Vowel detection and vowel identification in long-term speech-shaped noise.

Abstract

Psychometric functions of vowel detection and vowel identification were measured in long-term speech-shaped noise (LTSSN) for normal-hearing listeners. A four-interval forced-choice procedure was used to examine the accuracy of vowel detection in LTSSN with speech level presented from −10 to +5 dB sensational level relative to vowel detection thresholds obtained from Liu and Eddins’ study [J. Acoust. Soc. Am. 123, 4539–4546 (2008)]. The accuracy of vowel detection was significantly influenced by vowel category and sensational level. The threshold of vowel detection for each vowel and each listener was defined as the speech level at which 70.7% accuracy of vowel detection was reached. Vowel identification was then measured in LTSSN with vowel levels presented from 0 to 12 dB sensational 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 sensational 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. Moreover, given the same sensational levels, vowels do not have the same identifiability, possibly due to the fact that some vowels have dominant confusing vowels while others do not.