The recognition of time-compressed speech as a function of age in listeners with cochlear implants or normal hearing

Abstract

Speech recognition is diminished when a listener has an auditory temporal processing deficit. Such deficits occur in listeners over 65 years old with normal hearing (NH) and with age-related hearing loss, but their source is still unclear. These deficits may be especially apparent when speech occurs at a rapid rate and when a listener is mostly reliant on temporal information to recognize speech, such as when listening with a cochlear implant (CI) or to vocoded speech (a CI simulation). Assessment of the auditory temporal processing abilities of adults with CIs across a wide range of ages should better reveal central or cognitive sources of age-related deficits with rapid speech because CI stimulation bypasses much of the cochlear encoding that is affected by age-related peripheral hearing loss. This study used time-compressed speech at four different degrees of time compression (0, 20, 40, and 60%) to challenge the auditory temporal processing abilities of younger, middle-aged, and older listeners with CIs or with NH. Listeners with NH were presented vocoded speech at four degrees of spectral resolution (unprocessed, 16, 8, and 4 channels). Results showed an interaction between age and degree of time compression. The reduction in speech recognition associated with faster rates of speech was greater for older adults than younger adults. The performance of the middle-aged listeners was more similar to that of the older listeners than to that of the younger listeners, especially at higher degrees of time compression. A measure of cognitive processing speed did not predict the effects of time compression. These results suggest that central auditory changes related to the aging process are at least partially responsible for the auditory temporal processing deficits seen in older listeners, rather than solely peripheral age-related changes.

Keywords: aging; behavior; cochlear implant; fast speech; hearing loss; speech perception; temporal processing; time compression.

FIGURE 1

Group average audiometric thresholds of the test ears of participating listeners with clinically normal hearing at audiometric frequencies between 250 and 4,000 Hz separated into younger (YNH), middle-aged (MNH), and older (ONH) age groups. Error bars are ± 1 SD.

FIGURE 2

The top row shows speech recognition performance in percent correct for listeners with normal hearing (NH) in three age groups (younger, middle-aged, and older) listening to various levels of vocoding (unprocessed, 16-channel, 8-channel, and 4-channel) and four rates of time compression (0, 20, 40, and 60%). Error bars show ± 1 standard error. The bottom row shows the difference from the performance of the younger age group in percent. The dotted blue line represents the performance of the younger listeners. Data points below the line represent worse performance than the younger group. Error bars show ± 1 standard error and are based on 10,000 bootstrapped differences.

FIGURE 3

The top panel shows speech recognition performance in percent correct for listeners with CIs in three age groups (younger, middle-aged, and older) listening to four rates of time compression (0, 20, 40, and 60%). Error bars show ± 1 standard error. The bottom panel shows the difference from the performance of the younger age group in percent. The dotted blue line represents the performance of the younger listeners. Data points below the line represent worse performance than the younger group. Error bars show ± 1 standard error and are based on 10,000 bootstrapped differences and the smallest group size of 16.

FIGURE 4

Speech recognition performance in percent correct for listeners with CIs and listeners with NH presented 8-channel noise vocoded speech. Each listening group had three age groups (younger, middle-aged, and older) and listened to four rates of time compression (0, 20, 40, and 60%). Error bars show ± 1 standard error.