Motion velocity thresholds in deaf signers: changes in lateralization but not in overall sensitivity.

In a series of three experiments, we tested whether deaf native signers process motion velocity information differently from hearing nonsigners. In Experiment 1, participants watched radially moving dots and were asked to detect the quadrant in which the velocity of the dots had changed. Similar 79% thresholds were observed in the two populations. In Experiments 2 and 3, peripheral and central thresholds were assessed separately as previous studies suggest early deafness leads mainly to changes in the processing of visual peripheral information. Neither condition produced an overall population difference. These negative results were not due to a lack of sensitivity in our experiments. Indeed, as has been previously reported, deaf native signers exhibited better thresholds in the right than in the left visual field, whereas the opposite pattern was observed in the hearing. This effect appears triggered by experience with American Sign Language (ASL) rather than deafness per se. Overall, this study confirms that early deafness does not enhance motion processing, and suggests that most of the changes previously described in the literature are instead attributable to changes in attention, and possibly special alterations of attention-to-motion processes.