FO processing and the separation of competing speech signals by listeners with normal hearing and with hearing loss

Normal-hearing and hearing-impaired listeners were tested to determine FO difference limens for synthetic tokens of 5 steady-state vowels. The same stimuli were then used in a concurrent-vowel labeling task with the FO difference between concurrent vowels ranging between 0 and 4 semitones. Finally, speech recognition was tested for synthetic sentences in the presence of a competing synthetic voice with the same, a higher, or a lower FO. Normal-hearing listeners and hearing-impaired listeners with small FO- discrimination (ΔFO) thresholds showed improvements in vowel labeling when there were differences in FO between vowels on the concurrent-vowel task. Impaired listeners with high ΔFO thresholds did not benefit from FO differences between vowels. At the group level, normal-hearing listeners benefited more than hearing-impaired listeners from FO differences between competing signals on both the concurrent-vowel and sentence tasks. However, for individual listeners, ΔFO thresholds and improvements in concurrent- vowel labeling based on FO differences were only weakly associated with FO- based improvements in performance on the sentence task. For both the concurrent-vowel and sentence tasks, there was evidence that the ability to benefit from FO differences between competing signals decreases with age.