular area of fascination for researchers in this area.3 Calculation spans of up to 40 000 years in range have been reported,4 but how this skill develops remains a source of speculation: is it rote memorization based on extensive practice; the ability to learn the templates derived from perpetual calendars; or the use of other strategies to determine calendrical regularities across the centuries? Good memory alone cannot be the answer, as calendrical calculators do not show any particular advantages in general memory. Unfortunately, it is usually impossible to gain any information on the processes involved from individuals themselves as most lack the communicative ability to describe how they have developed such exceptional ability.
In an attempt to solve some of these questions Heavey et al.5 devised an ingenious set of experiments to determine how savant calculators might acquire their skills. The findings indicate that memory for dates that reflect specific rules (e.g. falling on the same day of the week, in leap years, or occurring at 28-year cycles) is superior to memory for dates that lack such structure. Although participants were not able to formulate these ‘rules’ themselves, the authors draw the analogy with the use of grammatical rules in the general population. Thus, although we follow grammatical rules every day of our lives, only a minority is able to state what these rules comprise. It is suggested that this, largely unconscious, awareness of the regularities that characterize the calendar may derive from an early interest in dates and numbers (as is typical of many young children with autism), combined with repeated exposure to multiple day-date pairings (birthdays, Christmas, holidays, other events). Happé and Vital6 have argued that the detail-focussed learning style characteristic of individuals with autism may facilitate their ability to derive patterns from frequently occurring and predictable events of this kind. This may also explain why memory for numbers can be exceptional whilst memory for other forms of verbal material is unremarkable.
Many questions, however, still remain. The most obvious is why such skills are evident in only a minority of individuals with autism or intellectual ability. The possible influence of genetic or environmental factors in the development of these abilities is also unexplored. A further issue of practical significance is why such extraordinary abilities seem to confer so little advantage in other aspects of individuals’ lives. Very few savants with autism, for example, prove able to use their skills in ways that advance them in education or employment.7 How we might help to facilitate the emergence of special skills in many more individuals with developmental disorders and, more crucially, how these skills might be used effectively in their daily lives, remain major challenges.