Autism is traditionally considered as a severe disorder involving some combination of repetitive behavior and restricted interests, deficits in social reciprocity and language, and mental retardation. But there is a long tradition of counterpoint to such disabilities, in so-called savant skills in fields that range from mathematical calculation and memory to art and music (Heaton and Wallace 2004). In each case, autistic savant skills represent rare yet astounding enhancements of human ability, beyond imagining for most of us. Understanding the cognitive and neurodevelopmental bases of such skills holds the promise of better understanding the causes of autism and enhancing human mental abilities to beyond the norm, if not at least helping us remember where we left the keys.

Enhanced abilities in autistics can involve not just such skills as calender calculation, hyperlexic reading, and perspective drawing, but also perception itself, as demonstrated by a study newly-published in Biological Psychiatry by Emma Ashwin and others. Motivated by a long history of studies showing that autism commonly involves sensory abnormalities and visual-spatial skills increased over verbal ones, Ashwin applied the first tests of visual acuity – analogous to the rows of ever-smaller letters on optometrist’s charts – to subjects with autism compared to controls. The autistic group exhibited not just significantly-increased visual acuity, but ‘acuity so superior it lies in the region reported for birds of prey’ (Ashwin et al. 2008) – an approximate twofold advantage over normal (see Figure). Savant skills are exceptional even in autism, but this study involved individuals with high-functioning autism or Asperger syndrome, otherwise unselected. As regards visual acuity, all of the autistic individuals thus exhibited enhanced, savant-like skill.

Figure from Ashwin et al. 2008 (Biological Psychiatry)

Might this be an isolated finding, a quirk of neurodevelopmental nature? Previous work has revealed enhanced auditory pitch discrimination in autism (Bonnel et al. 2003; O’Riordan and Passetti 2006), as well as increased sensitivity to vibration and thermal pain (Cascio et al. 2008), increased tactile sensitivity (Blakemore et al. 2006), olfactory sensitivities comparable to those of canines (Bogdashina 2003, p. 54), superior abilities in visual search tasks (O’Riordan et al. 2001), generally enhanced perception of relatively simple, static stimuli (Mottron et al. 2006), and evidence for ‘enhanced functioning and role of the primary visual cortex’ (Caron et al. 2006). More generally, autistics have recently been shown to exhibit higher ‘fluid intelligence’ – a form of problem-solving intelligence independent of acquired knowledge, higher than that of non-autistic controls (Dawson et al. 2007; Hayashi et al. 2008), also lending support to the idea that the previously-perceived association of autism with mental retardation is due to biases in ascertainment and diagnosis (Skuse 2007).

The implications of these findings for our understanding of the autistic and so-called normal brains, the evolutionary bases of autism, and societal perception of autistics, are difficult to overstate. The simplest, albeit preliminary, neurological explanation for perceptual and analytic enhancements in autistics is that their brains are ‘tuned’ to higher frequencies (Blakemore et al. 2006) due to differences in neuronal micro-architecture (Casanova et al. 2003) and greater emphasis on left-hemispheric, local-processing, high-frequency abilities (Ivry and Robertson 1998; Cook 2002; Han et al. 2002; Wang et al. 2007). At an evolutionary level, Grandin and Johnson (2005) have likened autistic savant talents to the enhanced sensory and memory skills of animals, and strong signals of positive Darwinian selection along the human lineage have consistently been reported for genes underlying sensory perception (e. g., Nielsen et al. 2005).

Whatever the proximate and ultimate explanations for eagle-eyed autism, Ashwin et al. (2008) have opened new doors to our understanding of perception, and the many meanings of what it means to be human and autistic.

Literature cited

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