Perception of patterned vibratory stimulation: An evaluation of the tactile vision substitution system

Sensory substitution--The replacing of an impaired sensory channel by a properly functioning one--is possibly best manifested today in attempts to provide visual aids for the blind. The tactile vision substitution system (T.V.S.S.) is an example of one such visual aid. The system presents patterned tactile stimulation to the skin of the observer provided by the output of a closed-circuit television system. Research conducted with congenitally blind Ss in evaluation of the T.V.S.S. has provided useful information concerning the potentialities and limitations of the prototype systems, similarities and differences between tactile and visual perception, and the development of visual perception in the congenitally blind Investigation demonstrated that the congenitally blind Ss can learn to make valid judgements of three-dimensional displays with the T.V.S.S. Such judgements are made on the basis of properties contained in the proximal stimulation properties analogous to the monocular clues of depth presence in vision, such as linear-perspective, apparent elevation in the visual field, size change as a function of distance, occlusion, and texural gradients. Similarities have been noted between judgements made by sighted Ss using vision and by blind Ss using the T.V.S.S. on comparable tasks. A display consisting of two slightly displaced alternating lights is perceived in both situations as a single spot of light moving back-and-forth between two display boundaries. A rotating drum made up of alternate black and white stripes is, when stopped, perceived as briefly moving in the opposite direction. External localization of the source of stimulation also occurs with both sensory inputs. The major differences between the visual and tactile inputs that have been noted have occurred in form recognition tacks. Although blind Ss using the patterned tactile stimulation are able to identify both geometric forms and abstract patterns, accuracy is consistently lower than that of sighted Ss using vision, and the latencies for the blind Ss are significantly longer. It is hypothesized that the longer latencies for the blind Ss using the T.V.S.S. can be accounted for primarily by the need to hand-position the television camera during scanning. A major factor in the lower accuracy for the tactile group is the noted difficulty in detecting and identifying display features located within a mass of stimulation. This difficulty with internal display detail may be a function of sensory inhibition and/or masking. The research findings support a concept of sensory substitution as well as a theory of perception which stresses the modality of many qualities contained in visible displays. Further research is needed to determine the significance of sensor movement--either eye movements or camera manipulation--in the perceptual process