Mechanical tuning of the moth ear: distortion-product otoacoustic emissions and tympanal vibrations

Abstract

SUMMARYThe mechanical tuning of the ear in the moth Empyreuma pugione was investigated by distortion-product otoacoustic emissions (DPOAE) and laser Doppler vibrometry (LDV). DPOAE audiograms were assessed using a novel protocol that may be advantageous for non-invasive auditory studies in insects. To evoke DPOAE, two-tone stimuli within frequency and level ranges that generated a large matrix of values (960 frequency-level combinations) were used to examine the acoustic space in which the moth tympanum shows its best mechanical and acoustical responses. The DPOAE tuning curve derived from the response matrix resembles that obtained previously by electrophysiology, and is V-shaped and tuned to frequencies between 25 and 45kHz with low Q 10dB values of 1.21±0.26. In addition, while using a comparable stimulation regime, mechanical distortion in the displacement of the moth's tympanal membrane at the stigma was recorded with a laser Doppler vibrometer. The corresponding mechanical vibration audiograms were compared with DPOAE audiograms. Both types of audiograms have comparable shape, but most of the mechanical response fields are shifted towards lower frequencies. We showed for the first time in moths that DPOAE have a pronounced analogy in the vibration of the tympanic membrane where they may originate. Our work supports previous studies that point to the stigma (and the internally associated transduction machinery) as an important place of sound amplification in the moth ear, but also suggests a complex mechanical role for the rest of the transparent zone.

The influence of bat echolocation call duration and timing on auditory encoding of predator distance in noctuoid moths

“…Moth auditory receptors respond to the displacement of the tympanum, and tympanal displacement does not differ between intact moths and moths that have been prepared for extracellular recordings at the frequencies and amplitudes of sound that we use here (ter Hofstede et al, 2011). Distortion-product otoacoustic emissions (DPOAEs), a non-invasive measure of auditory cell activity, have been used effectively to assess moth hearing (Coro and Kössl, 1998;Mora et al, 2013), but it is currently unknown how these values correspond with the number of action potentials produced by cells, so DPOAEs could not be used to address the objectives of our study.…”

Critical waves and the length problem of biology

“…It is thus not surprising that the wave signals easiest to observe in biology are often nonlinear. But amplification in the linear regime is known to occur as well, notably in hearing organs [35][36][37][38][39][40] .…”