Development of a novel Italian speech-in-noise test using a roving-level adaptive method: adult population-based normative data.

In recent years the increasing development of hearing devices has led to a critical analysis of the standard methods employed to evaluate hearing function. Being too far from reality, conventional investigation of hearing loss based on pure-tone threshold audiometry and on mono/disyllabic word lists, presented in quiet conditions, has been shown to be inadequate. A speech-in-noise test using a roving-level adaptive method employs target and competing signals varying in level in order to reproduce everyday life speaking conditions and explore a more complete sound range. Up to now, only few roving-level adaptive tests have been published in the literature. We conducted a rovinglevel adaptive test in healthy Italian adults to produce new normative data on a language of Latin origin.

[Audiological results with cochlear implants for single-sided deafness]. / Audiologische Ergebnisse mit Cochlear implant bei einseitiger Taubheit.

INTRODUCTION: Single-sided deafness has a strong impact on quality of life. Besides the difficulties in sound localization, patients also require increased effort to hear. The latter makes it difficult to follow conversations for an extended period, leading to social isolation. Cochlear implantation (CI) represents a possible treatment option for deafness in one ear. METHODS: In the present study, 13 patients with unilateral deafness where treated with CI. All patients were examined by pure tone audiometry and speech tests (Freiburger; HSM; OlSa), as well as sound localisations tests. The single-sided deaf situation is compared to CI-aided binaural hearing. RESULTS: At 100%, the acceptance rate was very high. The two different auditory inputs were well integrated. Patients reported satisfactory restoration of acoustic orientation and sound localization as well as great ease of listening in noisy surroundings. There was no negative impact on the normal hearing side. CONCLUSION: These preliminary results confirm the effectiveness of CI treatment in unilateral deafness.

Sound localization and sensitivity to interaural cues in bilateral users of the Med-El Combi 40/40+cochlear implant system.

OBJECTIVE: The purpose of this study was to investigate sound localization in subjects bilaterally implanted with MED-EL COMBI 40/40+ cochlear implants. In addition, the sensitivity to interaural cues was assessed. METHODS: In the localization test (11 subjects), CCITT noise (500 ms, original and HRTF-filtered, 70/75/80 dB sound pressure level) was presented from one of seven loudspeakers between -90 degrees and 90 degrees azimuth. The subject had to indicate which loudspeaker the noise was presented from. Sensitivity to interaural level differences (ILD) was assessed by performing localization tests (4 subjects) with the loudness of the two speech processors unbalanced to various degrees. To investigate the subjects' sensitivity to interaural time differences (ITD), lateralization was measured (7 subjects) as a function of the time difference between two Gaussian-like pulses, each directed to one of the subject's speech processor microphones by way of headphones. RESULTS: The judgments of all subjects significantly correlated with the positions of the loudspeakers. The scatter in the judged azimuth measured by the standard deviation of the responses was on average 27.5 degrees . Unbalanced loudness of the speech processors produced a bias in azimuth toward the speech processor with the louder volume setting. The mean rate of shift was 1.4 degrees per unit on the Wuerzburg loudness scale. Six of seven subjects showed a significant sensitivity to ITDs with the approximate time difference required for complete lateralization being 1,200 micros on an average. The one subject not showing a sensitivity to ITDs performed worst in the localization test. CONCLUSIONS: Bilateral cochlear implantation can restore spatial hearing in cochlear implant users. Both ILDs and ITDs are used by bilateral cochlear implant users in sound localization with ILDs appearing to be the dominant cue.

Head shadow, squelch, and summation effects in bilateral users of the MED-EL COMBI 40/40+ cochlear implant.

OBJECTIVE: The aim of the study was to investigate the impact of bilateral cochlear implant use on speech perception in noise in bilateral users of the MED-EL COMBI 40/40+ cochlear implants. DESIGN: Speech reception thresholds were measured in 21 subjects using the Oldenburg sentence test. Speech was always presented from the front. Noise was either presented from the front, from the left side, or from the right side. Each condition was measured for unilateral and bilateral implant use. RESULTS: For three subjects, the test was too difficult to be administered. The 18 subjects from whom a complete data set could be obtained showed a significant head shadow effect and summation effect for all test conditions, whereas the squelch effect was significant for noise from the left side only. Average effect sizes were significant for all effects and amounted to 6.8 dB for the head shadow effect, 0.9 dB for the squelch effect, and 2.1 dB for the summation effect. Effect sizes were not correlated with duration of deafness. CONCLUSIONS: Bilateral cochlear implant users can at least qualitatively benefit from the effects that are known from normal-hearing subjects, that is, head shadow, summation, and squelch effect. Bilateral cochlear implantation also reduces the performance gap between cochlear implant users and normal-hearing subjects.

Sound localization in bilateral users of MED-EL COMBI 40/40+ cochlear implants.

OBJECTIVE: The purpose of the study was to investigate sound localization with bilateral and unilateral cochlear implants. DESIGN: Sound localization tests were performed on 20 bilaterally implanted MED-EL COMBI 40/40+ users. All subjects were bilaterally implanted during adolescence or later. Sound localization was tested in the frontal horizontal plane by using 9 equally spaced loudspeakers and speech-shaped noise bursts at randomized levels. RESULTS: The group of subjects who were bilaterally deafened after 5 to 6 yr of age (18 subjects) showed a statistically significant improvement in sound localization when using both implants, compared with when using only one. The mean deviation between the presentation azimuth and the response azimuth was 16.6 degrees when using both implants, which was on average 37.1 degrees smaller than when using one implant only. When adjusted for the localization error that was constant across loudspeakers, the mean deviation was 15.9 degrees for bilateral implant use, representing an improvement of 30.1 degrees over unilateral implant use. Statistical analysis showed that in this group, performance measures were not correlated with subject details such as age at onset of deafness or duration of unilateral implant use. In contrast, subjects who were bilaterally deafened before 6 yr of age (2 subjects) did not show a benefit in sound localization from bilateral implants. CONCLUSIONS: Bilateral cochlear implants offer a substantial benefit in sound localization to late-deafened, late-implanted subjects. The very limited data from early-deafened subjects implanted at a later age could suggest that these subjects may not benefit in sound localization from bilateral cochlear implants. It is possible that early implantation for early deafened subjects might allow better acquisition of spatial hearing, thus leading to improved localization performance.

Speech understanding with the CIS and the n-of-m strategy in the MED-EL COMBI 40+ system.

Speech tests have been performed on 6 subjects for comparing the standard 12-channel continuous interleaved sampling (CIS) strategy (CIS12), the 7-channel CIS strategy (CIS7) and the 7-of-12 strategy in the MED-EL COMBI 40+ system. An ABAB experimental design was used whereby each strategy was reversed and replicated. Speech tests were performed in quiet (vowels, consonants, monosyllables, sentences) and noise (sentences). Results showed that for vowels, CIS12 is significantly superior to CIS7, for consonants and sentences CIS12, CIS7 and 7-of-12 performed equally well, and that for monosyllables 7-of-12 is significantly superior to both CIS12 and CIS7. In addition, 7-of-12 is superior to CIS7 by almost the same amount as CIS12, but in this case the difference is not significant. Further, all strategies have been found to be equally robust in noise with respect to sentence understanding. The differences between CIS12 and 7-of-12 on the one hand and CIS7 on the other hand may be attributed to decreased spectral resolution of the latter. The fact that - in contrast to what has been reported for the SPEAK strategy - 7-of-12 is equally robust in noise as the CIS strategies is explained by the use of higher stimulation rates, wider frequency bands and a higher percentage of channels stimulated in each cycle.

A comparison of neonatal and adult lung impedances derived from EIT images.

An objective method of extracting respiratory data from lung images is presented, together with a technique for automatically generating regions of interest delineating the anterior and posterior regions of the lungs. The method is used to extract data on the change in lung impedance with frequency, and on calculated Cole parameters, from 19 normal neonates (gestational age 32 to 42 weeks) and 8 normal adults (age 21 to 82 years). A comparison of the impedance properties of neonatal and adult lungs was made. The variation of lung impedance with frequency in neonates, as derived from EIT images, is significantly different from that found for adults. The implications for a model of the electrical impedance of lung tissue are discussed.

Model for the dielectric properties of human lung tissue against frequency and air content.

Electrical impedance tomographic spectroscopy measurements of the lungs are taken from nine normal subjects, in the frequency range 9.6 kHz-1.2 MHz. The results show that resistivity rho'FRC relative to functional residual capacity increases almost linearly with inspiration volume V, with the slope of the curve increasing with frequency f. Resistivity rho'9.6 kHz relative to 9.6 kHz decreases with f. rho'9.6 kHz increases with V, at any given frequency. Curves for rho'9.6 kHz show a roughly linear trend with log10(f). Based on a discussion of the measurement results, a mathematical lung tissue model is designed that involves extra-capillary blood vessels and alveoli, the walls of which consist of blood-filled capillaries, epithelial cells and intercellular liquid. Using this model, the increase in rho'FRC with V is explained by the thinning of alveolar walls with increasing air content. The almost linear shape of curves for rho'9.6 kHz is attributed to four partly overlapping main dispersions caused by extra-capillary blood vessels, epithelial cells, blood and the capillary network.

EITS changes following oleic acid induced lung water.

We present the results of using electrical impedance tomographic spectroscopy (EITS) to follow the changes in lung water induced by oleic acid. Measurements were made on three goats before and after the injection of oleic acid. In addition to the EITs measurements, lung water was also measured using a double-indicator technique. Large falls in lung electrical impedance were seen as a result of the increase in lung water but the size of the fall was a function of the frequency at which the measurements were made. These changes have been modelled using the Cole equation. Four-electrode measurements were also made on two extracted porcine lungs and Cole equation modelling carried out following the introduction of saline into the lungs. Results were similar in the two sets of animal experiments.

Cardiac-related changes in lung resistivity as a function of frequency and location obtained from EITS images.

ECG-gated electrical impedance tomographic spectroscopy (EITS) measurements of the lungs were taken on seven normal subjects in the frequency range 9.6 kHz to 614.4 kHz. The results show that in late systole the resistivity p' relative to the R-wave (i.e. p' = 1 at the R-wave) decreases consistently within the lung. In addition there arises an increase in p' in early systole towards the periphery of the lung. Frequency behaviour of p' changes with location. At all times after the R-wave, in the centre of the lung p' is higher at higher frequency f whereas in the periphery it is lower at higher f. The principal decrease in p' can be explained by increasing pulmonary blood volume due to cardiac contraction. The early systolic increase is presumably due to venous return to the left atrium locally leading blood output from the right ventricle which is delayed by the windkessel effect. Based on a model taking extracapillary and capillary blood volume increase into account, the change in frequency behaviour of p' is explained by regional variations in extracapillary blood vessel size determining the relative contributions of extracapillary blood volume and capillary blood volume change to p' at a certain frequency.

Modelling of cardiac-related changes in lung resistivity measured with EITS.

Resistivity data from 9.6 kHZ to 1.2 MHz were recorded from eight normal subjects using an electrical impedance tomographic spectroscopy (EITS) system and then averaged to a mean cardiac cycle using the ECG gating technique. The Cole-Cole model, that is, extracellular resistance R connected in parallel with intracellular resistance S and membrane capacitance C in series, with a distribution parameter a, was applied to model the frequency characteristics and to produce parametric images. During systole, SC and RC were found to decrease and FR increase. The changes in R/S were not consistent among the subjects. We estimated the peak changes in R, S and C to be -2.5%, -3.3% and -7.6% respectively. The results can be explained by considering the blood vessels as spheres of different sizes with blood inside them. The decrease in R during systole might be caused by the increased blood content in relatively large vessels, whereas that in S by the increased blood volume in relatively small vessels. The capacitance of blood is normally smaller than that of lung tissue, whereas FR blood is higher than that of lung tissue. Hence, as blood content increases, C should decrease and FR increase.

Time-frequency spectral analysis of electric field plethysmography signals.

Cardiac activity contaminates respiratory electric field plethysmography (EFPG) signals, and vice versa, and is usually treated as an artefact. On the other hand, simultaneous information on respiration and cardiac activity is often required in clinical practice. Hence, we use time-frequency spectral analysis (TFSA) by means of the spectrogram (SG) to investigate the instantaneous cardio-respiratory information contained in EFPG-signals and show that it is a practical means of extracting this information out of a single EFPG-signal. Comparisons with a Wigner distribution reveal sufficient time-frequency resolution of the SG for detection of physiological events in EFPG-signals. SG-analysis indicates spectral peaks related to respiration and cardiac activity (depending on the electrode configuration, up to the third and fifth harmonic, respectively) and the possibility to detect respiratory sinus arrhythmia by means of EFPG-measurements. Intermodulation products cause overlaps of respiratory and cardiac spectra pointing out nonlinear relationships. Additionally, SG-analysis supplies essential information for the separation of EFPG-signals into respiratory and cardiac components, by means of filter techniques.

Electric field plethysmography signals of the human thorax as determined by a 2-D FE-model.

Electric field plethysmography (EFPG) signals of the human thorax consist of a baseline component, a respiratory component and a cardiac component. This paper investigates to what extent a two-dimensional finite-element model of the human thorax can serve as a tool for signal prediction allowing for both optimisation of electrode position and effective signal interpretation. In the model inspiration is taken into account by decreasing lung conductivity. Modelling of cardiac activity involves heart geometry changes and lung conductivity increase. Comparison with experiments shows that the model is more effective for strip than spot electrodes for current injection. Modelling results suggest that the thorax behaves approximately as a homogeneous structure with an inspiratory conductivity increase of about 5%. Two electrode pairs are preferable for monitoring respiration in general. As cardiac activity involves two counter-acting signal sources in the thorax, optimum electrode position is obtained using four separated electrodes. However, recommendable positions for two electrode pairs are on the left sternal and right parasternal line. The investigation shows that in providing a proper modelling of respiration and cardiac activity, a 2-D model provides a practical tool for modelling EFPG signals with the cost of a few structural and systematical restrictions.

Five-electrode field plethysmography technique for separation of respiration and cardiac signals.

Respiration monitoring by means of electric field plethysmography is influenced by cardiac activity, which represents an artefact although of physiological relevance itself. For a separation of respiration and cardiac signals, a portable plethysmograph was developed, which uses a fifth electrode in addition to the conventional tetrapolar electrode arrangement. The separation is attained by weighted software subtraction of two detected signals. In a comparative way, three mathematical methods are discussed for the effective determination of individual weighting factors. Results of the practical applications indicate the best results for a method based on Fast Fourier Transformation.

Dielectric properties of lung tissue as a function of air content.

Dielectric measurements were made on lung samples with different electrode systems in the frequency range 5 kHz-100 kHz. In the case of plate electrodes and spot electrodes, the effects of electrode polarization were partly corrected. An air filling factor F is defined, which is determined from the mass and volume of the sample. The results indicate that the electrical properties of lung tissue are highly dependent on the condition of the tissue. Furthermore they show that the conductivity sigma as well as the relative permittivity epsilon r decreases with increasing F. This is discussed using histological material. Using a simple theoretical model, the decrease of sigma and epsilon r is explained by the thinning of the alveolar walls as well as by the deformation of the epithelial cells and blood vessels through the expansion of the alveoli.