No abstract

The appropriateness of direct magnitude estimation and interval scaling procedures for assessing the speech intelligibility of hearing-impaired adults was investigated by determining whether the continuum of the talkers' intelligibility was prothetic or metathetic. The intelligibility of 20 hearing-impaired talkers was scaled by 20 listeners using direct magnitude estimation and by 20 listeners using interval scaling. The two sets of scaling data were related in the curvilinear fashion that is typical of prothetic continua, indicating better construct validity for direct magnitude estimation than for interval scaling of speech intelligibility.

The purpose of this study was twofold: to determine through psychophysical comparison of scaling data whether speech naturalness is a prothetic or a metathetic continuum, and to examine the relationship between selected acoustic characteristics of the speech of nonstutterers and treated stutterers and listeners' judgments of their speech naturalness. Comparison of magnitude estimation and interval scaling data indicated that speech naturalness behaves like a metathetic continuum, suggesting that either scaling procedure is valid for the quantification of this dimension. The speech of the nonstutterers was judged more natural than the speech of the treated stutterers, and a global voice onset time (VOT) measure (averaged across places of articulation) and a sentence duration measure were found to be the acoustic parameters most highly correlated with and predictive of speech naturalness. These results suggest the possibility that stuttering treatments that employ strategies like gentle voicing onset and prolonged speech may result in somewhat slower posttherapy speech patterns characterized by prolonged VOTs that could influence listeners to judge the speech as more unnatural than the speech of nonstutterers.

Previous research has indicated that hearing-impaired speakers' intelligibility scores are better when sentences are used than when word lists are used as speech material in word identification tests. The speech intelligibility of 20 hearing-impaired speakers was measured with word identification tests using isolated words (W-22 monosyllables) and words in sentences context (CID sentences). Analysis of individual speaker' intelligibility data revealed that sentence intelligibility scores were higher than word intelligibility scores only for the better speakers and that no differences were apparent between sentence and single-word intelligibility for the poorer speakers. These findings agree with the results of research with normal speeds degraged in intelligibility by noise or filtering and indicate that an interaction may exist between context and overall intelligibility in which only speech that has a certain degree of overall intelligibility may show further intelligibility improvement with increased contextual clues.

Regression and principal components analyses were employed to study the relationship between 28 segmental and suprasegmental acoustic parameters of speech production and measures of speech intelligibility for 40 severely to profoundly hearing-impaired persons in an effort to extend the findings of Metz, Samar, Schiavetti, Sitler, and Whitehead (1985). The principal components analysis derived six factors that accounted for 59% of the variance in the original 28 parameters. Consistent with the findings of Metz et al., a subsequent regression analysis using these six factors as predictor variables revealed two factors with strong predictive relationships to speech intelligibility. One factor primarily reflected segmental production processes related to the temporal and spatial differentiation of phonemes, whereas the other primarily reflected suprasegmental production processes associated with contrastive stress. However, the predictive capability of the present factor structure was somewhat reduced relative to the findings of Metz et al. (1985). Data presented indicate that the populations sampled in the two studies may have differed on one or more dimensions of subject characteristics. Considered collectively, the present findings and the findings of Metz et al. support the tractability of employing selected acoustic variables for the estimation of speech intelligibility.