Effects of fatiguing tone frequency on temporary threshold shift in bottlenose dolphins (Tursiops truncatus)

Temporary threshold shift (TTS) was measured in two bottlenose dolphins (Tursiops truncatus) after exposure to 16-s tones between 3 and 80 kHz to examine the effects of exposure frequency on the onset, growth, and recovery of TTS. Hearing thresholds were measured approximately one-half octave above the exposure frequency using a behavioral response paradigm featuring an adaptive staircase procedure. Results show frequency-specific differences in TTS onset and growth, and suggest increased susceptibility to auditory fatigue for frequencies between approximately 10 and 30 kHz. Between 3 and 56 kHz, the relationship between exposure frequency and the exposure level required to induce 6 dB of TTS, measured 4 min post-exposure, agrees closely with an auditory weighting function for bottlenose dolphins developed from equal loudness contours [Finneran and Schlundt. (2011). J. Acoust. Soc. Am. 130, 3124-3136].