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Article Excerpt
INTRODUCTION
Even simple driving tasks can become complex for drivers who are also dealing with in-vehicle interactive systems, such as navigation systems that provide real-time route guidance (e.g., Schraagen, 1993). Interaction with such systems, which may take place while driving, requires the user to enter the destination. The driver can be concurrently engaged in both the driving task and the task of parameter entry into the navigation system.
The driving context can be characterized generically as a hands-busy, eyes-busy situation. A designer of a navigation system for such situations is often faced with an interaction design challenge: How should parameters be entered? If the answer is via a keyboard or other direct manipulation device, then such a solution potentially imposes increased workload on the user because of the possible conflict between the demands of the situation (driving and entering parameters) and the available human resources (hands and eyes). This can become detrimental to both driving performance and safety.
Speech-based user interfaces are considered appropriate as a complementary interaction channel when there are real hands-busy, eyes-busy multitask situations (e.g., Lee, Caven, Haake, & Brown, 2001; Marshall, 1992; G. L. Martin, 1989; T. B. Martin, 1976; McCallum, Campbell, Richman, & Brown, 2004; Simpson, McCauley, Rolan, Ruth, & Williges, 1985; White, 1997). However, the benefits of using speech-based interaction in multitask situations are not obvious, and research findings are not conclusive. Some studies have shown that assigning speech-based interaction to one task, in dual-task situations, benefited the overall dual-task performance (e.g., Graham & Carter, 2001; Hapeshi & Jones, 1989; Murata, 1998; Wickens, Sandry, & Vidulich, 1983). However, other studies showed that using speech-based interaction in multitask contexts did not affect the overall performance (e.g., Damos & Lyall, 1986) or even degraded performance (e.g., Baber, Mellor, Graham, Noyes, & Tunley, 1996; Lee et al., 2001; Linde & Shively, 1988).
Various factors play a role in the success or failure of speech-based interaction in multitask situations. Among those is the automated speech recognition (ASR) technology itself and its recognition accuracy, the ambient noise, the domain expertise of the user, and the user's familiarity with the system. In addition, several basic issues are involved in the design of dialogue in speech-based interaction (Bradford, 1995). Among those are the dialogue styles or strategies, the design of system prompts and feedback, and the approaches to error handling (Rudnicky, 1995; Schmandt, 1994; Yankelovich, 1996; Yankelovich, Levow, & Marx, 1995).
One of the aspects that make the design of speech-based interaction such a challenge is that speech is short term and sequential in nature and consequently may take a heavy toll on human working memory (Bradford, 1995). A strategy used often in order to reduce memory load is to guide the user in a question-and-answer dialogue, prompting the user with the appropriate commands (Baber, 1993; Hansen, Novick, & Sutton, 1996; Waterworth, 1982). A question associated with this strategy is which modality should deliver the prompts to the user.
Resource theory (e.g., Moray, 1967; Kahneman, 1973) is a theoretical framework within which one can address this question empirically. Simply put, the performance of tasks requires allocation of resources from a limited pool. The increased allocation of resources (or "effort," in Kahneman's terms) to one task will improve that task's performance, but at the same time it will decrease the resources available to other concurrent tasks, and their performance will consequently be degraded. In a hands-busy, eyes-busy situation, resource theory would predict that the use of visual prompts in speech dialogue will interfere with performance in situations in which the visual channel is engaged in a primary task such as driving. However, using visual prompts can be more beneficial as part of a speech-based dialogue because...
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