Properties of maximum length sequence and nonlinear volterra slice otoacoustic emissions

Evoked otoacoustic emissions (EOAEs) are produced by the cochlea and provide anobjective and non-invasive measure of cochlear function. A new technique, based onMaximum Length Sequences (MLSs) enables stimulus rates of up to 5000 clicks/s to beused, and gives increased speed and sensitivity of testing. Volterra slice otoacousticemissions (VSOAEs) can be extracted from the response using this technique. Theserepresent nonlinear temporal interaction components and are more sensitive to changes incochlear pathology than the conventional response. Conventional EOAE amplitude differsbetween ears and sexes; female subjects having responses of greater amplitude than malesubjects and right ears larger responses than left ears. As a pre-requisite to clinical use it isnecessary to establish if these differences occur with the Maximum length sequenceotoacoustic (MLSOAE) technique and with VSOAEs and whether they change with stimulusrate, order or slice. The relationship between VSOAEs, Spontaneous otoacoustic emissions(SOAEs), Distortion product otoacoustic emissions (DPOAEs) and the input/output function(I/O) for click-evoked OAEs (CEOAEs) recorded at the conventional rate (40 clicks/s) wasalso investigated to assess if these measures of cochlear nonlinearity were related to oneanother.In the first set of experiments 80 ears of normally hearing adults were tested. MLSOAEswere recorded at eight stimulus rates and two stimulus levels. For the second and thirdexperiments 45 ears of normally hearing adults were tested. SOAEs, DPOAEs, theinput/output function (I/O) for CEOAEs at the conventional rate (40 clicks/s) and at fourstimulus levels, and VSOAEs at three stimulus rates were recorded.Female subjects were found to have statistically significantly larger MLSOAEs than malesubjects and gave larger amplitude responses in their right ears. This sex difference wasobserved with VSOAEs. A rate effect was also demonstrated with the amplitude of theMLSOAEs decreasing with an increase in rate. The VSOAE amplitude was greater for thesecond order compared with the third order response, and slice one had a greater amplitudethan slice two. VSOAEs of higher amplitude were obtained in SOAE-positive ears. There wasa significant relationship between the slope of the I/O function of the CEOAE and theVSOAEs.The study has provided normative data for MLSOAE testing and for VSOAEs. The dataobtained suggest that the amplitude (CEOAE I/O function) and temporal (VSOAEs)nonlinearities arise from the same generators, whereas the frequency domain nonlinearities(SOAEs & DPOAEs) have different generators. MLSOAEs and VSOAEs have great potentialfor clinical use

Using otoacoustic emissions to evaluate efferent auditory function in humans

The auditory system continually adapts to changes in the acoustic environment over short periods of time. This fine-tuning of its dynamics is mediated in part by the medial olivocochlear (MOC) bundle, a neural feedback loop which aids in the regulation of cochlear micro-mechanics. The ability to measure the response of the MOC system in humans may provide significant insight into unique cochlear functions, such as its sharp frequency selectivity and wide dynamic range. In humans the efferent system can be investigated non-invasively using otoacoustic emissions (OAEs). However, how OAEs can best be used to evaluate efferent function, the pitfalls associated with such measurements, as well as the relationship between OAEs and perception are not fully understood. This dissertation presents three experiments that explore the use of OAEs to assess efferent function in humans. The first study examined the advantages of separating the major components of distortion product otoacoustic emissions (DPOAEs) when evaluating efferent function using contralateral acoustic stimulation (CAS). CAS-induced activation of the medial olivocochlear reflex (MOCR) was found to produce both reductions and enhancements of total DPOAE level. Analysis of the separated components of the DPOAE revealed that these changes could be accounted for by the contribution of an efferent-induced phase change in the reflection component of the DPOAE. In the second, analysis of DPOAE primary level and phase changes over a wide range of CAS levels used to induce MOCR revealed that middle ear muscle reflex (MEMR) activation could be simultaneously monitored. CAS levels commonly used to elicit MOCR could also elicit MEMR responses, which results in contamination of MOCR estimates. Finally, a novel technique to measure simultaneous OAEs and masked behavioral thresholds is presented and used to investigate a perceptual phenomenon thought to be associated with an efferent activation. While a direct association between physiological and behavioral masked thresholds was not observed, a strong relationship was found between the physiological measure of masked thresholds and a measure of CAS-induced efferent suppression, suggesting that although efferent-mediated suppression of basilar membrane mechanics is related to the phenomenon, more central mechanisms may be required to modulate the perceptual response

Individual Differences in Stimulus Frequency Otoacoustic Emission Phase

Otoacoustic emissions (OAEs) are sounds that originate in the cochlea and are measured in the ear canal. OAEs provide a noninvasive tool for investigating cochlear mechanics. Stimulus-frequency OAEs (SFOAEs) are evoked by presenting a single frequency tone, called a probe tone, which have an advantage over other OAEs because they are the least influenced by cochlear nonlinearities. However, because the SFOAE are generated in the cochlea with the same frequency as the stimulus, additional techniques, such as the use of suppressor tones are needed to enable separation of the probe tone from the SFOAE. The primary goal of this investigation was to explore individual differences in SFOAE phase gradient delays. These delays were hypothesized to improve estimates of cochlear health, inferred from hearing thresholds. Efficient measures of phase gradient delays can be obtained using frequency swept tones analyzed with time-frequency filtering, such as the least squares (LS) fit. The least squares fit is a time-frequency filter because the LS fit estimates coefficients for a subset of the total signal which are then used to separate and estimate signals of interest. However, the limitations of the frequency swept tone procedure and LS fit for estimating SFOAEs are not well understood. This investigation first focused on identifying limitations of such SFOAE and refining the LS fitting procedure. It was determined that including a suppressor was necessary for obtaining optimal SFOAE estimates, and the investigation shifted from further refining the LS fitting procedure to exploration of alternative time-frequency analyses which permit clearer characterization of the various latency contributions to suppressor based SFOAEs estimates. The use of a fast, continuous filtered wavelet transform provided a unique perspective on the distribution of SFOAE energy in the time-frequency domain and confirmed that SFOAEs are a sum of both long and short latency contributions. The distributions of long and short SFOAE energy explain some the discrepancies between discrete tone and swept tone SFOAEs procedures. Predicting behavioral thresholds from SFOAE phase, magnitude, or phase and magnitude combined may be misleading when the analysis is not focused around the SFOAE latency contributions from the region where SFOAEs are most affected by cochlear damage. It was revealed that more focus should be given to understanding the best ways to separate the long and the short latencies for different stimulus parameters and individuals, in order to improve sensitivity to cochlear health

Narrowband signal processing techniques with applications to distortion product otoacoustic emissions.

by Ma Wing-Kin.Thesis (M.Phil.)--Chinese University of Hong Kong, 1997.Includes bibliographical references (leaves 121-124).Chapter 1 --- Introduction to Otoacoustic Emissions --- p.1Chapter 1.1 --- Introduction --- p.1Chapter 1.2 --- Clinical Significance of the OAEs --- p.2Chapter 1.3 --- Classes of OAEs --- p.3Chapter 1.4 --- The Distortion Product OAEs --- p.4Chapter 1.4.1 --- Measurement of DPOAEs --- p.5Chapter 1.4.2 --- Some Properties of DPOAEs --- p.8Chapter 1.4.3 --- Noise Reduction of DPOAEs --- p.8Chapter 1.5 --- Goal of this work and Organization of the Thesis --- p.9Chapter 2 --- Review to some Topics in Narrowband Signal Estimation --- p.11Chapter 2.1 --- Fourier Transforms --- p.12Chapter 2.2 --- Periodogram ´ؤ Classical Spectrum Estimation Method --- p.15Chapter 2.2.1 --- Signal-to-Noise Ratios and Equivalent Noise Bandwidth --- p.17Chapter 2.2.2 --- Scalloping --- p.18Chapter 2.3 --- Maximum Likelihood Estimation --- p.19Chapter 2.3.1 --- Finding of the ML Estimator --- p.19Chapter 2.3.2 --- Properties of the ML Estimator --- p.21Chapter 3 --- Review to Adaptive Notch/Bandpass Filter --- p.23Chapter 3.1 --- Introduction --- p.23Chapter 3.2 --- Filter Structure --- p.24Chapter 3.3 --- Adaptation Algorithms --- p.25Chapter 3.3.1 --- Least Squares Method --- p.25Chapter 3.3.2 --- Least-Mean-Squares Algorithm --- p.27Chapter 3.3.3 --- Recursive-Least-Squares Algorithm --- p.28Chapter 3.4 --- LMS ANBF Versus RLS ANBF --- p.31Chapter 3.5 --- the IIR filter Versus ANBF --- p.31Chapter 4 --- Fast RLS Adaptive Notch/Bandpass Filter --- p.33Chapter 4.1 --- Motivation --- p.33Chapter 4.2 --- Theoretical Analysis of Sample Autocorrelation Matrix --- p.34Chapter 4.2.1 --- Solution of Φ (n) --- p.34Chapter 4.2.2 --- Approximation of Φ (n) --- p.35Chapter 4.3 --- Fast RLS ANBF Algorithm --- p.37Chapter 4.4 --- Performance Study --- p.39Chapter 4.4.1 --- Relationship to LMS ANBF and Bandwidth Evaluation . --- p.39Chapter 4.4.2 --- Estimation Error of Tap Weights --- p.40Chapter 4.4.3 --- Residual Noise Power of Bandpass Output --- p.42Chapter 4.5 --- Simulation Examples --- p.43Chapter 4.5.1 --- Estimation of Single Sinusoid in Gaussian White Noise . --- p.43Chapter 4.5.2 --- Comparing the Performance of IIR Filter and ANBFs . . --- p.44Chapter 4.5.3 --- Harmonic Signal Enhancement --- p.45Chapter 4.5.4 --- Cancelling 50/60Hz Interference in ECG signal --- p.46Chapter 4.6 --- Simulation Results of Performance Study --- p.52Chapter 4.6.1 --- Bandwidth --- p.52Chapter 4.6.2 --- Estimation Errors --- p.53Chapter 4.7 --- Concluding Summary --- p.55Chapter 4.8 --- Appendix A: Derivation of Ts --- p.56Chapter 4.9 --- Appendix B: Derivation of XT(n)Λ(n)ΛT(n)X(n) --- p.56Chapter 5 --- Investigation of the Performance of two Conventional DPOAE Estimation Methods --- p.58Chapter 5.1 --- Motivation --- p.58Chapter 5.2 --- The DPOAE Signal Model --- p.59Chapter 5.3 --- Preliminaries to the Conventional Methods --- p.60Chapter 5.3.1 --- Conventional Method 1: Constrained Stimulus Generation --- p.60Chapter 5.3.2 --- Conventional Method 2: Windowing --- p.61Chapter 5.4 --- Performance Comparison --- p.63Chapter 5.4.1 --- Sidelobe Level Reduction --- p.63Chapter 5.4.2 --- Estimation Accuracy --- p.65Chapter 5.4.3 --- Noise Floor Level --- p.67Chapter 5.4.4 --- Additional Loss by Scalloping --- p.68Chapter 5.5 --- Simulation Study --- p.69Chapter 5.5.1 --- Sidelobe Suppressions of the Windows --- p.69Chapter 5.5.2 --- Mean Level Estimation --- p.70Chapter 5.5.3 --- Mean Squared Error Analysis --- p.71Chapter 5.6 --- Concluding Summary --- p.75Chapter 5.7 --- Discussion --- p.75Chapter 5.8 --- Appendix A: Cramer-Rao Bound of the DPOAE Level Estimation --- p.76Chapter 6 --- Theoretical Considerations of Maximum Likelihood Estimation for the DPOAEs --- p.77Chapter 6.1 --- Motivation --- p.77Chapter 6.2 --- Finding of the MLEs --- p.78Chapter 6.2.1 --- First Form: Joint Estimation of DPOAE and Artifact Pa- rameter --- p.79Chapter 6.2.2 --- Second Form: Artifact Cancellation --- p.80Chapter 6.3 --- Relationship of CM1 to MLE --- p.81Chapter 6.4 --- Approximating the MLE --- p.82Chapter 6.5 --- Concluding Summary --- p.84Chapter 6.6 --- Appendix A: Equivalent Forms for the Minimum Least Squares Error --- p.85Chapter 7 --- Optimum Estimator Structure and Artifact Cancellation Ap- proaches for the DPOAEs --- p.87Chapter 7.1 --- Motivation --- p.87Chapter 7.2 --- The Optimum Estimator Structure --- p.88Chapter 7.3 --- References and Frequency Offset Effect --- p.89Chapter 7.4 --- Artifact Canceling Algorithms --- p.92Chapter 7.4.1 --- Least-Squares Canceler --- p.93Chapter 7.4.2 --- Windowed-Fourier-Transform Canceler --- p.93Chapter 7.4.3 --- FRLS Adaptive Canceler --- p.95Chapter 7.5 --- Time-domain Noise Rejection --- p.97Chapter 7.6 --- Regional Periodogram --- p.98Chapter 7.7 --- Experimental Results --- p.99Chapter 7.7.1 --- Artifact Cancellation via External Reference --- p.99Chapter 7.7.2 --- Artifact Cancellation via Internal Reference --- p.99Chapter 7.7.3 --- Artifact Cancellation in presence of Transient Noise --- p.101Chapter 7.7.4 --- Illustrative Example: DPgrams --- p.102Chapter 7.8 --- Conclusion and Discussion --- p.111Chapter 7.9 --- Appendix A: Derivation of the Parabolic Interpolation Method . --- p.113Chapter 7.10 --- Appendix B: Derivation of Weighted-Least-Squares Canceler . . --- p.114Chapter 8 --- Conclusions and Future Research Directions --- p.118Chapter 8.1 --- Conclusions --- p.118Chapter 8.2 --- Future Research Directions --- p.119Bibliography --- p.12

Peripheral and Central Auditory Processing in People With Absolute Pitch

Absolute pitch (AP) is a rare ability that is defined by being able to name musical pitches without a reference standard. This ability has been of interest to researchers studying music cognition and the processing of pitch information because it is very rarely expressed and raises questions about developmental interactions between biological predispositions and musical training. This dissertation focuses mainly on the peripheral and central neural substrates and is divided into seven chapters. The first chapter reviews the anatomy, function, and frequency resolution of the auditory peripheral and central nervous system. It includes background information pertaining to the origins of AP and describes inconsistencies reported throughout a number of studies that characterize AP emergence. Chapter two details a series of peripheral experiments on twenty AP and thirty-three control subjects recruited for testing at two locations. The goal was to test whether frequency resolution differences could be resolved at the level of the cochlea within both groups as a potential correlate for the genesis of AP. Chapter three details two behavioural tests that were administered to assess the smallest frequency difference that AP musicians could resolve and to test how well they could detect melodic mistuning excerpts compared to non-AP musicians and controls without musical experience. Both AP musicians and non-AP musicians did significantly better in both tests compared to non-musicians. However, there were no differences between the AP and non-AP musician groups. Chapter four details a functional MRI study that measured frequency tuning in the cortex using a population receptive field (pRF) model that estimates preferred frequency bandwidth in each voxel. This method was also tested in auditory subcortical nuclei such as the inferior colliculus and medial geniculate nucleus. Chapter five reports the neuro-anatomical correlates of musicianship and AP using structural MRI. Here we investigated cortical thickness and volume differences among the three groups and found a number of regions differed significantly. Cortical thickness was significantly greater in the left Heschls gyrus (an area that acts as a central hub for auditory processing) in AP musicians compared to non-AP musicians and non-musicians. AP and non-AP musicians also exhibited increased cortical thickness and volume throughout their cortex and subcortex. In line with previous studies, AP musicians showed decreased cortical thickness and volume in frontal regions such as the pars opercularis part of the inferior frontal gyrus. Chapter six reports the neuro-anatomical correlates of musicianship and AP using diffusion tensor imaging (DTI) to measure connectivity and white matter structural integrity in regions associated with audition and language processing. Tracts connecting language processing regions were reduced in volume in AP musicians compared to their non-AP counterparts. Chapter seven includes the general discussion, which integrates the findings and results from the five experiments. Our findings indicate that the sharpness of frequency tuning did not differ in either peripheral or central auditory processing stages among AP and non-AP groups. This implies that AP possessors do not encode or represent auditory frequency any differently than other groups, from the periphery through auditory cortex; instead, the neural substrate of their abilities must lie elsewhere. The automatic and working memory independent categorization abilities in AP may reflect more refined efficiency in local but not global functional connectivity

Noise Exposure, Self-Reported Speech-in-Noise Percpetion, and the Auditory Brainstem Response in Normal-Hearing Human Ears

Difficulty understanding speech-in-noise (SIN) is a common complaint among many listeners. There is emerging evidence that noise exposure is associated with difficulties in speech discrimination and temporal processing despite normal audiometric thresholds. At present, evidence linking temporary noise-induced hearing loss and selective loss of low spontaneous rate fibers in human ears is limited and inconsistent. Likewise, results of SIN measures in relation to noise-induced cochlear synaptopathy varied across studies. The goals of this study are to further our understanding of the effects of noise exposure on the auditory system and to investigate novel approaches for detecting early noise-induced auditory damage. Data were collected from 30 normal-hearing subjects (18-35 years old) with varying amounts of noise exposure. Auditory brainstem responses (ABR) were recorded to both a click (measure of auditory nerve function) and speech stimulus (/da/; measure of temporal processing). The speech hearing subscale of the Speech, Spatial and Qualities of Hearing Scale (SSQ) was also administered to quantify individual self-reported SIN abilities. The data resulted in mixed findings. Overall click-ABR wave I results provided no evidence for noise-induced synaptopathy in this cohort. However, differences in the wave I amplitude between males and females were observed suggesting noise effects may vary between sexes. Transient components of the speech-ABR showed no evidence of neural slowing but revealed enhanced neural responses in individuals with greater amounts of noise exposure. This later finding may be a manifestation of either musical training or increased central neural gain as a result of pathology. Lastly, individuals with greater amounts of noise exposure reported experiencing more difficulties hearing SIN (as per the SSQ) but ABR data did not show the predicted physiologic evidence to explain the self-perceived SIN deficit

The clinical utility of the Vivosonic Integrity Auditory Brainstem response system in children with cerebral palsy

Determining auditory functioning in difficult-to-test populations such as cerebral palsy (CP) remains a challenge in paediatric audiology. The auditory brainstem response (ABR) is favoured as the procedure to assess auditory functioning in difficult-to-test populations such as CP. The CP population, however, offers unique challenges for the ABR procedure due to the presence of involuntary muscular movements that may compromise the signal-to-noise ratio (SNR) of the ABR. Conventional ABR technology attempts to improve the SNR by the modification of acquisition parameters e.g. adjusting the low cut filter or implementing stricter artifact rejection criteria. However, such modifications may compromise the waveform morphology of the ABR. Furthermore, sedation or general anesthesia can also be used to improve the SNR by reducing excessive muscular movements. The CP population, however, displays a high risk for developing upper airway obstruction when being sedated or anesthetized. Thus, the feasibility and reliability of the conventional ABR may be compromised when being employed in the CP population. In recent years a novel ABR system, the Vivosonic Integrity (VS) ABR has become clinically available. The device incorporates features such as pre-amplification of the ABR signal, Kalman filtering and wireless recording. These features promise to address the limitations of conventional ABR technology to obtain a reliable recording in the midst of excessive myogenic artifact. The aim of this study was therefore to evaluate the clinical utility of the VS system when assessing a sample of children with CP without the use of sedation. The clinical utility of the VS ABR system was determined by comparing its success rates, the threshold correspondence to behavioural pure tone (PT) thresholds and recording time to a conventional ABR system when using click and 0.5 kHz TB stimuli. A cross-sectional within-subject comparison research design was selected in order to compare thresholds obtained with different procedures. The experimental part of this study was represented by the within-subject control condition where the VS ABR system and the conventional ABR system were simultaneously conducted in each subject. This unique setup was important in the research as equivalent test conditions in terms of EEG and environmental conditions had to be ensured for both ABR systems. 15 CP subjects between the ages of 12 and 18 years were included in the project. A diagnostic audiological test battery including immittance, distortion product otoacoustic emissions and behavioural audiometry was conducted on each subject prior the administration of the ABR procedures. The variability of the audiological test battery results – between the subjects and when compared to previous research – emphasized the heterogeneity of the CP population. Furthermore, more than half of the research sample (53%; n=15) responded inconsistently to behavioural pure tone (PT) stimuli. It was suggested that the severity of physical impairments as well as additional impairments such as mental retardation might have influenced the consistency of the subjects’ responses during behavioural PT audiometry. The ABR results indicated that there were no significant differences with regards to threshold correspondence and recording time between the two ABR systems when using click and 0.5 kHz TB stimuli (p>0.05). With regards to the success rates, the VS system was successful in more cases than the conventional ABR system using click and 0.5 kHz TB stimuli. Although results also showed no statistically significant value for click p=.1121) and 0.5 kHz TB stimuli p=.1648), there was a tendency towards the 95% confidence level in both cases suggesting that the VS ABR system may produce a statistically significant success rate for click as well as for 0.5 kHz TB stimuli, provided a larger sample is tested. The research indicated that, since the VS ABR system was more successful across a wider range of subjects during click-evoked and 0.5 kHz TB recordings, it may increase the clinical usefulness of the ABR especially in terms of hearing screening in the CP population. The research suggested that excessive muscular movements during the recordings influenced not only the VS ABR’s, but also the conventional ABR’s threshold correspondences to PT thresholds as well as the recording time of the measurements. Therefore it may still be necessary to use a light sedative in some CP patients to reduce excessive myogenic interference despite the possible advantages of the VS ABR system.Dissertation (MCommunication Pathology)--University of Pretoria, 2010.Speech-Language Pathology and Audiologyunrestricte