Modifications in sign under conditions of impeded visibility.

This study investigated the effects of reduced visibility on the distance of signing hands from the bodies of adult signers who are deaf and on their rates of sign production. Subjects were videotaped as they signed with partners in each of three experimental conditions: unimpeded, moderately impeded, and severely impeded visibility. Visual impedance was created by placing screens between signing partners. The distance of a hand from the body, in terms of lateral, vertical, and forward-depth dimensions, was determined from digitized measurements of single video frames randomly selected from those in which the subject was actively signing. Sign rate was calculated as the number of signs produced in a given segment of time. Signs produced in the severely impeded visibility condition were found to be made at a slower rate and with a mean hand position further forward and vertically higher than signs produced in the unimpeded visibility condition.