People with savant syndrome are characterised by their remarkable talent in one or more domains (e.g. music, memory) but also by the presence of some form of developmental condition such as autism spectrum conditions (henceforth autism) [1]. Autism describes a set of symptoms involving difficulties in social communication, unusually repetitive/routine behaviours, unusually narrow interests, and atypical sensitivity to sensory stimuli [2]. Recent models of autism also focus on strengths associated with the condition (not just on their difficulties), in areas such as perceptual and cognitive processing [3], systemising [4], and attention to detail [5], as well as areas of interest, aptitude, and talents. In savant syndrome, talents and skills observed in such individuals far exceed their own overall level of intellectual or developmental functioning.
Exceptional cases of prodigious savant syndrome occur when an autistic individual’s level of skill goes beyond that seen even in the general population. A well-known example of a prodigious savant is the artist Stephen Wiltshire who is capable of drawing hyper-detailed cityscapes from memory and who also has autism [6]. Savant skills can exist in a variety of areas, but most savants show skills in art (e.g. hyper-detailed drawings), music (proficiency in musical instrument playing), maths (fast mental arithmetic), calendar calculation (the ability to provide the day of the week for any given date), and memory recall of facts, events, numbers etc. [7].
Although savant syndrome can co-occur with a range of developmental conditions, most cases involve autism in some form [8, 9] and savant syndrome has been reported to occur in up to 37% of autistic individuals [10]. The emergence of savant skills in autistic adults is not fully understood, and there is a lack of empirical evidence to support current theories. The motivation for the current research is to understand the condition of savant syndrome in more depth by contrasting a group of autistic savant individuals with a group of autistic individuals who do not have a savant skill. A third group of typical controls without autism or savant skills serve as a comparison. With this approach, we aim to separate features that are tied to savant syndrome from features that are tied to autism per se. We ask what individual differences lie within the autistic population that might allow some to develop savant skills while others do not. We first summarise current theoretical frameworks on the origins of savant skills. We then present two experiments that consider the development of savant skills at multiple levels of cognition, perception, and behaviour.
There is no consensus on exactly how savant skills are developed in autistic individuals. Bölte and Poustka [11] showed that savants do not show differences in standard intelligence compared to other autistic individuals. It could therefore be that their skills develop simply through many hours of extended practice. This would be similar to the abilities of neurotypical ‘memory athletes’ who can, for instance, memorise thousands of digits of pi using mnemonic techniques, with top performers relying on thousands of hours of practice—as in other sports [12,13,14]. Savants too appear to require practice, but here we ask exactly why they practice and whether they also have cognitive or perceptual differences beyond practice alone.
Two theoretical models have bridged the gap between need-for-practice and autistic symptoms in savants [15, 16]. Happé and Vital [15] proposed that one way in which savant skills might emerge could be through the autism-related trait of mind-blindness, which is the difficulty in attributing mental states to others [17, 18]. Happé and Vital [15] suggest that a lack of interest in the social world could serve to free up cognitive and time resources that are usually dedicated to monitoring social interactions. As a result, these extra resources could be re-allocated to the development of talent by permitting more time (i.e. practice) to the nurturing of restricted interests commonly observed in autistic individuals. Since these cognitive resources have been allocated away from monitoring social interactions, a further expected consequence might also be lower social and communication skills in savants and we explore this in experiment 1 below.
In contrast, Simner et al. [16] suggest that the hours spent achieving savant ability are the result not of mind-blindness, but of the autism-linked trait of obsessiveness—i.e. savants have an obsessive urge to over-rehearse their skills to prodigious levels. Tentative support for this comes from LePort et al. [19] who showed that a group of individuals with prodigious event-memory (some of whom are likely to be savants [16]) showed higher obsessional traits than controls. However, the controls they tested did not have autism, making it unclear whether obsession was tied to savant skills per se or simply to autism (or other co-occurring neurodevelopmental differences [20]). O’Connor and Hermelin [21] compared savants to controls with autism and drew similar conclusions about obsessiveness—but their questionnaire also contained items unrelated to obsessions (e.g. decision-making). In addition, they may not have corrected their question-by-question statistics for multiple comparisons, making it difficult to tie their findings to any particular trait. Similarly, Howlin et al. [10] used a questionnaire of just five questions, testing repetitive behaviours with a number of other traits (e.g. sensory sensitivity), again making it difficult to interpret their findings (of no difference between autistic-savants and autistic-nonsavants).
Finally, Bennet and Heaton [22] found higher scores for savant children on a five-question factor they named ‘obsessions and special interests’ compared to autistic-nonsavants, but traced this back to an individual question related to becoming absorbed in different topics. Given these differences across studies in their focus, questionnaire length, and testing groups, it remains unclear whether savants are particularly notable for their obsessional traits, above and beyond what we would expect from autism alone. Here we test both models described above, i.e. to see whether savants are particularly notable for their obsessional traits or for traits that are linked to mind-blindness (e.g. social and communication skills), compared to autistic individuals without savant skills.
Although both types of rehearsal (from mind-blindness or obsessiveness) could influence savant skills, this practice alone probably does not act as the only catalyst for talent to emerge. There may also be differences in certain cognitive abilities, linked to autism, which manifest themselves more strongly in individuals who acquire savant skills compared to those who do not. Specifically, we propose here and previously [16, 23] that talent could emerge from autism traits such as excellent attention-to-detail, hyper-systemising, and sensory differences. For example, the combination of attention-to-detail and hyper-systemising may predispose some autistic individuals to develop talent through the increased detection of ‘if p, then q’ rules [23]. These rules can be found in savant skills such as calendar calculation (i.e. stating the weekday for a given date) and can be learned from predictable patterns within the calendar itself.
A related proposal is Mottron et al.’s [24] ‘veridical mapping’ that links savant talent to the enhanced ability of autistic individuals to detect regularities within and between systems. Some savant skills do indeed depend on mapping regularities across systems (e.g. mapping from musical pitch to note-label in absolute pitch). In addition, savants appear to show a particular cognitive style of enhanced local processing, as outlined in the enhanced perceptual functioning model [3], and less global interference (e.g. in a target-detection task [25]) at least when activities demand active interaction [26]. Again, however, it is not clear whether these influences are tied to being a savant or simply having autism. Here we test groups of autistic individuals with and without savant syndrome to examine whether savants have a particular cognitive style (e.g. local bias), as well as elevated autism-related traits such as systemising.
Savant talent may also have important sensory components. Baron-Cohen et al. [23] argue that heightened sensory sensitivity may be the pre-requisite for excellent attention-to-detail, which they theorise as an autistic trait linked to savant syndrome. Subjective accounts of sensory irregularities in autism have been shown previously [27,28,29,30], and multiple studies have objectively demonstrated superior visual, auditory, and tactile sensory perception in autism [31,32,33,34,35,36]. These sensory differences may bring about the emergence of talent by affecting information processing at an early stage [23] although this suggestion is not universally supported [22].
One final sensory link between autism and savant syndrome is the presence of synaesthesia, where stimuli such as letters, numbers, and sounds invoke automatic and additional sensory experiences such as colours [37, 38]. Hughes et al. [39] found that synaesthesia occurs at higher levels among autistic individuals with savant skills (but not those without savant skills). Simner et al. [37] hypothesised that the obsessive over-rehearsal of savants may focus particularly on skills born out of synaesthesia, building on earlier work [25]. Elsewhere, we have already supported one branch of this model by showing that people with synaesthesia have elevated skills in savant domains (e.g. event recall [16]). Here we test the other branch of the model by examining whether their rehearsal is born out of obsessive traits [16] or mind-blindness which might predict lower social or communication skills [15]. Finally, we test the role of sensory sensitivities more generally, by comparing the sensitivities of autistic individuals with and without savant skills.
In our experiments, we look at two groups of autistic individuals, with and without a savant skill (specifically, prodigious talents which are above the skills of the general population). In experiment 1, we contrast our groups on cognitive and sensory self-report measures predicted by previous theoretical accounts. We test differences related to sensory sensitivity using the Glasgow Sensory Questionnaire (GSQ) [30], we test obsessive-behaviours using the Leyton Obsessional Inventory (LOI) [40], we test cognitive styles (e.g. local bias) using the Sussex Cognitive Styles Questionnaire (SCSQ) [41], and we test autistic traits such as systemising using the Systemising Quotient-Revised (SQ-Revised) [42] and the Autism Spectrum Quotient (AQ) [43]. In addition to our two groups of autistic individuals, with and without savant skills, we also test a typical control group with neither autism nor prodigious talents.
As stated above, there is very little empirical evidence to evaluate current theories of savant syndrome apart from tentative pointers towards increased obsessionality [16] and evidence for links to synaesthesia [16, 39]. Our goal is to test all theories directly; therefore, our predictions are based on the above theoretical frameworks. Following the theory by Baron-Cohen et al. [23], we predict that savants, relative to autistic individuals without a savant skill, will report more traits or behaviours related to sensory sensitivity, attention-to-detail, and systemising. We also predict they will report a more local (as opposed to global) cognitive style since this has previously been implicated in (e.g. visual search) advantages in autism and has been theorised to contribute to the development of savant skills [44]. Based on the model of autism-linked obsessive rehearsal [16], we predict that autistic-savants will report more obsessional behaviours compared to autism individuals without a savant skill. Alternatively, the rehearsal account based on mind-blindness [15] predicts that autistic savants would have lower social or communication skills (here measured using the AQ) compared to autistic individuals without a savant skill. Finally, we predict that both autism groups, regardless of the presence of a savant skill, will report heightened traits or behaviours in all of the above areas compared to the typical control group.
Experiment 2 investigates how a distinct psychological or behavioural profile in savants (explored in experiment 1) might influence performance on a behavioural task. We test the same three groups, to determine whether savants have a particular style of learning when presented with a novel savant skill: calendar calculation. As noted above, calendar calculation is the ability to give the correct day of the week for a given date in the past or future (e.g. 18th September 1990 was a Tuesday) and is considered one of the most characteristic savant abilities [7]. In experiment 2, three groups of participants (autistic-savants, autistic-nonsavants, controls) learned how to calendar calculate through a series of tutorials about different patterns and rules of the calendar. It is unclear whether calendar-calculating savants rely on rote memorisation of dates [45] or internalisation of the inherent rules of the calendar (e.g. 1st March 2013, 2014, 2015 = Friday, Saturday, Sunday respectively) or indeed whether they use some multi-faceted approach [44]. No studies to date have investigated the learning of calendar calculation skills in savants (who do not already possess this skill) compared to nonsavant autistic individuals and controls; therefore, our predictions below are again based on current theoretical models of savant syndrome.
If savant syndrome is linked to pre-existing abilities or dispositions (as opposed to practice alone), then we predict that savants may show a superior level of accuracy. In particular, the ‘enhanced perceptual functioning’ and ‘veridical mapping’ models predict more accurate performance by savants from their superiority in learning pattern/rule-based skills [3, 24, 44]. In contrast, accounts of savant skills that emphasise obsession or practice may not predict immediate advantages without extended training but might predict a different learning approach. Thus, if savants show increased repetitive/obsessive tendencies, we might expect them to engage in a slower, more careful approach to our calendar calculation task from, for example, increased answer checking.
In summary, our studies investigate savant syndrome by directly contrasting savants against a group of autistic individuals without a savant skill as well as a typical control group. Our investigation is the first to take an empirical approach to test a number of theoretical accounts of savant syndrome [15, 16, 23, 24, 44], some of which currently lack a clear empirical foundation.