Dear Colleagues:
The following paper was just published in JEB:
http://jeb.biologists.org/cgi/content/abstract/215/17/3055
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 inputoutput 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 octave1 up to 93
dB at 5.6 kHz. The thresholds at high frequencies above 108 kHz increased
steeply at a rate of 130 dB octave1 up to 127 dB at 152 kHz.
If you are interested in a pdf copy, please send an email to l...@ihb.ac.cn or
tms...@nus.edu.sg
Best Regards
Songhai Li Ph.D
2012-08-09
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