Biomedical subjects

S T Neely

Publications and source records attributed to S T Neely.

33 records · Page 2Linked to original sources

PubMed1995

Estimating residual noise in the auditory brain-stem response.

Estimation of the residual noise in the auditory brain-stem response waveform is considered. The residual noise measures one aspect of waveform quality. Moreover, it is an important component of signal detection algorithms used for automatic termination of the test. It is shown that the most commonly used method for estimating residual noise can be severely biased. Reasons for this bias are explored and two alternative estimators are presented.

Computer Simulation↗

PubMed1995

Preliminary descriptions of transient-evoked and distortion-product otoacoustic emissions from graduates of an intensive care nursery.

Transient-evoked (TEOAE) and distortion-product otoacoustic emissions (DPOAE) were measured in 51 graduates of an intensive care nursery and compared to data obtained from 80 normal-hearing children and adults. All infants had click-evoked auditory brainstem responses (ABR) at 30 dB nHL or less while the older subjects had pure-tone thresholds of 20 dB HL or less for octave frequencies from 250 to 8000 Hz. OAE data were collected using commercially available devices. All data were analyzed in terms of emission amplitude, emission-to-noise ratio, and response reproducibility as a function of frequency. DPOAEs were measured at three points per octave between f2 frequencies of approximately 500 and 8000 Hz. TEOAEs were elicited by clicks and were analyzed in both octave and 1/3-octave bands centered at frequencies from 500 to 4000 Hz, as well as in the broadband condition. In addition, stimulus amplitudes for the clicks used to elicit TEOAEs were analyzed within octave and 1/3-octave bands to determine whether any age-related differences in responses can be accounted for on the basis of stimulus differences. Both emission amplitude and noise amplitude were greater in neonates than adults, although there was variability across frequency. Emission-to-noise ratio and response reproducibility were more similar between groups. For TEOAEs, high-frequency emission-to-noise ratios were larger in neonates compared to older subjects, while the reverse was true in the lower frequencies. Less obvious frequency effects were observed for DPOAEs. These findings are discussed in relation to the potential use of OAEs as screening measures for neonatal hearing loss.

Acoustic Stimulation↗

PubMed1994

Towards understanding the limits of distortion product otoacoustic emission measurements.

Distortion product otoacoustic emission (DPOAE) data were obtained with a custom-designed system from 20 subjects with normal hearing. Cavity measurements, using this system and an Etymotic ER-10B low-noise microphone system, resulted in estimates of recording system distortion of -20 dB SPL for f2 frequencies ranging from 500 to 8000 Hz, and primary levels ranging from 20 to 75 dB SPL (L2 = L1-10 dB). Using this system it was possible to automatically adjust averaging time in order to obtain the same residual noise levels across frequencies. In all subjects with normal hearing, DPOAEs were measurable over a wide range of primary levels for octave f2 frequencies from 1000 to 8000 Hz, but not at 500 Hz. At 500 Hz, only half of the normal-hearing subjects produced DPOAEs that were above the noise floor. When they did, DPOAE amplitude was less than that observed at higher f2 frequencies. While the cause for response absence in some normal ears may have been due to residual noise, the reduced amplitude suggests that the other factors influence the measurement of DPOAEs at low frequencies. This result may be due to reduced cochlear production of DPOAEs at lower frequencies or reduced transmission through the middle ear.

Acoustic Stimulation↗

PubMed1993

Otoacoustic emissions from normal-hearing and hearing-impaired subjects: distortion product responses.

Distortion product otoacoustic emissions (DPOAE) were measured in normal-hearing and hearing-impaired human subjects. Analyses based on decision theory were used to evaluate DPOAE test performance. Specifically, relative operating characteristic (ROC) curves were constructed and the areas under these curves were used to estimate the extent to which normal and impaired ears could be correctly identified by these measures. DPOAE amplitude and DPOAE/noise measurements were able to distinguish between normal and impaired subjects at 4000, 8000, and, to a lesser extent, at 2000 Hz. The ability of these measures to distinguish between groups decreased, however, as frequency and audiometric criterion used to separate normal and hearing-impaired ears decreased. At 500 Hz, performance was no better than chance, regardless of the audiometric criterion for normal hearing. Cumulative distributions of misses (hearing-impaired ears incorrectly identified as normal hearing) and false alarms (normal-hearing ears identified as hearing impaired) were constructed and used to evaluate test performance for a range of hit rates (i.e., the percentage of correctly identified hearing-impaired ears). Depending on the desired hit rate, criterion values of -5 to -12 dB SPL for DPOAE amplitudes and 8 to 15 dB for DPOAE/noise accurately distinguished normal-hearing ears from those with thresholds greater than 20 dB HL for the two frequencies at which performance was best (4000 and 8000 Hz). It would appear that DPOAE measurements can be used to accurately identify the presence of high-frequency hearing loss, but are not accurate predictors of hearing status at lower frequencies, at least for the conditions of the present measurements.

Acoustic Stimulation↗

PubMed1993

A model of cochlear mechanics with outer hair cell motility.

The outer hair cell (OHC) is known to have the ability to change its length in response to voltage changes across its membrane. The apparent function of this OHC motility is to enhance the tuning of the basilar membrane. The model presented in this paper represents the displacement-to-voltage and voltage-to-displacement transducers of the OHC explicitly, each as low-pass filter functions. The model results show that this OHC representation is sufficient to provide a model of cochlear mechanics with mechanical tuning at the inner hair cell which is comparable to the threshold tuning curves observed in single auditory nerve fibers. The enhancement of tuning provided by OHC motility can be interpreted as the combined action of a cochlear amplifier and a second filter. This model demonstrates that realistic cochlear tuning does not require intrinsic resonance in any cochlear structure other than the basilar membrane.

Acoustic Stimulation↗

PubMed1993

A comparison of transient-evoked and distortion product otoacoustic emissions in normal-hearing and hearing-impaired subjects.

The ability of transient-evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs) to distinguish normal hearing from hearing impairment was evaluated in 180 subjects. TEOAEs were analyzed into octave or one-third octave bands for frequencies ranging from 500 to 4000 Hz. Decision theory was used to generate receiver operating characteristic (ROC) curves for each of three measurements (OAE amplitude, OAE/noise, reproducibility) for each OAE measure (octave TEOAEs, 1/3 octave TEOAEs, DPOAEs), for octave frequencies from 500 to 4000 Hz, and for seven audiometric criteria ranging from 10 to 40 dB HL. At 500 Hz, TEOAEs and DPOAEs were unable to separate normal from impaired ears. At 1000 Hz, both TEOAE measures were more accurate in identifying hearing status than DPOAEs. At 2000 Hz, all OAE measures performed equally well. At 4000 Hz, DPOAEs were better able to distinguish normal from impaired ears. Almost without exception, measurements of OAE/noise and reproducibility performed comparably and were superior to measurements of OAE amplitude, although the differences were small. TEOAEs analyzed into octave bands showed better performance than TEOAEs analyzed into 1/3 octaves. Under standard test conditions, OAE test performance appears to be limited by background noise, especially for the low frequencies.

Acoustic Stimulation↗

PubMed1991

Otoacoustic emissions in an adult with severe hearing loss.

The present study describes the unexpected finding of evoked otoacoustic emissions (EOAEs) from the left ear of a subject with severe-to-profound bilateral sensorineural hearing loss. No EOAEs could be measured from the right ear. To ensure that the EOAEs were not artifacts, two different instrumentation systems were used and both provided similar results. It is suggested that the subject may have a group of surviving outer hair cells in some regions of her left cochlea with corresponding inner hair cell or neural damage.

Acoustics↗

PubMed1989

Changes in spontaneous otoacoustic emissions produced by acoustic stimulation of the contralateral ear.

Spontaneous otoacoustic emissions (SOAEs) were measured in human ear canals before, during and after presentation of tonal stimuli to the contralateral ear. Stimuli were presented in 1/8 octave steps from 2 octaves below to 1 octave above the SOAE frequency at sound levels below the observed contralateral acoustic reflex threshold. For certain conditions there was an abrupt upward frequency shift at stimulus onset. For a fixed level the effect was frequency selective; the maximum frequency shift was obtained with tones approximately 1/2 octave below the SOAE. SOAE amplitude usually decreased but in some cases increased or remained unchanged. When amplitude changes were observed, the maximum shifts were observed for tones at or near the SOAE frequency. Changes in SOAEs were not observed for stimulus levels below 60 dB SPL. The effect is believed to be mediated by medial efferent neurons of the uncrossed olivocochlear bundle which arise in the medial region of the superior olivary complex and terminate on outer hair cells (OHCs). These results support those models which attribute SOAE generation to OHCs, and are indicative of an efferent influence on cochlear mechanics. A simple model is presented that proposes that efferent activity alters the tuning of the emission generator by causing changes in OHC membrane conductance.

Acoustic Stimulation↗

PubMed1989

Auditory brainstem responses from children three months to three years of age: normal patterns of response. II.

Auditory brainstem responses (ABR) were measured in 535 children from 3 months to 3 years of age. The latencies reported in this paper should be unaffected by peripheral hearing loss because each child had bilateral wave V responses at 20 dB HLn. Wave V latencies decreased as age increased, at least to 18 months of age, while little or no change was noted in wave I latencies over the same age range. Thus, interpeak latency differences followed the same developmental time course as wave V. The shapes of wave V latency-level functions were comparable across age groups. These results suggest that changes in wave V latency with age are due to central (neural) factors and that age-appropriate norms should be used in evaluations of ABR latencies in children. Interaural differences in absolute wave V latencies and interpeak latency differences were similar to those observed in infants and adults, indicating that response symmetry is independent of age. Statistical analyses suggested that the distributions of absolute and relative latency measurements are normal, making it possible to describe norms in terms of means and standard deviations. A simple model is described that accounts accurately for changes in mean wave V latencies as function of age from preterm through the first three years of life.

Audiometry, Evoked Response↗

PubMed1988

Latency of auditory brain-stem responses and otoacoustic emissions using tone-burst stimuli.

A comparison of the latency of auditory brain-stem responses (ABR) and evoked otoacoustic emissions (EOAE) has led to an interpretation for the travel of transients in the peripheral auditory system that is consistent with both sets of data. The "cochlear echo" theory for the origin of the EOAE indicates that the latency of a particular frequency component back to the ear canal should be twice the forward latency of its characteristic place in the cochlea. The latency of wave V of the ABR to tone-burst stimuli can be described as the sum of two components: (1) a component that varies with intensity and frequency in an orderly and predictable manner and (2) a component that is independent of both intensity and frequency. Because the EOAE data can be predicted by taking twice the value of component (1) of the ABR latency, this component is interpreted to be due to mechanical travel through the cochlea. A consequence of this interpretation is that the remaining neural component of the ABR latency must be relatively independent of frequency and intensity.

Acoustic Stimulation↗

PubMed1987

Tone-burst-evoked otoacoustic emissions from normal-hearing subjects.

Tone-burst-evoked otoacoustic emissions were measured as a function of tone-burst sound pressure level and frequency in normally hearing ears. Although the spectral and temporal properties varied across individual ears, there was a close correspondence between stimulus and response spectra. Both the spectral and latency characteristics of tone-burst-evoked emissions are consistent with the hypothesis that they are generated at sites along the cochlear partition corresponding to their frequency.

Acoustic Stimulation↗

PubMed1986

A model for active elements in cochlear biomechanics.

A linear, mathematical model of cochlear biomechanics is presented in this paper. In this model, active elements are essential for simulating the high sensitivity and sharp tuning characteristic of the mammalian cochlea. The active elements are intended to represent the motile action of outer hair cells; they are postulated to be mechanical force generators that are powered by electrochemical energy of the cochlear endolymph, controlled by the bending of outer hair cell stereocilia, and bidirectionally coupled to cochlear partition mechanics. The active elements are spatially distributed and function collectively as a cochlear amplifier. Excessive gain in the cochlear amplifier causes spontaneous oscillations and thereby generates spontaneous otoacoustic emissions.

Biomechanical Phenomena↗

PubMed1985

Mathematical modeling of cochlear mechanics.

The recent discovery of oto-acoustic emissions [see Zurek, J. Acoust. Soc. Am. 78, 340-344 (1985)] and the newer measures of the micromechanics of the inner ear have generated renewed interest in quantitative descriptions of the biomechanics of the cochlea. Active elements (mechanical force generators) are thought to be essential for producing the high sensitivity and sharp tuning typically associated with normal cochlear function. A mechanical model with active elements is described which can simulate basilar membrane displacements with neural-like tuning and peak amplitudes of about 1 nm at the threshold of hearing. In addition, such models might help explain the source of oto-acoustic emissions. The paper describes the power of the recent attempts at providing quantitative descriptions and predictions of the mechanics of the cochlea.

Animals↗

PubMed1983

An active cochlear model showing sharp tuning and high sensitivity.

Recent in vivo measurements of cochlear-partition motion indicate very high sensitivity and sharp mechanical tuning similar to the tuning of single cochlear nerve fibers. Our experience with mathematical models of the cochlea leads us to believe that this type of mechanical response requires the presence of active elements in the cochlea. We have developed an active cochlear model which incorporates negative damping components; this model produces partition displacement in good agreement with many of the mechanical and neural tuning characteristics which have been observed in vivo by other researchers. We suggest that the negative damping components of our model may represent an active mechanical behavior of the outer hair cells, functioning in the electromechanical environment of the normal cochlea.

Animals↗

PubMed1981

Finite difference solution of a two-dimensional mathematical model of the cochlea.

A current, linear, two-dimensional mathematical model of the mechanics of the cochlea is solved numerically by using a finite difference approximation of the model equations. The finite-difference method is used to discretize Laplace's equation over a rectangular region with specified boundary conditions. The resulting matrix equation for fluid pressure is solved by using a Gaussian block-elimination technique. Numerical solutions are obtained for fluid pressure and basilar membrane displacement as a function of distance from the stapes. The finite difference method is a direct, versatile, and reasonably efficient means of solving the two-dimensional cochlear model.

Basilar Membrane↗