Auditory Weighting Functions and Frequency-Dependent Effects of Sound in Bottlenose Dolphins (Tursiops truncatus)
Abstract
The long-term goal of this effort is to develop meaningful auditory weighting functions for marine mammals. These weighting functions will improve the assessments of the effects of anthropogenic sound by emphasizing frequencies to which animals are most sensitive and de-emphasizing those to which they are not. The specific objective of this effort is to develop auditory weighting functions for bottlenose dolphins with normal hearing and those with high-frequency hearing loss. The weighting functions were defined by measuring subjective loudness and temporary threshold shift (TTS) as functions of the sound frequency. TTS is defined as the difference between hearing thresholds measured before and after an intense (fatiguing) sound exposure. Hearing thresholds were estimated using either a behavioral response paradigm, where the subject is trained to perform a specific action when it hears a test tone, or an electrophysiological method, where auditory evoked potentials (AEPs) were measured in response to test tones. Hearing tests are typically conducted approximately 1/2-octave above the exposure frequency, where the largest TTS is expected. Behavioral methods developed at the Navy Marine Mammal Program (MMP) allowed thresholds to be obtained within 4 minutes of intense sound exposures. This was accomplished using computer-controlled stimulus presentations, recording acoustic responses emitted by the subject in response to those stimuli, and presenting multiple trials before subject reinforcement. Dolphins typically produce an acoustic response (a whistle or burst pulse) within a few hundred milliseconds of tone onset, allowing a rapid pace of stimulus presentation and fast threshold estimates. A modified up/down descending staircase technique was used to adjust the stimulus level in an adaptive fashion from one trial to the next and bracket the threshold.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 30, 2011
- Accession Number
- ADA601149
Entities
People
- James J Finneran
Organizations
- Naval Information Warfare Center Pacific