3D signal sounds for driver assistance systems

Abstract: With an increasing number of advanced driver assistance systems in cars, it is important to know how the driver is affected by different kinds of information signals. Many of the systems already used in cars rely on visual information, and therefore require visual attention. This can lead to an increase in inattention, as well as in cognitive and visual workload. By the use of other types of signals, the risk of overloading one sensory modality is reduced. Previous research has shown a correlation between visual inattention and unsafe driving behaviour, so the use of 3D signal sounds or spatial multisensory signals may be of importance for improving driver safety.The first study focused on the question of how driving performance and secondary task performance are affected by spatial placement of sound signals, and if the position of the sound source plays a role in the ability to capture attention correctly. Earlier studies indicated that information signals which were spatially congruent with the visual task improved response times. Furthermore, sound has been proven to be an effective means of capturing attention and re-orienting people’s attention to a specific location. The first study compared three cases of sound signals to inform the driver of a lane change task as well as a visual secondary task. The driving scenario was projected in front of the driver, and the secondary task was displayed on a computer screen at 45° to the right. In two of the cases, the sound signals’ position was congruent to one of the tasks, either driving or the secondary task. In the third case, the lane change signal was congruent with the projected driving and the secondary task signal was congruent with the secondary task screen. It was found that presenting signal sounds in front of the driver significantly improved driving performance.Previous research has shown that combining sensory modalities increases the robustness of perception. Using a driving simulator and a multisensory secondary task, the second study investigated the difference in directional attention capture capabilities with different combinations of visual, auditory and vibrotactile signals. In this study, visual signals alone, or in combination with other modalities, provided the shortest response time. Interestingly, the auditory and vibrotactile signals gave equally short response times. No significant differences in localisation error rates were observed between the different combinations.As shown in Study 1, spatially congruent signals are important in the driving environment, so can crosstalk cancellation be used to reproduce 3D sound in a car compartment? The third study evaluated how well we can reproduce 3D sound in a car compartment utilising the crosstalk cancellation technique in combination with binaural synthesis. Since the main focus is on signal sounds, these can be processed offline, reducing the need for real time filtering and allowing the use of very detailed crosstalk cancellation filters. Due to the acoustic properties of car compartments, placement of the loudspeakers plays an important role in the reproduction quality. In a listening test, the subjects were requested to judge where the sound was perceived to come from as well as the sound quality of the reproduction. This was done for three different loudspeaker positions and two distinctly different types of sound signals (speech and lane departure warning). The study showed that loudspeakers placed closely behind the driver correctly reproduced sound sources in the back hemisphere, while loudspeakers placed in front of or above the listener gave a high number of front/back confusions for all source angles. It was also found that the loudspeaker placement above the listener received a significantly higher quality rating for speech signals than the loudspeaker placement behind the ears or on the dashboard. For a typical warning sound signal, the loudspeaker positions above and behind the driver were rated equally, but still significantly higher than the dashboard position. Loudspeakers placed close to the ears produce less singularities and thereby higher reproduction quality.The first main finding from this work is that it is important to consider the placement of signal sounds in the car compartment, since a well selected signal sound position can help to focus attention, and thereby enhance driving performance and driver safety. Crosstalk cancellation can be used for implementation of virtual 3D sound in the car compartment using loudspeakers. Vibrotactile signals can be as effective in reducing reaction time as auditory signals, but it may be beneficial to combine the modalities for a more robust perception.