Hearing loss is very common in the general population, with a prevalence of 82.9 per 1000 (U.S. Public Health Service, 1990). It becomes more common with age as a result of noise exposure, vascular disease, ototoxic agents, and other otological diseases. After arthritis and hypertension, hearing loss is the third most common chronic condition in persons over 65 (National Center for Health Statistics, 1982). In a study of 3556 adults from Beaver Dam, Wisconsin, Cruickshanks et al. (1998) found prevalence rates for hearing loss of 21% in adults ages 48–59 years, 44% for those ages 60–69, 66% for those ages 70–79, and 90% for those ages 80–92. The prevalence of perceived hearing handicap, however, is lower than the true prevalence of hearing loss. By age 70, approximately 30% of the population perceives themselves as hearing impaired, and by 80 years, 50% report being hearing impaired (Desai et al., 2001). There is also some indication that the prevalence of hearing impairment in persons 45–69 years old is increasing, especially among men (Wallhagen et al., 1997).

The typical hearing loss configuration in adults is a bilateral high-frequency sensory loss with normal or near normal hearing in the low frequencies (Moscicki et al., 1985; Cruickshanks et al., 1998). Men tend to have more hearing loss than women, and white individuals report greater hearing impairment than African Americans (Cruickshanks et al., 1998; Desai et al., 2001).

Although hearing loss is common in the general population, its effects on speech production are most pronounced in individuals who have congenital hearing loss or hearing losses acquired in early childhood. For individuals who acquire hearing loss as adults, the impact on speech production is limited and usually does not result in any perceptible speech differences (Goehl and Kaufman, 1984). The preservation of speech in most adults with hearing loss likely is a consequence of residual hearing sufficient for auditory feedback.

Speech differences have, however, been reported for some persons with complete loss or nearly complete loss of hearing. These individuals tend to remain intelligible, although the speaking rate may be reduced by about a third when compared with normal-hearing speakers (Leder, Spitzer, Kirchner, et al., 1987). A decreased speaking rate is reflected in increased sentence and pause durations as well as increased word, syllable, and vowel durations (Kirk and Edgerton, 1983; Leder et al., 1986; Leder, Spitzer, Kirchner, et al., 1987; Waldstein, 1990; Lane et al., 1998). Movement durations associated with articulatory gestures also are prolonged in some adventitiously deafened adults (Matthies et al., 1996), and it has been suggested that this overall decrease in rate contributes to a reduction in speech quality and communication effectiveness (Leder, Spitzer, Kirchner, et al., 1987).

Changes in respiratory and vocal control have been noted, as evidenced by abnormal airflow, glottal aperture, and air expenditure per syllable as well as frequent encroachment on respiratory reserve (Lane et al., 1991, 1998). Adventitiously deafened adults also tend to exhibit increased breathiness, vocal intensity, and mean fundamental frequency (Leder, Spitzer, and Kirchner, 1987; Leder, Spitzer, Milner, et al., 1987; Lane et al., 1991; Lane and Webster, 1991; Perkell et al., 1992). In addition, the fundamental frequency tends to be more variable, particularly on stressed vowels (Lane and Webster, 1991).

Reduced phonemic contrast also characterizes the speech of some adventitiously deafened adults. Lane et al. (1995) observed that voice-onset time tends to decrease for both voiced and voiceless stop consonants, while Waldstein (1990) observed this effect only with voiceless stop consonants. Vowel, plosive, and sibilant spectra become less distinct, and vowel formant spacing for some speakers becomes more restricted and centralized (Waldstein, 1990; Lane and Webster, 1991; Matthies et al., 1994, 1996; Lane et al., 1995). The first vowel formant commonly is elevated, with some speakers also exhibiting a reduction in second formant frequency (Perkell et al., 1992; Kishon-Rabin et al., 1999). A greater overlap in articulator postures and placements has also been observed, with a tendency for the consonant place of articulation to be displaced forward and vowel postures to be neutralized (Matthies et al., 1996). Fricatives and affricates appear particularly prone to deterioration with profound hearing loss (Lane and Webtser, 1991; Matthies et al., 1996). Many of these changes, although subtle in many cases and variable in expression across this population, are consistent with the speech differences common to speakers with prelingual hearing loss. Although the evidence is limited, owing to the small numbers of subjects examined, the data across studies suggest that the effects of hearing loss on speech production are most pronounced if the hearing loss occurs in the teens and early twenties than if it occurs in later adulthood.

The primary management procedure for adults with acquired hearing loss severe enough to compromise speech is to restore some degree of auditory feedback. The initial intervention typically consists of fitting traditional amplification in the form of hearing aids. For first-time hearing aid wearers, postfitting rehabilitation consisting of counseling and auditory training improves auditory performance and retention of the hearing aid, although secondary benefit in respect to speech production in adults has not been studied systematically (Walden et al., 1981).

A sensory implant often is recommended for adults who do not receive sufficient benefit from hearing aids or who cannot wear hearing aids (see cochlear implants). Individuals with an intact auditory nerve and a patent cochlea are usually candidates for a cochlear implant. Persons who cannot be fitted with a cochlear implant, such as persons with severed auditory nerves or ossified cochleae, may be candidates for a device that stimulates the auditory system intracranially, such as a brainstem implant. As with hearing aids, adult patients receiving sensory implants benefit from pre-and postfitting counseling and frequent monitoring. With current technologies, many patients show substantial improvement in auditory and speech function within months of device activation with little or no additional intervention, although normalization of all speech parameters may never occur or may take years to achieve (Kishon-Rabin et al., 1999). Some speech parameters, such as vocal intensity and fundamental frequency, show some degree of reversal when an implant is temporarily turned off and then on, but the extent and time course of overall recovery after initial activation vary with the individual. The variability in speech recovery after initial implant activation appears to result from a number of factors, among them age at onset of hearing loss, improvement in auditory skills after implant activation, extent of speech deterioration prior to activation, and the speech parameters affected (Perkell et al., 1992; Lane et al., 1995, 1998; Kishon-Rabin et al., 1999; Vick et al., 2001). As a result, some patients may benefit from behavioral intervention to facilitate recovery. In particular, persons with poor speech quality prior to receiving an implant, as well as persons with central auditory deficits and compromised devices, might benefit from systematic auditory, speech, and communication skills training, although the relationship between speech recovery and behavioral treatment has received little investigation in these patients.

See also auditory training; cochlear implants; hearing loss screening: the school-age child; noise-induced hearing loss; ototoxic medications; presbycusis; speechreading training and visual tracking.