OVERVIEW

A voice user interface (VUI) is the script to a conversation between an automated system and a user. This script contains all the utterances that the automated system will speak to the user and the logic to decide which utterances to speak in response to user input. Underlying the voice user interface is speech recognition technology that has the ability to capture and decode the user's spoken input to allow the system to "understand" what the user has said. The majority of these automated conversations between a user and a VUI take place over the phone, as most speech technology is currently deployed in speech-enabled interactive voice response interfaces (see Chapter 7). Increasingly, VUIs are being added to the user experience of mobile and handheld devices, in-vehicle navigation systems, and desktop computer applications.

Users come into automated conversations with a set of expectations about how spoken conversation should work and the appropriate way to behave as a cooperative speaker and listener. The overwhelming majority of users' experience comes from unscripted human-to-human speech, a feat that is far outside the capabilities of today's speech technology. This limitation is largely unknown to most users, a great many of whom approach VUIs with the Star Trek model in mind: To such users, speech-enabled systems are an always-listening intelligence awaiting one's every command. What Captain Picard requests is always understood, and his spoken interactions with "Computer" appear effortless. Therefore, it is no surprise that users' expectations are somewhat out...