Acoustic variability in dysarthria and computer speech recognition

This paper examines the nature and extent of intra-speaker variability in normal and dysarthric speech and considers its relationship to computer speech recognition. Moderately dysarthric speech was found to exhibit greater intra-speaker variability on parameters of voice onset time, vowel duration, fricative duration and on vowel formants. Also noted for these speakers were patterns of merging acoustic boundaries, overlap in values for acoustic minimal pairs and shifting of the minimal pair boundary. Mildly dysarthric speech was found to follow a similar pattern to the controls with some additional shifts in contrast boundaries. Computer speech recognition levels were lower for moderately dysarthric speakers than for their associated controls. The mildly dysarthric speakers recognition pattern was similar to the controls. Correlation analysis of the relationship between acoustic variability and computer recognition found only a small proportion of the tokens to be significantly correlated at the 0.05 level of significance. Violation of minimal pair marking rules, along with merging of acoustic space and shifts in boundary positions between minimal pairs, were found to interact with variability to impact on computer recognition. The clinical implications are discussed with reference to the use of computer recognition as an augmentative communication tool.