Exposure to sound may produce elevated hearing thresholds or threshold shifts in mammals. If the hearing threshold returns to baseline levels then it is known as a temporary threshold shift (TTS). Hearing loss depends on the intensity of the sound, the frequency of the sound, and how long the animal is exposed to the sound (duration). The following tables summarize the available data regarding minimum sound exposures that have been found to cause TTS in a few species of marine mammals. The TTS investigations introduce sounds (pure tones, octave band noise or impulsive sound) at varying frequencies, intensities, and durations to determine sound exposures that cause temporary threshold shifts. The measurements were made on a small number of animals. Individual differences in hearing sensitivities are substantial in land mammals. Without additional data it is impossible to know if the same is true of marine mammals, although it would be surprising if they did not have different hearing sensitivities too.

Combining the data from all of these studies shows that longer exposures to quieter sounds have the same effect as shorter exposures to louder sounds. The total energy of the sound to which an animal is exposed (a combination of the sound intensity and the duration of exposure to that intensity) is a much better predictor of whether or not TTS will occur than is the sound intensity alone.