Sonifying the location of an object: A comparison of three methods

Auditory displays are promising for informing operators about hazards or objects in the environment. However, it remains to be investigated how to map distance information to a sound dimension. In this research, three sonification approaches were tested: Beep Repetition Rate (BRR) in which beep time and inter-beep time were a linear function of distance, Sound Intensity (SI) in which the digital sound volume was a linear function of distance, and Sound Fundamental Frequency (SFF) in which the sound frequency was a linear function of distance. Participants (N = 29) were presented with a sound by means of headphones and subsequently clicked on the screen to estimate the distance to the object with respect to the bottom of the screen (Experiment 1), or the distance and azimuth angle to the object (Experiment 2). The azimuth angle in Experiment 2 was sonified by the volume difference between the left and right ears. In an additional Experiment 3, reaction times to directional audio-visual feedback were compared with directional visual feedback. Participants performed three sessions (BRR, SI, SFF) in Experiments 1 and 2 and two sessions (visual, audio-visual) in Experiment 3, 10 trials per session. After each trial, participants received knowledge-of-results feedback. The results showed that the three proposed methods yielded an overall similar mean absolute distance error, but in Experiment 2 the error for BRR was significantly smaller than for SI. The mean absolute distance errors were significantly greater in Experiment 2 than in Experiment 1. In Experiment 3, there was no statistically significant difference in reaction time between the visual and audio-visual conditions. The results are interpreted in light of the Weber-Fechner law, and suggest that humans have the ability to accurately interpret artificial sounds on an artificial distance scale.