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@PHDTHESIS{Kettler:478381,
author = {Kettler, Lutz},
othercontributors = {Wagner, Hermann and Mey, Jörg},
title = {{M}orphological and behavioral mechanisms underlying sound
localization in barn owls},
school = {Aachen, Techn. Hochsch.},
type = {Dissertation},
address = {Aachen},
publisher = {Publikationsserver der RWTH Aachen University},
reportid = {RWTH-2015-02576},
pages = {IV, 85 S. : Ill., graph. Darst.},
year = {2015},
note = {Aachen, Techn. Hochsch., Diss., 2015},
abstract = {In this thesis, properties of the acoustic system and
sound-localization behavior of barn owls were investigated.
The influence of adaptation on sound localization behavior
was examined in the first experiment. Payne (1971) was able
to observe that barn owls wait for at least a second sound
before they approach their prey. This situation was mimicked
in a behavioral experiment to investigate how a preceding
stimulus accuracy of the response to the second stimulus. It
is known that the response of neurons to a second stimulus
is decreased compared to the response to the first stimulus.
This phenomenon is called response adaptation. This means
that the detection threshold of the second stimulus may be
elevated stimulus and, therefore, response-adaptation
influences localization accuracy of the owl. Response
adaptation was examined with a double stimulus paradigm. The
owl had to locate a broadband noise token, which was
preceded by another broadband noise token. I found out that
the accuracy and precision with which the barn owls
localized the sound source, decreased with double
stimulation compared to the condition with only a single
stimulus. By varying the interval between the end of the
first and onset of the second stimulus I was able to show
that the adaptive or masking effect of the first stimulus
expires after a few hundred milliseconds. The results
suggest that waiting for the second stimulus actually caused
costs in terms of decreasing accuracy. In the second study,
the head-turning behavior was used to compare responses to
frequency-modulated and stimuli with stationary stimulus
content. Barn owls detect time differences in the arrival of
sound at both ears and can thus determine the azimuth of a
sound source. When stimulated with narrow-band stationary
stimuli, however, barn owls locate so-called phantom
sources, i.e. they turn their head to a position that does
not correspond to the actual sound source. The position of
the phantom source can be predicted by the period of the
center frequency and a known factor that converts the time
differences in an angle. The percentage of phantom
localization was determined as a function of stimulus
bandwidth. Phantom sound sources are not localized at high
stimulus bandwidths. Integration of frequency information in
the auditory pathway of the barn owl leads to a reduction of
phantom-source locations. Frequency-modulated tones offered
the opportunity to present the same frequency content as
with stationary noise, but within a certain time interval.
This allows determination of the duration of the time window
in which the frequency information is integrated. The
behavioral data could be well explained with a model that
simulates two important processes in the auditory pathway of
the barn owl: 1) binaural interaction 2) integration of
frequency information. The time constants of the time
windows had a duration between 2 and 17 ms for both model
steps and did not depend on the stimulus duration. In the
third series of experiments I investigated whether the
tympanic membrane of the barn owl functions as pressure
receiver or as pressure-gradient receiver. In a pressure
receiver, as it occurs in mammals, both middle ears are not
acoustically coupled. This means that no sound is
transmitted through an intracranial, interaural canal.
Especially in small lizards, but also birds, however, there
are cavities that couple both middle ears. Sound does not
only reach the eardrum from outside, but also through the
interaural canal. The incoming signals are phase shifted.
The phase shift depends on stimulus location. In the case of
lossless sound transmission through the interaural canal
certain sound directions lead to complete extinction of the
eardrum vibration. Consequently, the reduction of the
eardrum vibration also depends on the degree of sound
attenuation through the canal. To measure ear coupling the
eardrum vibration was measured with a laser Doppler
vibrometer. Eardrum vibration was measured as a function of
stimulus frequency and azimuth. In addition, the actual
attenuation of acoustic signals by the interaural canal was
measured. The tympanic membrane was directional up to 3 kHz.
That is, the eardrum vibration amplitude varied by more than
3 dB in 360° of stimulation angles. These data can be
explained by attenuation of sound through the interaural
canal. For frequencies higher than 3 kHz attenuation was too
high to produce significant directionality.},
cin = {162110 / 160000},
ddc = {570},
cid = {$I:(DE-82)162110_20140620$ / $I:(DE-82)160000_20140620$},
typ = {PUB:(DE-HGF)11},
urn = {urn:nbn:de:hbz:82-rwth-2015-025763},
url = {https://publications.rwth-aachen.de/record/478381},
}
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