Larsson 1 EMOTIONAL AND BEHAVIORAL RESPONSE TO AUDITORY ICONS AND EARCONS IN DRIVER-VEHICLE INTERFACES

Adequately designed, auditory displays in DriverVehicle Interfaces (DVIs) may give shorter reaction times, improved attention direction, and an increased quality impression. In this paper, we argue that emotional reactions may guide the design of such auditory displays since emotion is central in our everyday life and have strong consequences for behavior and information processing. A simulator study with 30 participants (20 of which were professional drivers) was conducted to investigate the connection between emotional and behavioral responses to auditory DVIs as well as to evaluate various sound design parameters in realistic driving situations. Auditory icons were contrasted to abstract earcon sounds in more or less imminent collision scenarios and 3D sounds were tested against monophonic sounds in different lane change scenarios. Self-report measures (Self-Assessment Manikins, SAM) and physiological measures (Galvanic Skin Response, GSR and facial Electromyogram, EMG) of emotional response as well as behavioral measures (e.g. brake response time) were used. It was found that auditory icons were more efficient and gave up to 600ms faster brake response times than abstract sounds in imminent collision scenarios and that 3D sound gave a stronger emotional response in lane change scenarios. Moreover, the results show that emotion can predict behavior, e.g. sounds rated as being more activating and negative also gave quicker response times. Contrary to our expectations however, the findings from the SAM ratings were not reflected in the physiological measurements. An explanation to this may be that the scenario itself caused a dominant stress reaction which overrode the physiological response to the warning sounds. Our findings nonetheless strengthen the importance of auditory displays as a means to enhance vehicle safety, and that emotions may be an efficient way of predicting behavioral response to auditory DVIs. Measurements of emotion may therefore facilitate the process of designing auditory DVIs. BACKGROUND Sound may be a very efficient mean of providing warnings and information in vehicles, especially in situations where the visual modality is loaded with information, but can also be used to increase the quality impression of the vehicle. A central characteristic of most auditory DriverVehicle Interfaces (DVIs) is that it should convey the appropriate level of urgency. Urgency can be defined as “. an indication from the sound itself as to how rapidly one should react to it. ” (Edworthy & Hellier, 2006). Too urgent sounds may cause annoyance, unwanted startle effects and even lead to the wrong behavior. On the other hand, if the sound is not urgent enough, reaction may be unnecessarily slow or result in that the warning is neglected. Parameters which have been found to influence the perceived urgency of a sound include repetition speed, number of repeating units, fundamental frequency, and inharmonicity (Hellier & Edworthy, 1996). Moreover, loudness appears to be one of the stronger cues for urgency (Haas and Casali, 1995). However, the range within which loudness can be varied before the sound becomes un-ergonomic is in practice rather small; the sound should of course be loud enough to be heard over the background noise in the operator’s environment and quiet enough not to cause annoyance or hearing impairment. This matter may seem trivial, but is often a central issue which is crucial for the acceptance of the sound. Although thorough research has been conducted on the correlation between basic psychoacoustic parameters and urgency and similar perceptual aspects of sound design, the cognitive response linked to the sound is much less well understood (Edworthy & Hellier, 2006). It is therefore important to systematically investigate and be able to measure how the sound is comprehended. Edworthy and Hellier (2006) suggest that abstract sounds can be interpreted very differently depending on the many possible meanings that can be linked to a sound, in large dependent on the