Underwater audiogram of the California sea lion by the conditioned vocalization technique.

Researchers taught a California sea lion to bark under water when it heard a tone.

Each correct bark earned fish. By raising and lowering tone loudness they mapped the animal’s full hearing range.

The method gave the first complete underwater audiogram for this species.

The sea lion heard best between 1 and 28 kHz, peaking at 16 kHz.

It could still detect sounds all the way up to 192 kHz.

Conditioned vocalization worked as a fast, reliable hearing test.

Jones et al. (1992) used the same pure-tone method with Down-syndrome teens and found poorer high-frequency hearing than peers. Both studies show the technique gives clear thresholds across very different subjects.

Fox et al. (2001) later taught sea lions to form equivalence classes using class-specific fish. Together the papers prove the same animals can serve both basic sensory and higher-order cognition work, strengthening marine lab programs.

Neves et al. (2018) used equivalence-based drills to improve sentence production in children with cochlear implants. The sea-lion vocal method underpins the hearing data that guide such implant mappings, linking basic audiogram work to clinical language gains.

You now have proof that a simple bark-for-tone procedure yields accurate thresholds. When you need a quick hearing check for non-verbal clients—whether they bark, press a switch, or sign—reinforce a clear, discrete response and sweep tones the same way. The study also reminds us that operant methods work across species; if a sea lion can learn the task, your learner can too.