Fig. 3. Up to 40 tones were presented to the whale during a dive. This example timing scheme shows 15 tones presented together with 12 responses (hits, H) and three misses (M) during the last 86 s of one dive. Together with each test tone, the computer digitized a 2 s sampling window. After the last correct response, the trainer sounded a 500 ms bridge sweeping up in frequency and amplitude, signaling the whale to return to the surface for a reward of several fish. HTP, hearing test platform.