Laura Hausmann, Mark von Campenhausen & Hermann Wagner (2010): Properties of
low-frequency head-related transfer functions in the barn owl (Tyto alba). J.
Comp. Physiol. A 196 (9), 601-612.
Abstract: The barn owl (Tyto alba) possesses several specializations regarding
auditory processing. The most conspicuous features are the directionally
sensitive facial ruff and the asymmetrically arranged ears. The
frequency-specific influence of these features on sound has consequences for
sound localization that might differ between low and high frequencies. Whereas
the high-frequency range (>3 kHz) is well investigated, less is known about the
characteristics of head-related transfer functions for frequencies below 3 kHz.
In the present study, we compared 1/3 octaveband-filtered transfer functions of
barn owls with center frequencies ranging from 0.5 to 9 kHz. The range of
interaural time differences was 600 Îs at frequencies above 4 kHz, decreased to
505 Îs at 3 kHz and increased again to about 615 Îs at lower frequencies. The
ranges for very low (0.5â1 kHz) and high frequencies (5â9 kHz) were not
statistically different. Interaural level differences and monaural gains
increased monotonically with increasing frequency. No systematic influence of
the body temperature on the measured localization cues was observed. These data
have implications for the mechanism underlying sound localization and we
suggest that the barn owlâs ears work as pressure receivers both in the high-
and low-frequency ranges.
For reprints please contact L. Hausmann (email:
Abhilash Ponnath & Hamilton E. Farris (2010): Calcium-dependent control of
temporal processing in an auditory interneuron: a computational analysis. J.
Comp. Physiol. A 196 (9), 613-628.
Abstract: Sensitivity to acoustic amplitude modulation in crickets differs
between species and depends on carrier frequency (e.g., calling song vs.
bat-ultrasound bands). Using computational tools, we explore how Ca2+-dependent
mechanisms underlying selective attention can contribute to such differences in
amplitude modulation sensitivity. For omega neuron 1 (ON1), selective attention
is mediated by Ca2+-dependent feedback: [Ca2+]internal increases with
excitation, activating a Ca2+-dependent after-hyperpolarizing current. We
propose that Ca2+ removal rate and the size of the after-hyperpolarizing
current can determine ON1âs temporal modulation transfer function (TMTF). This
is tested using a conductance-based simulation calibrated to responses in vivo.
The model shows that parameter values that simulate responses to single pulses
are sufficient in simulating responses to modulated stimuli: no special
modulation-sensitive mechanisms are necessary, as high and low-pass portions of
the TMTF are due to Ca2+-dependent spike frequency adaptation and post-synaptic
potential depression, respectively. Furthermore, variance in the two
biophysical parameters is sufficient to produce TMTFs of varying bandwidth,
shifting amplitude modulation sensitivity like that in different species and in
response to different carrier frequencies. Thus, the hypothesis that the size
of after-hyperpolarizing current and the rate of Ca2+ removal can affect
amplitude modulation sensitivity is computationally validated.
For reprints please contact H. E. Farris (email:
Konstantinos Kostarakos & Heiner RÃmer (2010): Sound transmission and
directional hearing in field crickets: neurophysiological studies outdoors. J.
Comp. Physiol. A 196 (9), 669-681.
Abstract: Many studies provide detailed behavioural and neurophysiological
information on the ability of crickets to localize a sound source under ideal
acoustic conditions, but very little is known about how they perform in real
habitats. We investigated directional hearing of crickets in the field using a
neurophysiological approach, by recording the activity of the two prominent,
bilaterally homologous AN1 neurons simultaneously in a cricketâs habitat. The
discharge and latency differences of the pair of neurons in response to
conspecific chirps presented at different distances and directions were taken
as a measure of directional information. The maximum hearing distance differed
between individuals and weather conditions from 1 to 15 m (mean 9.2 m).
Although the AN1 activity generally decreased with increasing distance, large
fluctuations in the magnitude of responses occurred with distance, indicating
that the intensity gradient over distance is often irregular. The directional
information provided in the discharge differences of the two neurons also
varied with distance. Again, there was no simple directional gradient on the
transmission channel; rather, with decreasing distance to the source there were
receiver locations providing suprathreshold responses, but no directional
information. The consequences for the ability of field crickets to communicate
acoustically close to the ground are discussed.
For reprints please contact K. Kostarakos (email:
Gerlind U. C. Lehmann, Sandra Berger, Johannes StrauÃ, Arne W. Lehmann &
Hans-Joachim PflÃger (2010): The auditory system of non-calling grasshoppers
(Melanoplinae: Podismini) and the evolutionary regression of their tympanal
ears. J. Comp. Physiol. A 196 (11), 807-816.
Abstract: Reduction of tympanal hearing organs is repeatedly found amongst
insects and is associated with weakened selection for hearing. There is also an
associated wing reduction, since flight is no longer required to evade bats.
Wing reduction may also affect sound production. Here, the auditory system in
four silent grasshopper species belonging to the Podismini is investigated. In
this group, tympanal ears occur but sound signalling does not. The tympanal
organs range from fully developed to remarkably reduced tympana. To evaluate
the effects of tympanal regression on neuronal organisation and auditory
sensitivity, the size of wings and tympana, sensory thresholds and sensory
central projections are compared. Reduced tympanal size correlates with a
higher auditory threshold. The threshold curves of all four species are tuned
to low frequencies with a maximal sensitivity at 3â5 kHz. Central projections
of the tympanal nerve show characteristics known from fully tympanate acridid
species, so neural elements for tympanal hearing have been strongly conserved
across these species. The results also confirm the correlation between
reduction in auditory sensitivity and wing reduction. It is concluded that the
auditory sensitivity of all four species may be maintained by stabilising
selective forces, such as predation.
For reprints please contact G. U. C. Lehmann (email:
Dr. Sonja Amoser