Intelligibility of Connected Discourse

Abstract

An approach to measuring the intelligibility of free-running connected discourse that contrasts with the quasi-statistical methods generally used with nonsense syllables, words, or sentences is described. With this approach, intelligibility is viewed as a decision by the listener that specifies how well the message was understood. The goal of testing, therefore, is to quantify the listener’s response with meaningful indices of performance. The various speech-Bekesy procedures are sensitive to a listener decision, but they fail to specify how the criterion of intelligibility was interpreted by the listener and have the additional disadvantage of specifying intelligibility as a threshold level in decibels rather than as a magnitude of intelligibility in percent. Experiments are reported in which systematic modifications were made to the speech-Bekesy procedures. The two major methods are “tracking to constant percentage criteria of intelligibility” and “estimation of intelligibility.” The results specify intelligibility of connected discourse by a performance-intensity function. The data are stable across alternative testing methods and compare favorably with sentence-repetition scores.

Hearing speech against spatially separate competing speech versus competing noise

“…The consistency and validity of the technique of adjusting a continuous speech signal to a nominated level of intelligibility has been demonstrated by Speaks, Parker, Harris, and Kuhl (1972). In that study, 3 normal hearing listeners each made 10 adjustments of a nonrepeating speech signal to each of 3 nominated percentage-ofintelligibility levels (25%, 50%, and 75%) in competing white noise: Standard deviations of the 10 adjustments ranged from 0.8 to 1.3 dB.…”

Intelligibility ratings of continuous discourse: Application to hearing aid selection

“…A third approach to quantifying the intelligibility of continuous discourse was investigated by Speaks et al (1972). With this approach, normal-hearing subjects used a percentage scale to rate the intelligibility of 15-s speech-innoise passages.…”

The intelligibility of words, sentences, and continuous discourse using the articulation index

“…The major drawback of this method is tha.t it involves two separate processes, a perceptual process and the motor skills involved in speaking. Speaks et al (1972) developed an estimation technique. Performance intensity functions were developed for subjects using a constant percentage criteria and for subjects estimating the percentage of material they understood.…”

“…Some researchers have concentrated solely upon techniques to measure aspects of intelligibility for these three types of speech. The result of their efforts have been well established methods for assessing Lhe intelligibility (or some aspect of intelligibility) for words (ANSI S3.2, 1991, Tillman, Carhart and Wilbur, 1963and Tillman and Carhart, 1966, sentences (Kalikow, 1977, Duffy and Giolas, 1974and Giolas, Cooker and Duffy, 1970 and CD (Speaks, Parker andKuhl, 1972 andGiolas, 1966). …”