Lexical boundary error analysis in hypokinetic and ataxic dysarthria

Abstract

This investigation is the second in a series to examine a potential source of reduced intelligibility in dysarthric speech, namely the mismatch between listeners' perceptual strategies and the acoustic information available in the dysarthric speech signal. Lexical boundary error (LBE) analysis was conducted on listener transcripts from phrases produced by speakers with hypokinetic dysarthria, ataxic dysarthria, and normal controls. By design, the hypokinetic and ataxic dysarthric tapes elicited similar intelligibility (words-correct) scores. However, they elicited different numbers and patterns of lexical boundary errors. The nature of the error pattern differences can be traced to the listeners' use of available syllabic strength information to segment the acoustic stream. Specifically, although both dysarthric speech samples elicited numerous lexical boundary errors, those for the hypokinetic speech generally conformed to predictions offered from studies of degraded normal speech. Those for the ataxic speech did not conform strongly to such predictions. It appears that the prosodic deficits of the ataxic speech (tendency toward syllabic isochrony, excessive loudness variation, and reduced vowel working space consequent to reductions in vowel strength) posed more of a problem for listeners than did the prosodic deficits of the hypokinetic speech (rapid rate, monotony, reduced vowel working space).

On building models of spoken-word recognition: When there is as much to learn from natural “oddities” as artificial normality

“…Great interpretive power can be achieved by directly comparing contrastive degradations (e.g., hypokinetic vs. ataxic dysarthria; cf. Liss et al, 2000). More generally, however, we argue that the multidimensional nature of naturally occurring degraded speech is often a better reflection of the complexity of everyday healthy speech, or at least of the mechanisms engaged in the processing of healthy speech, than are many laboratory manipulations.…”

“…If the hypotheses generated from laboratory degraded speech are valid, they should apply to naturally occurring degraded speech that varies on theoretically relevant dimensions. This was the case in Liss et al's (1998Liss et al's ( , 2000 work. First, Liss et al found that stress-based segmentation is robust: Listeners used stress to guide lexical segmentation even when key prosodic cues were attenuated by dysarthria.…”

“…This is of interest because, prior to these reports, studies evaluating differences in the application of stress-based strategies were largely cross-linguistic in focus, showing differences related to the rhythmic properties of the language (e.g., Vroomen & de Gelder, 1995;Vroomen, Tuomainen, & de Gelder, 1998). Liss et al's (1998Liss et al's ( , 2000 work showed that, for English speakers, the constellation of prosodic distortion in one type of dysarthric speech (hypokinetic) was less detrimental to the application of metrical segmentation than was that in another type (ataxic). Although the hypokinetic samples lacked in f 0 variation and were generally speeded, speech rhythm was largely preserved.…”

The Relationship Between Listener Comprehension and Intelligibility Scores for Speakers With Dysarthria

“…For example, speakers were similar in that they all had cerebral palsy. Research suggests that listeners may perform differently on perceptual tasks such as those used in the present study when presented with dysarthria of different etiology (Klasner & Yorkston, 2005;Liss, Spitzer, Caviness, Adler, & Edwards, 2000). All speakers produced narratives in a sentence-by-sentence fashion following a model.…”

Vowel Contrast and Speech Intelligibility in Dysarthria

“…Previous studies have noted vowel centralization and reduced vowel space as the common characteristics of vowels in dysarthric speech [1][2][3][4][5][6][7][8][9] . However, the strength of the relationship between intelligibility and the vowel space area varied widely across studies, ranging from 0 to 71%.…”