title: Superior orientation discrimination and increased peak gamma frequency in autism spectrum conditions.
abstract: While perception is recognized as being atypical in individuals with autism spectrum conditions (ASC), the underlying mechanisms for such atypicality are unclear. Here we test the hypothesis that individuals with ASC will show enhanced orientation discrimination compared with neurotypical observers. This prediction is based both on anecdotal report of superior discriminatory skills in ASC and also on evidence in the auditory domain that some individuals with ASC have superior pitch discrimination. In order to establish whether atypical perception might be mediated by an imbalance in the ratio of neural excitation and inhibition (E:I ratio), we also measured peak gamma frequency, which provides an indication of neural inhibition levels. Using a rigorous thresholding method, we found that orientation discrimination thresholds for obliquely oriented stimuli were significantly lower in participants with ASC. Using EEG to measure the visually induced gamma band response, we also found that peak gamma frequency was higher in participants with ASC, relative to a well-matched control group. These novel results suggest that neural inhibition may be increased in the occipital cortex of individuals with ASC. Implications for existing theories of an imbalance in the E:I ratio of ASC are discussed.
authors.affiliation: Department of Psychology, University of Sheffield.
authors.forename: Abigail
authors.initials: A
authors.lastname: Dickinson
authors.affiliation: School of Systems Engineering, University of Reading.
authors.forename: Michael
authors.initials: M
authors.lastname: Bruyns-Haylett
authors.affiliation: Sheffield Adult Autism and Neurodevelopmental Service, Michael Carlisle Centre.
authors.forename: Richard
authors.initials: R
authors.lastname: Smith
authors.affiliation: Department of Psychology, University of Sheffield.
authors.forename: Myles
authors.initials: M
authors.lastname: Jones
authors.affiliation: Department of Psychology, University of Sheffield.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Milne
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000067877:Autism Spectrum Disorder / Q000503:physiopathology / Q000523:psychology*; D001921:Brain / Q000503:physiopathology*; D004192:Discrimination, Psychological / Q000502:physiology*; D005260:Female; D065818:Gamma Rhythm / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D009949:Orientation / Q000502:physiology*; D010775:Photic Stimulation; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult