Improvement in Detectability of Alarm Signals in Noisy Environments by Utilizing Spatial Cues

We measured how well alarm signals could be detected in the presence of car noise as a function of interaural time difference (ITD) and interaural phase difference (IPD). Alarm signals intended to warm people of dangerous situations need to be perceived accurately in real environments because noise in a real environment can mask the alarm signals and make them undetectable. Pulse train signals and five alarm signals were used to check whether the spatial release from masking (SRM) occurred. The results showed that SRM occurred for all signals and that alarm signal detectability could be improved by utilizing not only ITD but also IPD of the signal. This effect depended on the relationship between ITD and IPD. In addition, ITD and IPD of the arrival direction difference of the alarm signal in the masker greatly influenced occurrence of SRM: this could be interpreted as binaural masking level difference (BMLD). These results suggest that spatial cues of the arrival direction of an alarm signal in comparison with the masker direction have to be considered in conveying warnings accurately and efficiently without loss of information.