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Biomedical subjects

O Ozdamar

Publications and source records attributed to O Ozdamar.

At least 19 recordsLinked to original sources
PubMed2000

Adaptive noise cancellation in a multimicrophone system for distortion product otoacoustic emission acquisition.

This study focuses on adaptive noise cancellation (ANC) techniques for the acquisition of distortion product otoacoustic emissions (DPOAEs). Otoacoustic emissions (OAEs) are very low level sounds produced by the outer hair cells of normal cochleas, spontaneously or in response to sound stimulation as a byproduct of a frequency and threshold sensitivity increasing mechanism. Current OAE recording systems rely on test probe noise attenuation and synchronous ensemble averaging for increasing signal-to-noise ratios (SNRs). The efficiency of an ANC algorithm for noise suppression was investigated using three microphones: one placed in the test ear, one in the nontest ear for internal noise reference; one near the subject's head for external noise reference. The system proposed was tested with simulations, off-line averaging and real-time implementation of the ANC algorithm. Simulation results showed that the technique had a potential noise reduction capability of 24 dB for complex multifrequency noise signals. Off-line results were positive, with a mean SNR improvement of 4.9 dB. Real-time results indicated that the use of an ANC algorithm in combination with standard averaging methods can reduce noise levels by as much as 10 dB beyond that obtained with standard noise reduction methods and probe attenuation alone.

Algorithms↗
PubMed1999

Median averaging of auditory brain stem responses.

OBJECTIVE: The primary aim of this study is to demonstrate the feasibility of acquiring auditory evoked potentials (AEPs) by median averaging and study its performance under various recording conditions. The auditory brain stem response (ABR) was used as the AEP of choice because it has the poorest signal to noise ratio (SNR) with inherent high susceptibility to extraneous noise. Secondary aim is to evaluate the characteristics of the median ABRs in comparison with the conventional mean averaged ABRs. DESIGN: Single sweep responses to clicks obtained from four subjects at 5 dB steps were saved in hard disk and used for off-line mean and median averaging. The characteristics of the median averaging technique were investigated by manipulating the averaging procedure using the same set of single sweep recordings and comparing them with the mean averaged responses. The effects of analog to digital input resolution (bit size) was simulated computationally by increasing quantization. RESULTS: The results showed that AEPs with low SNRs such as the ABR can be successfully acquired using median averaging with about the same number of sweeps as was required for mean averaging, provided the EEG signal is digitized with a high number of bits. The resulting waveform generally contained more identifiable waves than the corresponding mean average and had a high-frequency noise superimposed on it. This high-frequency noise was successfully filtered out using a digital, running mean smoothing filter. The median average showed an advantage over the mean average when occasional artifacts were recorded. CONCLUSION: The results showed that ABRs can be acquired successfully by median averaging provided EEG is digitized with high bit size. Compared with conventional mean averaging, median averaging is less sensitive to infrequent, externally and internally generated noise that plagues conventional techniques and may help improve wave identification.

Auditory Perception↗
PubMed1999

Comparison of the auditory-evoked brainstem response wave I to distortion-product otoacoustic emissions resulting from changes to inner ear blood flow.

OBJECTIVE/HYPOTHESIS: Examine and compare in detail the time courses of the auditory brainstem response (ABR) wave I amplitude and latency to the distortion-product otoacoustic emission (DPOAE) amplitude and phase measured in the rabbit model following deliberate obstruction of cochlear blood flow (CBF). METHODS: Using a posterior fossa craniotomy in five rabbits, the internal auditory artery (IAA) was compressed with a probe. ABR and otoacoustic emission were continuously monitored before, during, and after the compressions. RESULTS: ABR wave I amplitudes demonstrated measurable decreases at a mean of 28.3 s after IAA compression, whereas DPOAE amplitudes decreased after a mean of 14.8 s. Wave I latencies began to increase at a mean of 18.3 s after occlusion, while DPOAE phase measures changed after a mean of only 4.8 s following IAA compression. The time-course patterns were similar for the amplitudes of both ABR wave I and DPOAE. CONCLUSIONS: ABR wave I amplitude follows a similar, though delayed (by approximately 10 s) time-course pattern to that of the DPOAE following IAA compression. The implication of these findings for intraoperative auditory monitoring is that changes in many currently employed measures will lag actual surgically induced alterations in CBF by at least 20 to 30 s.

Action Potentials↗
PubMed1998

Detection of spikes with artificial neural networks using raw EEG.

Artificial neural networks (ANN) using raw electroencephalogram (EEG) data were developed and tested off-line to detect transient epileptiform discharges (spike and spike/wave) and EMG activity in an ongoing EEG. In the present study, a feedforward ANN with a variable number of input and hidden layer units and two output units was used to optimize the detection system. The ANN system was trained and tested with the backpropagation algorithm using a large data set of exemplars. The effects of different EEG time windows and the number of hidden layer neurons were examined using rigorous statistical tests for optimum detection sensitivity and selectivity. The best ANN configuration occurred with an input time window of 150 msec (30 input units) and six hidden layer neurons. This input interval contained information on the wave component of the epileptiform discharge which improved detection. Two-dimensional receiver operating curves were developed to define the optimum threshold parameters for best detection. Comparison with previous networks using raw EEG showed improvement in both sensitivity and selectivity. This study showed that raw EEG can be successfully used to train ANNs to detect epileptogenic discharges with a high success rate without resorting to experimenter-selected parameters which may limit the efficiency of the system.

Adolescent↗
PubMed1997

Time-frequency distribution of evoked otoacoustic emissions.

Otoacoustic emissions (OAE) are non-stationary signals that vary in time depending on the characteristics of the stimulus. Traditional spectral analysis using Fourier methods ignores the effects of time and can miss important temporal information. Therefore, a better form of spectral analysis requires the use of time-frequency distribution methods. Traditionally, short time Fourier transforms (STFT), commonly known as spectrograms, are used to provide such time-frequency representations. STFT however, suffer from poor resolution and do not provide enough detail about the characteristics of the emissions. In this study, recently developed time-frequency distributions, the Wigner Distribution (WD) and the Choi-Williams Distribution (CWD) are investigated to provide high resolution representations of transient evoked OAEs. Although WD has excellent properties for time-frequency analysis, it suffers from cross-term artefacts generated when multiple sinusoids are present. CWD provides a solution to this problem at the expense of poor time and frequency support. In this study, we use both distributions to estimate the cross-products and provide a relatively artefact-free time-frequency distribution of OAEs. This method is applied to both click and tone burst evoked OAE and shows a more detailed time-frequency representation with as many crests and valleys as different latencies.

Acoustic Stimulation↗
PubMed1996

Two-dimensional spectral processing of sequential evoked potentials.

The processing of sequential evoked potentials (EPs) is investigated using two-dimensional processing techniques. Two-dimensional EP arrays or images are formed by stacking sequential recordings. Processing is accomplished in the frequency domain by 2-D low-pass filtering using Gaussian filters. Auditory brainstem responses (ABRs), which are the early auditory EPs, are used to investigate the effects of the 2-D filtering on real data. Gaussian filtering improves signal-to-noise ratios by reducing high frequency noise effectively in both intra-EP and inter-EP dimensions. Applications to intra-operative monitoring are simulated with real ABR data.

Evoked Potentials, Auditory, Brain Stem↗
PubMed1994

Automated electrophysiologic hearing testing using a threshold-seeking algorithm.

The efficacy of utilizing an automated algorithm to identify auditory brainstem responses (ABR) was studied. A microcomputer-based threshold-seeking algorithm utilizing click-evoked ABR was developed to determine evoked-response thresholds for automated hearing screening. The software consists of an evoked-response recognizer unit, which determines the presence or absence of a response, and a threshold-tracking unit, which controls the click intensity in order to track the threshold. The response recognizer is based upon correlation methods. Threshold tracking is accomplished using a Parameter Estimation by Sequential Testing (PEST) procedure, which is commonly used to study psychophysical properties of the auditory system. Sound level is automatically adjusted, based on the results of the recognizer and the threshold tracker. Test results were generally obtained in less than 15 minutes per ear. The results of the automated procedure correlate very highly with expert judgments of ABR threshold and show good test-retest reliability, suggesting that automated procedures are viable alternatives to traditional testing methods.

Adolescent↗
PubMed1993

Classification of audiograms by sequential testing: reliability and validity of an automated behavioral hearing screening algorithm.

In 1990, CAST (classification of audiograms by sequential testing) was proposed and developed as an automated, innovative approach to screening infant hearing using a modified Bayesian method. The method generated a four-frequency audiogram in a minimal number of test trials using VRA (visual reinforcement audiometry) techniques. Computer simulations were used to explore the properties (efficiency and accuracy) of the paradigm. The current work is designed to further test the utility of the paradigm with human infants and young children. Accordingly, infants and children between 6 months and 2 years of age were screened for hearing loss. The algorithm's efficacy was studied with respect to validity and reliability. Validity was evaluated by comparing CAST results with tympanometric data and outcomes of staircase-based testing. Test-retest reliability was also assessed. Results indicate that CAST is a valid, efficient, reliable, and potentially cost-effective screening method.

Acoustic Impedance Tests↗
PubMed1992

FFT-based digital tactile vocoder system for real-time use.

A microprocessor-based real-time digital vibrotactile vocoder system has been developed to train the deaf and for artificial hearing research. The system is composed of a microcomputer module with a digital signal processor, interface units and an attenuator/driver circuit. Live or digitised (stored or synthetic) speech is presented to the skin spectrally through a belt housing eight or 16 vibrators. Speech is processed in real time using a fast Fourier transform. The system is also capable of presenting any arbitrary spatiotemporal pattern on the skin for artificial hearing experiments. A preliminary experiment with a deaf subject indicates that the system is potentially an effective device for artificial hearing.

Biomedical Engineering↗
PubMed1991

Optimization of automated hearing test algorithms: simulations using an infant response model.

Computer simulation was used to evaluate several parameters of an automated hearing test algorithm in an attempt to optimize the algorithm for accuracy and efficiency. An infant response model was developed to guide the simulations. Test parameters of interest were starting intensity and stopping rule and their interaction with a measure that is thought to emulate infant reliability, probability of task orientation. Results indicated that stopping rule, within the ranges investigated, had little effect on accuracy but had major impact on efficiency. Starting intensity interacted with the hearing status of pseudosubjects in influencing accuracy. Accuracy was most influenced by probability of task orientation. The simulated test data are compared to data from infants and young children in the accompanying article so that the response model can be evaluated.

Algorithms↗
PubMed1990

Computer methods for on-line hearing testing with auditory brain stem responses.

On-line computer methods were developed and evaluated for automated hearing testing with auditory brain stem responses (ABR). The system contained (1) a response recognition unit which recognized the presence or absence of an ABR response and (2) a threshold tracking unit which adjusted stimulus intensity and determined the ABR threshold. Two methods, one nontemplate (variance ratio) and one template (cross-correlation), were evaluated for response recognition while three threshold tracking methods were explored: clinical, Békésy, and PEST (parameter estimation by sequential testing). Both response recognition and threshold tracking units were evaluated by computer simulations for on-line operation using a standard set of experimentally recorded ABRs. The results indicated that while all the response recognition methods were reasonably accurate, their on-line use resulted in significant differences in test efficiency due to differences in tracking methods.

Acoustics↗
PubMed1990

Classification of audiograms by sequential testing using a dynamic Bayesian procedure.

A new method for estimating audiograms using behavioral responses is presented. The method is based upon a modification of the Bayesian probability formula in which an outcome is predicted from a static set of events. In the new method, classification of audiograms by sequential testing (CAST), the probabilities of occurrence of audiogram patterns are dynamically updated according to the outcome of each test trial. Computer simulation using an infant response model suggests that the procedure is efficient, sensitive, and specific.

Algorithms↗
PubMed1989

The effects of vocoder filter configuration on tactual perception of speech.

Perception of synthetic speech continua through the sense of touch and audition was compared utilizing a 32-channel spectrally-oriented electrocutaneous vocoder display and standard auditory psychophysical procedures. Perception of a consonantal and a vocalic continuum was evaluated utilizing three vocoder filter configurations: logarithmic, linear, and average (geometric mean of logarithmic and linear). Results indicated a close correspondence between tactual and auditory discrimination and identification for the vowel (/a/-/e/) and the consonant (/sta/-/sa/) continuum regardless of the filter characteristics.

Deafness↗
PubMed1988

Computer system for quantitative evaluation of an electrotactile vocoder for artificial hearing.

A computer-controlled experimental electrotactile vocoder system is designed to evaluate quantitatively the transmission of speech information and to test various design options for tactual vocoders. The system is composed of a digital speech synthesizer, a digital vocoder, a computer-driven electrotactile display, and an adaptive controller for psychophysical experimentation. Samples of continua representing speech contrast types occurring in natural languages are synthesized by systematically manipulating selected subphonemic features. The synthesized speech stimuli are processed using a programmable vocoder and presented to the skin with an electrotactile display belt worn on the abdomen. Transmission of significant speech parameters is quantitatively evaluated using adaptive psychophysical techniques and labeling tests. The system is used to assess the potential of speech transmission through the skin and to evaluate different vocoder configurations and processing techniques for tactual vocoders to be used as artificial hearing devices by the deaf.

Adult↗
PubMed1988

Similarities between tactual and auditory speech perception.

Perception of synthetic speech continua through the sense of touch and audition was compared utilizing a 32-channel spectrally oriented electrocutaneous display and standard auditory psychophysical procedures. Results indicated a close correspondence between tactual and auditory discrimination and identification for a vowel (/a/-/e/) and a consonant (/sta/-/sa/) continuum. These results suggest that at least some aspects of speech perception are amodal.

Humans↗
PubMed1987

Hearing loss in an institutionalized mentally retarded population. Identification by auditory brainstem response.

We report the results of auditory brainstem response testing of 122 profoundly retarded institutionalized children, a segment of the retarded population heretofore generally regarded as untestable by behavioral audiometry. Major findings include: 32% of the study population showed, by auditory brainstem response, hearing loss exceeding 20 decibels of hearing level in one or both ears (12% showed conductive loss and 20% sensorineural loss); of the 15.6% with evidence of bilateral sensorineural loss, 7.37% had losses in the 30- to 50-dB range, and 8.19% had losses of 60 dB or greater; and evidence of abnormal brain-stem function was found in 11%. Results of otologic examinations and audiologic habilitative follow-up in selected children are also reported.

Adolescent↗
PubMed1987

Computer monitoring of auditory brainstem responses.

A relatively low cost, bedside, portable, microcomputer based system for long-term monitoring of human auditory evoked responses in critical care environments is described, and test data are presented. The system enables the user to acquire responses, detect significant peaks (usually peaks I, III, and V), store information and display trends (latency vs time graphs) automatically. Prior to processing, responses are digitally filtered so that no phase distortion is introduced. A peak detection algorithm takes into consideration both the different morphologies of the IV-V wave complex and the time-varying characteristics of the ABR waveform. Evaluations using normal subjects and intensive care unit patients show the clinical potential of automated long-term auditory brainstem monitoring.

Brain Stem↗