The role of cuticular flapsIn certain bush-cricket species, tympanal membranes are covered by cuticular pinna. It has been previously theorized that these pinnae not only protect the tympanic membranes, but also contribute to auditory directionality. A mechanistic investigation using non-contact measurements of tympanal vibrations, by means of micro-scanning laser Doppler vibrometry (LDV) could yield insight of the role of pinnae as omnidirectional sound guides.
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We hypothesized that the oscillation phase of a sound wave would be different in each tympanum with the pinnae present and would be the same with the removal of the pinnae. Since the tympanal chambers have a narrow slit, sound accesses the external surface of the tympanal membrane directly and thereby causes tympanal vibrations that are 60-80 microseconds earlier than the arrival of the tracheal input. From previous research we know that insects can hear these external vibrations the are magnified by the lever action of the middle ear (the tympanal plate). Due to the delays of vibratory events, the insect can localise sound (particularly at higher frequencies). The question remains if the external input contributes to directional hearing or to the very least, localizing sound when the sound emanates from specific azimuth in relation to the tympanal chambers. Did they evolve to protect a thin tympanic membrane only? Do they have any diffraction effect for directional hearing of specific calls? Do they favour the reception of ultrasonic sound waves?
This project conducted by PhD student Christian Pulver and Dr. Celiker uses experimental and numerical analysis to compare species with naked tympana with species with cuticular pinna.
This project conducted by PhD student Christian Pulver and Dr. Celiker uses experimental and numerical analysis to compare species with naked tympana with species with cuticular pinna.
Ear response to multiple sound ports
In this project we expose the insect in a free sound field, but also access the tracheal or external input separately using special sound isolating platforms. Tympanal motion is the vibrations of the tympanal membrane caused by an acoustic stimulus traveling from the spiracle, through the trachea, and hitting the inner surface of tympana. By investigating tympanal displacement mechanics, we can observe how tympanal motion changes in response to varying sound azimuth at different frequencies. Understanding this motion will yield insight into directional hearing.