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INTRODUCTION

Assistive technology is concerned with "devices or other solutions that assist people with deficits in physical, mental or emotional function" (LaPlante et al., 1992). This technology can be as simple as a walking stick or as sophisticated as a cochlear implant with advanced microelectronics embedded surgically in the ear. Recent advances in computers and biomedical engineering have greatly increased the capabilities of assistive technology for a wide range of disabilities. This paper is concerned with those forms of assistive technology that involve voice communication.

It is important in any discussion of assistive technology to distinguish between impairment, disability, and handicap. According to the International Classification of Impairments, Disabilities, and Handicaps (World Health Organization, 1980), an impairment is "any loss or abnormality of psychological, physiological or anatomical structure or function"; a disability is "a restriction in the ability to perform essential components of everyday living"; and a handicap is a "limitation on the fulfillment of a role that is normal for that individual." Whereas handicap may be the result of a disability that, in turn, may be the result of an impairment, these consequences are not necessarily contingent on each other. The fundamental aim of assistive technology is to eliminate or minimize any disability that may result from an impairment and, concomitantly, to eliminate or minimize any handicap resulting from a disability.

Figure 1 shows the extent to which different forms of assistive technology are being used in the United States, as measured by the 1990 Health Interview Survey on Assistive Devices (LaPlante et al., 1992). Of particular interest are those forms of assistive technology that involve voice communication. Assistive devices for hearing loss are the second most widely used form of assistive technology (4.0 million Americans as compared to the 6.4 million Americans using assistive mobility technology). It is interesting to note that in each of these two widely used forms of assistive technology one specific device dominates in terms of its relative use—the cane or walking stick in the case of assistive mobility technology (4.4 million users) and the hearing aid in the case of assistive hearing technology (3.8 million users). It should also be noted that only a small number of people with hearing loss who could benefit from acoustic amplification actually use hearing aids. Estimates of the number of people in the United States who should wear hearing aids range from 12 million to 20 million, or three to five times the number who actually do (Schein and Delk, 1974). A less widely used form of assistive technology