ACCURACY, SPEED AND EASE OF FILTERED SPEECH INTELLIGIBILITY.

Abstract

Nineteen normal-hearing university undergraduates performed an "objective" and a "subjective" test of speech intelligibility accuracy (SIA), speed (SIS) and ease (SIE) for different levels of low-pass filtered speech. During objective testing subjects listened to monosyllabic words low-pass filtered through an earphone, and repeated words as correctly and quickly as possible. They simultaneously turned off a probe light as quickly as possible whenever it appeared. Objective SIA was assessed as percentage of incorrectly-repeated phonemes, objective SIS as elapsed time between word presentation and a subject's voice response, and objective SIE as probe-reaction time to turning off the light. During subjective testing subjects listened to common sentences low-pass filtered through a loudspeaker in a background of competing speech. Subjective SIA, SIS and SIE were assessed using magnitude estimation in which subjects assigned numbers to how accurately, quickly or easily they understood the sentences. The most important finding was generally improved accuracy, speed and ease of objectively- and subjectively-measured speech intelligibility with decreased filtering. The experimenter further analyzed results by determining how well each measure of SIA, SIS and SIE met assumptions of test sensitivity, selectivity, reliability, convergence, discriminability and sufficiency. Overall, the objective SIA measure best met assumptions, followed by the three subjective measures, the objective SIS measure, and the objective SIE measure. Results have clinical and research implications for testing and understanding normal and impaired speech intelligibility and perception. First, results are encouraging for audiologists who use objective SIA and subjective measures to test speech intelligibility of their patients. Second, results suggest that persons listening to degraded speech, or persons with auditory problems, may have difficulties in SIS and SIE as well as problems already documented for SIA. Accordingly, audiologists should consider SIS and SIE during audiologic evaluations, aural rehabilitation, and auditory research. Finally, a few subjects showed exceptionally fast voice-response and probe-reaction times which has implications for understanding the nature and limits of human auditory processing.