Laser interferometry with human temporal bones.
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Acoustic Stimulation↗
Biomedical subjects
M S Vlaming
Publications and source records attributed to M S Vlaming.
Directional hearing in the grassfrog (Rana temporaria L.). II. Acoustics and modelling of the auditory periphery.
In an earlier paper (Vlaming et al., 1984) we reported on optical measurements (laser-doppler interferometry) of the vibrations characteristics of the grassfrog's tympanic membrane. In the present paper these measurements were extended to include acoustic measurements concerning the functional role of the mouth cavity in frog hearing. Based on these measurements a model of the frog's acoustic periphery, consisting of three coupled linear oscillators with three entrance ports for sound, was developed and analyzed mathematically to give the various relevant transfer functions. The model is characterized by six parameters, all of which could be estimated from the available experimental data. For frequencies up to some 1500 Hz the model adequately describes the experimental data, both our own and earlier, seemingly conflicting data in the literature. For higher frequencies deviations occur, possibly due to nonuniform vibrations of the membranes. The model was used to evaluate the monaural directional sensitivity of the frog under free-field stimulation. Essentially it behaves as a combined pressure-gradient receiver, with highly frequency-dependent directional sensitivity. Directional sensitivity of the tympanic membrane could be modulated drastically by changing the resonance properties of the mouth cavity, without affecting the intrinsic membrane properties. This, theoretically, allows the frog to manipulate its direction sensitivity by actively tuning the volume of its mouth cavity. In order to account for discrepancies with known properties of low-frequency auditory nerve fibers an additional, extra-tympanic channel was included into the model. The extended model, the second-channel possibly involving the opercularis complex, provides a good quantitative fit to the available data on tympanic membrane movement as well as auditory nerve activity. Finally, the model enables to simulate a (moving) sound source in space, while stimulating the frog via closed couplers.
Acoustics↗
Studies on the mechanics of the normal human middle ear.
The middle ear was studied in temporal bone preparations using a laser-Doppler interferometer. For measurements at a sound level of 80 dB SPL this method proved to be very reliable, as was shown by good reproducibility of results in experiments over more than 6 hours. The vibrations of the tympanic membrane and stapes footplate were studied from 200 Hz to 10 KHz and the results demonstrate a piston-like movement of the stapes footplate up to 120 dB SPL. The damping effect of the normal ear is located mainly at the footplate/cochlea level and the middle ear cavity per se does not contribute significantly to the stiffness of the middle ear system.
Acoustic Stimulation↗
Studies on the mechanics of the reconstructed human middle ear.
Using a laser-Doppler interferometer the influence of different positions of an incus prosthesis on hearing performance was examined in human temporal bone preparations. The influence of position and tension of a malleus to footplate prosthesis (columella) was studied in the same way. It is concluded that an incus prosthesis should be placed along an imaginary line through the centre of the footplate and the head of the stapes. With a malleus to footplate prosthesis the position on the footplate is relatively unimportant. Tension between the malleus, prosthesis and footplate, however, is quite important and should be as low as possible, and compatible with a stable situation. The malleus to footplate prosthesis provides a columella type of prosthesis which for lower frequencies works better than an incus prosthesis, and occasionally even better than the normal ear.
Biomechanical Phenomena↗
Digital A-scan ultrasonography used to measure ocular distances.
Digital A-scan ultrasonography provided a digital display of intraocular distances with an overall accuracy of 0.05 mm. Since the control setting was easy and calibration was unnecessary, the time of measurement is reduced and hence the apparatus is useful in clinical practice.
Anthropometry↗