Looking into autism

http://news.bmn.com/magazine/commentary?uid=CMTR.9081

Looking into autism
24 April 2002
by Wil Readinger wor1@cornell.edu
Milne E et al. (2002). High motion-coherence thresholds in children with autism. J Child Psychol Psychiatry, 43:255-263.


 
When one thinks of autism, it is probably the communicative and social impairments that come to mind first – behaviors such as social avoidance, lack of eye contact, or speech impairments. Indeed, it is these symptoms that are used in the diagnosis of autism, and most research on this developmental disorder has focused on the manifestation and treatment of these overt behaviors. Elizabeth Milne and her colleagues, however, have new evidence that might help us to understand the lower-level mechanisms behind autism. Children with autism were compared with age-matched control children on a motion-coherence task. Thresholds for motion detection were measured by presenting an array of moving dots on a computer screen; in each array, some of the dots move coherently (that is, in a common direction) and others move randomly. Importantly, each individual dot has a lifetime of only four frames, so to detect coherent motion, the child must be able to extract some global information from the display. Tracking an individual dot provides insufficient evidence to detect the coherent motion direction. The task thus provides a measure of sensitivity to global information in the stimulus.

 
The results revealed that children with autism showed a significantly higher threshold (lower sensitivity) for motion coherence than did controls. The authors suggest that these results represent impairment of the magnocellular visual pathway, which projects via the dorsal stream to the parietal regions of the brain. Several parietal lobe structures are known to be abnormal in people with autism, and this could result from the dearth of information coming from the low-frequency, magnocellular pathway early in development. Although it is presently more speculation than fact, such a model could provide an exceedingly parsimonious account of early perceptual and later behavioral aspects associated with autism. These findings are also consistent with the ‘weak central coherence’ hypothesis put forward to explain other biases for preferential processing of local features in autism. Milne et al. take an important first step in looking at perceptual deficits, which now should be followed by further perceptual investigation and functional imaging.



 


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