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Dear Colleagues:
The following paper was just published in JEB:
Evoked-potential audiogram of an Indo-Pacific humpback dolphin (Sousa
chinensis). Songhai Li, Ding Wang, Kexiong Wang, Elizabeth A. Taylor, Emilie
Cros, Wenjing Shi, Zhitao Wang, Liang Fang, Yuefei Chen, and Fanming Kong. J Exp
Biol 2012;215 3055-3063
SUMMARY
An evoked-potential audiogram was measured for an Indo-Pacific
humpback dolphin (Sousa chinensis) living in the dolphinarium of
Nanning Zoo, China. Rhythmic 20 ms pip trains composed of cosine-enveloped 0.25
ms tone pips at a pip rate of 1 kHz were presented as sound stimuli. The dolphin
was trained to remain still at the water surface and to wear soft latex
suction-cup EEG electrodes used to measure the animal's envelope-following
evoked potentials to the sound stimuli. Responses to 1000 rhythmic 20 ms pip
trains for each amplitude/frequency combination were averaged and analysed using
a fast Fourier transform to obtain an evoked auditory response. The hearing
threshold was defined as the zero crossing point of the response input–output
function using linear regression. Fourteen frequencies ranging from 5.6 to 152
kHz were studied. The results showed that most of the thresholds were lower than
90 dB re. 1 μPa (r.m.s.), covering a frequency range from 11.2 to 128 kHz, and
the lowest threshold of 47 dB was measured at 45 kHz. The audiogram, which is a
function of hearing threshold versus stimulus carrier frequency,
presented a U-shape with a region of high hearing sensitivity (within 20 dB of
the lowest threshold) between approximately 20 and 120 kHz. At frequencies lower
than this high-sensitivity region, thresholds increased at a rate of
approximately 11 dB octave–1 up to 93 dB at 5.6 kHz. The thresholds
at high frequencies above 108 kHz increased steeply at a rate of 130 dB
octave–1 up to 127 dB at 152 kHz. If you are interested in
a pdf copy, please send an email to or m("nus.edu.sg","tmsshl");">
Best Regards
Songhai Li Ph.D
2012-08-09
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