Discrimination of pure-tone intensities by the California sea lion

On the basis of previous behavorial experiments on sound localization under water along with sound-skull measurements in water, it was hypothesized that the California sea lion (Zalophus californianus) is capable of discriminating an intensity difference of approximately 3 dB at 16 kHz. The present experiment confirmed this hypothesis by means of a series of behavorial psychophysical experiments. The ultrasonic absorption and reflection properties of sexually mature, freshly excised mouse, rabbit, cat, and dog testes have been investigated at 37°C in the frequency range 0.5-7 MHz by the transient thermoelectric absorption, the pulse-reflection, and the pulse-transmission methods. The absorption coefficient is found to exhibit values considerably less than those of other parenchymal tissues and to possess a frequency dependence mimicking a simple relaxation process of characteristic frequency approximately 0.9 MHz.