Communication of Speech Sounds by a Tactual Vocoder

Tests of tactual speech perception were conducted using a special frequency-analyzing vocoder. The vocoder presented a running frequency analysis of speech mapped into a spatial array of tactual vibrations which were applied to the fingers of the receiving subject. Ten vibrators were used, one for each finger. The position of a vibrator represented a given frequency region of speech energy; the total range covered was 210 to 7 700 cps; all the vibrations had a frequency of 300 cps; the vibration amplitudes represented the energy distribution over the various frequencies. Discrimination and identification tests were performed with various sets of test vowels; consonant discrimination tests were performed with certain consonants including those that might be difficult to lipread. Performance with vowels appeared to be related to formant structure and duration as measured on the test vowels, and to tactual masking effects. Consonant discrimination was good between stops and continuants; consonant features of nasality, voicing, and affrication were also discriminated to some extent. It is concluded that the skin offers certain capacities for transmitting speech information which may be used to complement speech communication where only an impoverished speech signal is normally received. This research was conducted at the Speech Transmission Laboratory, Royal Institute of Technology, Stockholm, Sweden.