an increase in the threshold of hearing that is permanent, not temporary. It is an unrecoverable deafening due to physiological damage to the hearing organs that does not diminish with time. PTS may occur as a result of long-term exposures and/or extremely loud noises. Repeated exposures that cause to temporary threshold shift (TTS) can induce PTS, as well. The mitigation measures proposed for implementation under the proposed research and discussed in the EA are designed to ensure that PTS does not occur from experiments under the proposed research.