Stapedius reflex thresholds obtained in a free sound field as an indicator for over- and understimulation in cochlear implant listeners.

OBJECTIVE: The goal of this study was to determine open field stapedius reflex thresholds (oSRTs) in CI patients with fittings based on subjective loudness ratings. A further objective was to compare these oSRTs and those of eSRT-based fittings that are similar to the oSRTs of normal hearing. DESIGN: Impedance measurements of the ear drum were taken while subjects were wearing their audio processors. The stapedius reflex was elicited by electrical stimulation transmitted through the activated CI system in response to an acoustic stimulus presented in the free sound field. STUDY SAMPLE: Subjects were 50 experienced CI users (n = 57 ears) with CI fittings based on subjective loudness scaling. RESULTS: A reference range for the oSRTs was defined that was identified in CI patients with eSRT-based fittings. Sound levels for stapedius reflex detection were inside the reference target range in 70% of the cases, below the reference range (i.e. down to 40 dB HL) in 20% of the cases, and above the reference range in 10% of the cases. CONCLUSION: Stapedius reflex detection in a free sound field may help detect fittings with too high or too low stimulation levels that might reduce audiological performance.

Relationship between epilarynx tube shape and the radiated sound pressure level during phonation is gender specific.

OBJECTIVE/HYPOTHESIS: The aim of the study was to measure the morphology of the epilaryngeal tube during sustained phonation as a function of loudness variation and to compare subjects of different genders. STUDY DESIGN: This is a prospective study. METHODS: Five female and five male classically trained singers were recorded by magnetic resonance imaging with simultaneous audio recordings while sustaining phonation at three different loudness conditions. Three-dimensional subsections of the vocal tract were segmented on multi-image-based cross-sections. Different volume and area measures were determined and their relation to sound pressure level and loudness condition was analyzed. RESULTS: Male singers tended to narrow the epilaryngeal tube when increasing sound pressure level whereas female singers did not. CONCLUSION: Strategies of vocal tract adjustments during loudness variation in classical singing appear to be gender specific.

Stapedius reflex evoked in free sound field in cochlear implant users compared to normal-hearing listeners.

OBJECTIVE: To determine the relation between stapedius reflex thresholds in cochlear implant users evoked once through direct electric stimulation on single channels (ESRT) and once through acoustic stimulation in free sound field. For comparison, stapedius reflex thresholds were obtained in free sound field in a normal-hearing control group. DESIGN: For each participant a new ESRT-based fitting was created. Stapedius reflex thresholds were obtained for this new fitting in free sound field for different loudness adjustments. Acoustic stimuli for eliciting the stapedius reflex were narrow band noise signals covering the audiometric frequency range. STUDY SAMPLE: N = 29 experienced CI users (34 ears) and N = 10 normal hearing listeners. RESULTS: ESRT-based fitting resulted in different stapedius reflex behaviour compared to normal-hearing listeners. A frequency dependence was observed. Stapedius reflex thresholds decreased with increasing centre frequencies of acoustic narrow band noise stimuli. A linear relation between upper stimulation levels on the implant channels and corresponding stapedius reflex thresholds evoked in free sound field was found. CONCLUSION: The found correlation may be a guideline for adjusting the electrical dynamic range during cochlear implant fitting. This allows the implant system to mimic the natural reflex behaviour in the best possible way and potentially avoid overstimulation.

Characteristics of the pulsating jet flow through a dynamic glottal model with a lens-like constriction.

A computational study of the pulsating jet in a squared channel with a dynamic glottal-shaped constriction is presented. It follows the model experiments of Triep and Brücker (J Acoust Soc Am 127(2):1537-1547, 2010) with the cam-driven model that replicates the dynamic glottal motion in the process of human phonation. The boundary conditions are mapped from the model experiment onto the computational model and the three dimensional time resolved velocity and pressure fields are numerically calculated. This study aims to provide more details of flow separation and pressure distribution in the glottal gap and in the supraglottal flow field. Within the glottal gap a 'vena contracta' effect is generated in the mid-sagittal plane. The flow separation in the mid-coronal plane is therefore delayed to larger diffuser angles which leads to an 'axis-switching' effect from mid-sagittal to mid-coronal plane. The location of flow separation in mid-sagittal cross section moves up- and downwards along the vocal folds surface in streamwise direction. The generated jet shear layer forms a chain of coherent vortex structures within each glottal cycle. These vortices cause characteristic velocity and pressure fluctuations in the supraglottal region, that are in the range of 10-30 times of the fundamental frequency.

Three-dimensional Vocal Tract Morphology Based on Multiple Magnetic Resonance Images Is Highly Reproducible During Sustained Phonation.

OBJECTIVES: The extraction of a three-dimensional (3D) morphology of the human vocal tract (VT) from magnetic resonance imaging (MRI) during sustained phonation can be used for various analyses like numerical simulations or creating physical models. The precision of visualizing techniques nowadays allows for very targeted acoustical simulation evaluating the influence of subsections of the VT for the transfer function. The aim of the study was to assess the accuracy of the 3D geometry based on MRI data in repetitive trials. STUDY DESIGN: This is a prospective study. METHODS: Four experienced singers underwent an MRI while repeating a specific vocal task 20 times consecutively. Audio recordings were made by means of an optical microphone. Images were restacked and subsections of the VT were segmented on multi-image-based cross sections using a semiautomatic algorithm. Different volume and area measures were evaluated. RESULTS: A high reproducibility of the morphologic data based on multiple images by means of the applied segmentation method could be shown with an overall variation of around 8%. CONCLUSIONS: 3D modeling of the VT during sustained phonation involves a complex experimental setting and elaborate image processing techniques. Functional comparative analysis or acoustical simulations based on such data should take the found variability into account.

Formant frequencies and bandwidths of the vocal tract transfer function are affected by the mechanical impedance of the vocal tract wall.

The acoustical properties of the vocal tract, the air-filled cavity between the vocal folds and the mouth opening, are determined by its individual geometry, the physical properties of the air and of its boundaries. In this article, we address the necessity of complex impedance boundary conditions at the mouth opening and at the border of the acoustical domain inside the human vocal tract. Using finite element models based on MRI data for spoken and sung vowels /a/, /i/ and /Ω(-1)/ and comparison of the transfer characteristics by analysis of acoustical data using an inverse filtering method, the global wall impedance showed a frequency-dependent behaviour and depends on the produced vowel and therefore on the individual vocal tract geometry. The values of the normalised inertial component (represented by the imaginary part of the impedance) ranged from 250 g/m(2) at frequencies higher than about 3 kHz up to about 2.5 × 10(5) g/m(2)in the mid-frequency range around 1.5-3 kHz. In contrast, the normalised dissipation (represented by the real part of the impedance) ranged from 65 to 4.5 × 10(5) Ns/m(3). These results indicate that structures enclosing the vocal tract (e.g. oral and pharyngeal mucosa and muscle tissues), especially their mechanical properties, influence the transfer of the acoustical energy and the position and bandwidth of the formant frequencies. It implies that the timbre characteristics of vowel sounds are likely to be tuned by specific control of relaxation and strain of the surrounding structures of the vocal tract.

Asymmetric glottal jet deflection: differences of two- and three-dimensional models.

Flow is studied through a channel with an oscillating orifice mimicking the motion of the glottal-gap during phonation. Simulations with prescribed flow and wall-motion are carried out for different orifice geometries, a 2D slit-like and a 3D lens-like one. Although the jet emerges from a symmetric orifice a significant deflection occurs in case of the slit-like geometry, contrary to the 3D lens-like one. The results demonstrate the dependency of jet entrainment and vortex dynamics on the orifice geometry and the interpretation of asymmetric jet deflection with regard to the relevance of the Coanda effect in the process of human phonation.