James J. Finneran, Hollis R. London, and Dorian S. Houser (2007):
Modulation rate transfer functions in bottlenose dolphins (Tursiops
truncatus) with normal hearing and high-frequency hearing loss. J. Comp.
Physiol. A 193(8), 835-843.
Abstract: Envelope following responses were measured in two bottlenose
dolphins in response to sinusoidal amplitude modulated tones with carrier
frequencies from 20 to 60 kHz and modulation rates from 100 to 5,000 Hz.
One subject had elevated hearing thresholds at higher frequencies, with
threshold differences between subjects varying from +4 dB at 20 and 30 kHz
to +40 dB at 50 and 60 kHz. At each carrier frequency, evoked response
amplitudes and phase angles were plotted with respect to modulation
frequency to construct modulation rate transfer functions. Results showed
that both subjects could follow the stimulus envelope components up to at
least 2,000 Hz, regardless of carrier frequency. There were no substantial
differences in modulation rate transfer functions for the two subjects
suggesting that reductions in hearing sensitivity did not result in
reduced temporal processing ability. In contrast to earlier studies, phase
data showed group delays of approximately 3.5 ms across the tested
frequency range, implying generation site(s) within the brainstem rather
than the periphery at modulation rates from 100 to 1,600 Hz. This
discrepancy is believed to be the result of undersampling of the
modulation rate during previous phase measurements.
For reprints please contact: James J. Finneran (Email:
Simone Schehka, Karl-Heinz Esser, and Elke Zimmermann (2007): Acoustical
expression of arousal in conflict situations in tree shrews (Tupaia
belangeri). J. Comp. Physiol. A 193(8), 845-852.
Abstract: Empirical research on human and non-human primates suggests that
communication sounds express the intensity of an emotional state of a
signaller. In the present study, we have examined communication sounds
during induced social interactions of a monogamous mammal, the tree shrew.
To signal their unwillingness to mate, female tree shrews show defensive
threat displays towards unfamiliar males paralleled by acoustically
variable squeaks. We assumed that the distance between interacting
partners as well as the behavior of the male towards the female indicates
the intensity of perceived social threat and thereby the arousal state of
a female. To explore this hypothesis we analyzed dynamic changes in
communication sounds uttered during induced social interactions between a
female and an unfamiliar male. Detailed videographic and sound analyzes
revealed that the arousal state predicted variations in communication
sound structure reliably. Both, a decrease of distance and a male
approaching the female led to an increase in fundamental frequency and
repetition rate of syllables. These findings support comparable results in
human and non-human primates and suggest that common coding rules in
communication sounds govern acoustic conflict regulation in mammals.
For reprints please contact Simone Schehka (Email:
Christine Schwartz, Jedidiah Tressler, Halli Keller, Marc Vanzant, Sarah
Ezell, and Michael Smotherman (2007): The tiny difference between foraging
and communication buzzes uttered by the Mexican free-tailed bat, Tadarida
brasiliensis. J. Comp. Physiol. A 193(8), 853-863.
Abstract: Echolocating insectivorous bats consummate prey captures using a
distinct vocal motor pattern commonly known as the terminal or feeding
buzz, which is widely considered a fixed motor pattern executed
independently of auditory feedback influences. The Mexican free-tailed
bat, Tadarida brasiliensis, offers an opportunity to explore the role of
sensory feedback in buzzing because they emit similar buzzes both in
flight during foraging and while stationary as communication sounds. Here
we compared the spectral and temporal patterns of foraging and
communication buzzes to address whether or not auditory feedback may
influence buzz patterns. We found that while foraging buzzes uttered in
open space were composed of generic FM calls, communication buzzes were
composed of an adapted CF-FM call similar to the call type used by T.
brasiliensis when navigating in confined spaces. This provides the first
evidence that some bats can make significant context-dependent changes in
the spectral parameters of calls within their buzz. We also found that
inter-pulse intervals, but not call durations, were different within the
two buzz types. These observations indicate that though a common pattern
generator hierarchically organizes all buzzes, T. brasiliensis retains a
significant capacity to adapt the spectral and temporal patterns of
elements within its buzzes.
For reprints please contact Christine Schwartz (Email:
Doreen M�ckel, Ernst-August Seyfarth, and Manfred K�ssl (2007): The
generation of DPOAEs in the locust ear is contingent upon the sensory
neurons. J. Comp. Physiol. A 193(8), 871-879.
Abstract: Tympanal organs of insects emit distortion-product otoacoustic
emissions (DPOAEs) that are indicative of nonlinear ear mechanics. Our
study sought (1) to define constraints of DPOAE generation in the ear of
Locusta migratoria, and (2) to identify the sensory structures involved.
We selectively destroyed the connection between the (peripheral) sensory
ganglion and the tympanal attachment points of the "d-cell" dendrites;
d-cells are most sensitive to sound frequencies above 12 kHz. This led to
a decrease of DPOAEs that were evoked by f2 frequencies above 15 kHz
(decrease of 15-40 dB; mean 28 dB; n = 12 organs). DPOAEs elicited by
lower frequencies remained unchanged. Such frequency-specific changes
following the exclusion of one scolopidial sub-population suggest that
these auditory scolopidia are in fact the source of DPOAEs in insects.
Electrical stimulation of the auditory nerve (with short current pulses of
4-10 uA or DC-currents of 0.5 uA) reversibly reduced DPOAEs by as much as
30 dB. We assume that retrograde electrical stimulation primarily affected
the neuronal part of the scolopidia. Severing the auditory nerve from the
central nervous system (CNS) did not alter the DPOAE amplitudes nor the
effects of electrical stimulation.
For reprints please contact Doreen M�ckel (Email:
Dr. Sonja Amoser