Krens thesis 'Reflectance measurement techniques for hearing diagnostics' is concerned with non-invasive objective measures of the auditory system, specifically measurements of the middle ear that can aid in diagnosing conductive hearing disorders. Such existing methods have also shown potential for increasing the reproducibility of noninvasive objective measures of the inner ear by compensating for the acoustic properties of the ear canal and middle ear. In this context, the term objective refers to an independence of these measures on a behavioral patient response as is standard practice in conventional audiometry and measurements of behavioral auditory thresholds. The project is not concerned with exploring the potential audiological value and diagnostic applications of such non-invasive auditory measures; instead, the project aims to improve underlying measurement methods and assess measurement reproducibility in order to facilitate and stimulate further research into the auditory system, and eventually enable a more thorough and accurate clinical diagnosis.
The thesis addresses the sources of errors in current state of the art methods for determining the source pressure and impedance for ear canal reflectance measurements and proposes several new techniques for improving the reliability, reproducibility and accuracy of such measurements. Based on a 54 page report, the thesis summarizes the work and give an overview of relevant theory and 9 journal papers, 8 of which have been published already. The thesis is well written with a clear structure and contains theoretical and numerical investigations as well as experimental work.
The examiners agreed that Krens work demonstrates a deep understanding of the literature, historical work, methodologies and technical and mathematical descriptions that relate to ear-canal based impedance measurements. Added to this the thesis is the first to offer a clear and complete analysis of how specific assumptions in the methodology lead to errors, and he successfully tests and quantitatively evaluates his ideas. Kren gave a clear and logical presentation of the large amount of work produced in the project, he answered all questions well, demonstrating a deep understanding of the topic. Overall the committee found the work impressive in both breadth and depth, covering theoretical analysis, corresponding measurements and deep knowledge of the application. The results were communicated clearly both in the report and in the oral presentation. The committee finds it particularly impressive that the work had resulted in 8 journal papers that are already published.
Congratulations to Kren on his achievement.