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Three experiments were performed to evaluate the use of subjective intelligibility estimations as a method for measuring hearing aid benefit. Subjective and objective speech intelligibility scores were compared for young normal-hearing and elderly hearing-impaired listeners. Objective intelligibility scores were obtained using the Connected Speech Test (CST). This test consists of conversationally produced passages of speech that the listener repeats sentence by sentence. To provide subjective intelligibility scores, listeners estimated the percentage that they understood of each CST passage. Comparison of the two types of scores revealed that they were closely related in both groups of subjects (r = .82-.92). Although the two types of scores were essentially equal for normal-hearing subjects, the hearing-impaired listeners tended to produce subjective estimations of intelligibility that were significantly lower than their objective scores. Manipulation of visual cues and amplification, in an attempt to influence the hearing-impaired listeners' expectation of understanding speech, had no effect on the subjective-objective score differential. The difference between subjective and objective scores in the hearing-impaired group was not related to audiometric variables such as speech reception threshold, audiogram, or duration of hearing loss. It was concluded that comparative hearing aid evaluations using subjective intelligibility estimates would usually produce the same relative outcome as evaluations using the objective intelligibility measurement procedure. However, scores obtained with the objective procedure had smaller critical differences. Thus, when both types of scores are based on the same number of passages, the objective measurement procedure would be the more sensitive to differences among hearing aids.
Cox et al. (1991) studied this question.