Vibrotactile identification of vowels

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Abstract
The ability of subjects to identify vowels in vibrotactile transformations of consonant-vowel syllables was measured for 2 types of displays: a spectral display (frequency by intensity) and a vocal tract area function display (vocal tract location by cross-sectional area). Both displays were presented to the fingertip via the tactile display of the Optacon transducer. In the 1st experiments the spectral display was effective for identifying vowels in /b\V\ context when as many as 24 or as few as 8 spectral channels were presented to the skin. Performance fell when the 12- and 8-channel displays were reduced in size to occupy 1/2 or 1/3 of the 24-row tactile matrix. The effect of reducing the size of the display was greater when the spectrum was represented as a solid histogram (filled patterns) than when it was represented as a simple spectral contour (unfilled patterns). Spatial masking within the filled pattern was postulated as the cause for this decline in performance. Another experiment measured the utility of the spectral display when the syllables were produced by multiple speakers. The resulting increase in response confusions was primarily attributable to variations in the tactile patterns caused by differences in vocal tract resonances among the speakers. The final experiment found an area function display to be inferior to the spectral display for identification of vowels. A 2-dimensional spectral display could be further developed as a basic vibrotactile display for speech.