Note on a New System for Vibratory Communication
W. D. Keidel · Perceptual and Motor Skills · 1958
Perception of speech by means of sound stimuli physiologically reaches the level of consciousness via the auditory sensory system. By coding of sound into adequate optical stimuli it is possible to use the eye and its pachways for conducting the same amount of information to the central nervous system (visible speech). It is rather difficult, however, to use the somesthetic system for carrying a similar amount of information. Geldard (2), however, succeeded in converting speech inco the somesthetic decoding systems of the central nervous system by transforming information inco special stimuli optimally adapted to skin receptors (vibratese language). His syscem is based upon three parameters for each symbol corresponding to a letter of a word: (i) intensity, (ii) duration of a sinusoidal vibration, and (iii) locus of the stimulus. In our laboratory we are exploring experimentally another system of vibratory communication which is reported here briefly. Speech is scored on a magnetic tape at a rate of 15 in. per sec. Playback speed is slowed down by a factor of approximately 8 (2 in. per sec.). The frequency range of the speech is shifted from 300 to 3000 cps (recording) down to from 40 to 400 cps (playback). The slow frequencies are fed into a special mechanical vibraror, an enlarged mechanical model of the inner ear. Such a model is described by Bekesy (1). The physical features of the model permit spatial dispersion of the frequencies between 40 and 400 cps so char the surface of the model sensitive to 40 cps vibrates 30 cm. distant from the point of vibration for 400 cps. When the volar side of the forearm is brought into contact with the vibrating surface of the model, each frequency excites another point of the skin within a length of 30 cm. Therefore, the DL for frequency discrimination is improved to such a degree that intelligibility of speech seems possible. Ss are able to discriminate single words and short melodies.