Measuring the augmented sound localization ability of humans in the underwater environment

Humans are poor, if not incapable, at localizing sound underwater due to significant reduction in Inter-aural Temporal Differences (ITD) and Inter-aural Intensity Differences (IID) caused by reduced impedance mismatch and the higher sound speed in water. An improvement in sound localization underwater will significantly enhance divers safety, the way divers perceive and appreciate the underwater environments. A system that augments and enhances the sound localization ability of humans underwater was built for this purpose. The system extracts directional cues from high frequency acoustic component of the received signal and reintroduce the cues in audio band to the diver that wears the system. The novelty of this approach is that it does not need any explicit information on the signals in advance to localize them. The system passes almost the entire signal band to its user with minimum relative distortion except the directional cue ti re-introduced. It is then up to the user to perceive, detect, and localize the sound. In this paper, we present the setup and results from an experiment that measures the localization performance of divers using the system. The experiment setup consists of a source transmitter that was randomly positioned in a contiguous, one-meter radius, semi-circular frame, and a blindfolded subject that attempts to localize the acoustic source. Both the headings of the transmitter and subject were digitally recorded and compared to gauge the localization performance. Experiments have been carried out across different signal to noise ratio and across different frequencies above 20kHz. The result from the experiment shows that a diver using the system was able to localize a source to within ±15 degrees nearly 75% of the time. It is also observed that SNR does not significantly affect the localization performance within the range of SNR that we were testing. The subjects were able to localize acoustic source in a noisy marina environment with the system. The localization performance of the subjects seemed to improve as the subjects gained experience using the system over a few experiment sets. This suggests that the human brain adapts its perception ability and learns to use the new directional cues rather quickly.