title: Marked selective impairment in autism on an index of magnocellular function.
abstract: Atypical high-level vision in autism is sometimes attributed to a core deficit in the function of lateral geniculate nucleus magnocells or their retinal drives. While some physiological measures provide indirect, suggestive evidence for such a deficit, support from behavioural measures is lacking and contradictory. We assessed luminance contrast increment thresholds on pulsed- and steady- pedestals in 17 children with autism spectrum conditions (ASC) compared to 17 typically developing children; these two conditions correspond to widely-used indices of magnocellular and parvocellular function. As a group, children with ASC had strikingly elevated thresholds on the steady pedestal-paradigm, yet performed similarly to controls on the pulsed pedestal paradigm, a finding that would typically be interpreted to reflect impaired magnocellular function. The effect size of the impairment was large and a substantial minority (41.2%) of the ASC group showed significantly impaired performance on an individual basis. This finding is consistent with a selective magnocellular deficit. It directly contradicts previous claims that such deficits are confined to 'complex' visual stimuli and likely does not reflect atypical attention, adaptation or high-level vision. The pattern of results is not clearly predicted by notions of imbalance of excitation versus inhibition, atypical lateral connectivity or enhanced perceptual function that account for a range of other findings associated with perception in autism. It may be amenable to explanation in terms of decreased endogenous neural noise, a novel alternative we outline here.
authors: Department of Experimental Psychology, University of Cambridge, Downing Street, Cambridge, CB2 3EB, UK. rebecca.greenaway@gosh.nhs.uk
authors: R
authors: R
authors: Greenaway
authors: G
authors: G
authors: Davis
authors: K
authors: K
authors: Plaisted-Grant
mesh_terms: D000293:Adolescent; D020817:Asperger Syndrome / Q000503:physiopathology / Q000523:psychology; D001321:Autistic Disorder / Q000503:physiopathology* / Q000523:psychology*; D020532:Basal Nucleus of Meynert / Q000502:physiology*; D002648:Child; D015350:Contrast Sensitivity; D004192:Discrimination, Psychological / Q000502:physiology; D005260:Female; D005403:Fixation, Ocular; D006801:Humans; D008029:Lighting; D008297:Male; D009434:Neural Pathways / Q000502:physiology; D010775:Photic Stimulation; D011597:Psychomotor Performance / Q000502:physiology; D012984:Software; D014795:Visual Pathways / Q000502:physiology; D014796:Visual Perception / Q000502:physiology