A comparison of speech synthesis intelligibility with listeners from three age groups

The use of computers in augmentative and alternative communication and in educational applications allows for the utilization of speech synthesis to instruct learners and to communicate messages. Of primary concern in these applications is the intelligibility of the synthesized voice for the individuals who will be potential listeners. To address this concern, the present investigation was designed to compare both single word and sentence intelligibility for four different types of voices (three speech synthesizers [Echo II+, Votrax Personal Speech System, and DECtalk] and a natural speaker) by listeners from three ages groups (children 6-8 years of age, children 10-12 years of age, and adults). The results indicated that single word intelligibility scores were lower than sentence intelligibility scores for all of the speech synthesizers but not the natural speaker. For the single word intelligibility task, there were no significant differences in intelligibility scores across the age groups, but significant differences were observed among the voices. For the sentence intelligibility task, there were significant differences in intelligibility scores across age groups and voices, as well as a significant age group-by-voice interaction. These results and their implications are described in detail.