Usable and Acceptable Response Delays of Conversational Agents in Automotive User Interfaces

With an increasing ability to answer and fulfill user requests, voice-enabled Conversational Agents (CAs) are becoming more and more powerful. However, as the complexity of the requests increase, the time for the CAs to process and fulfill the tasks can become longer. In other cases where input prediction is available, some requests can be processed and answered even before the user is finished saying the command. However, the effects of these positive and negative delays in system response time are still under-explored. In this paper, we systematically analyze the effects of different response delays on usability and acceptability considering three common interaction techniques for voice-enabled CAs. Our results reveal that an unnaturally long positive delay in system response time leads users to assume that an error occurred, while a negative delay is perceived by the users as rude. Based on our findings, we present design guidelines for voice-enabled CAs.