Direct Measurements of Subjective Loudness in a Bottlenose Dolphin

  • Carolyn E. Schlundt
  • James J. Finneran
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 730)


For humans and terrestrial mammals, the variation in susceptibility to noise as a function of frequency is handled by “weighting” sound exposures to emphasize frequencies where auditory sensitivity is highest and lessen the importance of frequencies outside the audible range. This technique allows the use of single, weighted numeric values for impact or damage-risk criteria regardless of the sound frequency. Human weighting schemes were derived from measurements of equal-loudness curves obtained from subjective experiments where a listener compares the loudness of sounds at different frequencies. Previous terrestrial mammal data have shown that response latencies measured in the context of a simple acoustic-detection task may be used to construct equal-latency contours that are analogous to equal-loudness contours, albeit measured indirectly (Pfingst et al. 1975; Stebbins 1966). Until now, there were no empirical measures of equal-loudness curves or auditory weighting functions in marine mammals. This data gap became especially apparent following certain marine mammal experiments of temporary threshold shift (TTS). Limited data at 75 kHz (Schlundt et al. 2000) and more recent TTS data at frequencies up to 28 kHz (Finneran and Schlundt 2010; Finneran et al. 2007) have been compared with results of midfrequency data at 3 kHz (Finneran et al. 2010) and reveal substantial differences between onset TTS levels. Specifically, TTS will occur after lower exposure levels for these higher frequencies. Data at higher frequencies should be used to create more accurate frequency-dependent estimates for onset TTS (i.e., TTS weighting functions). Similarly, equal-loudness data would show the relationship between the frequency of sound and the subjective loudness of the sound. The objective of this effort was to develop auditory weighting functions for Tursiops truncatus. The weighting functions would be defined by measuring subjective loudness as a function of the sound frequency. Loudness contours may be more appropriate for assessing behavioral effects of sound, assuming behavioral reactions are more strongly related to loudness than to sound pressure level (SPL).


Sound Pressure Level Probe Trial Sound Frequency Baseline Trial Auditory Sensitivity 
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  1. Finneran JJ (2003) An integrated computer-controlled system for marine mammal auditory testing. Technical Report, Space and Naval Warfare Systems Center Pacific, San Diego, CA.Google Scholar
  2. Finneran JJ, Carder DA, Schlundt CE, Dear R (2010) Growth and recovery of temporary threshold shift at 3 kHz in bottlenose dolphins: Experimental data and mathematical models. J Acoust Soc Am 127:3256–3266.PubMedCrossRefGoogle Scholar
  3. Finneran JJ, Schlundt CE (2007) Underwater sound pressure variation and bottlenose dolphin (Tursiops truncatus) hearing thresholds in a small pool. J Acoust Soc Am 122:606–614.PubMedCrossRefGoogle Scholar
  4. Finneran JJ, Schlundt CE (2010) Frequency-dependent and longitudinal changes in noise-induced hearing loss in a bottlenose dolphin (Tursiops truncatus). J Acoust Soc Am 128:567–570.PubMedCrossRefGoogle Scholar
  5. Finneran JJ, Schlundt CE, Branstetter B, Dear RL (2007) Assessing temporary threshold shift in a bottlenose dolphin (Tursiops truncatus) using multiple simultaneous auditory evoked potentials. J Acoust Soc Am 122:1249–1264.PubMedCrossRefGoogle Scholar
  6. Fletcher H, Munson WA (1933) Loudness, its definition, measurement and calculation. J Acoust Soc Am 5:82–108.CrossRefGoogle Scholar
  7. Gellerman LW (1933) Chance orders of alternating stimuli in visual discrimination experiments. J Gen Psychol 42:206–208.Google Scholar
  8. Houser DS, Finneran JJ (2006) Variation in the hearing sensitivity of a dolphin population obtained through the use of evoked potential audiometry. J Acoust Soc Am 120:4090–4099.PubMedCrossRefGoogle Scholar
  9. Pfingst BE, Hienz R, Kimm J, Miller J (1975) Reaction-time procedure for measurement of hearing. I. Suprathreshold functions. J Acoust Soc Am 57:421–430.PubMedCrossRefGoogle Scholar
  10. Robinson DW, Dadson RS (1956) A re-determination of the equal-loudness relations for pure tones. Brit J Appl Phys 7:166–181.CrossRefGoogle Scholar
  11. Schlundt CE, Finneran JJ, Carder DA, Ridgway SH (2000) Temporary shift in masked hearing threshold of bottlenose dolphins, Tursiops truncatus, and white whales, Delphinapterus leucas, after exposure to intense tones. J Acoust Soc Am 107:3496–3508.PubMedCrossRefGoogle Scholar
  12. Stebbins WC (1966) Auditory reaction time and the derivation of equal loudness contours for the monkey. J Exp Anal Behav 9:135–142.PubMedCrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  1. 1.ITT CorporationSan DiegoUSA
  2. 2.US Navy Marine Mammal ProgramSpace and Naval Warfare Systems Center PacificSan DiegoUSA

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