Eagle-eye visual acuity in autism

Background: Autism spectrum conditions (ASC) are neurodevelopmental conditions diagnosed on the basis of difficulties with social interaction and communication, alongside overly narrow interests and repetitive behaviour. The first reports of autism and Asperger's Syndrome noted that people with these conditions commonly show atypical perceptual processing, including greater perception of details. Cognitive theories of ASC have focused on high-level processes such as impaired empathy, but it has also become evident that there is superior sensory discrimination in the modalities of vision, audition, and touch. These differences may underlie their excellent attention to local detail and a strong drive to systemise. However, no studies to date have used fundamental measures of visual acuity in ASC.

Objectives: To test the possibility that cognitive differences in visual discrimination and attention to detail may actually involve atypical low-level visual thresholds.

Methods: 15 adult males diagnosed with High-Functioning autism (HFA) & Asperger Syndrome (AS) and 15 control adult males took part in the study. Participants were administered the Freiberg Visual Acuity and Contrast test (FrACT), a standardised optometric test.

Results: The ASC group scored a mean visual acuity measure (20:7) that was significantly better than the control group (20:13) by a factor of two. To put this in perspective, birds of prey have visual acuity approximately two and a half times better than humans.

Conclusions: The results provide a possible explanation for enhanced perceptual functioning and attention to detail seen in ASC; indicating that remarkable visual acuity may be an underlying factor. The results of this study also suggest that inclusion of measures of sensory hypersensitivity as diagnostic criteria is justified and that basic standardised tests of sensory thresholds may inform causal theories of ASC. Since ASC are genetic in origin, this points to genes involved in sensory neurophysiology playing a key role.