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

Abstract

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.

Keywords: Auditory stream segregation; Fundamental frequency; Hearing loss; Vocal tract length.

Figure 1

Audiograms of the three groups of listeners: YNH (young normal hearing listeners), ANH (age-matched normal hearing listeners), AHI (aged with hearing impairment). The black lines correspond to the mean audiogram of all the participants in each group and the grey lines correspond to the individual audiograms. The pure tone average (PTA), based on the thresholds at 0.5, 1, 2 and 4 kHz, were 1.9, 9.5, and 39.3 dB HL for the YNH, ANH, and AHI groups, respectively.

Figure 1

Audiograms of the three groups of listeners: YNH (young normal hearing listeners), ANH (age-matched normal hearing listeners), AHI (aged with hearing impairment). The black lines correspond to the mean audiogram of all the participants in each group and the grey lines correspond to the individual audiograms. The pure tone average (PTA), based on the thresholds at 0.5, 1, 2 and 4 kHz, were 1.9, 9.5, and 39.3 dB HL for the YNH, ANH, and AHI groups, respectively.

Figure 2

Mean results across the participants within each group in terms of RAU. Black, gray, and white bars represent the means of the YNH, ANH and AHI listeners, respectively. The left and right collections of bars represent results using the male and female voice, respectively. Error bars represent ±1 standard error of the mean.

Figure 3

Mean results across the participants within each group in terms of RAU. Black, grey, and white bars represent the means of the YHN, ANH, and AHI groups, respectively. The left and right collections of bars represent the scores from the overlap and sequential condition, respectively. Error bars represent ±1 standard error of the mean.

Figure 4

The results for the Gender task in terms of sensitivity d'. The different shades correspond to the different conditions, as shown in the legend, and the different groups of bars correspond to the different participant groups (YNH, ANH and AHI).

Figure 5

F0 and VTL tasks presented in terms of sensitivity d'. The top panel corresponds to the sensitivity for the F0 task and the bottom panel to the VTL task. For each panel, the different shades correspond to a condition and the groups of bars correspond to the different groups (YNH, ANH and AHI). The error bars correspond to ±1 standard error of the mean.

Figure 6

Results for the streaming task with temporal overlap in terms of sensitivity d'. The different shades correspond to the different conditions, as shown in the legend. Each group of bars corresponds to a group (YNH, ANH and AHI). Error bars correspond to ±1 standard error of the mean.