Savant skills in autism: psychometric approaches and parental reports (2024)

(a) What are ‘savant skills’?

Reports of individuals who despite having severe intellectual impairments nevertheless show remarkable skills in a particular area can be traced back centuries (see Southall 1979; Smith 1983; ). Down (1887) 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. Subsequently, the American Association on Mental Deficiency (AAMD; Grossman 1983) defined ‘savants’ as ‘persons with obvious mental retardation who are capable of performing in sharply circ*mscribed areas (e.g. arithmetic, calendar calculating) at a remarkably high level’. Miller (1998) argued that the term savant should be used for those individuals who show (i) normatively superior performance in an area and (ii) a discrepancy between their performance in that area and their general level of functioning. Miller (1999) also noted that very few savants for whom assessment details were available had IQ scores below 50, and many had at least some subtest scores within the normal range. Treffert (1989) differentiated ‘prodigious’ savants (i.e. individuals possessing an exceptional ability in relation to both their overall level of functioning and the general population) from ‘talented’ savants (individuals showing an outstanding skill in comparison with their overall level of functioning). There is a parallel literature on the marked intra-individual discrepancies in the cognitive profiles of many individuals with autism (Joseph et al. 2002; Kuschner et al. 2007). Typically, cognitive peaks involve visuospatial skills (notably block design and object assembly) or rote memory; scores tend to be lowest on tests involving verbal abstraction or comprehension. Curiously, there has been no systematic comparison between these isolated exceptional cognitive skills and savant skills as usually conceptualized. That comparison constituted a key aim of our study.

(b) Savant skills in individuals with neurodevelopmental disorders

Savant skills are reported much more frequently in males than in females (ratio approximately 3 : 1), and have been identified in a wide range of neurological and neurodevelopmental disorders (Miller 1998; Treffert 2000). Specific skills, in relation to overall levels of function but not population norms, have also been reported in genetic conditions such as Smith–Magenis syndrome (computing and memory; I. A. Horn 1999, unpublished thesis; C. Webber 1999, unpublished thesis), Prader–Willi syndrome (memory and visuospatial skills; Milner et al. 2005) and Williams syndrome (music and memory; Howlin et al. 1998; Levitin et al. 2004). However, the condition in which both prodigious and talented savants are most frequently reported is autism/autism spectrum disorder (ASD).

(c) Specific areas of savant skill

Early anecdotal accounts of savants and more recent experimental studies (see Young 1995; Miller 1998; for reviews) indicate that savant skills fall within a fairly circ*mscribed range. The most commonly reported are mathematical skills (calendrical calculations, lightening arithmetic and prime number calculations), music (especially the ability to replay 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. Less frequently reported are ‘pseudo-verbal’ skills (hyperlexia or facility with foreign languages), coordination skills and mechanical aptitude (Tredgold 1952; Rimland 1978).

(d) Savant skills in autism

In Kanner's (1971) follow-up of his original 11 cases, six individuals were described as having an outstanding skill, mainly in the areas of music and rote memory. Two of the four cases described in detail by Asperger (1944, translated by Frith 1991) had outstanding calculating skills; another had exceptional spelling skills. Rimland (1978), in a postal survey of 5400 parents of children with autism, found that 531 (9.8%) were reported to have savant skills. Of those with reported skills, the most common were music (53%), memory (40%), mathematical/calculating skills (25%) and art (19%); 53 per cent had multiple special abilities (). , in a study of 254 individuals with autism, identified 33 (13%) with at least one special skill as assessed on the Autism Diagnostic Interview—Revised (ADI-R; Le Couteur et al. 2003). Exceptional memory was the most frequently reported and 29 individuals had multiple savant skills. Treffert (2000) concluded that approximately 50 per cent of individuals with savant skills described in the literature appeared to meet criteria for autism/ASD—a prevalence much higher than the less than 1 per cent figure he estimates for savant skills in other syndromes. Miller (1998) also noted that out of the total of 45 individuals described in his review, 22 had autism or showed symptoms highly suggestive of this diagnosis. Similarly, reported that 50 per cent of the individuals with savant skills in their experimental studies had autism.

(e) Association with cognitive levels and presence of stereotyped and ritualistic behaviours

Although early studies by O'Connor & Hermelin (1984, 1987; Hermelin & O'Connor 1986, 1990) used the traditional definition of idiot savant (i.e. special skills in individuals with severe cognitive impairment), some of their participants (and all of those with outstanding mnemonic skills) had IQ scores within the normal range. In a later study, noted that the mean IQ of savants with autism was considerably higher than that of non-savants (non-verbal IQ 72 versus 52; verbal IQ equivalent 70 versus 59). Miller (1999), in a review of studies providing more detailed IQ information, reported that the mean overall IQ/IQ estimate for the savants with autism was 71 (range 40–99), mean verbal IQ 77 (range 52–114) and mean non-verbal IQ 75 (range 47–92). Thus, although savant syndrome can occur in individuals with autism of very low IQ, in the majority of reported cases cognitive ability falls within the mild learning disability range or above.

O'Connor & Hermelin (1988, 1991) suggested that a tendency to repetitive behaviour and/or preoccupations with a restricted area of interest were crucial features of individuals with savant syndrome. They also found that ‘autistic savants’ showed a particular interest in one specific topic (names, buttons, birthdates, etc.) and in the repetitive ordering of possessions.

(f) Summary

Although there have been many single case or small group studies of individuals with autism who possess savant abilities or exceptional cognitive skills, there have been few systematic, large-scale investigations in this area. Inconsistencies in definition and wide variation in diagnostic ascertainment, ages and ability levels of the cases reported also give rise to problems, and there is little valid information on rates of savant skills in ASDs.

(a) Aims

The aim of the present study was to investigate the nature and frequency of savant skills in a large sample of individuals with autism who had been initially diagnosed as children. The specific issues investigated were as follows.

1. What are the types and frequency of savant skills or exceptional cognitive skills in individuals with a confirmed diagnosis of autism?

2. What is the degree of association between the two?

3. Are savant skills associated with overall levels of cognitive ability?

4. Do rates of such skills differ between males and females?

5. What is the relationship between savant or exceptional cognitive skills and the presence of repetitive, restricted and stereotyped behaviours?

(b) Sample

The total sample comprised 137 individuals, first diagnosed with autism at the Maudsley Hospital, London between 1950 and 1985, who have subsequently been involved in an ongoing, longitudinal follow-up study (Howlin et al. 2004; Hutton et al. 2008; see appendix A for process of sample identification). All initial diagnostic and cognitive assessments were conducted when individuals were aged 3–16 years. No participants had experienced any prolonged period in institutional care; all were Caucasian and singletons. Follow-up cognitive data were collected when participants were aged, on average, 24 years. Parental report data on savant skills were obtained approximately 10 years later, at a subsequent follow-up (mean age 34 years).

Inclusion criteria for the present study were as follows.

1. Lifetime diagnosis of autism confirmed on Autism Diagnostic Interview (ADI; Le Couteur et al. 1989).

2. Initial IQ ≥30 (this cut-off was chosen owing to the difficulties of making a reliable diagnosis of autism when IQ<30).

3. Aged ≥11 at follow-up (as savant skills may not be evident in early childhood).

4. No evidence of a specific medical disorder possibly related to autism (e.g. tuberous sclerosis, phenylketonuria, infant spasms, neurofibromatosis) or evidence of major physical or sensory impairment. (This criterion derived from the original follow-up studies.)

(c) Diagnostic and cognitive assessments

(d) Statistical analysis

Parametric analyses were used for comparisons where data permitted. Probability tests were two-tailed and, as multiple comparisons were conducted, the significance level for p was set at less than 0.01.

(a) Exceptional cognitive skills

(b) Parental reports of savant skills

(c) Relationship between exceptional cognitive savant skills and skills identified by parental report

Of the 93 individuals for whom parental questionnaire and cognitive data were available, 16 (17.2%) met criteria for a parent-rated skill, 15 (16.8%) had an exceptional cognitive skill and 8 (8.6%) met criteria for both.

All participants who met criteria for both unusual cognitive skill and parent-reported savant skill were male and, in each case, the parent-reported skill involved either mathematical or calendrical calculating abilities (table 1). For six out of these eight individuals, the exceptional area of cognitive ability identified on the Wechsler test also involved either the arithmetic or digit span subtests (one individual with exceptional mathematical ability was non-verbal and thus could not attempt the Wechsler arithmetic subtest).

Table 2

IQ scores of individuals with or without special areas of skill.

(a) Theoretical implications

From a theoretical perspective, two rather different questions arise. First, why is the rate of savant skills among individuals with autism so high (see )? On our findings, at least a quarter, but probably over a third, of individuals with autism show unusual skills or talents that are both above population norms and above their own overall level of cognitive functioning. Adequate studies comparing autism with other neurodevelopmental disorders have yet to be undertaken, but the rate of such unusual talents or skills seems particularly high in autism. Why? Second, within the realm of special talents, why (in autism) do these particularly involve computational skills, and is their basis the same as that underlying, say memory or artistic skills? There is plenty of speculation on both these questions but very little in the way of systematic testing of alternative mechanisms. Such research is much needed.

Contrary to suggestions that the presence of savant skills is associated with ritualistic behaviours or special interests (e.g. ), there was no evidence in the present study that those individuals with either exceptional cognitive or parent-rated skills had higher rates of repetitive or stereotyped behaviours/interests than those who did not. Thus, although all participants showed abnormalities in this domain, the severity of such behaviours was not related to savant abilities.

Finally, the fact that savant skills are not unique to autism, but are reported in a number of other syndromes with very different cognitive and behavioural phenotypes (e.g. Prader–Willi, Smith–Magenis and Williams syndromes), also requires further exploration. However, to date, the very different assessment methods and varying definitions used make it impossible to draw reliable conclusions about the relative rates and types of savant skills in other disorders. This is clearly an area in which better standardized measures and ascertainment criteria are crucial if comparative studies on syndrome-specific savant skills are to progress.

Methodological differences between studies also limit conclusions concerning the overall rates of savant skills in ASD. Lack of clear diagnostic criteria, inadequate definition of savant skills, the age of the cohort studied (savant skills may be less apparent in younger children) and the sex ratio (cohorts with a higher preponderance of males may well contain greater numbers of savants) all contribute to different estimates of prevalence. Questions also remain about the most effective way of collecting valid information on savant skills. Cognitive data, although the most objective, are also the most circ*mscribed; parental reports, while more detailed, are frequently highly subjective. Detailed observational and experimental studies such as those of Hermelin (2001) are feasible only for individual case studies or small case series. Moreover, definitions of what constitutes a skill that is truly exceptional in terms of population norms are also variable and highly unusual characteristics may not necessarily be equivalent to special skills. One individual in the present study, for example, had synaesthesia, seeing people, objects and numbers in colours, in a way that was often distressing for him. In our view, this did not meet criteria for a savant skill but drawing distinct boundaries between this and other savant abilities clearly presents difficulties.

Although the study is not without methodological problems—in particular, the fact that cognitive and parental data were collected at different times and parental information was available for a smaller proportion (73%) of the total sample—the findings are considered valid for a number of reasons. Sample size was relatively large; standardized diagnostic criteria for autism were met in all cases; criteria for savant skills were clearly defined; data were derived from two separate sources (cognitive assessment and parental information); the parental questionnaires used provided detailed descriptions of savant-type skills; and inter-rater reliability was high. The results suggest that the rates of savant skills in autism are substantial, particularly among males, and although these estimates are higher than reported by other researchers, in other ways our findings parallel those of previous studies (e.g. ). Thus, females seem less likely than males to develop savant skills, and in both this study and that of , the average non-verbal IQ of the savant group was over 80, consistently higher than that of the non-savant group. Indeed, in our study, no individual with a non-verbal IQ below 50 was judged as having any special talents. These data offer no support to claims that savant skills occur most frequently in individuals with autism who are intellectually impaired.

Despite the fact that savant abilities reported in the literature cover a relatively circ*mscribed range, the underlying cognitive mechanisms appear to vary widely. The ability to make rapid calendrical calculations (which is clearly not simply a feat of memory; Heavey et al. 1999; Iavarone et al. 2007), to calculate prime numbers, to remember dates/places/events from many years in the past or recite a long list of digits backwards may all require very different cognitive skills. Similarly, a high level of expertise in art or music is very different from being able to score highly on tests of block design or object assembly. It is possible that an overarching explanation may exist for why certain individuals go on to develop any area of exceptional skill, but understanding why these skills encompass such different areas and what the underlying basis of such skills is may require a rather different, research-based theoretical approach than adopted thus far.

Finally, there is the issue of how innate talents can be developed to form the basis of truly functional skills. In the present study, only five individuals with exceptional abilities (four related to maths and one related to visuospatial ability) had succeeded in using these skills to find permanent employment. For the majority, the isolated skill remained just that, leading neither to employment nor greater social integration. The practical challenge now is to determine how individuals with special skills can be assisted, from childhood onwards, to develop their talents in ways that are of direct practical value (in terms of educational and occupational achievements), thereby enhancing their opportunities for social inclusion as adults.

Table 3

Examples of savant skills reported on parental questionnaire.

One contribution of 18 to a Discussion Meeting Issue ‘Autism and talent’.

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