would predict, however, that in the underwater environment humans will either 

 totally lose their sound localizing capabilities or have them seriously 

 impaired. This observation would appear to be supported by Bauer and Torick 

 (1965), de Haan (1956), and others. 



Directional perception of sound in air is based on the utilization of internal 

 phase (time-of-arrival) and/or intensity information provided to the auditory 

 mechanism by the arriving signal. For the low frequencies, phase is most 

 important, but at higher frequencies the head creates a shadow effect which in 

 turn produces a marked intensity difference between the two ears. In the 

 water, however, a different situation exists. First, sound velocity is four 

 to five times greater in water than it is in air (depending on salinity, tem- 

 perature, etc.). Due to this many-fold increase in the speed of sound, the 

 time interval of an arriving signal across the head would be correspondingly 

 diminished, thus virtually eliminating the directional perception attributable 

 to time delay (phase). The process is somewhat different with respect to inten- 

 sity; that is, in air, the impedance mismatch between the air and the head is 

 sufficiently great so that the head constitutes an effective acoustic barrier. 

 This relationship does not hold in water as the impedance of the head is similar 

 to that of the fluid. Therefore, sounds virtually go through the skull, reduc- 

 ing by a substantial amount (or eliminating altogether) this shadowing effect 

 and its concommitant intensity differential. 



A number of studies (Hollien, 1971) have suggested that divers do, indeed, 

 exhibit at least some primitive underwater sound localization ability. The 

 experiments in the TEKTITE series replicated our earlier experiments which had 

 taken place in fresh water excepting that the salt water experiments were 

 carried out with the source 40 feet from the listener. 



Procedures 



The basic protocols of the earlier studies were as follows: The first step 

 was to develop a Diver Auditory Localization System (DALS) which allows the 

 diver/subject's head either to be held in a rigidly fixed position or to be 

 moved, with his body fixed. In the first experiment, 17 diver/talkers were 

 positioned in DALS, at a depth of 40 ft., with their bodies fixed but their 

 heads mobile; four different experimental signals (250- , 1000- , 6000-Hz 

 sinusoids and thermal noise) were transduced via J-9 projectors. The site of 

 these projects was the NRL Underwater Sound Reference Division's Bugg Springs 

 facility. Each signal was presented to the listeners five times randomly from 

 each of the five transducers at a distance of eight feet and consisted of five 

 1-sec. bursts at 40 db re hearing threshold. Listeners responded by means of 

 a specially constructed 5-position underwater switch coupled to an IBM keypunch 

 at the surface. 



It is of some importance to study these phenomena at distances other than the 

 relatively close range (8") situation previously employed. Accordingly, a set 

 of two related investigations were carried out in order to discover if divers 

 exhibit the predicted levels of localization also in salt water. Procedures 

 similar to those utilized previously were adopted except that transducers were 

 placed at distances of 40 feet from the diver/ subject. Instead of using DALS, 

 a mini-DICORS was utilized and the transducers were suspended at the midpoint 

 level in 40 feet of water on taut lines tied at one end to cement clumps and at 

 the other to partially filled inner tubes. This arrangement prevented the 



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