| Milne E et al. (2002). High
motion-coherence thresholds in children with autism. J Child Psychol
Psychiatry, 43:255-263.
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 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.
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| 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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