equipment from varying in position due to the effects of currents, etc. The 

 divers' bodies were fixed in relation to the five transducers, but their heads 

 were mobile. In the first study, each of the four signals (250-, 1000-, 6000-Hz 

 sinusoids and thermal noise) were presented in duty cycles of one second; in 

 the second, the signals were a series of sinusoids sweeping from 500-1000 Hz, 

 1000-500 Hz, 4000-6000 Hz, 6000-4000 Hz, a dolphin whistle and pulse trains of 

 15 and 50 pps. All stimuli were presented at 100 db SPL which is approximately 

 40 db re underwater hearing threshold. 



Results 



A comparison of scores obtained at Bugg Springs with those during TEKTITE II 

 can be seen in Table 1. Diver performance for the second study can be compared 

 in Table 2 to scores collected at Bugg Springs using the same stimuli. In this 

 regard, it will be noted that the values for the first of the present studies 

 are lower than those obtained in fresh water and are minimally above chance. 

 However, the depressed scores are partially due to one subject whose responses 

 approached zero. Subjects also reported that the task was quite difficult at 

 first. Evidence of this may be found in Table 2 where the scores now are based 

 on the responses of "trained" divers. Since the values here relate well to 

 previous studies, they strongly suggest that sound localization in the sea is 

 governed by the same laws as it is in fresh water. The implications of this 

 finding to diver navigation seem obvious. 



Table 1. --Comparison of sound localization scores 1) near field in 

 fresh water at USRD (Bugg Springs) and 2) at 40 feet in 

 salt water at TEKTITE II. 



Bugg Springs 

 Stimuli (fresh water) 

 (hz} N=17 



250 50.67o 



1000 38.87o 



6000 33.47o 



Noise 52.57o 



Table 2. --Comparison of the effectiveness of different types of 

 signals used in underwater sound localization tasks 



Bugg Springs * TEKTITE II 



Stimuli (fresh water) (salt water) 



N^6 N=4 



15 pps 40.07o 50.07o 



50 pps 52.27„ 46.67, 



Dolphin & whistle 40.07. 50.07. 



500 to 1000 Hz 50.07. 40.07o 



1000 to 500 Hz 60.07 38.37. 



4000 to 6000 Hz 41.07 33.37 



6000 to 4000 Hz 41.07 28.37 



The actual stimuli for this procedure was slightly different in most cases. 



X-6 



