Page 48 - Spring 2019
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Heptuna and Eiosunar
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naud and Popper, 1975). The results showed that Heptuna
(and other dolphins) could localize sounds in water almost 535»-'7"-"».'a."m """"I.',':"""‘
as well as humans can in air. «"33; um-
Because dolphins live in a three-dimensional acoustic world. " - ____i_e At en: t.-
Donna decided to ask whether Heptuna could localize sound """" Iv-nun-M
in the vertical plane. The problem was that the study site was
quite Shallow and the? e W35 "0 WHY t° P“t 50“iCe5 el’°Ve end Figure 4. A mrtwn efHeptimu’s station and the apparatus EurIMur-
below the animal T0 reS°lVe thi5— Dohhe deeided that it‘ She chisnn used te present the targets (see text fur details). AR, change in
Wild ii°t bring the Vertical Plane to l'lePt“he— She W°“ld preselected target distances. Frnm Murchisan (1980).
bring Heptuna to the vertical plane. She switched the bite bar
to a vertical position and trained Heptuna to do the whole
5t“dY °h hl5 5lde- A5 "‘ e°t"5e‘l“el"ee> the Same 5°“hd 5°“l'ee5 threshold, Heptuna’s threshold was at a level of 77.3 dB re 1
that were left “hd rlght lh the earlier eXPel’l-"l"el"t5 Were l"°W iiPa/Hz, whereas it was 74.8 dB for a second dolphin, Ehiku.
“h°Ve and hel°W the ahlmelts headt D0111“ f°“hd that the Whit went on to speculate that this difference may have been
MAA for vertical localization was as good as that for hori- due to the abilities of the two ai.ii_i.i.ia15 to distinguish time
Zohtel l°C“h“ti°h> suggestlhg 3 t'e“"“l’k3hlY 5°Phl5tle“ted separation pitch (TSP). In human hearing, TSP is the sensa-
l°e“hZ3tl°h "‘hl-htY l-t" d°lPhlt"5~ tion of a perceived pitch due repetition rate. For dolphins, the

concept suggests that the ripples in the frequency domain of
An overview De Hapeeunala studies echoes provides a cue, an idea that persists in modeling dol-
Shortly after completing the localization study, Heptuna Phil.‘ Sonar today (Murchison, 1976; A“, 1938)_
started to “collaborate” with another well-known male dol-
phin, Sven. Heptuna and Sven began trainingto detect targets Heptuna and Echoiocatiun studiaa
oh 3 “Sky H°°k” devleev which m°Ved end Placed Calibrated Heptuna’s biosonar career continued under the tutelage of
stainless steel spheres and cylinders underwater at various Earl and Ralph‘ Earl had begun a long series of experiinenis
dlstahees from the eeholmetlhg et"l-"l"“l5- The P“l’P°5e °fthe on echolocation range resolution of dolphins, and Heptuna
Sky H°°k W“ to determine the mexhhmh distance at which was the animal of choice because of his experience. Heptuna
d°lPhll"5 e°“ld detect objects ofdtfleereht sizes and tYPe5 (All faced a new experimental paradigm in this study, requiring
et at" 1978)‘ him to place his rostrum in a “chin cup” stationing device
As training continued, Dr. Whitlow Au, a senior scientist at and eCh0l°C3te 5“5Pel"ded P°lY“l’eth“he foam tergets t°
the NUC, attended the sessions conducted by Ralph Penner his left and 1‘ ight (Figure 4)- Hi5 W51‘ W35 to P1?“ 3 Paddle
or Arthur (Earl) Murehtsont whit recorded the al-ii_|-gals out. on his right or left corresponding to the closer target. Earl
going echolocation signals (see Au_ 2015 for 3 general history would randomly adjust the targets to one of three preselected
of dolphin biosonar research). These signals were analyzed ranges (1, 3. 01‘ 7 metel'5)- HePt“m‘ W35 5t“tl°l"ed hehlhd an
in an atternpt to understand and quantify the echolocation acoustically opaque visual screen so that he could not see or
abilities of dolphins. As W'hit clearly stated, “In order to bet- echolocate the targets, and Earl would move one target ever
ter understand the echolocation Process and quantify the so slightly, moving it a set distance closer or further away in
echolocation sensitivity of odontocetes, it is important to de- l'el’n\ti0Ii C0 the teSt 1‘ ange-
termtne the 5tgt1et't°'t1°-tee ratio (SNR) at detection t‘ttreSh' Heptuna was the subject for three of Earl’s studies of range
old” (Au and Penner’ 1981‘ P‘ 687)‘ Whtt wanted to refine his resolution. Earl found that Heptuna’s performance indicated
earlier estimates of the animal’s detection threshold based on that his range resolution Conformed Closely to the Weber_
the transient form ofthe sonar equation‘ Fechner function. In human psychophysics, the law relates
Because the earlier thresholds were done in Kaneohe Bay to the perception of a stimulus; the magnitude of the stimulus
where the background noise was variable and not uniform when it is just noticeable is a constant ratio (K) of the origi-
with respect to frequency, a flat noise floor was needed. nal stimulus (AD/D =K) or conforms to Stevens power law.
Thus, Heptuna was exposed to an added “nearly white-noise The results led Earl to speculate how Heptunak performance
source” that was broadcast while he performed the target de- would compare with the results of other echolocation exper-
tection task. The results showed that at the 75% detection iments. One important observation from Heptuna’s results
45 1 AI:uuII:l:I Tbday 1 Spring 2019

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