Academic journal article Human Factors

A New Class of Auditory Warning Signals for Complex Systems: Auditory Icons

Academic journal article Human Factors

A New Class of Auditory Warning Signals for Complex Systems: Auditory Icons

Article excerpt

This simulator-based study examined conventional auditory warnings (tonal, nonverbal sounds) and auditory icons (representational, nonverbal sounds), alone and in combination with a dash-mounted visual display, to present information about impending collision situations to commercial motor vehicle operators. Brake response times were measured for impending front-to-rear collision scenarios under 6 display configurations, 2 vehicle speeds, and 2 levels of headway. Accident occurrence was measured for impending side collision scenarios under 2 vehicle speeds, 2 levels of visual workload, 2 auditory displays, absence/presence of mirrors, and absence/presence of a dash-mounted iconic visual display. For both front-to-rear and side collision scenarios, auditory icons elicited significantly improved driver performance over conventional auditory warnings. Driver performance improved when collision warning information was presented through multiple modalities. Brake response times were significantly faster for impend ing front-to-rear collision scenarios using the longer headway condition. The presence of mirrors significantly reduced the number of accidents for impending side collision scenarios. Subjective preference data indicated that participants preferred multimodal displays over single-modality displays. Actual or potential applications for this research include auditory displays and warnings, information presentation, and the development of alternative user interfaces.


Driving is a visually intensive manual control tracking task, and the vast majority of in-vehicle displays are visual. As intelligent transportation systems (ITSs) are introduced, the number of in-vehicle displays will probably increase, each competing for the driver's limited resources. Even in well-conceived integrated systems, an overload of the visual modality can easily occur. To avoid visual overload, the use of other sensory modalities must be investigated as a means of conveying critical information, and the most promising and robust of these modalities is audition. Specifically, auditory displays may be used to augment, supplement, or even replace some visual displays.

System designers often fail to consider the limitations of the human operator when specifying auditory warning signals, thereby compromising their effectiveness. For example, some systems rely on an excessive number of auditory alarms presented at unreasonably high volumes, often occurring simultaneously. This can create startle and prioritization problems for an operator and even confusion if the coding is poor (Patterson, 1990).

Conventional nonverbal auditory displays (e.g., a pulsed 1000-Hz pure tone with a 1-s period and 50% duty cycle) are defined by their acoustic parameters, typically including amplitude, spectral (frequency) makeup, and temporal characteristics, whereas auditory icons (e.g., the sound of breaking glass) are representational sounds that have specific stereotypical meanings defined by the objects or actions that created the sound (Mynatt, 1994). Auditory icons have been demonstrated to be superior to conventional signals with respect to recognition performance in specific experimental scenarios, but there has been limited success in implementing them in complex systems. This lack of success may be attributable to a mismatch between the operator's perception of the iconic warning signal and the event the signal represents.

An attempt to formalize the auditory icon design process was reported by Belz, Winters, Robinson, and Casali (1997, 1998). This methodology required participants to assign a meaning to the auditory icon, rate its perceived urgency, and rate its level of association with its intended (experimenter-selected) meaning. The investigation described here made use of this procedure to choose experimental auditory icons. These auditory icons were then integrated into a commercial vehicle simulator driving task to determine the effectiveness of the auditory icon design methodology and the potential effectiveness of auditory icons as warning signals. …

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