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INTRODUCTION
The quest for the development of an optimal objective diagnostic procedure to aid in the assessment of persons regarded as difficult-to-test, such as neonates and infants, has kept many researchers intensely occupied in the last two decades (Kemp, 1979; Tanaka, O-Uchi, Arai & Suzuki, 1987; Bonfils & Uziel, 1989; Lonsbury-Martin, 1994; Stover, Gorga & Neely & Montoya, 1996a; Koivunen, Uhari, Laitakari, Alho & Luotonen, 2000). Despite phenomenal advances in the ability to record electrical potentials generated at various levels of the nervous system and discoveries of active biological mechanisms in the cochlea, audiologists are still spending large amounts of time (Lee, Kimberley & Brown 1993; Vohr, White, Maxon & Johnson, 1993; Quinonez & Crawford, 1997) and money (Mauk & Behrens 1993; Weber, 1994) to attempt to evaluate difficult-to-test populations with equipment that allows only a limited frequency range of evaluation (Kemp & Ryan, 1993).
The purpose of this chapter is to present a brief overview of the ongoing struggle for the development of an optimal objective diagnostic audiologic procedure to aid in the assessment of difficult-to-test populations. This overview clearly indicates the need for a simple, cost effective, non-invasive yet accurate and objective method and states the reasons for difficulties experienced in this seemingly impossible quest. Furthermore, this chapter will present the purpose of this study, and plot a brief course of how the main objectives would be obtained. Lastly, this chapter will outline the objectives of following chapters to provide a more detailed description of the scope and objectives of the study.
1.1 Introduction
1.2 The Origin of Objective Procedures
1.3 Purpose of this study
1.4 Outline ofthe Thesis
1.5 Conclusion
Chapter 2: The Ouest for Optimal Objective Pure ToneThreshold Prediction
2.1 Introduction
2.2 Objective diagnostic procedures
2.2.1 Overview and definition of terms
2.2.2 Current objective procedures available to predict pure tone thresholds
2.3 DPOAEs as an objective, non-invasive technique
2.3.1 Definition of DPOAE
2.3.2 Measurement Procedures and Instrumentation for DPOAEs
2.3.3 Literature overview
2.3.4 PIT prediction with DPOAEs in perspectiv
2.3.4.1 Audiometric threshold is determined by factors not included in OAE generation
2.4 Requirements for an optimal objective pure tone threshold prediction procedure
2.4.1 Frequency specificity
2.4.2 Evaluation of broad frequency span
2.4.3 Efficiency of the procedure
2.4.4 Good test-retest repeatability
2.4.5 Differential diagnosis between sensory and neural hearing impairment
2.4.6 Fast test performance
2.4.7 Economic test performance
2.4.8 Non-invasive, comfortable for the patient
2.4.9 Age differences
2.5 DPOAEs as an optimal objective pure tone threshold prediction procedure
2.5.1 Frequency specificity
2.5.2 Evaluation of broad frequency span
2.5.3 Efficiency of the procedure
2.5.4 Differential diagnosis between sensory and neural hearing impairment.
Chapter 3: Parameters that Influence Pure Tone Threshold Prediction Accuracy with Distortion Product Otoacoustic Emissions and Artificial
3.1 Introduction
3.2 Stimulus Parameters of DPOAEs
3.3 Subject variables: The Effect of Age and Gender on DPOAEs
3.4 Which aspect of the DPOAE can best be correlated with pure tone thresholds
3.5 Aspects of the artificial neural network that influences prediction accuracy ofPTTs .
4.1 Introduction
4.2 Aims of research .
4.2.1 Main aim
4.2.2 Sub aims
4.3 Research design
4.4 Subjects
4.4.1 Criteria for the selection of subjects
4.4.1.1 Normal and impaired hearing ability
4.4.1.2 Normal middle ear functioning
4.4.1.3 Good or normal attention span
4.4.1.4 Criteria regarding subject age and gender
4.4.2 Subject selection procedures
5.1 Introduction
5.2 Aspects regarding differences in methodology
for the present (2000) and previous (1998) study
5.3 The prediction of 4000 Hz
5.3.1 Results obtained from the present study for the prediction of 4000 Hz
5.3.2 Results of present study (2000) in comparison to the previous study (1998) for 4000 Hz
5.4 The prediction of 2000 Hz
5.4.1 Results obtained from the present study for the prediction of 2000 Hz
5.4.2 Results of present study (2000) in comparison to the previous study (1998) for 2000 H
5.5 The prediction of 1000 Hz
5.5.1 Results obtained from the present study for the prediction of 1000 H
5.5.2 Results of present study (2000) in comparison to the previous study (1998) for 1000 Hz
5.6 The prediction of 500 Hz
5.6.1 Results obtained from the present study for the prediction of 500 Hz
5.6.2 Results of present study (2000) in comparison to the previous study (1998) for 500 Hz
5.7 Subject-, DPOAE- and ANN-variables experimented with to determine optimal PIT prediction accuracy
5.7.1 The effect of the subject variable AGE presented to the network in 5 year or 10 year categories on PTT prediction accuracy
5.7.2 The effect of DPOAE threshold defined as 1,2 or 3 dB above the noise floor on PIT prediction accuracy
5.7.3 The effect of the emission or inclusion oflow frequency DPOAE information for ANN training on PIT prediction accuracy
6.1 Introduction
6.2 Indication of a Correlation between DPOAE Measurements and Pure Tone Thresholds
6.3 Prediction of 500 Hz
6.4 Possible reasons for poor prediction of categories representing hearing loss
6.5 Prediction of 1000 Hz
6.6 Prediction of 2000 Hz
6.7 Prediction of 4000 Hz .
6.8 Results ofthe current study in perspective: Readiness for broad clinical use
6.9 Case studies where the audiogram was predicted accurate
6.10 Case studies where the audiogram was predicted inaccurately
7.1 Summary
7.2 Evaluation of research methodology
7.2.1 The research design
7.3 Recommendations for further research
7.4 General implications of the study and concluding remarks
