For the harp seal ( Pagophilus groenlandicus ) (Terhune and Ronald, 1971; 

 1972) the aquatic audiogram was from 760 Hz - 100 kHz. Maximum sensitivities 

 were at 68 dB at 2 kHz and 63 dB zt 22.9 kHz. Frequencies were tested in 1/2 

 octave steps. In-air responses were obtained from 1-50 kHz. Maximum 

 sensitivity was at 5 kHz at -57 dB (re 1 uW/cm). If expressed as power units 

 (rather than intensity units) the water audiograms are comparable to 

 sensitivities noted for terrestrial mammals. The intensity threshold of air 

 audiograms was generally 10 - 30 dB less than the water audiograms when 

 comparing like dB units. 



Male and female test subjects were used to determine the auditory 

 threshold of Pusa hispida (Terhune and Ronald, 1975). Test frequencies from 

 1-90 kHz were used with the upper and lower frequency limits fixed by the 

 equipment. Both test subjects responded throughout the test band. The female 

 test subject had slightly more acute hearing than the male. However, the male 

 had relatively better hearing at higher frequencies than the female. Maximum 

 sensitivity for the female was at 11 and 16 kHz at 68 dB with a high 

 sensitivity from 8-22.9 kHz. Maximum sensitivity for the male was at 44.9 kHz 

 with high sensitivity from 4-44.9 kHz. 



Schusterman, Balliet and Nixon (1972) tested Zalophus cal ifornianus at 

 frequencies from 250 Hz - 64 kHz. The upper frequency threshold was 

 considered to be between 36 and 48 kHz. Maximum sensitivity was approximately 

 79 dB at 16 kHz. Above 18 kHz sensitivity decreased at 60 dB/octave to 36 kHz 

 and by 14 dB/octave to 64 kHz. Responses were noted to frequencies as high as 

 192 kHz with intensities at approximately 138 dB. The authors maintain that 

 at levels above 48 kHz the animals were responding to pressure conducted 

 through the skull, whereas at lower frequency conventional (ossicular chain 

 conduction) hearing was used. 



Electrophysiological Tests 



Electrophysiological audiograms have been obtained in two ways: a) 

 evoked potentials from deep cortical probes (Bullock, Grinnel, Ikezono, 

 Kameda, Katsuki, Nomoto, Seto, Suga and Yanagisawa, 1968; Bullock and Ridgway, 

 1972; Bullock, Ridgway and Suga, 1971; and Ridgway and Joyce, 1975); or from 

 electrodes mounted to the skull, with an artifact inhibiting system to monitor 

 EEG (Seeley, Ridgway and Flanigan, 1976); b) and cochlear microphonics 

 (McCormick, 1968). 



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