Psychometric functions of vowel detection and vowel identification in multi-talker babble.

Abstract

Psychometric functions of vowel detection and vowel identification were measured in multi-talker babble for young normal-hearing listeners. A four-interval forced-choice procedure was used to examine the accuracy of vowel detection in babble with speech level presented from 0- to +15-dB sensation level relative to vowel detection thresholds obtained with method of limits. The accuracy of vowel detection was significantly influenced by vowel category and sensation level. The threshold of vowel detection for each vowel and each listener was defined as the speech level at which 71% accuracy of vowel detection was reached. Vowel identification was then measured in babble with vowel levels presented from 0- to 12-dB sensation level relative to individual thresholds of vowel detection, using a close-set 12-choice procedure. Results suggest that vowel identification was significantly affected by vowel category and sensation level. Altogether, the results of vowel detection and vowel identification indicate that, given the same signal-to-noise ratio, vowels are not equally audible and identifiable, possibly due to the fact that some vowels are more audible than others, and that the slope of psychometric functions of vowel identification is vowel-dependent.