Masked underwater pure tone thresholds of the northern fur seal (Callorhinus ursinus)

Masked underwater pure tone thresholds were obtained for two female northern fur seals using an “up‐down stair case” method and a “go/no‐go” response procedure. Thresholds were determined at three continuous broadband masked noise levels at frequencies of 2, 4, 8, 16, and 32 kHz. The critical ratio (C. R.), defined as the ratio of signal power to spectrum level at masked threshold, were calculated for both animals. A psychometric function relating the pooled C. R.'s to frequency was plotted and found to be similar and showed parallel functions with C.R.'s of other marine and terrestrial mammals. These results support the contention that similar functions represent similar mechanisms that are related across species. [Work supported by ONR.]