Dissociation of chromatic discrimination ability in developmental disorders: Autism Spectrum Disorder and Williams Syndrome.

UNLABELLED: Atypical visual processing, particularly in dorsal stream functions, has been reported in both Autism Spectrum Disorder (ASD) and Williams Syndrome (WS), two developmental disorders which are typically said to have contrasting social profiles despite overlapping socio-communicative deficits. Here we aim to dissociate visual processing deficits between the two syndromes by examining ventral stream function, which underlies key aspects of socio-communicative ability such as face and object recognition; we specifically examine colour perception.

METHODS: Children (7-18 years) with ASD (N = 15) or WS (N = 26) and mental-age equivalent typically developing (TD) children (6-9 years) (N = 29) each completed two chromatic discrimination tasks: (1) the Farnsworth-Munsell 100-Hue Test (FM100), a manual cap-sorting task requiring the ordering of hues at equal lightness and saturation to form a smooth chromatic gradient, and (2) a computer-based threshold discrimination test, which assessed discrimination along cone-opponent ("red-green", "blue-yellow") and luminance cardinal axes using a controlled staircase procedure. Participants were required only to report, on each trial, the direction of a single arrow briefly shown against a grey background.

RESULTS: In FM100 performance, there was a significant difference between the WS and TD groups, but not between ASD and TD groups. Yet, in each group, performance was significantly related to non-verbal IQ, and this relationship was stronger in the ASD and WS groups. For the threshold task, a significant group by colour-axis interaction was found between TD and ASD, driven by significantly poorer "blue-yellow" discrimination in ASD. Between the WS and TD groups there were no significant differences in performance. Crucially, there were no significant correlations between threshold task performance and non-verbal ability.

CONCLUSION: Chromatic discrimination is reduced in ASD but not in WS, relative to TD, but this dissociation is not revealed by a task which confounds visual discrimination ability with general intellectual ability. Meeting abstract presented at VSS 2015.