threshold shift threshold shiftan increase (worsening) in the threshold of hearing for an ear at a specified frequency Related Articles: Hot Topic - Guidance on Determining Potential Effects to Marine Mammal HearingReference List: Animals and SoundHearing Loss in MammalsPile drivingMarine Mammal Hearing AttenuationOcean Sound PoliciesSeismic Airguns Chris Knowlton2017-02-26T20:10:02-05:00