The perception of obstacles by the blind.

Abstract

The present study was undertaken to determine the distrib. of the ability to perceive obstacles among 34 totally blind subjects, to determine the need for an obstacle avoidance device, and to serve as a basis for evaluating the efficiency of an obstacle avoidance device. A movable obstacle was placed at predetermined positions on an outdoor concrete walk. The subject was placed in a planned, haphazard manner 6, 12, 18, 24, 30, or 36 ft. from the obstacle in 54 trials. Six blank trials were interspersed during the latter half of the series. The subject was instructed to report as soon as he perceived the obstacle (1st perception), and then stop when he approached as closely as possible without touching it (final appraisal). Large individual differences were found in the ability to first perceive the obstacle. Consistency was shown in the "final appraisals" of those subjects who showed evidence of possessing the "obstacle sense." Seven of the 34 subjects (21%) did not possess the "obstacle sense" as detd. by the no. of collisions, the no. of false perceptions, the size of the mean variation of the mean "first-perception" and "final appraisal" with starting-distance.