Hz In Steps Research Articles

Triangular-shaped two-dimensional vibrational electromagnetic energy harvester

Energy harvested from vibrations can be used to power e.g. wearables and Internet-of-things devices. Here we investigate a two-dimensional triangular-shaped electromagnetic vibration energy harvester with tunable resonance frequency. The harvester has rotatable arrays of fixed magnets, that can be turned to adjust the magnetic forces, a free-to-move structure with three cylindrical magnets, and a set of coils to generate a current. Using an experimental 2D shaker, the power produced by the harvester is measured as function of a vibrational frequency in the x-direction from 1 Hz to 11 Hz in steps of 0.25 Hz and in the y-direction from 1 Hz to 10 Hz in steps of 1 Hz, both at 2 mm amplitude, and at five different angles of the fixed magnets. The harvester produces up to 30 mW of power, and the resonance frequency in both the x- and y-directions shifts from around 7 Hz to around 11 Hz as the fixed magnets are rotated, clearly demonstrating that the resonance frequency can be tuned.

Feasibility of Phase Velocity Imaging Using Multi Frequency Oscillation-Shear Wave Elastography.

To assess viscoelasticity, a pathologically relevant biomarker, shear wave elastography (SWE) generally uses phase velocity (PV) dispersion relationship generated via pulsed acoustic radiation force (ARF) excitation pulse. In this study, a multi-frequency oscillation (MFO)- excitation pulse with higher weight to higher frequencies is proposed to generate PV images via the generation of motion with energy concentrated at the target frequencies in contrast to the broadband frequency motion generated in pulsed SWE (PSWE). The feasibility of MFO-SWE to generate PV images at 100 to 1000 Hz in steps of 100 Hz was investigated by imaging 6 and 70 kPa inclusions with 6.5 and 10.4 mm diameter and ex vivo bovine liver with and without the presence of an aberration layer and chicken muscle ex vivo, and 4T1 mouse breast tumor, in vivo with comparisons to PSWE. MFO-SWE-derived CNR was statistically higher than PSWE for 6 kPa (both with and without aberration) and 70 kPa (with aberration) inclusions and derived SNR of the liver was statistically higher than PSWE at higher frequency (600-1000 Hz). Quantitatively, at 600-1000 Hz, MFO-SWE improved CNR of inclusions (without and with) aberration on an average by (8.2 and 156)% and of the tumor by 122%, respectively, and improved SNR of the liver (without and with) aberration by (20.2 and 51.5)% and of chicken muscle by 72%, respectively compared to the PSWE. These results indicate the advantages of MFO-SWE to improve PV estimation at higher frequencies which could improve viscoelasticity quantification and feature delineation.

Study of Errors in Tremor Amplitude Estimates

We developed an analyzing system for tremor using the three-axis accelerometer built into the Wii Remote in 2008. We propose a theory of estimating the tremor amplitude and mounted it in our system. The aim of the study was to study of errors in tremor amplitude estimates. To test our system using a small accelerometer (WAA-006), mechanical oscillations generated by an oscillation generator were sent to a small accelerometer that was attached to the device. The oscillating amplitude was set at 0.5, 1.0, 1.5, and 2.0 cm, and the oscillating frequency was varied from 1 Hz to 15 Hz in steps of 1 Hz. The relative error of the amplitude estimates calculated from the accelerations measured by the WAA-006 was 103.9 % at 3 Hz and 1 cm. Since this experiment covered the measurement range of the accelerometer, we were able to present the limits of amplitude measurement and analysis by the accelerometer.

High-Resolution Sensors for Mass Deposition and Low-Frequency Vibration Based on Phase-Shifted Bragg Gratings

This work presents high-resolution sensors based on phase-shifted Bragg gratings (PSBGs) for low-frequency vibrations monitoring and mass deposition sensing. We analyzed the reflected spectrum using a commercial interrogator for six values of deposited mass: 0, 0.22, 0.27, 0.32, 0.40, and 0.47 g. For the experimental data, a linear regression was calculated for PSBG 1 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{{2}} = {0.9379}$ </tex-math></inline-formula> with a sensitivity of 0.0491 nm/g) and for uniform fiber Bragg grating (FBG) ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{{2}} = {0.909}$ </tex-math></inline-formula> with a sensitivity of 0.05182 nm/g). Machinery fault simulator (MFS) was used for the vibration monitoring setup for engine rotation frequency of 4–14 Hz in steps of 2 Hz. We used an alternative noncommercial interrogation system that consisted of a tunable laser, an optical circulator, an optical power acquisition board, and a prefixed phase-shifted Bragg. The proposed alternative interrogation system has the ability to center the tunable laser in the narrow valley region of the PSBG reflected spectrum, increasing the resolution for monitoring vibration at low frequencies. As a reference, the PSBG measurement results were compared with those of a piezoelectric accelerometer (PZT) fixed at the same bearing. For 4, 6, 8, 10, and 14 Hz, the relative error was 15%, 10%, 0%, 0%, and 1.43%, respectively. According to these results, PSBGs are a suitable option for monitoring low-frequency vibrations and for mass deposition sensing.

High power electromagnetic vibration harvesting using a magnetic dumbbell structure

This paper considers an electromagnetic energy harvester consisting of a tube with two fixed magnets and two coils and containing a floating free-to-move dumbbell structure with two magnets. The dumbbell shape has a number of benefits, including an increased changing magnetic flux, a controllable resonance frequency and reduced friction. We experimentally characterize the power produced by the harvester between 4 Hz and 20 Hz in steps of 0.5 Hz for a fixed excitation amplitude of 3 mm. The frequency is swept in both ascending and descending order. The maximum power produced by the harvester is 1.04 mW which occurs at 8.5 Hz in descending frequency sweep where the maximum acceleration of the harvester is 0.87 g. The power density of the harvester is 50 μW/cm3 and the power per unit mass is 32 μW/g. The dumbbell harvester shows a softening resonator response with hysteresis between ascending and descending frequency sweeps. Furthermore, the harvester has two resonance peaks in power as a function of the drive frequency, with the peaks being of almost equal magnitude. Finally, a Fourier analysis shows the two resonance peaks have different harmonics, with the first resonance peak being characterized by higher-order harmonics whereas the second resonance peak is characterized by a response at the excitation frequency.

Shear Wave Speed estimator using Continuous Wavelet Transform for Crawling Wave Sonoelastography.

Crawling Wave Sonoelastography (CWS) is an elastography ultrasound-based imaging approach that provides tissue stiffness information through the calculation of Shear Wave Speed (SWS). Many SWS estimators have been developed; however, they report important limitations such as the presence of artifacts, border effects or high computational cost. In addition, these techniques require a moving interference pattern which could be challenging for in vivo applications. In this study, a new estimator based on the Continuous Wavelet Transform (CWT) is proposed. This allows the generation of a SWS image for every sonoelasticity video frame. Testing was made with data acquired from experiments conducted on a gelatin phantom with a circular inclusion. It was excited with two vibration sources placed at both sides with frequencies ranging from 200 Hz to 360 Hz in steps of 20 Hz. Results show small variation of the SWS image across time. Additionally, images were compared with the Phase Derivative method (PD) and the Regularized Wavelength Average Velocity Estimator (R-WAVE). Similar SWS values were obtained for the three estimators within a certain region of interest in the inclusion (At 360 Hz, CWT: 5.01±0.2m/s, PD: 5.11±0.28m/s, R-WAVE: 4.51±0.62m/s) and in the background (At 360 Hz, CWT: 3.67±0.15m/s, PD: 3.69±0.23m/s, R-WAVE: 3.58±0.24m/s). CWT also presented the lowest coefficient of variation and the highest contrast-to-noise ratio for most frequencies, which allows better discrimination between regions.Clinical relevance-This study presents a new Shear Wave Speed estimator for Crawling Wave Sonoelastography, which can be useful to characterize soft tissue and detect lesions.

Kinematics and kinetics of alternating electric field induced liquid mass transport on chromium thin films

Long range mass transport driven by an electric field has many applications in the fields of nanoscience and technology. Liquid-phase mass transport ranging from the micrometer to the millimeter scale and its application to nanopatterning have been demonstrated on chromium (Cr) thin films using a DC electric field. Under the influence of an electric field, the metal seems to undergo a chemical reaction, and the resulting liquid material flows out radially in all directions. In this study, we have explored the effect of an alternating (AC) electric field on this kind of liquid-phase material transport. Within the scope of this work, mass transport has been studied on Cr films 30 nm thick using an alternating square waveform with frequencies ranging from 100 Hz to 1000 Hz in steps of 50 Hz. The dependence of the material’s formation, flow distance, and flow velocity on frequency, for a constant applied root mean square (RMS) voltage, was studied in detail. An analytical model is presented to explain the experimental results. This study, in particular the frequency parameter and the intermittent nature of the applied bias, will help us get a better control over the mass flow process, will lead to better resolutions for the electrolithography process.

Preserved flexibility of dynamic postural control in individuals with Parkinson's disease

BackgroundContinuous oscillation of the support base requires anticipatory and reactive postural adjustments to maintain a stable balance. In this context, postural control flexibility or the ability to adjust balance mechanisms following the requirements of the environment is needed to counterbalance the predictable, continuous perturbation of body balance. Considering the inflexibility of postural responses in individuals with Parkinson's disease (PD), maintaining stability in the support base's continuous oscillations may be challenging. Varying the frequency of platform oscillation is an exciting approach to assess the interactions between reactive and anticipatory adjustments. Research questionThis study aimed to analyze postural responses of individuals with PD on an oscillatory support base across different frequencies. MethodsThirty participants with moderate PD diagnosis (M = 64.47 years, SD = 8.59; Hoehn and Yahr scale 3) and fifteen healthy age-matched controls (M = 65.8 years, SD = 4.2) were tested. Subjects maintained a dynamic balance on a platform oscillating in sinusoidal translations. Four oscillation frequencies were evaluated in different trials that ranged from 0.2 to 0.8 Hz in steps of 0.2 Hz. ResultsAnalysis showed similar performance between PD and healthy participants, with modulation of amplitudes of head displacement, center of pressure, center of mass and feet-head coordination to platform oscillation frequency. DiscussionOur findings suggest a preserved ability of individuals with PD to dynamically control body balance on a support base with predictable oscillatory translations.

Auditory Perceptual History Is Propagated through Alpha Oscillations.

SummaryPerception is a proactive, “predictive” process, in which the brain relies, at least in part, on accumulated experience to make best guesses about the world to test against sensory data, updating the guesses as new experience is acquired. Using novel behavioral methods, the present study demonstrates the role of alpha rhythms in communicating past perceptual experience. Participants were required to discriminate the ear of origin of brief sinusoidal tones that were presented monaurally at random times within a burst of uncorrelated dichotic white noise masks. Performance was not constant but varied with delay after noise onset in an oscillatory manner at about 9 Hz (alpha rhythm). Importantly, oscillations occurred only for trials preceded by a target tone to the same ear, either on the previous trial or two trials back. These results suggest that communication of perceptual history generates neural oscillations within specific perceptual circuits, strongly implicating behavioral oscillations in predictive perception and with formation of working memory.

Frequency-dependent and montage-based differences in phosphene perception thresholds via transcranial alternating current stimulation.

It is well known that applying transcranial alternating current stimulation (tACS) to the scalp can generate artefactual visual perceptions of flashing or shimmering light known as phosphenes. The thresholds for generating these phosphenes have been used by international standards bodies to provide conservative estimates of the field strength required to interfere with human neural functioning and set safety limits accordingly. However, the precise relationship between electric currents and phosphene perception thresholds remains uncertain. The present study used tACS to systematically investigate the effects of the location and the frequency of stimulation on phosphene perception thresholds. These thresholds were obtained from 24 participants using a within-subject design as a function of scalp stimulation sites (FPz-Cz versus Oz-Cz) and stimulation frequency (2-30 Hz in steps of 2 Hz). Phosphene perception thresholds were consistently lower for FPz-Cz stimulation, and regardless of tACS location were lowest for 16 Hz stimulation. Threshold variation between participants was very small, which is meaningful when setting standards based on phosphenes. Bioelectromagnetics. 2019;40:365-374. © 2019 Bioelectromagnetics Society.

Wideband signal transceiver module with a Doppler shift function.

The wideband signal transceiver module forms the core component of the radar signal target simulator and the key module in measuring the Doppler shift. In this paper, we present a design for a miniaturized wideband signal transceiver module based on a PXIe bus, with an operating frequency range of 65 MHz-3 GHz, an instantaneous measurement bandwidth of 800 MHz on a standard 3U (where 1U = 4.445 cm) board with three slots. The module adopts a zero intermediate frequency transceiver, and the baseband uses two analog to digital converters, a field programmable gate array, and two digital to analog converters as the core hardware architecture. The module combines key technologies including variable-frequency local oscillator synthesis, radio-frequency broadband signal conditioning, and high-speed high-resolution baseband signal acquisition and generation. This paper describes a novel design for the Doppler shift function. Considering the limited size and volume of the module, Doppler shift technology combining a complex signal and a real signal was adopted to achieve full band coverage with an operating frequency range of 65 MHz-3 GHz. We verified that this module could generate the Doppler shift in the frequency band from -400 Hz to 400 Hz in steps of 2 Hz and with an error of ±2 Hz.

Binaural Interaction Effects of 30-50 Hz Auditory Steady State Responses.

Auditory stimuli modulated by modulation frequencies within the 30 to 50 Hz region evoke auditory steady state responses (ASSRs) with high signal to noise ratios in adults, and can be used to determine the frequency-specific hearing thresholds of adults who are unable to give behavioral feedback reliably. To measure ASSRs as efficiently as possible a multiple stimulus paradigm can be used, stimulating both ears simultaneously. The response strength of 30 to 50Hz ASSRs is, however, affected when both ears are stimulated simultaneously. The aim of the present study is to gain insight in the measurement efficiency of 30 to 50 Hz ASSRs evoked with a 2-ear stimulation paradigm, by systematically investigating the binaural interaction effects of 30 to 50 Hz ASSRs in normal-hearing adults. ASSRs were obtained with a 64-channel EEG system in 23 normal-hearing adults. All participants participated in one diotic, multiple dichotic, and multiple monaural conditions. Stimuli consisted of a modulated one-octave noise band, centered at 1 kHz, and presented at 70 dB SPL. The diotic condition contained 40 Hz modulated stimuli presented to both ears. In the dichotic conditions, the modulation frequency of the left ear stimulus was kept constant at 40 Hz, while the stimulus at the right ear was either the unmodulated or modulated carrier. In case of the modulated carrier, the modulation frequency varied between 30 and 50 Hz in steps of 2 Hz across conditions. The monaural conditions consisted of all stimuli included in the diotic and dichotic conditions. Modulation frequencies ≥36 Hz resulted in prominent ASSRs in all participants for the monaural conditions. A significant enhancement effect was observed (average: ~3 dB) in the diotic condition, whereas a significant reduction effect was observed in the dichotic conditions. There was no distinct effect of the temporal characteristics of the stimuli on the amount of reduction. The attenuation was in 33% of the cases >3 dB for ASSRs evoked with modulation frequencies ≥40 Hz and 50% for ASSRs evoked with modulation frequencies ≤36 Hz. Binaural interaction effects as observed in the diotic condition are similar to the binaural interaction effects of middle latency responses as reported in the literature, suggesting that these responses share a same underlying mechanism. Our data also indicated that 30 to 50 Hz ASSRs are attenuated when presented dichotically and that this attenuation is independent of the stimulus characteristics as used in the present study. These findings are important as they give insight in how binaural interaction affects the measurement efficiency. The 2-ear stimulation paradigm of the present study was, for the most optimal modulation frequencies (i.e., ≥40 Hz), more efficient than a 1-ear sequential stimulation paradigm in 66% of the cases.

Vagal nerve stimulation reduces metabolic rate and uncouples the relationship between heart rate and oxygen consumption in conscious mice (LB775)

We tested the hypothesis that an increase in metabolic rate contributes to the weight loss associated with chronic vagal nerve stimulation (VNS) that has been observed in patients with epilepsy or depression and in animal studies. Blood pressure (BP) sensors (DSI) and cervical vagal nerve stimulators were implanted in C57Bl6 mice (n=5). On the following day, arterial BP, heart rate (HR), oxygen consumption (VO2), and respiratory exchange rate (RER) were recorded in conscious mice during application of different VNS intensities (3V, max. current 1mA, 1ms pulses at frequencies ranging from 1 Hz to 10 Hz in steps of 1 Hz, randomized order). Each VNS intensity was applied for 20 min and preceded by a baseline (20 min). In average (all VNS intensities pooled), VNS reduced HR (374±37 vs. 504±14 bpm, P&lt;0.05), mean BP (95±5 vs. 107±8 mmHg, P&lt;0.05), and VO2 (1,556±231 vs. 2,201±178 mL/kg/h, P&lt;0.05) but did not alter RER (0.85±0.09 vs. 0.77±0.03). The significant linear correlation between HR and VO2 during baseline without VNS (R2: 0.34±0.08) was lost during VNS (R2: 0.06±0.03). These data suggest that an increase in metabolic rate does not contribute to weight loss associated with chronic VNS. Furthermore, VNS uncouples the linear relationship between HR and VO2. We speculate that VNS may shift energy homeostasis to a “starvation‐like” mode that is associated with reduced food intake and, subsequently decreased metabolic rate.

An Acoustic-Perceptual Study of Vocal Tremor

Essential tremor of the voice (ETV) is an involuntary intention tremor of the vocal folds that causes fluctuations in fundamental frequency (f(0)) and/or intensity leading to an unsteady voice. There is limited data on how different acoustic variables affect perception of severity of tremor. The purpose of the study was to determine if systematic changes in f(0), rate or modulation frequency (f(f0m)), extent or depth of modulation (d(f0m)), and signal-to-noise ratio (SNR) affect perception of severity of tremor. Vowel phonations of four speakers (two male and two female) with a clinical diagnosis of ETV were selected from the Kay Elemetrics Disordered Voice Database (Lincoln Park, NJ). A high fidelity speech vocoder (STRAIGHT; Kawahara, 1997) was used to synthesize the f(0) contour for each of these voices, which were varied in mean f(0), f(f0m), and d(f0m). The f(0) contour was modified 30 Hz above and below the mean f(0) for each speaker. f(f0m) ranged from 3 to 12 Hz in steps of 3 Hz. d(f0m) ranged from 2 to 32 Hz in steps of 6 Hz. Six (three experts and three naïve) listeners rated the "severity" of tremor on a seven-point rating scale. Significant main effects and interactions were found between the study variables. Perceived severity of tremor increased with f(f0m) and d(f0m). There was no systematic effect of SNR on perceived tremor severity. The perception of severity for steady-state tremor results from a complex interaction of multiple acoustic cues with d(f0m) acting as the primary acoustic cue.

Experimental investigation of an external turret-moored FPSO system by VALM arrangement

This article deals mainly with an experimental study on a typical external turret-moored floating, production, storage and offloading (FPSO) system by a vertical anchor leg mooring (VALM) arrangement in order to investigate the effect of parameters influencing the mooring and hawser line forces and motion response for different loading conditions with different hawser lengths. A 1:100 scale model of 140,000 DWT turret-moored FPSO system was tested for three loading conditions (i.e. 40% DWT, 70% DWT and 100% DWT) with three hawser lengths (i.e. 15%, 20% and 25% of the length of the FPSO model). The tests were conducted in a 2-m wide wave flume at the Department of Ocean Engineering, Indian Institute of Technology Madras, Chennai. The model tests were carried out under regular waves for the wave frequencies ranging from 0.55 to 1.25 Hz in steps of 0.04 Hz at a water depth of 1 m for head sea condition. The motion response was measured using rotary-type potentiometers, and mooring forces were measured using specially fabricated ring-type load cells. The test results of the mooring forces and motion response are analysed and presented with discussion.

Experimental Study on the Hydrodynamics of a Floating, Production, Storage, and Offloading System

This paper highlights an experimental investigation on the dynamic response of a typical floating, production, storage, and offloading system (FPSO) moored externally with a fixed structure and by a vertical anchor leg mooring arrangement. A 1:100 scale model of 140,000 t DWT FPSO system was tested for these two types of mooring arrangements under regular waves for three operating conditions, i.e., 40, 70, and 100%DWT with three hawser lengths, i.e., 15, 20, and 25% of the length of FPSO. Model tests were conducted in a 2 m wide wave flume at a water depth of 1 m for wave frequencies from 0.55 to 1.25 Hz in steps of 0.04 Hz for head sea condition. The motions were measured by rotary type potentiometers and a ring type load cell was used to measure the hawser line force. The experimental results of motions and hawser line force of FPSO moored for the two mooring arrangements are compared and presented with discussions.

Distortion product otoacoustic emission (DPOAE) input/output functions and the influence of the second DPOAE source

Distortion product otoacoustic emissions (DPOAEs) at 2f1-f2 (f2/f1 = 1.2) have two components from different cochlear sources, i.e., a distortion component generated near f2 and a reflection component from the characteristic site of fDP. The interaction of the two sources may negatively affect the DPOAE input/output (I/O) functions that are used to predict either auditory thresholds or the compression characteristics of the basilar membrane. This study investigates the influence of the reflection component on DPOAE I/O functions in a frequency range for f2 from 1500 to 4500 Hz in steps of 18 Hz. A time windowing procedure is used to separate the components from the two DPOAE sources. With decreasing stimulus level, the relative contribution of the reflection component increases. I/O functions from the separated distortion component (DCOAE I/O functions) only show smooth changes in shape and slope with frequency, while "standard" DPOAE I/O functions show rapid changes between adjacent frequencies, indicating a strong influence from the interference with the second DPOAE source. A reduced variability for adjacent frequencies can be seen as well for prediction of hearing thresholds, when using DCOAE instead of DPOAE I/O functions.

Less is more: high pass filtering, to remove up to 99% of the surface EMG signal power, improves EMG-based biceps brachii muscle force estimates

It is generally assumed that raw surface EMG (sEMG) should be high pass filtered with cutoffs of 10–30 Hz to remove motion artifact before subsequent processing to estimate muscle force. The purpose of the current study was to explore the benefits of filtering out much of the raw sEMG signal when attempting to estimate accurate muscle forces. Twenty-five subjects were studied as they performed rapid static, anisotonic contractions of the biceps brachii. Biceps force was estimated (as a percentage of maximum) based on forces recorded at the wrist. An iterative approach was used to process the sEMG from the biceps brachii, using progressively greater high pass cutoff frequencies (20–440 Hz in steps of 30 Hz) with first and sixth order filters, as well as signal whitening, to determine the effects on the accuracy of EMG-based biceps force estimates. The results indicate that removing up to 99% of the raw sEMG signal power resulted in significant and substantial improvements in biceps force estimates. These findings challenge previous assumptions that the raw sEMG signal power between about 20 and 500 Hz should used when estimating muscle force. For the purposes of force prediction, it appears that a much smaller, high band of sEMG frequencies may be associated with force and the remainder of the spectrum has little relevance for force estimation.

The human primary somatosensory cortex response contains components related to stimulus frequency and perception in a frequency discrimination task

Somatosensory stimulation of primary somatosensory cortex (SI) using frequency discrimination offers a direct, well-defined and accessible way of studying cortical decisions at the locus of early input processing. Animal studies have identified and classified the neuronal responses in SI but they have not yet resolved whether during prolonged stimulation the collective SI response just passively reflects the input or actively participates in the comparison and decision processes. This question was investigated using tomographic analysis of single trial magnetoencephalographic data. Four right-handed males participated in a frequency discrimination task to detect changes in the frequency of an electrical stimulus applied to the right-hand digits 2+3+4. The subjects received approximately 600 pairs of stimuli with Stim1 always at 21 Hz, while Stim2 was either 21 Hz (50%) or varied from 22 to 29 Hz in steps of 1 Hz. Both stimuli were 1 s duration, separated by a 1 s interval of no stimulation. The left-SI was the most consistently activated area and showed the first activation peak at 35–48 ms after Stim1 onset and sustained activity during both stimulus periods. During the Stim2 period, we found that the left-SI activation started to differ significantly between two groups of trials (21 versus 26–29 Hz) within the first 100 ms and this difference was sustained and enhanced thereafter (approximately 600 ms). When only correct responses from the above two groups were used, the difference was even higher at later latencies (approximately 650 ms). For one subject who had enough trials of same perception to different input frequencies, e.g. responded 21 Hz to Stim2 at 21 Hz (correct) and 26–29 Hz (error), we found the sustained difference only before 650 ms. Our results suggest that SI is involved with the analysis of an input frequency and related to perception and decision at different latencies.

Objective measures of frequency selectivity.

A common difficulty often reported by hearing-impaired listeners is an inability to understand speech in a background of noise. A number of investigations have suggested that a possible explanation for speech understanding difficulties, especially in noise, is impaired frequency selectivity. Unfortunately, the length and complexity of current psychophysical methodologies preclude their widespread utilization in clinical environments. Investigations that show a reliable correlation between electrophysiologic measures and critical bandwidth [S. Zerlin, J. Acoust. Soc. Am. 79, 1612–1616 (1986)] may overcome these limitations. However, additional researchers have not confirmed these relationships [D. L. Burrows and S. J. Barry, J. Acoust. Soc. Am. 88, 180–184 (1990)]. Because the concept of reliable electrophysiological measures of frequency selectivity remains uncertain, the present investigation examined electrophysiologic measures of frequency selectivity by recording the amplitude of wave V of the auditory brainstem response as a function of the frequency separation of two components of a tonal complex. Seven young adult listeners with normal hearing served as subjects. The frequency separation of the two component tones in the complex was varied as a function of center frequency from 100–500 Hz in steps of 100 Hz around a center frequency of 2 kHz and from 400–1200 Hz in steps of 200 Hz around a center frequency of 4 kHz. The width of the critical band was defined as the smallest amount of separation of the two-tone complex that exhibited a reliable increase in the amplitude of wave V. Results indicate significant enhancements in wave V as a function of the frequency separation of the tonal complex. The critical bandwidths measured, however, were slightly larger than those reported in psychophysical studies. The implications for clinical measures of frequency selectivity in normal and hearing impaired listeners will be discussed.