The influence of acoustic and biological noise on signal quality measurements of otoacoustic emissions

Biološka osnova nastanka signala otoakusticke emisije (OAE), akusticka priroda njegovog nastanka i izuzetna maskiranost raznim oblicima smetnji jesu polazna osnova razvoja raznih metoda detekcije, obrade i interpretacije signala OAE, odnosno samog efekta otoakusticke emisije u svetlu karakterizacije funkcionisanja kohlee. Metode merenja OAE se razlikuju po nacinu generisanja stimulusa, mehanizmima generisanja odziva kao i po nacinima obrade signala i statistickog tumacenja dobijenih rezultata. Postojece metode merenja i obrade signala OAE jesu osnova savremenih sistema za merenje OAE, koji su našli široku primenu u klinickoj praksi. Meutim, nisu iscrpljene sve mogucnosti, pre svega teorijske a zatim i metodološke prirode, prvenstveno u domenu ekstrakcije signala OAE iz šuma. Poboljšanjem uslova merenja smanjuje se uticaj spoljašnje buke (šumova) na mogucnost ekstrakcije signala otoakusticke emisije i biološki šum postaje dominantan izvor smetnji. Istraživanje karakteristika bioloških šumova je jedan od preduslova za uspešno rešavanje problema detekcije OAE u prisustvu biološkog šuma. Na pažljivo odabranom uzorku, u skladu sa potrebama istraživanja, analizirani su biološki šumovi snimljeni u ušnom kanalu. Pokazalo se da postoji znacajna korelacija bioloških šumova u levom i desnom uhu i da koeficijent korelacije raste sa porastom intenziteta bioloških šumova. Ovakvo ponašanje bioloških šumova predstavlja povoljnu okolnost sa stanovišta primene adaptivnih metoda filtriranja i adaptivnih metoda potiskivanja šuma. U disertaciji su analizirane karakteristike najznacajnijih bioloških smetnji koje su prisutne kod merenja signala OAE. Ova saznanja su omogucila izbor optimalane adaptivne metode za detekciju TEOAE u prisustvu biološkog šuma. Osnovna ideja za potiskivanje biološkog šuma sastojala se u korišcenju biološkog šuma iz drugog ušnog c kanala za adaptivno potiskivanje biološkog šuma u ušnom kanalu u kome se meri OAE signal. Pošto je signal OAE duboko uronjen u šum, neophodno je bilo kombinovati nekoliko postupaka u toku predobrade signala kako bi se postiglo dobro potiskivanje šuma. Primenjeni su postupci adaptivnog filtriranja, ponderisanog usrednjavanja i oduzimanja procenjene vrednosti signala OAE od signala odziva snimljenog u ušnom kanalu...Biological basis of the otoacoustic emission signal (OAE), acoustic nature of its generation and exceptional masking with various forms of interference are the starting point for the development of various methods of detection, signal processing and interpretation of OAE signal, or the effect of otoacoustic emission in light of the characterization of the cochlea functioning. OAE measurement methods differ in the way of stimulus generation, response generation mechanisms and the methods of signal processing and statistical interpretation of results. Existing methods of measurement and OAE signal processing are the basis of modern systems for OAE measurement, which have found wide application in clinical practice. However, all possibilities are not exhausted, especially the theoretical and methodological nature aproaches, primarily in the field of OAE signal extraction from the noise. Improvement of the measuring conditions reduces the influence of external noise on the possibility of extraction of otoacoustic emissions, and biological noise becomes the dominant source of interference. The study of characteristics of biological noise is one of the prerequisites for successful troubleshooting OAE detection in the presence of biological noise. In carefully selected sample, in accordance with the needs of research, we analyzed the biological noise recorded in the ear canal. It turned out that there was a significant correlation of biological noise in the left and right ear and the correlation coefficient increases with the intensity of biological noise. This behavior of biological noise is a favorable circumstance from the point of application of adaptive filtering methods and adaptive noise suppression method. The dissertation analyzes the characteristics of the most important form of biological interference that are present during OAE measurement. These findings have enabled the selection of optimal adaptive methods for the detection of TEOAE in the presence of biological noise. The basic idea of suppressing biological noise consisted in e the use of biological noise from the other ear canal for adaptive suppression of biological noise in the ear canal in which OAE signal is measured. Since the OAE signal is deeply immersed in the noise it was necessary to combine several steps during preprocessing the signal to achieve good noise suppression. The applied methods are adaptive filtering, weighted averaging and estimated value of OAE signal subtraction from the signal response recorded in the ear canal..