Modeling the level-dependent changes of concurrent vowel scores.

The difference in fundamental frequency (F0) between talkers is an important cue for speaker segregation. To understand how this cue varies across sound level, Chintanpalli, Ahlstrom, and Dubno [(2014). J. Assoc. Res. Otolaryngol. 15, 823-837] collected level-dependent changes in concurrent-vowel identification scores for same- and different-F0 conditions in younger adults with normal hearing. Modeling suggested that level-dependent changes in phase locking of auditory-nerve (AN) fibers to formants and F0s may contribute to concurrent-vowel identification scores; however, identification scores were not predicted to test this suggestion directly. The current study predicts these identification scores using the temporal responses of a computational AN model and a modified version of Meddis and Hewitt's [(1992). J. Acoust. Soc. Am. 91, 233-245] F0-based segregation algorithm. The model successfully captured the level-dependent changes in identification scores of both vowels with and without F0 difference, as well as identification scores for one vowel correct. The model's F0-based vowel segregation was controlled using the actual F0-benefit across levels such that the predicted F0-benefit matched qualitatively with the actual F0-benefit as a function of level. The quantitative predictions from this F0-based segregation algorithm demonstrate that temporal responses of AN fibers to vowel formants and F0s can account for variations in identification scores across sound level and F0-difference conditions in a concurrent-vowel task.