Speaking clearly for the hard of hearing. III: An attempt to determine the contribution of speaking rate to differences in intelligibility between clear and conversational speech.

Previous studies (Picheny, Durlach, & Braida, 1985, 1986) have demonstrated that substantial intelligibility differences exist for hearing-impaired listeners for speech spoken clearly compared to speech spoken conversationally. This paper presents the results of a probe experiment intended to determine the contribution of speaking rate to the intelligibility differences. Clear sentences were processed to have the durational properties of conversational speech, and conversational sentences were processed to have the durational properties of clear speech. Intelligibility testing with hearing-impaired listeners revealed both sets of materials to be degraded after processing. However, the degradation could not be attributable to processing artifacts because reprocessing the materials to restore their original durations produced intelligibility scores close to those observed for the unprocessed materials. We conclude that the simple processing to alter the relative durations of the speech materials was not adequate to assess the contribution of speaking rate to the intelligibility differences; further studies are proposed to address this question.