The light-from-above prior is intact in autistic children

Abstract

Sensory information is inherently ambiguous. The brain disambiguates this information by anticipating or predicting the sensory environment based on prior knowledge. Pellicano and Burr (2012) proposed that this process may be atypical in autism and that internal assumptions, or "priors," may be underweighted or less used than in typical individuals. A robust internal assumption used by adults is the "light-from-above" prior, a bias to interpret ambiguous shading patterns as if formed by a light source located above (and slightly to the left) of the scene. We investigated whether autistic children (n=18) use this prior to the same degree as typical children of similar age and intellectual ability (n=18). Children were asked to judge the shape (concave or convex) of a shaded hexagon stimulus presented in 24 rotations. We estimated the relation between the proportion of convex judgments and stimulus orientation for each child and calculated the light source location most consistent with those judgments. Children behaved similarly to adults in this task, preferring to assume that the light source was from above left, when other interpretations were compatible with the shading evidence. Autistic and typical children used prior assumptions to the same extent to make sense of shading patterns. Future research should examine whether this prior is as adaptable (i.e., modifiable with training) in autistic children as it is in typical adults.

Keywords: Autism; Bayesian priors; Bias; Development; Light-from-above; Perception.

Fig. 1

Stimulus with light and shadow as though lit from directly above (A) and rotated + 150° to maximize the appearance of concavity in the central hexagon according to mean adult priors (B).

Fig. 2

Examples of slides introducing the shape judgment task. Panel D shows the stimulus rotated 150° and is followed by an animation of the bee filling the central cell with honey.

Fig. 3

Example data for one autistic participant and one typical child participant. Magenta and cyan dots indicate the proportion of convex judgments for the orientation values tested for one autistic participant (left) and one typical participant (right). Blue lines indicate the predictions of the fitted bimodal distribution. Yellow dots show the estimate of the light source biases for these two participants. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 4

Light source bias estimates for autistic children, typical children, and typical adults estimated from Eq. (3). Negative values correspond to biases to the left of the vertical. Red bands indicate median values; boxes extend from lower to upper quartile values; and whiskers show the full range of values. (For interpretation of the reference to color in this figure legend, the reader is referred to the Web version of this article.)