An analysis is presented of the mechanical response to a sound field of the ears of the parasitoid fly Ormia ochracea. This animal shows a remarkable ability to detect the direction of an incident sound stimulus even though its acoustic sensory organs are in very close proximity to each other. This close proximity causes the arrival times of the sound pressures at the two ears to be less than 1 to 2 microseconds depending on the direction of propagation of the sound wave. The small differences in these two pressures must be processed by the animal in order to determine the incident direction of the sound. In this fly, the ears are so close together that they are actually joined by a cuticular structure which couples their motion mechanically and subsequently magnifies interaural differences. The use of a cuticular structure as a means to couple the ears to achieve directional sensitivity is novel and has not been reported in previous studies of directional hearing. An analytical model of the mechanical response of the ear to a sound stimulus is proposed which supports the claim that mechanical interaural coupling is the key to this animal's ability to localize sound sources. Predicted results for sound fields having a range of incident directions are presented and are found to agree very well with measurements.
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"In particular, interaural intensity differences (IID) or interaural temporal differences (ITD) between both ears can be used for extracting directional information (Michelsen 1992). These differences are rather small in a fly, but it has been shown that both tympanal membranes of the ear are mechanically coupled (Miles et al. 1995; Robert et al. 1998, 1999). This mechanism increases temporal differences between the ears and thereby provides a directional cue in the horizontal plane. "
[Show abstract][Hide abstract] ABSTRACT: Two taxa of parasitoid Diptera have independently
evolved tympanal hearing organs to locate sound
producing host insects. Here we review and compare functional
adaptations in both groups of parasitoids, Ormiini
and Emblemasomatini. Tympanal organs in both groups
originate from a common precursor organ and are somewhat
similar in morphology and physiology. In terms of
functional adaptations, the hearing thresholds are largely
adapted to the frequency spectra of the calling song of
the hosts. The large host ranges of some parasitoids indicate
that their neuronal filter for the temporal patterns of
the calling songs are broader than those found in intraspecific
communication. For host localization the night active
Ormia ochracea and the day active E. auditrix are able to
locate a sound source precisely in space. For phonotaxis
flight and walking phases are used, whereby O. ochracea
approaches hosts during flight while E. auditrix employs
intermediate landings and re-orientation, apparently separating
azimuthal and vertical angles. The consequences of
the parasitoid pressure are discussed for signal evolution
and intraspecific communication of the host species. This
natural selection pressure might have led to different avoidance
strategies in the hosts: silent males in crickets, shorter
signals in tettigoniids and fluctuating population abundances
"By a comparison of binaural response levels directional hearing in insects is possible with very limited computational brain capacity. There are large differences in the particular layout and position of pressure difference receivers (Michelsen 1998; Miles et al. 1995), but nevertheless insects are equipped with directional information for further use by an apparatus that performs computations mechanically. "
[Show abstract][Hide abstract] ABSTRACT: Hearing in insects serves to gain information in the context of mate finding, predator avoidance or host localization. For these goals, the auditory pathways of insects represent the computational substrate for object recognition and localization. Before these higher level computations can be executed in more central parts of the nervous system, the signals need to be preprocessed in the auditory periphery. Here, we review peripheral preprocessing along four computational themes rather than discussing specific physiological mechanisms: (1) control of sensitivity by adaptation, (2) recoding of amplitude modulations of an acoustic signal into a labeled-line code (3) frequency processing and (4) conditioning for binaural processing. Along these lines, we review evidence for canonical computations carried out in the peripheral auditory pathway and show that despite the vast diversity of insect hearing, signal processing is governed by common computational motifs and principles.
[Show abstract][Hide abstract] ABSTRACT: The technique for estimation of sound source direction is one of the important methods necessary for various engineering fields such as monitoring system, military services and so on. As a new approach for estimation of sound source direction, this paper propose the bio-mimetic localization sensor based on mechanically coupling structure motivated by hearing structure of fly, Ormia Ochracea. This creature is known for its outstanding recognition ability to the sound which has large wavelength compared to its own size. ITTF (Inter-Tympanal Transfer Function) which is the transfer function between displacements of the tympanal membranes on each side has the all inter-tympanal information dependent on sound direction. The peak and notch features of desired ITTF can be generated by using the appropriate mechanical properties. A example of estimation of sound source direction using generated ITTF with monotonically changing notch and peak patterns is shown.
Journal of Institute of Control 02/2012; 18(2). DOI:10.5302/J.ICROS.2012.18.2.126