Perception of shadows in children with autism spectrum disorders

Abstract

Background: Cast shadows in visual scenes can have profound effects on visual perception. Much as they are informative, they also constitute noise as they are salient features of the visual scene potentially interfering with the processing of other features. Here we asked i) whether individuals with autism can exploit the information conveyed by cast shadows; ii) whether they are especially sensitive to noise aspects of shadows.

Methodology/principal findings: Twenty high-functioning children with autism and twenty typically developing children were asked to recognize familiar objects while the presence, position, and shape of the cast shadow were systematically manipulated. Analysis of vocal reaction time revealed that whereas typically developing children used information from cast shadows to improve object recognition, in autistic children the presence of cast shadows--either congruent or incongruent--interfered with object recognition. Critically, vocal reaction times were faster when the object was presented without a cast shadow.

Conclusions/significance: We conclude that shadow-processing mechanisms are abnormal in autism. As a result, processing shadows becomes costly and cast shadows interfere rather than help object recognition.

Figure 1. Examples of images used to depict the various object–shadow combinations.

The shape of the shadows could be either congruent (A) or incongruent (B) with the shape of the objects. Shadows were presented to both the right and the left of the objects. Panel C depicts an object (a bottle) without a shadow.

Figure 2. Graphical representation for the interaction between group (autistic, typically developing) and experimental condition (congruent, incongruent, no-shadow).

The error bars correspond to the standard errors of the means.