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Regarding “Eagle-Eyed Visual Acuity: An Experimental Investigation of Enhanced Perception in Autism”

      Low-level perceptual abnormalities are increasingly seen to play an important role in some features of autistic spectrum disorder (ASD) (review [
      • Dakin S.
      • Frith U.
      Vagaries of visual perception in autism.
      ]) by contributing to impairments of social communication through limiting higher-level visual processing of faces, for example. Arguably the most interesting findings are that individuals with ASD can sometimes perform better than matched control subjects when the task involves attention to detail (e.g., in visual search [
      • Plaisted K.
      • O'Riordan M.
      • Baron-Cohen S.
      Enhanced discrimination of novel, highly similar stimuli by adults with autism during a perceptual learning task.
      ], finding hidden figures [
      • Shah A.
      • Frith U.
      An islet of ability in autistic children: A research note.
      ], or resisting the influence of context within illusions [
      • Happe F.G.
      Studying weak central coherence at low levels: Children with autism do not succumb to visual illusions A research note.
      ]), suggesting that ASD might be associated with enhanced processing of local information (
      • Plaisted K.
      • O'Riordan M.
      • Baron-Cohen S.
      Enhanced discrimination of novel, highly similar stimuli by adults with autism during a perceptual learning task.
      ). A recent article by Ashwin et al. (
      • Ashwin E.
      • Ashwin C.
      • Rhydderch D.
      • Howells J.
      • Baron-Cohen S.
      Eagle-eyed visual acuity: An experimental investigation of enhanced perception in autism.
      ) has suggested that enhanced perceptual processing in ASD might include superior visual acuity (VA), a measure of individuals' ability to identify symbols of a set size (5 arc min width) presented foveally at standardized viewing distances. Specifically, Ashwin et al. report mean decimal visual acuities of 2.79 in their group of observers with ASD and 1.44 in an age-matched control group (VA is typically expressed as a fraction with the numerator referring to the distance at which the subject can just identify the letter, and the denominator the distance at which an observer with standard VA could identify the same letter; although, by definition, “normal” acuity must be 1.0 [or 20/20 = 6/6 in Snellen notation], when measured with good psychometric procedures [
      • Harvey Jr, L.O.
      Efficient estimation of sensory thresholds.
      ], young adults have a median acuity of 1.6 [
      • Rassow B.
      • Cavazos H.
      • Wesemann W.
      Normgerechte Sehschärfenbestimmung mit Buchstaben.
      ]) If true, Ashwin et al.'s finding would be very important for two reasons. First, as far as we are aware, this is the first report of consistently superior VA in any clinical population (neuropsychological or otherwise). Second, VA is generally considered limited by the earliest stages of the visual system (i.e., optical properties of the eye, photoreceptor density) so that this result would suggest either that: 1) this is not true, acuity is limited by other (higher level) factors; or 2) there are structural differences in the eyes of observers with ASD. The authors consider both possibilities by suggesting that either higher number of foveal cone cells or higher numbers of dopamine receptors at the retinal or neural level could contribute to their findings.
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      Linked Article

      • Eagle-eyed Visual Acuity in Autism
        Biological PsychiatryVol. 66Issue 10
        • Preview
          We thank Michael Bach and Steven Dakin and David Crewther and Alexandra Sutherland for their interesting commentaries with regard to the technical issues associated with use of the Freiberg Visual Acuity and Contrast Test (FrACT) (version 1.3) (1) in our study (2). We chose the FrACT for use in our study, because it is both quick and easy to implement and provides us with a quantitative measure of visual acuity (VA) that can be readily interpreted. As outlined in the commentaries, there are a number of settings within the FrACT that can be changed from their default values.
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      • Eagle-Eyed Visual Acuity: An Experimental Investigation of Enhanced Perception in Autism
        Biological PsychiatryVol. 65Issue 1
        • Preview
          Anecdotal accounts of sensory hypersensitivity in individuals with autism spectrum conditions (ASC) have been noted since the first reports of the condition. Over time, empirical evidence has supported the notion that those with ASC have superior visual abilities compared with control subjects. However, it remains unclear whether these abilities are specifically the result of differences in sensory thresholds (low-level processing), rather than higher-level cognitive processes.
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