Underwater Sound Localization in Humans

Theory and some empirical evidence are cited which predict that humans should exhibit little or no ability to localize sounds underwater; however, other evidence is presented also which seems to contradict this position. In order to provide relevant data on the issue, a pilot study was conducted with results suggesting that man can localize sounds underwater--at least to some degree. Accordingly, a series of experiments were carried out; the first is reported. It utilized 17 divers who were free to move their heads but not their bodies in an underwater localization task. In order to allow precision in the experiment, a Diver Auditory Localization System (DALS) was developed. DALS consists of an open polyvinyl chloride (PVC) framework to which five 8.5-foot arms and other equipment can be attached. The five arms allow placement--at ear level--of underwater projectors at angles (to the diver) of 0, 45, 90, 27 and 315 deg. Subjects responded to four different signals--250, 1000, 6000 Hz sinusoids and thermal noise--at an SPL of 110 dB (approximately 40 dB re: underwater hearing thresholds) by means of a specially constructed five- position underwater switch coupled to an IBM key punch on the surface. The obtained correct mean scores were (1) 250 Hz: 51%; (2) 1 kHz: 39%; (3) 6 kHz: 33%; (4) Noise: 52% and (5) Overall: 44%. These data demonstrate that humans are capable of at least some primitive sound localization underwater; mechanisms are postulated that may explain this ability.
Report on Underwater Speech Communication. See also Progress rept. no. 21, AD716793.