Abstract
BackgroundCast 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 FindingsTwenty 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/SignificanceWe 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.
Highlights
Produced by the blockage of light from a light source by objects, cast shadows can provide valuable information about the presence and number, as well as the relative position of objects in the visual scene [1]
We propose that performance of typically developing children might be explained in these terms, assuming that shadows are labelled by the visual system as shadows for the congruent, but not for the incongruent condition
This would explain why in typically developing children congruent. Much as they are informative, cast shadows constitute noise as they are salient features of the visual scene and it takes very little to make them look like independent surface features
Summary
Produced by the blockage of light from a light source by objects, cast shadows can provide valuable information about the presence and number, as well as the relative position of objects in the visual scene [1] As they are images of the objects that cast them, they might be helpful in retrieving the 3D structure of objects [2] and recognizing objects [3]. In order to fulfil this function, cast shadows must be labelled by the visual system as shadows, i.e. as patterns of light, as opposed to permanent, independent features (shadow labelling problem) They must be linked with the objects that cast them (shadow correspondence problem) [4]. 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
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