The effects of four variables on the intelligibility of synthesized sentences

Abstract

The experiments reported here examined the effects of four variables on the intelligibilty of synthetic speech: (1) listener age, (2) listener experience, (3) speech rate, and (4) the presence versus absence of interword pauses. The stimuli, eighty IEEE–Harvard Sentences, were generated by a DynaVox augmentative/alternative communication device equipped with a DECtalk synthesizer. The sentences were presented to four groups of 12 listeners each (children (9–11 years), teens (14–16 years), young adults (20–25 years), and adults (38–45 years). In the first experiment the sentences were heard at four rates: 105, 135, 165, and 195 wpm; in the second experiment half of the sentences (presented at two rates: 135 and 165 wpm), contained 250 ms interword pauses. Conditions in both experiments were counterbalanced and no sentence was presented twice. Results indicated a consistent decrease in error rates with increased exposure to the synthesized speech for all age groups. Error rates also varied inversely with listener age. Effects of rate variation were inconsistent across listener groups and between experiments. The presences versus absences of pauses affected listener groups differently: The youngest listeners had higher error rates, and the older listeners lower error rates when interword pauses were included in the stimuli. [Work supported by St. John’s University and New York City Board of Education, Technology Solutions, District 75.]