Equal-latency curves and auditory weighting functions for bottlenose dolphins (Tursiops truncatus) and California sea lions (Zalophus californianus)

Abstract

Reaction time (RT) data obtained from simple tonal detection tasks have been used to estimate frequency-specific equal-loudness contours in non-human animals. In order to guide the design of auditory weighting functions for marine mammals, equal-latency contours were generated using RT data from a simple tonal detection including two bottlenose dolphins (under water) and three California sea lions (in air). Median RT increased exponentially with decreased SPL in all cases. Equal-latency contours for near-threshold RTs were similar to audiograms in both species. Data for the sea lions showed some compression of equal-latency contours with increases in SPL; however, large inter-subject differences in the data for dolphins made results for that species more difficult to interpret. The equal-latency contours for all subjects progressively diverged from predicted equal-loudness contours at higher SPLs, likely a result of very small changes in RT with relatively large increases in SPL. As a result, the contours of most interest for designing weighting functions for high-level noise exposures were also the least reliable. The general similarity of most of the contours to species-typical audiograms suggests that more easily obtained auditory thresholds may provide useful approximations for weighting. [Funded by U.S. Navy Living Marine Resources Program.]