mpiad winners (N = 16) and autistic individuals (N = 58), and we treat Mathematics Olympiad Winners as a comparable group to autistic-savants in our own study (i.e. both groups display some form of exceptional skill). This comparison was chosen because we are looking to see whether differences truly exist between our autistic-savants and autistic-nonsavants. Our Bayes factors suggested support for the null hypothesis (i.e. no differences between groups) for four of the five AQ factors (social skills BF < .33; communication BF < .33; attention switching BF < .33; imagination BF =.35) with the exception of attention-to-detail, for which no firm conclusions could be drawn (BF = 0.96). Refer to Additional file 1 for more information regarding our calculation of the above Bayes factors including our choice of parameters as well as a sensitivity analysis.
SQ-R data was collected for 31 autistic-savants, 33 autistic-nonsavants, and 27 controls, and their data is shown in Fig. 3. A one-way ANOVA comparing these differences revealed a significant main effect, F(2, 90) = 23.94, p < .001, ηp2 = .35. Post hoc comparisons with Bonferroni correction revealed significant differences between the autistic-savant and autistic-nonsavant group (p = .022), the autistic-savant and control group (p <.001), and the autistic-nonsavant and control group (p <.001). In other words, the pattern was autistic-savants > autistic-nonsavants > controls.
All participants completed this test. Figure 4 displays participants’ total GSQ scores for the autistic-savant, autistic-nonsavant, and control group. A one-way ANOVA comparing these differences revealed a significant main effect, F(2, 110) = 29.35, p <.001, ηp2 = .35. Post hoc comparisons with Bonferroni correction revealed significant differences in total GSQ scores between the autistic-savant and autistic-nonsavant group (p = .030), the autistic-savant and control group (p <.001), and the autistic-nonsavant and control group (p <.001). In other words, the pattern again was autistic-savants > autistic-nonsavants > controls.
All participants completed this test. Figure 5 shows all factors of the SCSQ. We conducted a 3 × 6 ANOVA contrasting group (autistic-savants, autistic-nonsavants, controls) and the individual SCSQ factors. We found a significant main effect of group (F(2, 108) = 6.06, p = .003, ηp2 = .10), a significant main effect of factor (F(5, 540) = 31.84, p < .001, ηp2 = .23), and an interaction between group and factor (F(10, 540) = 7.69, p < .001, ηp2 = .13).
Post hoc comparisons with Bonferroni correction revealed significant differences (all p < .05) between autistic-savants and controls on technical/ spatial, need for organisation, global bias, and systemising. Significant differences (all p < .05) were also found between autistic-nonsavants and controls on need for organisation, global bias, and systemising. A significant difference was also found between autistic-savants and autistic-nonsavants on technical/spatial (p = .005). No significant differences were found between any group for ‘imagery ability’ or ‘language and word forms’. As before, we calculated Bayes factors to determine whether these null results indicated no difference or a lack of statistical power. This time, however, no suitable previous studies exist from which to draw informed priors. We therefore used an uninformative prior with the H1 (prior distribution) modelled as a uniform distribution in which all effects within a specified interval are considered equally likely (given no previous evidence to inform our decision). Following the standard procedure, we entered the lowest and highest possible mean differences between groups (i.e. zero and [maximum score per factor minus minimum score] respectively). Our calculation of Bayes factors suggests evidence for the null hypothesis for both imagery (BF = .22) and language (BF = .30). In summary, we found that autistic individuals, irrespective of savant syndrome, scored higher than controls on need for organisation, systemising, and local bias (i.e. low global bias). In addition, autistic-savants out-performed controls and autistic-nonsavants in technical/spatial traits.
All participants completed this test. Figure 6 shows all factors of the LOI across groups. We conducted a 3 × 4 ANOVA contrasting group (autistic-savants, autistic-nonsavants, controls) and the individual LOI factors (contamination, doubts/repeating, checking/detail, worries/just right). There was a significant main effect of group (F(2, 108) = 16.28, p < .001, ηp2 = .23), a significant main effect of factor (F(3, 324) = 90.78, p < .001, ηp2 = .46), and a significant interaction (F(6, 324) = 2.85, p = .01, ηp2 = .05).
Post hoc comparisons with Bonferroni correction revealed significant differences between autistic-savants and controls on every factor (all p < .05). Significant differences were also found between autistic-nonsavants and controls on every factor (all p < .05) apart from the worries/just right factor (p = .58). Finally, a significant difference between autistic groups emerged on the worries/just right factor with autistic-savants scoring higher than autistic-nonsavants (p = .02).
We also found that seven autistic-savants as well as two autistic-nonsavants and one control scored above the threshold of a score of 20 or more which suggests obsessive-compulsive disorder (OCD) symptoms. However, a chi-square test of association between the rates of OCD symptoms in the three groups did not reach significance (χ2(2) = 4.34, p = .11.
All participants completed this test, whose aim had been to separate our autism sample into our two autism sub-groups (autistic-savants and autistic-nonsavants). Table 1 shows the categories of skills asked about during the study along with the number of cases of each skill reported by participants. For completeness, the Additional file 2 contain descriptive statistics for the various sub-scales of our above questionnaire measures broken down according to the presence or absence of particular savant skills, but we do not consider them in detail here due to the large number of measures and lack of power when smaller samples are divided in this way.
Our results reveal a distinct profile of group differences between autistic-savants and autistic-nonsavants. The autistic-savants differed from autistic-nonsavants in that the former had heightened sensory sensitivity, greater obsessional behaviours (relating to excessive worries and getting things ‘just right’), more systemising traits, and increased technical/spatial traits (i.e. technical interests, mathematical abilities, and the use of spatial mental imagery). In all instances, these traits are features of autism more generally (i.e. they also discriminated between autistic-nonsavants and controls) but were particularly enhanced in savant syndrome specifically (i.e. discriminating autistic-savants from autistic-nonsavants). However, it is not the case that savants are simply shifted upwards along the autism spectrum. We did not find any differences between autistic-savants and autistic-nonsavants on the AQ or on subscales relating to attention-to-detail or social and communication skills, which might otherwise have been expected based on previous theoretical accounts [15, 23]. The implications of these findings for other theoretical models are discussed in more depth in the ‘General discussion’ section.
The purpose of experiment 2 was to explore whether participants could be trained to perform a characteristic savant skill—calendar calculation—and to investigate whether autistic-savants would show differences in accuracy or learning-style compared to autistic-nonsavants. As before, controls without autism or savant skills were included to separate effects linked to autism from effects linked to savant syndrome. Participants learned a number of different calendar rules throughout a training session and were given a final test that tapped all the rules. For example, the ‘matching month’ rule states that within any non-leap year, certain months have matching structures (January = October; March = November = February; September = December; July = April; e.g. if 1 March is a Sunday, then it necessarily follows that 1 November and 1 February will also be Sundays in that year). Savants who have calendar calculating within their repertoire are already sensitive to these rules. For instance, they are faster at saying that 1 November is Sunday if it has been ‘