Word identification and sentence comprehension of synthetic speech by individuals with mental retardation

The purpose of this study was to examine the performance of two text-to-speech systems (DECtalk and Real Voice) by individuals with mental retardation and matched controls. Each subject participated in two experimental sessions designed to measure word recognition, sentence verification accuracy, and sentence response latency. A pretest was administered to exclude the subjects who were unable to recognize the words or sentences when presented via natural speech. A total of 40 words was selected for evaluation of word recognition from a list of words provided by parents of nonspeaking children. Twenty three-word sentences were constructed to measure sentence verification accuracy and latency.

The results indicated that both individuals with mental retardation and nondisabled individuals performed significantly better on DECtalk synthetic speech than on Real Voice. Additionally, performance of individuals with mental retardation was significantly poorer than that of nondisabled individuals on the sentence verification task. Across groups, subjects performed significantly better on the word identification task than on the sentence verification task. A non-significant trend towards greater response latencies was observed for individuals with mental retardation. In summary, the results of this study indicate that individuals with mental retardation have significant difficulty in identifying and comprehending synthetic speech. The results of this investigation raise several issues related to comprehension of synthetic speech by nonspeaking individuals who rely on voice output communication aids to achieve effective and efficient communication.