The Evolution & Medicine Review

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

Ashwin E, Ashwin C, Rhydderch D, Howells J, Baron-Cohen S (2008) Eagle-eyed visual acuity: an experimental investigation of enhanced perception in autism. Biological Psychiatry PMID: 18649873

Blakemore SJ, Tavassoli T, Calò S, Thomas RM, Catmur C, Frith U, Haggard P (2006) Tactile sensitivity in Asperger syndrome. Brain and Cognition 2006 61:5-13. PMID: 16500009

Bogdashina, O. (2003). Sensory perceptual issues in autism and Asperger Syndrome: different sensory experiences – different perceptual worlds. Jessica Kingsley, London. (Order book)

Bonnel A, Mottron L, Peretz I, Trudel M, Gallun E, Bonnel AM (2003) Enhanced pitch sensitivity in individuals with autism: a signal detection analysis. Journal of Cognitive Neuroscience 2003 15:226-35. PMID: 12676060

Caron MJ, Mottron L, Berthiaume C, Dawson M (2006) Cognitive mechanisms, specificity and neural underpinnings of visuospatial peaks in autism. Brain 129:1789-802. PMID: 16597652

Casanova MF, Buxhoeveden D, Gomez J (2003) Disruption in the inhibitory architecture of the cell minicolumn: implications for autisim. Neuroscientist 9:496-507. PMID: 14678582

Cascio C, McGlone F, Folger S, Tannan V, Baranek G, Pelphrey KA, Essick G (2008) Tactile perception in adults with autism: a multidimensional psychophysical study. Journal of Autism and Developmental Disorders 2008 38:127-37. PMID: 17415630

Cook ND (2002). Bihemispheric language: how the two hemispheres collaborate in the processing of language. In: T.J. Crow (ed.), The Speciation of Modern Homo sapiens. Proceedings of the British Academy 106:169–194. Oxford University Press, Oxford. (Order book)

Dawson M, Soulières I, Gernsbacher MA, Mottron L (2007) The level and nature of autistic intelligence. Psychological Science 18:657-62. PMID: 17680932

Grandin, T. and Johnson, C. (2005) Animals in Translation: Using the Mysteries of Autism to Decode Animal Behavior. Scribner, New York. (Order book)

Han S, Weaver JA, Murray SO, Kang X, Yund EW, Woods DL (2002) Hemispheric asymmetry in global/local processing: effects of stimulus position and spatial frequency. Neuroimage 17:1290-9. PMID: 12414268

Hayashi M, Kato M, Igarashi K, Kashima H (2008) Superior fluid intelligence in children with Asperger’s disorder. Brain and Cognition 66:306-10. PMID: 17980944

Heaton P, Wallace GL (2004) Annotation: the savant syndrome. Journal of Child Psychology and Psychiatry 2004 45:899-911. PMID: 15225334

Ivry, RB and Robertson LC (1998) The Two Sides of Perception. MIT Press. (Order Book)

Mottron L, Dawson M, Soulières I, Hubert B, Burack J (2006) Enhanced perceptual functioning in autism: an update, and eight principles of autistic perception. Journal of Autism and Developmental Disorders 36:27-43. PMID: 16453071

Nielsen R, Bustamante C, Clark AG, Glanowski S, Sackton TB, Hubisz MJ, Fledel-Alon A, Tanenbaum DM, Civello D, White TJ, J Sninsky J, Adams MD, Cargill M (2005) A scan for positively selected genes in the genomes of humans and chimpanzees. PLoS Biology 2005 3:e170. doi:10.1371/journal.pbio.0030170 (Full text; synopsis)

O’Riordan MA, Plaisted KC, Driver J, Baron-Cohen S (2001) Superior visual search in autism. Journal of Experimental Psychology 27:719-30. PMID: 11424657

O’Riordan M, Passetti F (2006) Discrimination in autism within different sensory modalities. Journal of Autism and Developmental Disorders 2006 36:665-75. PMID: 16639532

Skuse DH (2007) Rethinking the nature of genetic vulnerability to autistic spectrum disorders. Trends in Genetics 23:387-95. PMID: 17630015

Wang L, Mottron L, Peng D, Berthiaume C, Dawson M (2007) Local bias and local-to-global interference without global deficit: a robust finding in autism under various conditions of attention, exposure time, and visual angle. Cognitive Neuropsychology 24:550-74. PMID: 18416507