Effect of age and hearing loss on auditory stream segregation of speech sounds.

Segregating and understanding speech in complex environments is a major challenge for hearing-impaired (HI) listeners. It remains unclear to what extent these difficulties are dominated by direct interference, such as simultaneous masking, or by a failure of the mechanisms of stream segregation. This study compared older HI listeners' performance with that of young and older normal-hearing (NH) listeners in stream segregation tasks involving speech sounds. Listeners were presented with sequences of speech tokens, each consisting of a fricative consonant and a voiced vowel (CV). The CV tokens were concatenated into interleaved sequences that alternated in fundamental frequency (F0) and/or simulated vocal tract length (VTL). Each pair of interleaved sequences was preceded by a "word" consisting of two random tokens. The listeners were asked to indicate whether the word was present in the following interleaved sequences. The word, if present, occurred within one of the interleaved sequences, so that performance improved if the listeners were able to perceptually segregate the two sequences. Although HI listeners' identification of the speech tokens in isolation was poorer than that of the NH listeners, HI listeners were generally able to use both F0 and VTL cues to segregate the interleaved sequences. The results suggest that the difficulties experienced by HI listeners in complex acoustic environments cannot be explained by a loss of basic stream segregation abilities.