Contextual Information Modulates Pupil Size in Autistic Children

Abstract

Recent Bayesian models suggest that perception is more "data-driven" and less dependent on contextual information in autistic individuals than others. However, experimental tests of this hypothesis have given mixed results, possibly due to the lack of objectivity of the self-report methods typically employed. Here we introduce an objective no-report paradigm based on pupillometry to assess the processing of contextual information in autistic children, together with a comparison clinical group. After validating in neurotypical adults a child-friendly pupillometric paradigm, in which we embedded test images within an animation movie that participants watched passively, we compared pupillary response to images of the sun and meaningless control images in children with autism vs. age- and IQ-matched children presenting developmental disorders unrelated to the autistic spectrum. Both clinical groups showed stronger pupillary constriction for the sun images compared with control images, like the neurotypical adults. However, there was no detectable difference between autistic children and the comparison group, despite a significant difference in pupillary light responses, which were enhanced in the autistic group. Our report introduces an objective technique for studying perception in clinical samples and children. The lack of statistically significant group differences in our tests suggests that autistic children and the comparison group do not show large differences in perception of these stimuli. This opens the way to further studies testing contextual processing at other levels of perception.

Keywords: autism; contextual effect; individual differences; pupillary light reflex; pupillometry.

FIGURE 1

Schematics of the experimental stimuli and procedure. Top: images (sun, moon, and meaningless control images) were presented for 1s each in random order, embedded within an animation movie (Chomet, 2010; for copyright reasons the frames of the cartoon are replaced by title and author of the movie in this Figure). Note: all tested stimuli were achromatic; the movie (in color) merely filled the inter-stimulus intervals and was common to all conditions. Bottom: the same protocol was used for the presentation of full-screen maximum or minimum luminance squares, for testing the pupillary light or dark response.

FIGURE 2

Results from Experiment 1 (neurotypical adults). (A) Timecourses of pupil constrictions (referenced to pre-stimulus baseline) evoked by the three image categories: sun, moon, and phase-scrambled sun images (“scrambled”); thin lines straddling the timecourse give s.e.m. at each timepoint. (B) Peak constriction for the three image categories, averaged across participants. Error-bars show s.e.m. across participants.

FIGURE 3

Results from Experiment 2 (autistic and comparison children). (A) Peak pupil response to luminance increments and decrements, averaged across observers in each group. (B) Peak pupil response to sun pictures and meaningless images (“scrambled”), averaged across observers in each group. In both panels, error bars show s.e.m. across participants.

FIGURE 4

Timecourses of pupillary constriction (referenced to pre-stimulus baseline) evoked by sun and phase-scrambled sun images (“scrambled”), in the group of autistic children (A) and in the comparison group (B); thin lines straddling the timecourse give s.e.m. at each timepoint. The dash-dot lines serve as reference to highlight the difference in response amplitude across panels.

FIGURE 5

Lack of association between autistic-like traits, as measured by the Autism-spectrum Quotient questionnaire (AQ score), and the difference in pupil response evoked by the sun images and the meaningless control images obtained by phase scrambling. (A) Data from neurotypical adults. (B) Data from children, from both the autistic (filled symbols) and the comparison groups (empty circles). The horizontal continuous black lines show the mean, and the red lines the best-fit linear regression with its 95% confidence interval. Text insets give the Pearson’s correlation (with sample size) and associated p-value and log Bayes Factor.