Automatic speech recognition and text-to-speech technology can support a speech-based driver interface for in-vehicle computers. Data regarding cellular telephones suggest that speech-based interfaces may distract the drivers. This study uses a car following task to evaluate how a speech-based email system affects drivers’ response to a braking lead vehicle. A simple and a complex email system are compared in simple and complex driving environments. The results show a 30% (300 msec) increase in reaction time when the speechbased system is present. Subjective workload ratings and probe questions show that speechbased interaction introduces a significant cognitive load, which is highest for the complex email system. These data show that speech-based email introduces a cognitive load that can degrade attention to the roadway, suggesting that indiscriminant use of speech-based interfaces for in-vehicle computers might compromise driving safety.
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