Effects of voice coding and speech rate on a synthetic speech display in a telephone information system

Abstract

Despite the lack of formal guidelines, synthetic speech displays are used in a growing variety of applications. Telephone information systems permitting human-computer interaction from remote locations are an especially popular implementation of computer-generated speech. Currently, human factors research is needed to specify design characteristics providing usable telephone information systems as defined by task performance and user ratings. Previous research used nonintegrated tasks such as transcription of phonetic syllables, words, or sentences to assess task performance or user preference differences. This study used a computer-driven telephone information system as a real-time, human-computer interface to simulate applications where synthetic speech is used to access data. Subjects used a telephone keypad to navigate through an automated, department store database to locate and transcribe specific information messages. Because speech provides a sequential and transient information display, users may have difficulty navigating through auditory databases. One issue investigated in this study was whether use of alternating male and female voices to code different levels in the database hierarchy would improve user search performance. Other issues investigated were basic intelligibility of these male and female voices as influenced by different levels of speech rate. All factors were assessed as functions of search or transcription task performance and user preference. Analysis of transcription accuracy, search efficiency and time, and subjective ratings revealed an overall significant effect of speech rate on all groups of measures but no significant effects for voice type or coding scheme. Results were used to recommend design guidelines for developing speech displays for telephone information systems.