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Abstract:
It has been proposed that motion processing is modified in
deaf signers. Accordingly there is converging evidence that the
lateralization of motion processing is different in deaf signers
and hearing controls. However, it is unclear whether the
sensitivity of motion processing is overall modified in deaf
signers. Unlike previous studies that have looked at direction of
motion processing, in this study, we focused on velocity
discrimination. We first compared behavioral performance of deaf
and hearing when asked to detect changes in the velocity of moving
dots. We then used fMRI to map the underlying neural structures
that participate in this task in each population. The results
confirmed a different lateralization of the motion area MT/MST in
the two populations. Additionally, unlike hearing, deaf also showed
marked activation in the posterior superior temporal sulcus. This
area is known to code preferentially for biological motion in
hearing individuals. Could this effect be due to the greater
expertise deaf signers have with biological motion? To control for
the role of early exposure to sign language, hearing subjects born
to deaf parents who are also native signers of American Sign
Language were investigated. Their data were similar to that of
hearing controls suggesting that the effect is specific to
deafness, Thus, processing of motion velocity relies on an
overlapping but different network of areas in deaf and hearing
individuals.
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