Hybridizing conversational and clear speech to investigate the source of increased intelligibility in speakers with Parkinson's disease

Abstract

Purpose: A speech analysis-resynthesis paradigm was used to investigate segmental and suprasegmental acoustic variables explaining intelligibility variation for 2 speakers with Parkinson's disease (PD).

Method: Sentences were read in conversational and clear styles. Acoustic characteristics from clear sentences were extracted and applied to conversational sentences, yielding 6 hybridized versions of sentences in which segment durations, short-term spectrum, energy characteristics, or fundamental frequency characteristics for clear productions were applied individually or in combination to conversational productions. Listeners (N = 20) judged intelligibility in transcription and scaling tasks.

Results: Intelligibility increases above conversation were more robust for transcription, but the pattern of intelligibility improvement was similar across tasks. For 1 speaker, hybridization involving only clear energy characteristics yielded an 8.7% improvement in transcription intelligibility above conversation. For the other speaker, hybridization involving clear spectrum yielded an 18% intelligibility improvement, whereas hybridization involving both clear spectrum and duration yielded a 13.4% improvement.

Conclusions: Not all production changes accompanying clear speech explain its improved intelligibility. Suprasegmental adjustments contributed to intelligibility improvements when segmental adjustments, as inferred from vowel space area, were not robust. Hybridization can be used to identify acoustic variables explaining intelligibility variation in mild dysarthria secondary to PD.

Figure 1

Block diagram summarizing hybridization process. CNV = conversational; CLR = clear; ins = insert; del = delete; aux = auxiliary; D = duration; E = energy; I = intonation; S = short-term spectrum; HYB-DS = hybrid of duration and short-term spectra.

Figure 2

Selected amplitude normalized hybrid stimuli as well as the amplitude normalized conversational and clear productions for PDM01 are shown. The waveform display corresponds to the conversational production. In each panel, root-mean-square intensity is shown in gray, and the F0 time history is shown in black. The aspect ratio of the x-axis for the clear production differs from other panels to facilitate comparison of energy and F0 traces from the clear production to the hybrids as well as the conversation production.

Figure 3

Selected amplitude normalized hybrid stimuli, as well as the amplitude normalized conversational and clear productions for PDM06 are shown.

Figure 4

Mean percentage correct scores and scale values pooled across sentences and listeners are reported. Vertical bars indicate ±1 SD. Results for conversational (CON) and clear stimuli are shown on the extremes of the x-axis, and results for hybrids—duration (D); the combination of duration and short-term spectrum (DS); energy (E); intonation (I); prosody, defined as the combination of intonation, energy, and duration (IED); and short-term spectrum (S)—are reported in the middle of the x-axes.

Figure 5

Transcription results for individual sentences are reported for PDM01.

Figure 6

Transcription results for individual sentences are reported for PDM06. White symbols indicate sentences for which the duration/spectrum hybrid was associated with the best intelligibility among the six hybrid variants as well as improved intelligibility above conversational (n = 3). Black symbols indicate sentences for which the spectrum hybrid was associated with the best intelligibility among the six hybrids as well as improved intelligibility relative to conversational (n = 6).