Across-frequency comparison of temporal speech information by listeners with normal and impaired hearing.

Listeners with normal hearing (NH) and with sensorineural hearing impairment (HI) were tested on a speech-recognition task requiring across-frequency integration of temporal speech information. Listeners with NH correctly identified a majority of key words in everyday sentences when presented with a synchronous pair of speech-modulated tones at 750 and 3,000 Hz. They could tolerate small amounts (12.5 ms) of across-frequency asynchrony, but performance fell as the delay between bands was increased to 100 ms. Listeners with HI performed more poorly than those with NH when presented with synchronous across-frequency information. Further, performance of listeners with HI fell as a function of asynchrony more steeply than that of their NH counterparts. These results suggest that listeners with HI have particular difficulty comparing and effectively processing temporal speech information at different frequencies. The increased influence of asynchrony indicates that these listeners are especially hindered by slight disruptions in across-frequency information, which implies a less robust comparison mechanism. The results could not be attributed to differences in signal or sensation level, or in listener age, but instead appear to be related to the degree of hearing loss. This across-frequency deficit is unlikely to be attributed to known processing difficulties and may exist in addition to other known disruptions.