Page 51 - Spring 2019
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dolphin emitted signals. Bills work was groundbreaking V y _ V _ _:$< _‘_7 _ ‘ §‘
echolocation research (Evans, 1967). Using Bill’s idea but in ‘ ' ’  -I ¥‘_' ""'_‘ 7 _e‘ ‘ e i-_ ‘.
reverse, Moore developed the concept of “jawphones” to test - —— T‘ 4'  3 - ' 
dolphin interaural hearing by measuring interaural intensity I H , e ' ‘ gs— ‘ ' 3 \
and tune differences. The first pair of jawphones used a Briiel —'t_ ,_ '  » ‘ e ‘ \
81 Kjzer (B&K) 8103 miniature hydrophone positioned hori- ‘ / Te ' r '> .‘  1, ‘
zontally along the lower jaw of the ani.rnal for maximum ef- ' _ ll ' Y: I‘ ’e_ . , e
ficiency (Figure 6). This position was used because the path- ‘ . » ' . . _ .
way of sound to the ear in dolphins is through the lower jaw ‘\ : . 
(Brill and Harder, 1991). — ‘ e .-  a
4:, . ., . ’
Heptuna had no issues with the jawphones because he was /- . -fir
trained to wear them as eye cups to occlude his vision for ‘ * '
past echolocation experiments. The jawphones were attached Figure 5- H€Pt“"“ W9“’i”E "J'“WPh”"e5" '1‘“'i”S’ ""9 0f P““'i5l‘
to Heptuna’s lower jaws, and subsequent thresholds for the M00??? Studies in the 99",)’ 19905-
pure-tone stimuli were determined. To assess Heptuna’s inte-  
raural intensity difference threshold, the level of the stimuli In Contrast when He mm‘ was tested at a E 26 with the .aw_
wee eel el e 30-40 dB seneellml level (ell) The study used hones his hearin :'as considered unregmarkable beclause
wldebend elleles lllel were slmllee lo dolplllel eelmloeellon iphde endent threshgolds for his ears were close] matched for
clicks but that were more suited to the animal’s hearing and P . . Y
_ _ test frequencies of 4-10 kHz (Moore and Brill, 2001). These
better represented signals that the animal would naturally . . . .

S _ 1_ _ _ d_ data for Heptuna are consistent with the findings of Ridgway
encounter. tu'nu iwere set to arepetition rate correspon ing and Carder (1993, 1997) Showing that dolphins Experience
lo e lergel eelloloeeled el 20 melers (40 me)‘ Use-lg e mode a e-related hearin loss Heptuna was another example of a
fied method of constants and a two-altemative forced-choice g . . g . l . .

_ _ male dolphin losing high-frequency hearing with age, a con-
response Peeedlgm’ dele were Collected for bolll mleeeueel dition that is similar to presb cusis in humans and that is
intensity and time difference thresholds. The results clearly now known to be Common in :1 def dol him (see the ankle
indicated that the dolphin was a highly sophisticated listener . . P

_ _ _ _ _ in Acoustics Today by Anderson et al., 2018 about age-related
and capable of using both time and intensity differences to h . .
_ _ earing loss in humans).
localize direct and reflected sounds (Moore et al., 1995).
The results of the free-field thresholds for Cascade at 30,
Hapguna |v|gVa3 to San Diagg 60, and 90 kHz provided additional support for the use of
In 1992, the Hawaii laboratory was closed and the personnel j’r*WPh01'|€5 35 3 1119335 to P1359 the 5°“nd 5'3"“? in 51°59’
and animals moved to what is now the Space and Naval War- proximitv 1° ‘he animal md Concentram the 5°“’Ce in 3
fare Systems (SPAWAR) Center in San Diego, CA. small, localized area. Iawphones have become a tool in the
_ _ exploration of hearing in dolphins and are used in many ex-
Rendy Belll’ who wee then woelemg el SPAWAR‘ Wee-‘led lo eri.rnents conducted at the US Na Marine Mammal Pro-
try to see if there were specific areas of acoustic sensitivity gum and other facilities and in fllevayssessmem ofhearing in
along the lower jaw of the dolphin and other areas around the stranded and rehabflitatin odomocetes
head. The first thing Randy wanted was to collect thresholds g '
from Heptuna and a-second younger animal named Cascade. Heptuna and E m control
Usmg lhe melelled Jewpllol-lee’ ll Wes Poeelble lo eolleel me Heptuna’s hearin loss notwitlistandin the investi ators
dependent thresholds for both the right and left ears of both forged ahead to eiplore the idea that doglephins may Cgmml
eellmele in me beelegmueld noise oesen Diego Bey‘ their emitted echolocation beam, allowing them to better
The resulting audiograms for Cascade revealed well-matched detect targets. This involved animals free swimming in the
hearing in both ears (Brill et al., 2001). However, the results open ocean as they echolocated. Using a new research device
for Heptuna were startling because they showed that Hep- that could be carried by the dolphin, the Biosonar Measure-
tuna, now about 33 years old, had hearing loss in both ears, ment Tool (Houser et al., 2005), it was found that a dolphin
with a more substantial loss in his right ear. Furthermore, could detect echoes from a target before the target entered to
Heptuna now had a significant hearing loss above 55 kHz. animals main echolocation beam.
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