Sonar System of the Blind

Abstract

Two blind subjects and 2 normal controls were tested for auditory scanning. Each observer made his own noises and used whatever natural sounds he considered best. These included talking, singing, whistling, hissing, snapping the fingers, and tongue-clicking. The method of constant stimuli (the method of constants) and the method of paired comparisons were employed to determine sensitivity. Psychophysical curves and threshold values were computed. The distance or depth perception of one of the blinded individuals was such that he could perceive a movement of 4.3 inches of a 1-foot disc placed 2 feet in front of him. Threshold fractions for this ability averaged about 1/4 and compared favorably with those for monocular depth perception. The discrimination between objects of different sizes, with distance constant, was not so accurate but was nevertheless remarkable. The blinded subjects could also distinguish between targets of the same size which were made of metal, wood, denim cloth, and velvet. Each of these objects simply "sounded different" from the others. Objects of similar density, [long dash]for example, painted and unpainted wood, or metal and glass - were indistinguishable. The judgments of the normal control subjects were almost never above the level of pure chance.