Perceptual Atypicalities in Autism Revealed By Pupillometry
It has long been known that perceptual processing is unusual in autism: they have superior performance on some tasks, such as the Embedded Figures Test and visual search tasks, and inferior performance on many complex tasks requiring a more holistic, global perception. Recently these differences have been well modelled within the Bayesian approach to perception, with the suggestion that autistic observers have reduced integration of sensory and predictive information. This study explores further the different styles of autistic perception with an objective measure that correlates well with autistic traits.
The aim of the study is to use an objective and non-invasive technique to characterize different perceptual styles correlated with autistic traits in the typical population.
We measured modulation of pupil-size in 50 typical adult humans viewing a bistable-rotating cylinder, constructed so the brightness of the front surface changes with perceived direction of rotation. Subjects reported perceptual switches as they viewed the stimulus. We correlated the amount of pupil modulation in pupil size associated with the perceptual switch of the bistable stimulus with the autistic traits of participants, measured by the Autism-Spectrum Quotient AQ.
In some but not all participants, pupil diameter oscillated in phase with the ambiguous perception, more dilated when the black surface was in front. Importantly, the magnitude of oscillation predicts autistic traits of participants, assessed by the Autism-Spectrum Quotient AQ. Further experiments suggest that these results are driven by differences in perceptual styles: high AQ participants focus attention on the front surface of the rotating cylinder, while those with low AQ distribute attention to both surfaces in a more global, holistic style.
This is the first evidence that pupillometry reliably tracks inter-individual differences in perceptual styles, quickly and objectively, without interfering with spontaneous perceptual strategies. The results confirm the relationship between high autistic traits and local perceptual-style, suggested by previous, less objective studies. This relationship will be discussed in terms of Bayesian models suggesting less use of predictive priors in autistic perception.
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