Hearing screening in bottlenose dolphins using single and multiple auditory evoked potentials

• Published in: The Journal of the Acoustical Society of America 2007-05, Vol.121 (5_Supplement), p.3093-3094
• Main Authors: Finneran, James J., Houser, Dorian S., Blasko, Dave, Hicks, Christie, Hudson, Jim, Osborn, Mike, Walsh, Kevin M.
• Format: Article
• Language: English
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.4808535

Auditory thresholds were estimated in four bottlenose dolphins (Tursiops truncatus) by measuring auditory evoked responses to single and multiple sinusoidal amplitude modulated tones. Subjects consisted of two males and two females with ages from 4 to 22 years. Testing was conducted in air using a jawphone transducer to couple sound into the subjects lower right jaw. Carrier frequencies ranged from 10 to 160 kHz in one-half octave steps. Amplitude-modulated stimuli were presented individually and as the sum of four, five, and nine tones with unique carrier and modulation frequencies. Evoked potentials were noninvasively recorded using surface electrodes embedded in silicon suction cups. The presence or absence of an evoked response at each modulation frequency was assessed by calculating the magnitude-squared coherence from the frequency spectra of the recorded epochs. All subjects exhibited traditional U-shaped audiograms with upper cutoff frequencies above 113 kHz. The time required for threshold estimates ranged from 30–45 min for single stimuli and 4–8 min for nine simultaneous stimuli. Agreement between thresholds estimated from single stimuli and multiple, simultaneous stimuli was generally good, suggesting that multiple stimuli may be used for quick hearing assessment when time is limited. [Work supported by ONR.]