Detection of vowels in long-term speech-shaped noise

Abstract

The method of calibration is a critical issue in studies of vowel identification in noise, especially when manipulating speech-to-noise ratio. Common methods focus on stable estimates of the intensity or sound pressure level for specific speech sounds. However, vowels with the same sound pressure level often differ in both loudness, when presented at supra-threshold levels, and audibility, when masked detection thresholds for the vowel stimuli are measured. In the present study, detection thresholds for 12 isolated American-English vowels naturally spoken by three male and three female talkers were measured for young normal-hearing listeners in the presence of a long-term speech shaped (LTSS) noise. The duration of the vowels was equalized to 170 ms. The spectrum of the LTSS noise was identical to the long-term average spectrum of a 12-talker babble. The LTSS noise was present at 70 dB SPL. Thresholds for vowel detection showed distinct pattern as a function of the vowel category that was similar across listeners and talkers. This indicates that certain vowels were more audible than others, regardless of listeners and talkers. To account for the vowel-detection thresholds in noise, various analyses including comparisons of excitation patterns and estimates of specific loudness will be considered.