Auditory perception of motor vehicle travel paths.

OBJECTIVE: These experiments address concerns that motor vehicles in electric engine mode are so quiet that they pose a risk to pedestrians, especially those with visual impairments. BACKGROUND: The "quiet car" issue has focused on hybrid and electric vehicles, although it also applies to internal combustion engine vehicles. Previous research has focused on detectability of vehicles, mostly in quiet settings. Instead, we focused on the functional ability to perceive vehicle motion paths. METHOD: Participants judged whether simulated vehicles were traveling straight or turning, with emphasis on the impact of background traffic sound. RESULTS: In quiet, listeners made the straight-or-turn judgment soon enough in the vehicle's path to be useful for deciding whether to start crossing the street. This judgment is based largely on sound level cues rather than the spatial direction of the vehicle. With even moderate background traffic sound, the ability to tell straight from turn paths is severely compromised. The signal-to-noise ratio needed for the straight-or-turn judgment is much higher than that needed to detect a vehicle. CONCLUSION: Although a requirement for a minimum vehicle sound level might enhance detection of vehicles in quiet settings, it is unlikely that this requirement would contribute to pedestrian awareness of vehicle movements in typical traffic settings with many vehicles present. APPLICATION: The findings are relevant to deliberations by government agencies and automobile manufacturers about standards for minimum automobile sounds and, more generally, for solutions to pedestrians' needs for information about traffic, especially for pedestrians with sensory impairments.

Comparison of different pointing methods for sound localizability measurement in the vision impaired subjects.

In order to find out the most suitable and accurate pointing methods to study the sound localizability of persons with visual impairment, we compared the accuracy of three different pointing methods for indicating the direction of sound sources in a semi-anechoic dark room. Six subjects with visual impairment (two totally blind and four with low vision) participated in this experiment. The three pointing methods employed were (1) directing the face, (2) directing the body trunk on a revolving chair and (3) indicating a tactile cue placed horizontally in front of the subject. Seven sound emitters were arranged in a semicircle 2.0 m from the subject, 0 degrees to +/-80 degrees of the subject's midline, at a height of 1.2 m. The accuracy of the pointing methods was evaluated by measuring the deviation between the angle of the target sound source and that of the subject's response. The result was that all methods indicated that as the angle of the sound source increased from midline, the accuracy decreased. The deviations recorded toward the left and the right of midline were symmetrical. In the whole frontal area (-80 degrees to +80 degrees from midline), both the tactile cue and the body trunk methods were more accurate than the face-pointing method. There was no significant difference in the center (-40 degrees to +40 degrees from midline). In the periphery (-80 degrees and +80 degrees ), the tactile cue pointing method was the most accurate of all and the body trunk method was the next best. These results suggest that the most suitable pointing methods to study the sound localizability of the frontal azimuth for subjects who are visually impaired are the tactile cue and the body trunk methods because of their higher accuracy in the periphery.