manipulandum or remaining at station if no signal was presented or perceived. 

 Frequency results were in close agreement with the earlier work of Schevill 

 and Lawrence (1953). The maximum dB intensity threshold was at 45 dB at 50 

 kHz. The frequency band of high sensitivity was from 12 - 115 KHz. The 

 frequency band of high sensitivity is defined as the frequency band where dB 

 intensity thresholds are within 10 dB of the frequency of maximum 

 sensitivity. In this case, it is the frequency band with at least a 55 dB 

 threshold. The 10 dB criterion is arbitrary. It is an approximation of the 

 frequency bandwidth where the test subject has acute hearing. Below 50 kHz, 

 the dB sensitivity gradually decreased to approximately 52 dB at 20 kHz (6 

 dB/octave). Below 15 kHz sensitivity decreased by approximately 12 dB/octave 

 to 1 kHz. Above 50 kHz intensity thresholds decreased to 55 dB at 100 kHz (10 

 dB/octave) and then rapidly to 135 dB at 150 kHz, an approximate decrease in 

 sensitivity of 700 dB/octave. 



Ljungblad (pers. comm. ) recently completed an audiogram for a single 

 Pacific bottlenose dolphin ( Tursiops truncatus gilli ). Frequencies from 1 - 

 160 kHz were tested. The animal responded from 2 - 135 kHz. Maximum 

 sensitivities at 47 dB at 20 kHz and 46 dB at 50 kHz were recorded. Decibel 

 intensity thresholds included 115 dB at 2 kHz, 58 dB at 25 kHz, 46 dB at 50 

 kHz, 74 dB at 100 kHz, and 118 dB at 135 kHz. Frequency and intensity 

 thresholds and maximum sensitivities were slightly lower than the Atlantic 

 bottlenose dolphin tested by Johnson (1966). 



Cetacean psychophysics has also been studied in the Soviet Union. 

 Golubkov, Ershova and Zhezherin (1969) reported that Tursiops truncatus 

 responded to signals up to 500 kHz. Intensity sensitivities were not 

 determined. Morozov, Akopian, Burdin, Donskov, Zaitseva and Sokovykh (1971) 

 reported an audiogram for Tursiops truncatus from delivered frequencies of 5 - 

 140 kHz. High sensitivity to pure tones was from 10 - 100 kHz, with maximum 

 intensity threshold of 60 dB at 80 kHz. Sensitivity below 80 kHz decreased by 

 approximately 10 dB/octave and above 100 kHz by 67 dB/octave. Note should be 

 taken of the decreased intensity thresholds as compared to those of Johnson 

 (1966). 



An audiogram for Phocoena phocoena was reported by Andersen (1970). A 

 single animal was tested from 1 - 150 kHz, the lower and upper limits of the 

 equipment. 



A- in 



