Influence of broad auditory tuning on across-frequency integration of speech patterns.

PURPOSE

The purpose of the present study was to assess whether diminished tolerance for disruptions to across-frequency timing in listeners with hearing impairment can be attributed to broad auditory tuning.

METHOD

In 2 experiments in which random assignment was used, sentences were represented as 3 noise bands centered at 530, 1500, and 4243 Hz, which were amplitude modulated by 3 corresponding narrow speech bands. To isolate broad tuning from other influences of hearing impairment, listeners with normal hearing (45 in Experiment 1 and 30 in Experiment 2) were presented with these vocoder stimuli, having carrier band filter slopes of 12, 24, and 192 dB/octave. These speech patterns were presented in synchrony and with between-band asynchronies up to 40 ms.

RESULTS

Mean intelligibility scores were reduced in conditions of severe, but not moderate, simulated broadening. Although scores fell as asynchrony increased, the steeper drop in performance characteristic of listeners with hearing impairment tested previously was not observed in conditions of simulated broadening.

CONCLUSIONS

The intolerance for small across-frequency asynchronies observed previously does not appear attributable to broad tuning. Instead, the present data suggest that the across-frequency processing mechanism in at least some listeners with hearing impairment might be less robust to this type of degradation.