Voice/mouth synthesis and tactual/visual perception of /pa, ba, ma/

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Abstract
The onset of voicing relative to onset of visible articulation is a potential cue for lipreaders to recognize nasal/stop consonants. The bilabial consonants /p, b, m/ were selected for study because of their high visibility and ease of optical synthesis. A phototransistor behind the teeth and an external microphone indicated mouth opening and voice onset, respectively, to measure relative timing of the 2 cues in natural speech. Average voicing leads for 10 adults were examined. To test relative timing of voice onset and mouth opening as a potential perceptual cue synthetic syllables were produced. The face substitute was an oscilloscope pattern, forming a mouth shape for 250, 400 or 550 ms. The voice substitute was a vowel-like buzz delivered through a hand-held vibrator. Buzz accompanied mouth opening with lead times of from +200 to -200 ms (40 ms steps), and ended simultaneously with mouth closure. Normal-hearing observers labeled each combination ma, ba or pa. Practiced lipreaders with knowledge of the onset cue subdivided the continuum with mean boundaries at +82 ms (/ma-ba/) and -87 ms (/ba-pa/). Individual differences occurred in sharpness and location of labeling boundaries. Because articulatory and perceptual boundaries are not coincident, this combined-mode cue appears insufficient for consonant recognition unless performance can be improved through extensive training.

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