May 2010


Autistic Children Have Difficulty Interpreting Shadows

This post was chosen as an Editor's Selection for Austistics perceive the world differently than others; for example, details are more readily recognized, and changing sensations are less readily recognized. Might the social challenges presented by autism be related to such perceptual differences?

People with autism generally have a hard time interpreting facial and other bodily cues useful for interpreting the emotions of others. It's easy to understand how this would affect social ability; if you can't tell whether your friend is bored, angry, or excited based on visual cues, how do you relate to each other?

It's unclear whether non-social objects (such as shadows) are perceived differently by autistics. Shadows are a part of everyday visual scenes, and can be helpful for recognizing objects (think of a typical horror movie, where the villain's shadow can be seen slowly creeping up on an unsuspecting victim).

However, shadows can interfere with object recognition. Changes in lighting may, for example, make faces harder to see, which may partly explain why those with autism find it difficult to recognize bodily cues.

Umberto Castiello (Università di Padova, Italy) and coworkers have added to our knowledge of this issue. They have demonstrated that shadows impair, rather than help, autistic children recognize objects.

Study questions and participants.

The scientists questioned whether the presence or absence of a shadow, or a shadow shaped the same as or differently than its parent object, helped or hindered object recognition. They studied twenty high-functioning autistic children and twenty normally developing children.

They went to considerable effort to make both groups very similar, except for the fact that one group had autism. The children were on average 12 years old, and there were an equal number of boys and girls in both groups.

None of the children were on medication. They had normal hearing, and normal (or corrected to normal) vision.

They had a similar IQ (between 100 and 110), and a similar socioeconomic status. Furthermore, they were all right-handed.

Testing shadow recognition.

The scientists tested the childrens' recognition of a digital object based on its shadow. Each of the objects had a well-defined geometry (fork, tennis racket, banana, etc).

The digital objects were pointing out of the image (along the z-axis, i.e. towards the children) at a 45° angle. The objects were digitally illuminated with light either from the left or right, ±34° along the x-y plane, at a 45° angle.

The scientists presented the children with the object along with its shadow, the object along with an incorrect shadow (e.g. a calculator with a pyramid shadow), or the object without its shadow. The time required for the children to identify the object was recorded.

Each child completed trials for each object under each condition, in random order. No set of trials lasted longer than 20 minutes, and a rest period of at least 5 minutes was given between each trial set.

Autistic children are fooled by shadows.

Normally developing children recognized objects roughly 11% faster than autistic children when the correct shadow was given. When the incorrect shadow was given, there was little difference in response time, i.e. the time for both groups was as slow as when the correct shadow was presented to autistic children.

Additionally, the autistic children recognized objects a little (roughly 5%) faster than normally developing children when no shadow was given. Given that the results were statistically significant, this is strong collective evidence that shadows significantly impede the ability of autistic children to perceive objects.

Children with autism recognize objects fastest when no shadow is present. Normally developing children recognize objects fastest when the correct shadow is present. Both groups of children are similarly fooled when the incorrect shadow is present.

The authors propose two different interpretations of these results. Both interpretations are based on the idea that autistics see detail (such as shadows) more readily than other people.

In either case, autistic people may be visually attracted to the shadow. The precise mechanism of how this behavior arises is still unclear.

More research is needed to elucidate the specific roles of perception and information processing in object recognition among autistic children. Such knowledge may ultimately help autistic individuals interact more readily with other people, and help others understand the world from an autistic perspective. for more information:
Becchio, C., Mari, M., & Castiello, U. (2010). Perception of Shadows in Children with Autism Spectrum Disorders PLoS ONE, 5 (5) DOI: 10.1371/journal.pone.0010582