This research was directed toward developing technology for generating, and presenting via headphones, audio signals which appear to come from a highly localized point in space. Critical issues in human auditory localization are reviewed to establish the feasibility of 3-D audio for cockpit applications. Current research suggests that the acoustic cues necessary for auditory localization could be simulated and presented by way of headphones with sufficient fidelity to achieve localization performance comparable to that with the unaided ear. It also appears that auditory localization can be highly accurate when the listener can turn his or her head toward the source. Potential benefits and issues related to cockpit applications of 3-D audio are also discussed. 3-D audio holds particular promise for relieving the often over-loaded visual modality, especially for functions which are customarily based on auditory cues.
A facility for synthesizing 3-D audio cues and presenting the same to human listeners is briefly described. The psychological fidelity of the facility was experimentally tested. After about one hour of practice, listener's accuracy of localization with synthesized cues was comparable to localization accuracy in normal, unaided conditions. Response time to point to a sound source was still somewhat greater for synthesized cues as opposed to normal listening conditions at the end of one hour of practice.
Two additional experiments are reported in which human listeners, who were free to move their head, localized sounds on the basis of simulated cues presented via headphones. The first experiment compared RMS localization accuracy and mean response time for high-and lowpass filtered noise signals. A second experiment used intermittent signals and examined the effects on localization performance of burst duration, duty cycle (repetition rate), and rise time for high- and low-frequency noise bursts. In contrast to previous studies in which the listener's head remained stationary, stimulus characteristics had relatively little effect on localization speed and accuracy. It is concluded that localization performance with simulated cues should not be seriously degraded for non-optimal audio signals such as aircraft warning tones and speech, as long as the listener's head is free to move.