title: Hearing Mechanisms and Noise Metrics Related to Auditory Masking in Bottlenose Dolphins (Tursiops truncatus).
abstract: Odontocete cetaceans are acoustic specialists that depend on sound to hunt, forage, navigate, detect predators, and communicate. Auditory masking from natural and anthropogenic sound sources may adversely affect these fitness-related capabilities. The ability to detect a tone in a broad range of natural, anthropogenic, and synthesized noise was tested with bottlenose dolphins using a psychophysical, band-widening procedure. Diverging masking patterns were found for noise bandwidths greater than the width of an auditory filter. Despite different noise types having equal-pressure spectral-density levels (95 dB re 1 μPa(2)/Hz), masked detection threshold differences were as large as 22 dB. Consecutive experiments indicated that noise types with increased levels of amplitude modulation resulted in comodulation masking release due to within-channel and across-channel auditory mechanisms. The degree to which noise types were comodulated (comodulation index) was assessed by calculating the magnitude-squared coherence between the temporal envelope from an auditory filter centered on the signal and temporal envelopes from flanking filters. Statistical models indicate that masked thresholds in a variety of noise types, at a variety of levels, can be explained with metrics related to the comodulation index in addition to the pressure spectral-density level of noise. This study suggests that predicting auditory masking from ocean noise sources depends on both spectral and temporal properties of the noise.
authors.affiliation: National Marine Mammal Foundation, 2240 Shelter Island Drive, #200, San Diego, CA, 92106, USA. brian.branstetter@nmmf.org.
authors.forename: Brian K
authors.initials: BK
authors.lastname: Branstetter
authors.affiliation: G2 Software Systems, Inc., San Diego, CA, 92110, USA. kimberly.bakhtiari@nmmf.org.
authors.forename: Kimberly L
authors.initials: KL
authors.lastname: Bakhtiari
authors.affiliation: G2 Software Systems, Inc., San Diego, CA, 92110, USA. trickyj@gmail.com.
authors.forename: Jennifer S
authors.initials: JS
authors.lastname: Trickey
authors.affiliation: US Navy Marine Mammal Program, Space and Naval Warfare Systems Center (SSC) Pacific, San Diego, CA, 92152, USA. james.finneran@navy.mil.
authors.forename: James J
authors.initials: JJ
authors.lastname: Finneran
mesh_terms: D000818:Animals; D001307:Auditory Perception / Q000502:physiology*; D050681:Bottle-Nosed Dolphin / Q000502:physiology*; D006309:Hearing / Q000502:physiology*; D008962:Models, Theoretical; D009622:Noise; D010470:Perceptual Masking / Q000502:physiology*; D013018:Sound Spectrography
keywords: Comodulation; Detection; Signal