Advances in augmentative communication technology have enabled individuals with severe disabilities to communicate independently in a variety of environments. The most sophisticated voice output communication aids (VOCAs) use electronic speech synthesis to generate the user's voice output. Researchers and clinicians in the field of AAC have extensively examined and compared the intelligibility of synthetic speech under a variety of conditions (Mirenda and Beukelman (1990), Fucci et al. (1995), Raghavendra, P. and Allen, G.D. (1993), Reynolds et al. (1996), and Ruppreche et al. (1995)). Curiously, one important condition, the telephone, has been given scant attention. Given the ubiquitous nature of the telephone and its importance as a communication tool in our daily life, there is a surprising paucity of published research examining the use of VOCAs and the telephone. The only study we were able to locate relating to the use of synthetic speech over the telephone was by Nakamura et al. (1993). In this study, the authors telephoned 137 subjects using a speaker telephone and a speech synthesizer, and asked them questions (e.g., "Is [name] there?"). They then called back using natural speech to interview the subjects regarding their attitudes and perceptions about the synthetic speech caller. Results of the study indicated that 81% of the telephone calls made using synthetic speech were judged to have been completed successfully. Results also indicated that female subjects responded more favourably, and that an introductory message resulted in a more positive attitude by the listener toward the synthetic speech user. The current study takes a step back from the study by Nakamura et al. (1993), to examine the basic question of intelligibility of synthetic speech versus natural speech over the telephone. The independent variables of the current study are text-to-speech synthesis and digitally recorded natural speech. The dependent variable is the intelligibility of the two voice output systems over the telephone.
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