The intelligibility of synthesized speech: ECHO II versus VOTRAX.

The intelligibility of two speech synthesizers [ECHO II (Street Electronics, 1982) and VOTRAX (VOTRAX Division, 1981)] was compared to the intelligibility of natural speech in each of three different contextual conditions: (a) single words, (b) "low-probability sentences" in which the last word could not be predicted from preceding context, and (c) "high-probability sentences" in which the last word could be predicted from preceding context. Additionally, the effect of practice on performance in each condition was examined. Natural speech was more intelligible than either type of synthesized speech regardless of word/sentence condition. In both sentence conditions, VOTRAX speech was significantly more intelligible than ECHO II speech. No practice effect was observed for VOTRAX, while an ascending linear trend occurred for ECHO II. Implications for the use of inexpensive speech synthesis units as components of augmentative communication aids for persons with severe speech and/or language impairments are discussed.