Cochlear Hearing Loss

Chapter 1. Physiological Aspects of Cochlear Hearing Loss.

I. INTRODUCTION.

II.LINEAR AND NONLINEAR SYSTEMS.

III. STRUCTURE AND FUNCTION OF THE OUTER AND MIDDLE EAR.

IV. STRUCTURE AND FUNCTION OF THE NORMAL COCHLEA.

1. The cochlea, the basilar membrane and the organ of Corti.
2. Tuning on the basilar membrane.
3. The nonlinearity of input-output functions on the BM.
4. Two-tone suppression.
5. Combination tone generation.
6. Responses of the BM to complex sounds.
7. Otoacoustic emissions.

V. NEURAL RESPONSES IN THE NORMAL AUDITORY NERVE.

1. Spontaneous firing rates and thresholds.
2. Tuning curves and iso-rate contours.
3. Rate-versus-level functions.
4. Two-tone suppression.
5. Phase locking.

VI. TYPES OF HEARING LOSS.

VII. PHYSIOLOGY OF THE DAMAGED COCHLEA.
 
1. BM responses.
2. Neural responses.
3. Structure-function correlation.
4. Otoacoustic emissions.
5. Phase locking.

VIII. CONCLUSIONS.

Chapter 2. Absolute Thresholds.

I.  INTRODUCTION.

II. MEASURES OF ABSOLUTE THRESHOLD.

1.  Minimum audible pressure (MAP).
2.  Minimum audible field (MAF).
3.  Comparison of MAP and MAF.
4. The audiogram.

III. DESCRIPTIONS OF THE SEVERITY OF HEARING LOSS.

IV.  CAUSES OF HEARING LOSS DUE TO COCHLEAR DAMAGE.

V. PERCEPTUAL CONSEQUENCES OF ELEVATED ABSOLUTE THRESHOLDS.

Chapter 3. Masking, Frequency Selectivity and BM Nonlinearity.

I.  INTRODUCTION.

II.  THE MEASUREMENT OF FREQUENCY SELECTIVITY USING MASKING.

1. Introduction.
2. The power spectrum model.
3. Estimating the shape of a filter.

III.  ESTIMATING FREQUENCY SELECTIVITY FROM MASKING EXPERIMENTS.

1. Psychophysical tuning curves.
2. The notched-noise method.

IV. CHARACTERISTICS OF THE AUDITORY FILTER IN NORMAL HEARING.

1. Variation with centre frequency.
2. Variation with level.
3. Summary.

V. MASKING PATTERNS AND EXCITATION PATTERNS.

1. Masking patterns.
2. Relationship of the auditory filter to the excitation pattern.
3. Changes in excitation patterns with level.
4. Possible effects of suppression.

VI. NON-SIMULTANEOUS MASKING.

1. Basic properties of non-simultaneous masking.
2. Evidence for suppression from non-simultaneous masking.
3. The enhancement of frequency selectivity revealed in non-simultaneous masking.
4. Relation between the growth of forward masking and the BM input-output function.

VII. THE AUDIBILITY OF PARTIALS IN COMPLEX TONES.

VIII. EFFECTS OF COCHLEAR DAMAGE ON FREQUENCY SELECTIVITY IN SIMULTANEOUS MASKING.

1. Complicating factors.
2. Psychophysical tuning curves.
3. Auditory filter shapes measured with notched noise.

IX. THE USE OF MASKING TO DIAGNOSE DEAD REGIONS.
 
1. The TEN test.
2. The TEN(HL) test.
3. Prevalence of dead regions assessed using the TEN(HL) test.

X. EFFECTS OF COCHLEAR DAMAGE ON FORWARD MASKING AND SUPPRESSION .

XI.  EFFECTS OF COCHLEAR HEARING LOSS ON BM INPUT-OUTPUT FUNCTIONS.

XII. PERCEPTUAL CONSEQUENCES OF REDUCED FREQUENCY SELECTIVITY, LOSS OF SUPPRESSION AND STEEPER BM INPUT-OUTPUT FUNCTIONS.
 
1. Susceptibility to masking.
2. Timbre perception.
3. Perceptual consequences of dead regions.

Chapter 4. Loudness Perception and Intensity Resolution.

I. INTRODUCTION.

II. LOUDNESS PERCEPTION FOR NORMALLY HEARING PEOPLE.

1. Equal-loudness contours and loudness level.
2. The scaling of loudness.
3. The detection of intensity changes.

III.  EFFECTS OF COCHLEAR HEARING LOSS ON LOUDNESS PERCEPTION.

IV.  A MODEL OF NORMAL LOUDNESS PERCEPTION.

V.  A MODEL OF LOUDNESS PERCEPTION APPLIED TO COCHLEAR HEARING LOSS.

1. Introduction.
2. Elevation of absolute threshold.
3. Reduced compressive nonlinearity.
4. Reduced IHC/neural function.
5. Reduced frequency selectivity.
6. Complete loss of functioning IHCs or neurones (dead regions).
7. Using the model to account for loudness recruitment.

VI. EFFECTS OF BANDWIDTH ON LOUDNESS .
 
1. Normal hearing.
2. Impaired hearing.

VII. EFFECTS OF COCHLEAR HEARING LOSS ON INTENSITY RESOLUTION.

VIII. PERCEPTUAL CONSEQUENCES OF ALTERED LOUDNESS PERCEPTION.

1. Consequences of loudness recruitment and reduced dynamic range.
2. Perceptual consequences of reduced loudness summation.
3. Perceptual consequences of altered intensity discrimination.

Chapter 5. Temporal Resolution and Temporal Integration.

I. INTRODUCTION.

II. MODELLING WITHIN-CHANNEL TEMPORAL RESOLUTION IN NORMAL HEARING.

1. Bandpass filtering.
2. The nonlinearity.
3. The sliding temporal integrator.
4. The decision device.
5. Characterising the nonlinear device and the sliding temporal integrator.

III.  TEMPORAL RESOLUTION IN NORMAL HEARING.

1. The effect of centre frequency on gap detection.
2.  Temporal modulation transfer functions.
3. The rate of recovery from forward masking.

IV. TEMPORAL RESOLUTION IN PEOPLE WITH COCHLEAR DAMAGE.

1. The influence of sound level on gap detection and the rate of decay of forward masking.
2. The influence of audible bandwidth on TMTFs and gap detection.
3. The influence of changes in the compressive nonlinearity.

V. TEMPORAL INTEGRATION AT THRESHOLD.

1. Temporal integration in normally hearing people.
2. Temporal integration in people with cochlear hearing loss.
3. Explanations for reduced temporal integration in people with cochlear hearing loss.

VI.  TEMPORAL INTEGRATION AT SUPRATHRESHOLD LEVELS.

VII. PERCEPTUAL CONSEQUENCES OF ABNORMAL TEMPORAL PROCESSING IN PEOPLE WITH COCHLEAR HEARING LOSS.

1. Consequences of abnormal temporal resolution.
2. Consequences of reduced temporal integration.

Chapter 6.  Pitch Perception and Frequency Discrimination.

I.  INTRODUCTION.

II.  THEORIES OF PITCH PERCEPTION.

III.  THE PERCEPTION OF THE PITCH OF PURE TONES BY NORMALLY HEARING PEOPLE.

1. The frequency discrimination of pure tones.
2. The perception of musical intervals.
3. The effect of level on pitch.

IV. FREQUENCY DISCRIMINATION OF PURE TONES BY PEOPLE WITH COCHLEAR HEARING LOSS.
 
1. Difference limens for frequency (DLFs).
2. Frequency modulation detection limens (FMDLs).

V.  THE PERCEPTION OF PURE-TONE PITCH FOR FREQUENCIES FALLING IN A DEAD REGION.

VI. PITCH ANOMALIES IN THE PERCEPTION OF PURE TONES.

VII. THE PITCH PERCEPTION OF COMPLEX TONES BY NORMALLY HEARING PEOPLE.

1. The phenomenon of the missing fundamental.
2. Discrimination of the repetition rate of complex tones.

VIII. THEORIES OF PITCH PERCEPTION FOR COMPLEX TONES.
 
1. The representation of a complex tone in the peripheral auditory system.
2. Spectro-temporal pitch theories.
3. The relative importance of envelope and temporal fine structure.

IX.  PITCH PERCEPTION OF COMPLEX TONES BY PEOPLE WITH COCHLEAR HEARING LOSS.

1. Theoretical considerations.
2. Experimental studies.

X. PERCEPTUAL CONSEQUENCES OF ALTERED FREQUENCY DISCRIMINATION AND PITCH PERCEPTION.
1. Effects on speech perception.
2. Effects on music perception.

Chapter 7.  Spatial Hearing and Advantages of Binaural Hearing.

I. INTRODUCTION.

II. THE LOCALISATION OF SINUSOIDS.

1. Cues for localisation.
2. Performance of normally hearing people in localisation and lateralisation.
3. Performance of hearing-impaired people in localisation and lateralisation.

III. THE LOCALISATION OF COMPLEX SOUNDS.

1. The role of transients and across-frequency comparisons.
2.  Performance of normally hearing people.
3. Performance of people with cochlear hearing loss.
4. Reasons for large ITD and IID thresholds in people with cochlear hearing loss.

IV. THE CONE OF CONFUSION, HEAD MOVEMENTS, AND PINNA CUES.

1.  The cone of confusion.
2. The role of head movements.
3. Information provided by the pinnae.
4. Localisation using pinna cues by normal and hearing-impaired people.

V. GENERAL CONCLUSIONS ON SOUND LOCALISATION.

VI. THE PRECEDENCE EFFECT.
 
1. The precedence effect for normal hearing.
2. The precedence effect for impaired hearing.

VII. BINAURAL MASKING LEVEL DIFFERENCES (MLDS).

1. MLDs for normally hearing people.
2. Mechanisms underlying MLDs.
3. MLDs for people with cochlear hearing loss.
4. Possible reasons for smaller MLDs in people with cochlear damage.

VIII. HEAD SHADOW EFFECTS.

1. Benefits of head shadow for normally hearing people.
2. Benefits of head shadow for hearing-impaired people.

IX. RELEASE FROM INFORMATIONAL MASKING.

X. DIOTIC ADVANTAGES.

XI. PERCEPTUAL CONSEQUENCES OF ABNORMAL BINAURAL AND SPATIAL HEARING IN PEOPLE WITH COCHLEAR DAMAGE.

Chapter 8.  Speech Perception.

I.  INTRODUCTION.

II. THE MAGNITUDE OF THE NOISE PROBLEM.

III. THE ROLE OF AUDIBILITY.

1. The Articulation Index and Speech Intelligibility Index.
2. Use of the AI or SII to predict speech intelligibility for the hearing impaired.
3. The intelligibility of speech in noise at high overall levels.
4. Comparison of detection and recognition for speech in noise.
5. The intelligibility of speech in quiet at high overall levels.
6. Simulation of hearing loss by selective filtering (frequency-dependant attenuation).
7. Simulation of hearing loss by masking.
8. Comparison of speech intelligibility for conductive and cochlear losses.
9. Conclusions on the role of audibility.

IV. INFLUENCE OF DEAD REGIONS ON SPEECH PERCEPTION.

V. CORRELATION BETWEEN PSYCHOACOUSTIC ABILITIES AND SPEECH PERCEPTION.

VI. ASSESSING THE EFFECTS OF FREQUENCY SELECTIVITY ON VOWEL AND CONSONANT PERCEPTION.
 
1. Consonant perception.
2. Vowel perception.

VII. INFLUENCE OF LOSS OF SENSITIVITY TO TEMPORAL FINE STRUCTURE.

VIII. THE USE OF SIMULATIONS TO ASSESS THE IMPORTANCE OF PSYCHOACOUSTIC FACTORS IN SPEECH PERCEPTION.
 
1. Simulations of loudness recruitment combined with threshold elevation.
2. Simulations of reduced frequency selectivity.
3. Simulation of the combined effects of threshold elevation, recruitment and reduced frequency selectivity.
4. Simulation of reduced temporal resolution.

IX. CONCLUSIONS.

Chapter 9.  Hearing Aids.

I. INTRODUCTION.

II. LINEAR AMPLIFICATION.

1. The difficulty of restoring audibility using linear aids.
2. Prescriptive fitting rules for linear hearing aids.

III. COMPRESSION AMPLIFICATION.
 
1. Basic characteristics of AGC systems.
2. Varieties of AGC systems.
3. Rationales for the use of multi-band compression (and noise reduction).
4. Research on the effectiveness of multi-band syllabic compression.
5. Methods of initial fitting of hearing aids with multi-band compression.
6. Methods for fine tuning hearing aids with multi-band compression.
7. Slow-acting AGC systems.
8. Comparisons of ssslow-acting and fast-acting systems.
9. General conclusions about compression.

IV. SOME GENERAL PROBLEMS WITH HEARING AIDS.
 
1. Inadequate gain at high frequencies.
2. Acoustic feedback.
3. Peakiness of frequency response.
4. The occlusion effect.
5. Time delays.

V. METHODS FOR IMPROVING THE SPEECH-TO-NOISE RATIO.

1. Multi-channel noise reduction.
2. Directional microphones.
3. Binaural processing algorithms.

VI. TRANSPOSITION AIDS FOR SEVERE AND PROFOUND HEARING LOSS.

VII. COCHLEAR IMPLANTS.

VIII. CONCLUDING REMARKS.

Glossary.
References.