The use of remote microphone systems in unilateral hearing loss: a preliminary study among Brazilian children and teenagers

Due to the large number of individuals with Unilateral Hearing Loss (UHL) and the recommendation to use hearing assistive devices, studies are required to define possibilities of intervention for this population.

OBJECTIVE

To evaluate the performance of the Remote Microphone System (RMS) in children with UHL.

METHODOLOGY

Prospective clinical study with a convenience sample. Eleven children (mean age of 9.2 years) with severe and profound sensorineural UHL, hearing aid users and enrolled in regular schools participated in the study. They were evaluated using the Hearing in Noise Test (HINT), the Classroom Participation Questionnaire (CPQ), and the Sustained Auditory Attention Ability Test (SAAAT) with RMS.

RESULTS

HINT results were analyzed using variance to three criteria of repeated measures, which revealed differences between intervention, position, and time factors and significant interaction between these three factors. The comparative analysis of the results from CPQ showed significant differences in the statistical t-test (p=<0.001) for all subscales. The analysis of variance at two repeated measures criteria used in the study of SAAAT revealed a difference between intervention and time, and both interacted significantly.

CONCLUSION

The RMS associated with a hearing aid was effective for individuals with UHL.

Improving an open-source commercial system to reliably perform activity-dependent stimulation

OBJECTIVE

Activity-dependent stimulation (ADS) is designed to strengthen the connections between neuronal circuits and therefore may be a promising tool for promoting neurophysiological reorganization following a brain injury. To successfully perform this technique, two criteria must be met: (1) spikes in the extracellular electrical field potential must be detected accurately at one site of interest, and (2) stimulation pulses generated at fixed (<1 ms jitter), low-latency (<10 ms) intervals relative to each detected spike must be delivered reliably to a second site of interest. Here, we aimed to improve noise rejection in a low-cost commercial system to reliably perform ADS in awake, behaving rats, while maintaining latency requirements.

APPROACH

We implemented a spike detection state machine on a field-programmable gate array (FPGA). Because the accuracy of spike detection can be heavily reduced in awake and behaving animals due to biological artifacts such as movement and chewing, the state machine tracks candidate spike waveforms, checking them against multiple programmable thresholds and rejecting any spikes that fail to meet a programmed threshold criterion.

MAIN RESULTS

A series of offline analyses showed that our implementation was able to appropriately trigger stimulation during epochs of biological artifacts with an overall accuracy between 72% and 97%, fixed computational latency of 167 µs, and an algorithmic latency of 300 µs to 800 µs.

SIGNIFICANCE

Our improvements have been made open-source and are freely available to all scientists working on closed-loop neuroprosthetic devices. Importantly, the improvements are easily incorporated into existing workflows that utilize the Intan Stimulation and Recording Controller.

Frequency-comb-referenced mid-infrared source for high-precision spectroscopy

We report on a tunable continuous-wave mid-infrared optical parametric oscillator (OPO), which is locked to a fully stabilized near-infrared optical frequency comb using a frequency doubling scheme. The OPO is used for 40 GHz mode-hop-free, frequency-comb-locked scans in the wavelength region between 2.7 and 3.4 μm. We demonstrate the applicability of the method to high-precision cavity-ring-down spectroscopy of nitrous oxide (N₂O) and water (H₂O) at 2.85 µm and of methane (CH₄) at 3.2 μm.

The impact of sound-field systems on learning and attention in elementary school classrooms

PURPOSE

The authors evaluated the installation and use of sound-field systems to investigate the impact of these systems on teaching and learning in elementary school classrooms. Methods The evaluation included acoustic surveys of classrooms, questionnaire surveys of students and teachers, and experimental testing of students with and without the use of sound-field systems. In this article, the authors report students' perceptions of classroom environments and objective data evaluating change in performance on cognitive and academic assessments with amplification over a 6-month period.

RESULTS

Teachers were positive about the use of sound-field systems in improving children's listening and attention to verbal instructions. Over time, students in amplified classrooms did not differ from those in nonamplified classrooms in their reports of listening conditions, nor did their performance differ in measures of numeracy, reading, or spelling. Use of sound-field systems in the classrooms resulted in significantly larger gains in performance in the number of correct items on the nonverbal measure of speed of processing and the measure of listening comprehension. Analysis controlling for classroom acoustics indicated that students' listening comprehension scores improved significantly in amplified classrooms with poorer acoustics but not in amplified classrooms with better acoustics.

CONCLUSIONS

Both teacher ratings and student performance on standardized tests indicated that sound-field systems improved performance on children's understanding of spoken language. However, academic attainments showed no benefits from the use of sound-field systems. Classroom acoustics were a significant factor influencing the efficacy of sound-field systems; children in classes with poorer acoustics benefited in listening comprehension, whereas there was no additional benefit for children in classrooms with better acoustics.

Construction, calibration, and validation of a simple patch-clamp amplifier for physiology education

A modular patch-clamp amplifier was constructed based on the Strickholm design, which was initially published in 1995. Various parts of the amplifier such as the power supply, input circuit, headstage, feedback circuit, output and nulling circuits were redesigned to use recent software advances and fabricated using the common lithographic printed circuit board fabrication process and commercially available electronic components. The calibration, validation, and regular recording procedures along with the results of an actual recording of inward Ca(2+) currents from PC12 neuronal cells are described in detail. This work describes the construction of a low-cost patch-clamp amplifier and setting up an electrophysiology recording system in a laboratory with regular technical expertise. The constructed amplifier provides an inexpensive yet practical tool for research and teaching purposes while the experience obtained during construction and setting up of the patch-clamp amplifier provides the basic and advanced understanding required for operating an advanced cell potential recording apparatus.

A note on determination of the diffuse-field sensitivity of microphones using the reciprocity technique

The diffuse-field response of a microphone is usually obtained by adding a random-incidence correction to the pressure response of the microphone. However, the random-incidence correction is determined from a relative measurement, and its accuracy depends not only on the relative response at all angles of incidence but also on the accuracy of the frequency response at normal incidence. By contrast, this paper is concerned with determining the absolute diffuse-field response of a microphone using the reciprocity technique. To examine this possibility, a reciprocity calibration setup is used for measuring the electrical transfer impedance between a pair of microphones placed in a miniature (2 m(3)) reverberation room. The transfer function between the microphones is measured using fast Fourier transform analysis and pseudorandom noise. The calculation of the diffuse-field sensitivity involves (a) separation of the reverberant response from the total response, (b) determination of the reverberation time, and (c) averaging over space and frequency. The resulting diffuse-field correction is compared with an estimate of the random-incidence correction determined in an anechoic room and with a numerical prediction.

Evaluation of the Benefit for Cochlear Implantees of Two Assistive Directional Microphone Systems in an Artificial Diffuse Noise Situation

OBJECTIVE

People with cochlear implants have severe problems with speech understanding in noisy surroundings. This study evaluates and quantifies the effect of two assistive directional microphone systems compared to the standard headpiece microphone on speech perception in quiet surroundings and in background noise, in a laboratory setting developed to reflect a situation whereby the listener is disturbed by a noise with a mainly diffuse character due to many sources in a reverberant room.

DESIGN

Thirteen postlingually deafened patients, implanted in the Leiden University Medical Centre with the Clarion CII device, participated in the study. An experimental set-up with 8 uncorrelated steady-state noise sources was used to test speech perception on monosyllabic words. Each subject was tested with a standard headpiece microphone, and the two assistive directional microphones, TX3 Handymic by Phonak and the Linkit array microphone by Etymotic Research. Testing was done in quiet at a level of 65 dB SPL and with decreasing signal-to-noise ratios (SNR) down to -15 dB.

RESULTS

Using the assistive directional microphones, speech recognition in background noise improved substantially and was not affected in quiet. At an SNR of 0 dB, the average CVC scores improved from 45% for the headpiece microphone to 67% and 62% for the TX3 Handymic and the Linkit respectively. Compared to the headpiece, the Speech Reception Threshold (SRT) improved by 8.2 dB SNR and 5.9 dB SNR for the TX3 Handymic and the Linkit respectively. The gain in SRT for TX3 Handymic and Linkit was neither correlated to the SRT score with headpiece nor the duration of CI-use.

CONCLUSION

The speech recognition test in background noise showed a clear benefit from the assistive directional microphones for cochlear implantees compared to the standard microphone. In a noisy environment, the significant benefit from these assistive device microphones may allow understanding of speech with greater ease.

Effect of amplifier gain setting on distal motor latency in normal subjects and CTS patients

OBJECTIVE

To determine normative cutoffs and sensitivities for median distal latency (MDL), median-thenar to ulnar-thenar latency difference (TTLD), and median-thenar to ulnar-hypothenar latency difference (THLD) at various amplifier gains for carpal tunnel syndrome (CTS) electrodiagnosis. A prior study utilized only an amplifier gain of 0.2 mV/division.

METHODS

Abnormal cutoffs for MDL, TTLD and THLD were determined based on 34 control hands at gains of 0.2, 0.5, 1, 2, and 5 mV. Diagnostic sensitivities were determined for 50 patients (80 hands) with clinically and electrodiagnostically defined CTS.

RESULTS

At a gain of 0.2 and 0.5 mV/division, abnormal cutoffs for MDL, THLD, and TTLD were: 3.7, 1.2, and 0.8 ms. At gains of 1, 2, and 5 mV the abnormal cutoffs were 4, 1.2, and 1 ms. The sensitivities at gains of 0.2, 0.5, 1, 2, and 5 mV for MDL, THLD, and TTLD were: 65, 66, 53, 57, 61/86, 83, 88, 86, 86/91, 91, 76, 73, 59.

CONCLUSIONS

MDL and THLD sensitivities are gain-independent. THLD is substantially more sensitive than MDL at all gains. TTLD sensitivity is maximized with 0.2 and 0.5 mV gains.

SIGNIFICANCE

TTLD and THLD increase diagnostic sensitivity with minimal additional effort. TTLD sensitivity is maximized with 0.2 or 0.5 mV gains. The electromyographer's preferred gain may be used.

A new method for dealing with the stimulus artefact in electrically evoked compound action potential measurements

OBJECTIVE

Residual charge on recording electrodes leads to elevated potentials after the end of the stimulus, which can easily overload the electrically evoked compound action potential (eCAP) recording systems (neural response imaging or neural response telemetry). A new method for dealing with this problem was tested in a series of animal experiments.

MATERIAL AND METHODS

We developed an amplifier with a compensation circuit that reduces the effect of the residual charge by electrical subtraction at the input. Using this amplifier we compared different artefact rejection protocols simultaneously in chronically implanted guinea pigs. A new, systematic nomenclature for the various forward masking schemes, based on the number of frames involved, is proposed.

RESULTS

Proper adjustment of the compensation circuit reduces the overload time from > 200 micros to < 30 micros, but the compensation signals influence the final output signal considerably. To eliminate this deliberately introduced, reproducible artefact, an additional artefact rejection scheme is necessary. With alternating polarity (AP) and forward masking paradigms we could reliably record the N1 peak. Forward masking responses reveal shorter latencies for cathodic-first biphasic stimuli than for anodic-first pulses. The average of these two closely resembles the response obtained with the AP paradigm.

CONCLUSIONS

It is worthwhile implementing the electrical compensation method proposed herein in clinical neural response imaging or neural response telemetry systems, as it represents a more robust way of assessing the eCAP.

Sensitive calibration and measurement procedures based on the amplification principle in motion perception

We compare two types of sampled motion stimuli: ordinary periodic displays with modulation amplitude m(o=e) that translate 90 degrees between successive frames and amplifier sandwich displays. In sandwich displays, even-numbered frames are of one type, odd-numbered frames are of the same or different type, and (1) both types have the same period, (2) translate in a consistent direction 90 degrees between frames, and (3) even frames have modulation amplitude m(e), odd frames have modulation amplitude m(o). In both first-order motion (van Santen, J.P.H. & Sperling, G. (1984). Temporal covariance model of human motion perception. Journal of the Optical Society of America A, 1, 451-73) and second-order motion (Werkhoven, P., Sperling, G., & Chubb, C. (1993). Motion perception between dissimilar gratings: a single channel theory. Vision Research, 33, 463-85) the motion strength of amplifier sandwich displays is proportional to the product m(o)m(e) for a wide range of m(e). By setting m(e) to a large value, an amplifier sandwich stimulus with a very small value of m(o) can still produce visible motion. The amplification factor is the ratio of two threshold modulation amplitudes: ordinary circumflexm(o=e) over amplified circumflexm(o), circumflexm(o=e)/circumflexm(o). We find amplification factors of up to about 8x. Light adaptation and contrast gain control in early visual processing distort the representations of visual stimuli so that inputs to subsequent perceptual processes contain undesired distortion products or 'impurities'. Motion amplification is used to measure and thence to reduce these unwanted components in a stimulus to a small fraction of their threshold. Such stimuli are certifiably pure in the sense that the residual impurity is less than a specified value. Six applications are considered: (1) removing (first-order) luminance contamination from moving (second-order) texture gratings; (2) removing luminance contamination from moving chromatic gratings to produce pure isoluminant gratings; (3) removing distortion products in luminance-modulated (first-order) gratings - by iterative application, all significant distortion products can be removed; (4) removing second-order texture contamination from third-order motion displays; (5) removing feature bias from third-order motion displays; (6) and the same general principles are applied to texture-slant discrimination in which x,y spatial coordinates replace the x,t motion coordinates. In all applicable domains, the amplification principle provides a powerful assay method for the precise measurement of very weak stimuli, and thereby a means of producing visual displays of certifiable purity.

Evaluation and design of a small portable EMG amplifier with potential RMS output

The present study attempted to design and evaluate a small portable electromyogram (EMG) amplifier that can output enhanced EMG and its root mean square (RMS) value. The production and design were of a laboratory scale without any special or high cost circuit construction. The designed amplifier was actually innovated according to the actual working conditions based on physiological anthropology. The present amplifier was compared with commercially available products and proved to be of practical use. The device was installed with a sufficiently small body depicting 8-channel variable gain AC amplifier and variable time-window RMS-to-DC converter. The prototype was battery-driven and well-shielded to minimize external noise interference.

Waveforms of cochlear implant-evoked auditory brain stem responses in anesthetized young children, recorded with a new preamplifier

An ultra-low-noise preamplifier has been specifically designed for the conditions in lightly anesthetized young children, to record cochlear implant--evoked auditory brain stem responses (impEABRs). The preamplifier linearly filters out the signal from the radio-frequency implant-driver. The preamplifier provides simultaneous accurate records of the stimulus-current artifact and impEABR, both ipsilaterally and contralaterally. It is convenient to label electrically evoked vertex-positive peaks, eg, eII, on probable analogy with acoustically evoked potentials. In order to label all the commonly observed peaks with latency less than 5 milliseconds, it is necessary at times to use labels eIIa, eIIb, eIIIa, eIIIb, eIVa, eIVb, eVa, and eVb. The records also show two distinct nadirs, with latencies about 2.5 milliseconds and about 6 milliseconds. The details of the waveforms are preserved as the stimulus strength descends towards threshold.

Myopotential inhibition of unipolar demand pacemakers: utility of provocative manoeuvres in assessment and management

Fifty patients with permanent unipolar pacemakers (48 multiprogrammable, 2 non programmable) with protective insulating sheath placed against the muscular side of the pacemaker pocket were studied to determine the occurrence of inhibition of pacing by sensing of the myopotentials. All the patients were subjected to a combination of different provocative manoeuvres at their nominal R wave sensitivity settings. Myopotential inhibition was exhibited in 35 (70%) patients. Only 3 patients however had reported symptoms suggesting loss of pacing. The most useful provocative manoeuvre was shoulder flexion with adduction against resistance (94.3% positivity). Appropriate sensitivity adjustments resulted in amelioration of the problem in 86% of the patients while still retaining R wave sensing. Myopotential interference continues to be a frequently observed problem even in the present generation of unipolar pacemakers. Provocative tests and appropriate reprogramming should be done in all such patients as a routine.

Optimization of a slow-acting automatic gain control system for use in hearing aids

This paper describes experiments evaluating and optimizing an automatic gain control system, called dual front-end AGC (abbreviated as D), intended for use in hearing aids. This system has two purposes: (1) to compensate for variations in the overall level of speech from one situation to another by slowly changing its gain; (2) to protect the user from sudden intense transients without affecting the long-term gain. This is achieved by using two control voltages to determine the gain. One changes slowly as the input varies in level. Normally this component determines the overall gain. The other comes into operation when an intense transient occurs. It acts rapidly to reduce the gain, avoiding over-amplification of the transient, but its action ceases quickly after the end of the transient. We describe four experiments measuring speech intelligibility for subjects with cochlear hearing loss in which we determine optimum values for two of the time constants of the D system, namely the recovery time of the fast component and the attack time of the slow component. The experiments also compare the D system with linear amplification (L) and 'adaptive compression' (A). The results show: (1) for the D system, optimum values are about 80-150 ms for the recovery time of the fast component and 150-325 ms for the attack time of the slow component; (2) in situations where intense transient sounds are present, and there is either no background sound (experiment 1) or continuous speech-shaped noise as a background (experiment 2), the D system gives significantly better performance than the L or A systems. When the background noise is a single voice, reversed in time (experiment 3), the D and L systems give similar performance, and both are markedly superior to the A system; (3) when the level of speech is varied over a range of 30 dB (experiment 4), both D and A systems allow good performance over the whole range of levels. Performance for the L system worsens markedly at the lower levels.

[Tissue ablation by focused ultrasound]

Tissue lesions can be induced at the focal point of highly focused transducers with a frequency of 1 and 2.25 MHz for exposure times of less than 1 second. The energy generated by a high power amplifier (7.5 kilowatts effective at 1 MHz) is delivered in the form of series of impulses lasting between 10 and 1,000 milliseconds. The experimentation was conducted in the rat kidney (the left kidney, normally supplied by its vascular pedicle, was exteriorised during ultrasound treatment and then returned to the abdomen). The animal was sacrificed 3 days later and the lesions were studied by serial histological sections. 248 ultrasound shots were performed between January and September 1990. They allowed the definition of the time and intensity constants necessary to induce total destruction of the renal tissue at the focal point. Depending on the energy delivered, an elliptical cavity with a mean height of 1.2 to 4.6 mm and a mean diameter of 0.6 to 3 mm is observed at the focal point after a single shot. No cell structures were visible in the cavities and, in general, the cavity was prolonged by a cone-shaped region of coagulated necrosis with an inferior base. The mechanism responsible for this focused ultrasonic tissue destruction (FUTD) involves a variable combination of thermal and mechanical effects which depends on the ultrasound intensity delivered at the focal point of the transducer.

Assistive listening device versus conventional hearing aid in an elderly patient: case report

An elderly patient with a relatively severe problem in speech understanding tried out, and rejected, use of a conventional hearing aid. She has accepted, however, and successfully used an assistive listening device (ALD). Her experience highlights the importance of considering trial use of an ALD in the elderly patient who rejects use of a conventional aid.