Hearing

Hearing sensitivity decreases with increasing age among both men and women. A longitudinal study of hearing thresholds among individuals screened for noise exposure, otologic disease, and hereditary hearing loss showed that hearing thresholds decline progressively above age twenty years in men, and above age fifty years in women (Pearson et al.). The decline in hearing thresholds of the men was more than twice as fast as that of the women, at certain ages. Women showed the greatest decline in hearing sensitivity in the low frequencies, whereas men showed the greatest decline in the higher frequencies. For the unscreened population, the average thresholds of older men, sixty-five years of age, show normal hearing sensitivity in the low frequencies, declining to a moderate hearing loss (42 dB HL) at 3000 cycles per second (Hz) and above (Robinson). For women, the average hearing thresholds at age sixty-five years indicate a slight hearing loss (16–25 dB HL) from 500 through 4000 Hz, and a mild hearing loss (30 dB HL) at 6000 Hz. The type of hearing loss typically is sensorineural, indicating that the site of lesion is the sensory mechanism of the inner ear or the nerve of hearing.

Hearing sensitivity in the ultra high audio-metric frequencies, above 8000 Hz, shows an age-related decline beginning in middle age that is greater than the decline in the lower audiometric frequencies (250–8000 Hz) (Wiley et al., 1998). These extended high-frequency thresholds are highly correlated with thresholds at 4000 Hz and 8000 Hz, suggesting that early monitoring of extended high-frequency thresholds among young and middle-aged adults may be useful for predicting the onset of presbycusis and for recommending preventive measures.

The ability to detect changes in temporal (timing) characteristics of acoustic stimuli appears to decline with age. Gap detection is the ability to detect a brief silent interval in a continuous tonal stimulus or noise, and reflects the temporal resolving power of the ear. Elderly listeners generally show longer gap detection thresholds than younger listeners (Schneider and Hamstra). Older listeners also require longer increments in tone duration to detect a change in a standard tone duration, compared to younger listeners (Fitzgibbons and Gordon-Salant, 1994). Finally, older listeners' performance for discriminating and identifying tones in a sequence is poorer than that of younger listeners, for tones of equivalent duration (Fitzgibbons and Gordon-Salant, 1998). Taken together, these findings indicate that older listeners have limited capacity to process brief changes in acoustic stimuli. This limitation could affect discrimination of the rapid acoustic elements that comprise speech.

Older people demonstrate difficulty understanding speech. In quiet listening environments, the speech recognition problem is attributed to insufficient audibility of the high-frequency information in speech by older people with age-related, high-frequency hearing loss (Humes). Substantial difficulty recognizing speech in noise also characterizes the performance of older listeners. Some studies have shown that the difficulties in noise are largely associated with the loss of sensitivity (Souza and Turner); other studies suggest that there is an added distortion factor with aging that acts to further diminish performance (Dubno, Dirks, and Morgan). The findings in noise are highly variable across studies and are largely dependent upon the speech presentation level, type of speech material (i.e., nonsense syllables, words, sentences), and availability of contextual cues.

In everyday communication situations, speech can be degraded by reverberant rooms and by people who speak at a rapid rate. Reverberation refers to a prolongation of sound in a room, and causes elements of speech to mask later-occurring speech sounds and silent pauses. With rapid speech, there is a reduction in the duration of pauses between words, vowel duration, and consonant duration. Time compression is an electronic or computer method to simulate rapid speech. Age effects are evident for recognition of both reverberant and time-compressed speech, which are independent and additive to the effects of hearing loss (Gordon-Salant and Fitzgibbons). Moreover, multiple speech distortions of reverberant and time-compressed speech, or either time-compressed or reverberant speech in noise, are excessively difficult for older people. Because both of these types of distortions involve a manipulation of the temporal (time) speech waveform, the recognition problem of older people may reflect a deficit in processing the timing characteristics of sound. An alternative hypothesis is that an age-related cognitive decrement in rapid information processing limits the older person's ability to process speech presented at a fast rate (Wingfield et al.). It should be noted, however, that older people are able to perform quite well on many speech recognition tasks if given adequate contextual cues (Dubno, Ahlstrom, and Horwitz, 2000).