Auditory Discrimination of Natural and High-Pass Filtered Bark Vocalizations in a California Sea Lion (Zalophus californianus).

A California sea lion performed a psychophysical auditory discrimination task with a set of six stimuli: three barks recorded from conspecific males and high-pass filtered versions of the barks that removed the majority of energy at fundamental frequencies. Discrimination performance and subject reaction times (RTs) suggested that the vocalizations were all perceived as fairly dissimilar. This preliminary study hints that low-frequency components are a salient part of the California sea lion bark despite elevation of this species' aerial hearing thresholds and the potential for elevated environmental noise levels at frequencies below 1 kHz.

Using Reaction Time and Equal Latency Contours to Derive Auditory Weighting Functions in Sea Lions and Dolphins.

Subjective loudness measurements are used to create equal-loudness contours and auditory weighting functions for human noise-mitigation criteria; however, comparable direct measurements of subjective loudness with animal subjects are difficult to conduct. In this study, simple reaction time to pure tones was measured as a proxy for subjective loudness in a Tursiops truncatus and Zalophus californianus. Contours fit to equal reaction-time curves were then used to estimate the shapes of auditory weighting functions.

Hearing Mechanisms and Noise Metrics Related to Auditory Masking in Bottlenose Dolphins (Tursiops truncatus).

Odontocete cetaceans are acoustic specialists that depend on sound to hunt, forage, navigate, detect predators, and communicate. Auditory masking from natural and anthropogenic sound sources may adversely affect these fitness-related capabilities. The ability to detect a tone in a broad range of natural, anthropogenic, and synthesized noise was tested with bottlenose dolphins using a psychophysical, band-widening procedure.