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Underwater frequency discrimination in the bottlenosed dolphin (1-140 kHz) and the human (1-8 kHz)

Roger K.R. Thompson and Louis Herman

(C) 1975 Acoustical Society of America

Frequency difference limens (DLs) were obtained for the frequencies (F) from 1 to 140 kHz for the bottlenosed dolphin, Tursiops truncatus (Montagu) and from 1 to 8 kHz for two human subjects tested underwater. Discriminations were required between constant –frequency (pure – tone) signals and frequency – modulated signals, using a successive discrimination procedure. Relative DLs (DL/F) for the dolphin generally ranged from 0.002 to 0.004 between 2 and 53 kHz and never exceeds 0.008 through to 130 kHz; at 1 to 140 kHz , relative DLs increased to 0.014. No responses were obtainable at 150 kHz. These findings demonstrated excellent frequency discrimination throughout the audible spectrum (above 1 kHz) of Tursiops and support electrophysiological evidence of highly sensitive frequency detection mechanisms. Results for the humans showed smaller DLs than the dolphin at 1 kHz, approximately equal at 2 kHz, and progressively larger DLs at 4 and 8 kHz. The human underwater thresholds were generally consistent with typical human in – air measurements of frequency DL.