Stimulus factors in perceptual confusability of tactile speech stimuli

Abstract

One possible limiting factor in performance by users of tactile aids for speech perception is the high confusability of tactile speech stimuli. This paper summarizes results of several experiments designed to identify the physical characteristics of tactile speech signals that make two stimuli seem perceptually confusable. First, sets of nonsense syllables were recorded onto digital audiotape and presented to subjects in an identification task. These same stimuli were input to a computer simulation of a multichannel vibrotactile speech aid, the Queen’s vocoder, showing the level of activity in each of the 16 vocoder channels over the duration of the stimulus. Perceptual confusion matrices obtained from the identification task were compared to matrices of temporal and spatial coincidences of physical activity in corresponding channels for each stimulus. In further experiments, tactile reception of individual nonsense syllables was compared to degraded auditory perception of the same stimuli. Several different methods of auditory stimulus degradation were employed, including reducing the number of vocoder channels and temporal distortion (smearing). Results are discussed in terms of insights into the processing of complex, spatially distributed vibrotactile stimuli, as well as implications for modifications of tactile aid processors and displays to improve stimulus identifiability. [Work supported by NIH.]