HA Final
1. Real-Ear Unaided Response (REUR)
Definition: The sound level in the ear canal when no hearing aid is worn.
SPL in the open (unaided).
The SPL measured inside the ear canal without a hearing aid. It is the baseline measure of sound level in the unaided ear.
Purpose: Serves as a baseline measure of the ear canal's natural resonance.
Measurement:
A probe microphone is placed in the ear canal.
A calibrated sound source plays a stimulus, and the response is recorded.
2. Real-Ear Aided Response (REAR)
Definition: The sound level in the ear canal when the hearing aid is worn and turned on.
The SPL is measured inside the ear canal when the hearing aid is in place and turned on.
Purpose: Shows the amplified sound reaching the eardrum with the hearing aid in place.
Measurement:
A probe microphone is placed in the ear canal alongside the hearing aid.
A calibrated sound source plays a stimulus, and the response is measured.
3. Real-Ear Insertion Gain (REIG)
Definition: The difference between the REAG and REUG.
The difference in dB between the gain provided by the hearing aid (REAG) and the natural gain of the unaided ear (REUG). It represents the net gain provided by the hearing aid after considering the ear’s natural amplification.
Purpose: Reflects the actual gain provided by the hearing aid in the ear canal.
Formula:
REIG = REAG - REUG
Measurement:
First measure the REUR, then measure the REAR with the same stimulus.
Subtract REUR from REAR to calculate REIG.
4. Real-Ear to Coupler Difference (RECD)
Definition: The difference in dB sound pressure level (SPL) between the real ear SPL and the 2cc coupler SPL produced by the same transducer driven by the same signal.
Purpose: Accounts for individual ear canal acoustics; often used for pediatric fittings.
Measurement:
Measure SPL in the ear canal with a probe microphone.
Measure SPL in the coupler using the same hearing aid and settings.
Subtract coupler SPL from ear canal SPL.
5. Real-Ear Saturation Response (RESR)
Definition: The maximum output of the hearing aid in the real ear, measured at high input levels.
The REAR obtained using a narrow-band signal at a level high enough to saturate the hearing aid (usually 85 – 90 dB SPL)
Purpose: Ensures the hearing aid does not produce output that could damage hearing.
Measurement:
A probe microphone is placed in the ear canal.
The hearing aid is tested with loud input sounds, and the maximum output is recorded.
Functional Gain: How It Is Measured
1. Definition:
o Functional gain is a behavioral measure comparing unaided thresholds and aided thresholds in a sound field. It shows the hearing improvement provided by the hearing aid.
2. Steps:
o Unaided Testing:
§ Perform pure-tone audiometry in a sound field without the hearing aid.
§ Record unaided hearing thresholds at specific frequencies (250 Hz to 6000 Hz).
o Aided Testing:
§ Fit the patient with a hearing aid.
§ Conduct pure-tone audiometry in the same sound field.
§ Record aided thresholds using the same frequencies as in the unaided test.
o Calculate Functional Gain:
§ Subtract unaided thresholds from aided thresholds at each frequency.
§ Formula:Functional Gain=Unaided Threshold−Aided ThresholdFunctional Gain=Unaided Threshold−Aided Threshold
3. Stimuli Used:
o Narrowband noise (NBN) or warble tones.
4. Advantages:
o Simple and easy for clients to understand.
5. Limitations:
o Subjectivity: Depends on patient response, which introduces variability.
o Time-Consuming: Behavioral measures take longer to complete.
o Compression Effects: May not accurately represent gain if the hearing aid is operating in a compression state
Reasons Not to Solely Rely on Electroacoustic Measures
1. Lack of Behavioral Perspective:
o Electroacoustic measures like Real-Ear Unaided Response (REUR) or Real-Ear Aided Response (REAR) assess the physical performance of a hearing aid but do not evaluate how the hearing aid works for the individual in a real-world setting.
o Functional gain incorporates patient-specific factors like perception, which is critical for evaluating the actual usability of the device.
2. Differences in Individual Ear Canal Acoustics:
o Electroacoustic measures may not account for unique anatomical variations in the ear canal that can affect sound delivery.
o Functional gain considers how sound is perceived by the wearer, addressing individual auditory responses.
3. Validation of Prescriptive Fitting:
o Electroacoustic measures validate whether the hearing aid meets prescribed targets.
o Functional gain tests whether these targets translate into meaningful hearing improvements for the patient.
4. Real-World Conditions:
o Functional gain simulates real-world hearing performance in a sound field, providing insight into practical hearing aid benefits.
o Electroacoustic measures often rely on controlled lab conditions, which might not fully represent real-life listening environments.
5. Compression and Nonlinear Amplification:
o Modern hearing aids use compression technology, which may not be reflected accurately in electroacoustic measures.
o Functional gain reveals how these settings impact the patient's perception.
6. Patient Satisfaction and Counseling:
o Behavioral testing like functional gain allows clinicians to directly involve the patient, helping to manage expectations and adjust the hearing aid for comfort and satisfaction.
When to Use Electroacoustic Measures Alone
Electroacoustic measures are crucial for ensuring that hearing aids function within specified parameters (e.g., output limits, feedback control).
They are preferred for quick verification and troubleshooting without requiring patient feedback.
Conclusion
While electroacoustic measures are indispensable for initial fitting and technical validation, they do not provide insight into how the patient perceives or benefits from the hearing aid in real-life scenarios. Functional gain complements electroacoustic measures by bridging this gap and ensuring optimal hearing aid performance
Microphone Technology Overview
Types of Microphones
1. Omnidirectional Microphones:
o How They Work: Pick up sound equally from all directions.
o Application: Used in quiet environments where spatial awareness is critical.
o Drawback: Amplifies background noise in noisy settings.
2. Directional Microphones:
o How They Work: Focus on sound from the front and reduce noise from the back or sides.
o Mechanism:
§ Utilize time delays (internal and external) to cancel noise from unwanted directions.
§ Acoustic damper in rear port creates internal delay for noise cancellation.
o Application: Improves speech understanding in noisy environments.
Microphone Configurations
1. Two-Port Microphones:
o A single microphone with two inlets (front and rear) to create directionality.
o Diaphragm movement depends on the pressure difference between the two ports.
2. Dual Microphones:
o Use two omnidirectional microphones to enhance directionality.
o Rear microphone signal is delayed and subtracted from the front microphone's output.
o Commonly used in Behind-the-Ear (BTE) and In-the-Ear (ITE) hearing aids.
3. Multi-Microphone Arrays:
o Combine outputs from multiple microphones for advanced directionality.
o Often referred to as “beamformers” to create narrow focus areas.
Two-Port Microphones
Structure:
A single microphone with two openings (ports)—front and rear.
Function:
Sound enters both ports.
The rear port introduces an acoustic delay, which helps cancel out sounds coming from behind the listener.
Application:
Creates a directional pattern by leveraging the difference in sound arrival times and pressure levels between the two ports.
Dual Microphones
Structure:
Two physically separate microphones, each with its own diaphragm and signal processing.
Function:
The front microphone captures sounds in the desired direction.
The rear microphone captures ambient or noise sounds.
Signals from both microphones are processed to subtract rear sounds, creating directionality.
Advantages:
Better noise suppression and flexibility compared to two-port microphones.
Application:
Commonly used in advanced hearing aids for enhanced speech clarity in noisy environments.
Multi-Microphone Arrays
Structure:
Multiple microphones distributed across the hearing aid (or an array).
Function:
Signals from all microphones are combined using beamforming algorithms.
Beamforming creates a focused sensitivity pattern, like a "beam," targeting specific directions.
Advantages:
Extremely precise directionality.
Effective in complex and dynamic noise environments.
Application:
Used in high-end hearing aids or devices for individuals with severe difficulties in noisy environments.
Problems with Microphones in Hearing Aids
1. Susceptibility to Noise
Wind Noise:
Directional microphones can amplify wind noise, making it uncomfortable for the wearer.
Internal Noise:
Microphones may generate internal electrical noise, which could be noticeable in quiet environments.
2. Limited Effectiveness in Complex Environments
Background Noise:
Even directional microphones struggle in environments with multiple noise sources or reverberations.
Localization Challenges:
Directionality may reduce the user’s ability to localize sounds, especially with fixed patterns.
3. Sensitivity to Physical Factors
Debris and Moisture:
Microphones can become clogged with dirt, wax, or moisture, affecting their performance.
Mechanical Damage:
Dropping or mishandling hearing aids can damage the delicate microphone components.
4. Polar Pattern Limitations
Fixed Directionality:
Fixed directional microphones are less effective when the noise source or the speaker moves.
Adaptive Directionality Delays:
Adaptive microphones may lag in adjusting to rapidly changing environments.
5. Acoustic Challenges
Front-to-Back Ratio (FBR) Issues:
Inconsistent FBR in low-end models leads to poor noise suppression.
Feedback Sensitivity:
Poor placement or calibration of microphones can increase susceptibility to feedback.
6. Environmental Dependency
Windy or Humid Conditions:
Environmental factors can degrade microphone sensitivity and reliability.
Background Noise Amplification:
Omnidirectional settings may amplify unwanted sounds in noisy settings, causing discomfort.
Factors that Limit Effectiveness of Directional Microphones
venting negatively affects directivity.
open fits and hearing aids with large vents only maintain directionality in the high frequencies
microphone ports need to be aligned on the horizontal plane!
directional mics reduce low frequency output so need increase amplification of low frequencies to compensate.
Directional Metrics
1. Directivity Index (DI):
o Represents the ratio of sound sensitivity from the front compared to all directions.
o Higher DI: Indicates better directionality, improving speech recognition by 7-10% for every 1 dB increase.
2. Articulation Index-Weighted DI (AI-DI):
o Adjusts DI based on speech frequency importance for intelligibility.
o High AI-DI scores indicate good performance in amplifying critical speech frequencies.
3. Front-to-Back Ratio (FBR):
o Measures sensitivity difference between sounds from the front and rear.
o High FBR values indicate effective noise suppression from the rear.
1. Directivity Index (DI)
Definition: The ratio of a microphone’s sensitivity to sounds from the front versus sounds from all other directions.
Purpose:
Measures how effectively a microphone focuses on the target sound in noisy environments.
Higher DI values indicate better performance in suppressing background noise.
Practical Application:
A DI improvement of 1 dB corresponds to a 7-10% increase in speech recognition in noise.
2. Articulation Index-Weighted Directivity Index (AI-DI)
Definition: A variation of DI that emphasizes the importance of frequencies critical to speech intelligibility.
Purpose:
Provides a more realistic assessment of how well a hearing aid improves speech understanding.
Weights the DI based on speech-dominant frequencies (e.g., 500 Hz to 4000 Hz).
Importance:
Reflects real-world benefits of directional microphones for speech in noise.
Use Case:
Ideal for assessing performance in environments where speech clarity is the primary goal.
3. Front-to-Back Ratio (FBR)
Definition: The sensitivity ratio of a directional microphone to sounds from the front compared to the back.
Purpose:
Quantifies how well a microphone suppresses noise from the rear while amplifying sounds from the front.
Key Feature:
High FBR indicates strong rear noise suppression, enhancing speech clarity in directional settings.
Polar Sensitivity Patterns
1. Cardioid: Maximum sensitivity to sounds in the front, minimal at the back (180° attenuation).
2. Super-Cardioid: Better sensitivity at the rear than cardioid, reduced side sensitivity.
3. Hyper-Cardioid: Increased rear sensitivity compared to super-cardioid (max attentuation at 110° and 250°).
4. Bi-Directional: Equal sensitivity to sounds in the front and back, none at the sides.
Adaptive Directionality
Mechanism: Electronically adjusts polar patterns based on the noise environment.
Features:
Tracks and suppresses moving noise sources.
Adjusts to the optimal directional mode for the listening environment
Comprehensive Breakdown of Prescriptive Measures
Linear/Threshold-Based Algorithms
These algorithms are designed for linear amplification, where the gain provided by the hearing aid is consistent across all input levels. They are simpler in design and rely directly on the patient's audiometric thresholds.
1. Lybarger Half-Gain Rule
· Concept: Gain should be approximately half of the hearing loss at each frequency.
· Example:
o Hearing loss of 50 dB → Gain = 25 dB.
· Application:
o Simple and quick method for initial hearing aid fitting.
· Limitations:
o Does not consider speech intelligibility or loudness perception.
2. Berger Method
· Purpose: Aims to amplify frequencies to approximate normal speech intensity.
· Key Features:
o More gain provided for higher frequencies where speech cues are crucial.
o Considers average speech energy distribution in its calculations.
· Application:
o Focused on restoring audibility for speech signals.
3. POGO (Prescription of Gain and Output)
· Purpose: Builds upon the Half-Gain Rule but introduces a low-frequency reduction.
· Key Features:
o Gain = Half the hearing loss minus 10 dB for low frequencies (below 500 Hz).
o Reduces upward spread of masking to improve clarity of high-frequency sounds.
· Application:
o Effective for patients with moderate hearing loss.
4. Libby Method
· Concept: Similar to the Half-Gain Rule but with additional refinements.
· Key Features:
o Provides more amplification in low frequencies compared to other methods.
o Focuses on restoring loudness perception.
· Application:
o Particularly useful for patients with specific loudness deficits.
Suprathreshold-Based Methods for Nonlinear Hearing Aids
These methods account for varying input levels (soft, moderate, and loud sounds) and provide gain adjustments accordingly. They aim to optimize speech intelligibility and comfort in real-world listening environments.
1. Fig 6
· Purpose: Provides gain for different levels of input (soft, moderate, loud).
· Key Features:
o Gain values are derived from loudness growth data.
o Focuses on natural loudness perception for all input levels.
· Application:
o Emphasizes a balanced approach to soft and loud sound amplification.
o Less commonly used today but forms the foundation for modern nonlinear prescriptive methods.
2. IHAFF (Independent Hearing Aid Fitting Formula)
· Purpose: Loudness normalization across frequencies.
· Key Features:
o Restores loudness perception so that soft sounds are audible, moderate sounds are comfortable, and loud sounds remain tolerable.
o Uses loudness growth data specific to the individual.
· Application:
o Suitable for individuals transitioning from linear to nonlinear hearing aids.
3. DSL I/O (Desired Sensation Level Input/Output)
· Purpose: Focused on ensuring audibility and comfort for users of nonlinear hearing aids, especially children.
· Key Features:
o Emphasizes speech audibility across a range of input levels.
o Considers real-ear-to-coupler difference (RECD) to account for individual ear canal acoustics.
o Provides age-specific targets for gain and output.
· Application:
o Widely used in pediatric fittings to ensure optimal speech development.
4. NAL-NL1 (National Acoustic Laboratories Nonlinear 1)
· Purpose: Maximizes speech intelligibility while maintaining overall loudness comfort.
· Key Features:
o Focuses on balancing audibility and loudness across frequencies.
o Prioritizes speech understanding over full loudness restoration.
· Application:
o Suitable for adult fittings with nonlinear hearing aids.
5. NAL-NL2
· Purpose: An updated version of NAL-NL1 with additional user-specific considerations.
· Key Features:
o Adjusts for factors like:
§ Binaural Fittings: Reduces gain to prevent overamplification for users with bilateral hearing aids.
§ Age: Provides less gain for older adults sensitive to loudness.
§ Experience: Gradual gain for new users to help them adapt.
o Improves comfort and user satisfaction.
· Application:
o Commonly used for adult fittings; integrates advanced fitting parameters.
Proprietary Hearing Aid Company Algorithms
· Definition: Algorithms developed by hearing aid manufacturers to optimize performance for their specific devices.
· Purpose: Enhance speech intelligibility, comfort, and user satisfaction by leveraging unique signal processing capabilities of the company's technology.
Examples of Proprietary Algorithms
1. Oticon VAC+ (Voice Aligned Compression Plus):
o Designed to improve speech clarity while maintaining natural sound.
o Adapts dynamically to the listening environment.
o Focuses on speech sounds by emphasizing important frequencies.
2. Phonak Adaptive Phoneme Perception (APD):
o Tailors amplification based on phoneme audibility for speech clarity.
o Integrates directional microphones and noise suppression for noisy environments.
o Balances audibility with user comfort.
3. Widex Universal Algorithm:
o Prioritizes natural sound reproduction.
o Focuses on enhancing sound in real-time, minimizing distortion.
o Includes features for reducing wind noise and sudden loud sounds.
4. Signia Nx (Own Voice Processing):
o Unique feature that distinguishes the wearer’s voice from external sounds.
o Reduces the occlusion effect by processing the user’s voice separately.
5. Starkey eSTAT:
o Utilizes environmental classification to adjust amplification dynamically.
o Focuses on maximizing speech intelligibility across various environments.
o Includes features like tinnitus masking and feedback cancellation.
Key Features of Proprietary Algorithms
1. Environment Adaptation:
o Algorithms adjust gain and compression settings based on detected sound environments (e.g., quiet, noisy, or music).
2. Speech Enhancement:
o Emphasizes critical speech frequencies for better understanding.
3. Noise Reduction:
o Suppresses unwanted background noise to improve comfort.
4. Binaural Synchronization:
o Coordinates settings between bilateral hearing aids for a seamless listening experience.
5. Feedback Cancellation:
o Prevents or minimizes whistling sounds caused by feedback loops.
Advantages of Proprietary Algorithms
· Custom-Tuned: Designed specifically for the brand’s hardware and processing capabilities.
· User-Focused: Incorporates unique features based on user needs (e.g., tinnitus relief, wind noise suppression).
· Dynamic Adjustments: Adapt to changing environments in real-time, improving user experience.
Limitations
· Lack of Standardization: Proprietary algorithms are specific to each manufacturer, making cross-brand comparisons difficult.
· Transparency: Limited access to detailed information about algorithm workings.
SPL-o-Grams
· Definition: A visual representation of sound pressure levels (SPL) within the ear canal across different frequencies, displayed on an audiogram-like graph.
· Purpose:
o Validate the performance of hearing aids.
o Compare unaided thresholds, aided thresholds, and amplified speech signals.
o Ensure speech audibility across the frequency range.
Components of an SPL-o-Gram
1. Input Levels:
o Displays soft, moderate, and loud inputs (e.g., 50 dB, 65 dB, 80 dB).
2. Frequency Range:
o Typically covers 250 Hz to 8000 Hz.
3. Audibility Range:
o Highlights the area where speech sounds should be amplified for effective hearing.
Key Features
1. Unaided Thresholds:
o The hearing levels of the individual without amplification.
2. Aided Thresholds:
o The hearing levels achieved with the hearing aid.
3. Speech Spectrum Overlay:
o Illustrates where speech sounds fall in the audibility range.
o Ensures critical speech sounds are audible while maintaining comfort for louder sounds.
Applications
1. Pediatric Fittings:
o Ensures speech audibility critical for language development.
2. Validation:
o Confirms that hearing aid amplification aligns with prescriptive targets.
3. Fine-Tuning:
o Helps identify and adjust frequency bands that may be over- or under-amplified.
Benefits
· Provides a clear visual representation of hearing aid performance.
· Ensures critical speech frequencies are audible and comfortable.
· Facilitates communication between audiologists and patients/parents by making data more accessible.
Troubleshooting
1. Determining Internal vs. External Feedback
· Feedback: A whistling or squealing sound caused by amplified sound re-entering the microphone.
Internal Feedback:
· Cause:
o Malfunctioning internal components.
o Loose or damaged microphones or receivers.
· How to Identify:
o Test the hearing aid outside the ear (e.g., in a quiet space).
o If feedback occurs when the device is off the ear, it's likely internal.
· Solution:
o Send the hearing aid for repair or replacement.
External Feedback:
· Cause:
o Sound leakage from the earmold or hearing aid shell.
o Poor fit or venting issues.
· How to Identify:
o Occurs only when the device is in or near the ear.
· Solution:
o Refit or modify the earmold.
o Use feedback suppression features or increase vent size cautiously.
2. Adjusting Compression Characteristics
Compression settings help manage the range of sound levels, making soft sounds audible and loud sounds comfortable.
Common Adjustments:
1. Compression Ratio:
o Higher ratios reduce the amplification of loud sounds more aggressively.
o Lower ratios preserve natural sound quality.
2. Knee Point:
o The input level at which compression begins.
o Lower knee points improve audibility for softer sounds.
3. Attack and Release Times:
o Attack Time: The speed at which compression activates.
o Release Time: The speed at which compression deactivates.
o Adjust to balance comfort and clarity for rapidly changing sounds.
When to Adjust:
· Patient Complaint: "Loud sounds are uncomfortable."
o Increase the compression ratio or lower the output limit.
· Patient Complaint: "Soft sounds are inaudible."
o Lower the compression threshold or reduce the compression ratio.
3. Gain Adjustments for Patient Complaints
Low-Frequency Gain Changes:
· Common Complaints:
o "My own voice sounds boomy or hollow." (Occlusion effect)
o "I hear too much background noise."
· Solutions:
o Reduce low-frequency gain.
o Increase venting size (if physically feasible).
High-Frequency Gain Changes:
· Common Complaints:
o "Speech sounds sharp or harsh."
o "I hear a whistling sound or feedback."
· Solutions:
o Reduce high-frequency gain.
o Adjust feedback cancellation settings.
Overall Gain Changes:
· Common Complaints:
o "Everything sounds too loud." (Overamplification)
o "I can’t hear speech well enough." (Underamplification)
· Solutions:
o For too loud: Reduce overall gain or increase compression.
o For speech clarity issues: Fine-tune mid-frequency gain (e.g., 500 Hz to 4000 Hz).
4. Patient Counseling
· Ensure patients understand the limitations and adjustment processes of hearing aids.
· Encourage realistic expectations for adapting to amplification.
Hearing Aid Candidacy
Who is a Candidate?
1. Adults:
o Hearing Loss: Mild to profound sensorineural, conductive, or mixed losses.
o Impact: Difficulty understanding speech in quiet or noisy environments.
o Motivation: Willingness to use and adapt to hearing aids.
2. Children:
o Hearing Loss: Any degree of loss impacting speech and language development.
o Parental Involvement: Crucial for monitoring and ensuring consistent use.
3. Other Considerations:
o Medical Clearance: Required for patients with conductive or asymmetrical losses (rule out retrocochlear pathology).
o Lifestyle Needs: Evaluates environments such as work, social, or leisure.
Fitting Hearing Aids
1. Assessment and Selection:
o Hearing Evaluation: Includes audiometry and speech testing to determine degree and type of hearing loss.
o Style Selection: Based on hearing loss, ear anatomy, and user preference (e.g., CIC, BTE, RIC).
o Prescriptive Formula: Choose from NAL-NL2, DSL I/O, or manufacturer algorithms for initial settings.
2. Fitting Asymmetrical Hearing Loss:
o CROS (Contralateral Routing of Signal):
§ Used for one ear with no hearing and one ear with normal hearing.
§ Routes sound from the poorer side to the better ear.
o BICROS (Bilateral Contralateral Routing of Signal):
§ Used for one "dead" ear and one with some hearing loss.
§ Amplifies sound for the better ear while routing sound from the poorer side.
o Bilateral Fitting:
§ For patients with asymmetrical losses where both ears benefit from amplification.
§ Adjust gain and compression settings independently for each ear.
Fine-Tuning Hearing Aids
1. Initial Programming:
o Based on prescriptive formulas and real-ear measurements.
o Adjustments made for audibility and comfort.
2. Patient Feedback:
o Complaints: "Speech is unclear" → Increase mid-frequency gain.
o "Background noise is overwhelming" → Adjust noise reduction and compression settings.
o "Soft sounds are inaudible" → Lower compression thresholds.
3. Real-Ear Measures (REM):
o Verify the hearing aid output matches prescriptive targets in the ear canal.
4. Fitting Asymmetry:
o Ensure balance between ears to avoid spatial disorientation.
o Use real-world speech tests to validate improvements in binaural speech understanding.
5. Follow-Up Appointments:
o Fine-tune settings based on real-world use.
o Address patient-specific needs as they adapt to the devices.
Key Considerations
· Counseling:
o Manage expectations: Hearing aids restore audibility but do not replicate normal hearing.
o Educate patients on device care and maintenance.
· Trial Period:
o Most fitting protocols include a trial period for adjustments and user adaptation.
Cochlear Dead Regions
1. Definition:
o Areas in the cochlea where inner hair cells (IHCs) and/or associated neurons are non-functional.
o These regions do not respond to acoustic stimulation, even with amplified sound.
2. Causes:
o Sensorineural hearing loss due to damage from noise exposure, aging, or ototoxic medications.
3. Characteristics:
o Speech and sound become distorted, even with amplification.
o Listeners may struggle with frequency discrimination in the affected areas.
TEN (Threshold Equalizing Noise) Test
1. Purpose:
o Identifies cochlear dead regions.
o Helps determine if hearing loss in specific frequencies is due to dead regions rather than reduced sensitivity.
2. How It Works:
o A narrowband noise is presented alongside a pure tone at the same frequency.
o If the patient cannot detect the tone despite sufficient amplification, a dead region is suspected.
o Criteria:
§ Tone threshold >10 dB above the masking noise level.
§ Indicates that amplification at this frequency will not improve speech intelligibility.
Implications for Hearing Aid Fitting
1. Avoid Over-Amplification:
o Amplifying frequencies corresponding to dead regions can result in distortion and discomfort.
o Focus on adjacent frequencies with functional hair cells (off-frequency listening).
2. Frequency Compression/Transposition:
o Shifts high-frequency sounds into lower, more accessible frequencies.
o Helps improve speech understanding for patients with high-frequency dead regions.
3. Realistic Expectations:
o Counsel patients that hearing aids cannot restore hearing in dead regions.
o Emphasize the importance of using visual cues and communication strategies.
4. Prescriptive Adjustments:
o Modify gain and output to avoid amplifying ineffective frequencies.
o Use wide dynamic range compression (WDRC) to enhance audible sounds.
5. Alternative Interventions:
o For severe dead regions, consider cochlear implants instead of hearing aids.
Key Considerations
· Patient Counseling:
o Ensure patients understand the limitations and adaptations required for optimal use.
· Validation:
o Use speech tests and patient feedback to confirm improvements in real-world listening environments.
Binaural Amplification
· Definition: The use of hearing aids in both ears for individuals with bilateral hearing loss.
· Purpose: Restores auditory input to both ears to improve sound quality, speech understanding, and spatial awareness.
1. Binaural Summation
· Definition: The improvement in loudness perception and clarity when sound is heard by both ears simultaneously.
· Mechanism:
o The auditory system integrates signals from both ears, enhancing perception.
· Benefits:
o Requires less amplification compared to monaural fitting (3-10 dB less gain needed).
o Increases the perceived volume and richness of sound.
2. Localization
· Definition: The ability to determine the direction and distance of a sound source.
· Mechanism:
o Interaural Time Differences (ITD): Sounds reach one ear slightly earlier than the other, helping localize low-frequency sounds.
o Interaural Level Differences (ILD): Sounds are louder in the ear closer to the source, aiding in localizing high-frequency sounds.
· Benefits:
o Helps distinguish speech from background noise.
o Critical for safety in identifying approaching dangers or movement.
3. Binaural Advantage
· Definition: The overall benefit derived from using both ears for hearing.
· Components:
1. Binaural Redundancy:
§ The brain receives duplicate signals from both ears, improving speech understanding, especially in noise.
2. Binaural Squelch:
§ The brain suppresses unwanted noise using interaural differences, improving speech clarity.
3. Spatial Release from Masking:
§ Improved ability to separate speech from background noise based on spatial cues.
· Benefits:
o Enhanced speech perception in complex environments.
o Reduced listening effort and fatigue.
Clinical Implications
· Fitting:
o Both hearing aids should be programmed and balanced for symmetrical performance.
o Gain adjustments may be needed to prevent over-amplification from binaural summation.
· Patient Counseling:
o Emphasize the benefits of binaural amplification for clarity, comfort, and spatial awareness.
o Discuss adaptation periods, as the brain may need time to integrate binaural input effectively.
Scenario 1: Mild to Moderate Sensorineural Hearing Loss
· Audiogram: Gradual slope from mild loss in low frequencies to moderate loss in high frequencies.
· Speech Testing: Good WRS in quiet but difficulty in noise.
· Recommendation:
o Type of Hearing Aid: Receiver-in-Canal (RIC) or Behind-the-Ear (BTE).
o Reason:
§ Discrete and suitable for progressive high-frequency loss.
§ Provides flexibility for adjustments as the loss progresses.
§ Directional microphones enhance speech clarity in noise.
Scenario 2: Severe to Profound Hearing Loss
· Audiogram: Flat severe to profound loss across all frequencies.
· Speech Testing: Poor WRS even at amplified levels.
· Recommendation:
o Type of Hearing Aid: Power BTE or Cochlear Implant (if criteria are met).
o Reason:
§ BTE provides maximum gain and output for residual hearing.
§ Cochlear Implant recommended if residual hearing provides no benefit, as it bypasses damaged hair cells.
Scenario 3: Asymmetrical Hearing Loss
· Audiogram: Normal hearing in one ear and profound loss in the other.
· Speech Testing: Difficulty localizing sound and understanding speech from the poorer side.
· Recommendation:
o Type of Hearing Aid: CROS or BICROS system.
o Reason:
§ Routes sound from the non-hearing ear to the hearing ear, improving awareness and localization.
Scenario 4: Conductive Hearing Loss
· Audiogram: Air-bone gap with normal bone conduction thresholds.
· Speech Testing: Good WRS with amplification.
· Recommendation:
o Type of Hearing Aid: Bone-Conduction Hearing Aid or BAHA (Bone-Anchored Hearing Aid).
o Reason:
§ Directly stimulates the cochlea via bone conduction, bypassing the conductive pathway.
Scenario 5: Pediatric Patient
· Audiogram: Moderate to severe hearing loss bilaterally.
· Speech Testing: Delayed speech development.
· Recommendation:
o Type of Hearing Aid: BTE with DSL I/O fitting formula.
o Reason:
§ Provides flexibility for growth.
§ Ensures speech audibility crucial for language development.
Study Overview
· Title: Hearing Aid Technology and Speech-in-Noise Difficulties.
· Authors: Davidson et al.
· Purpose:
o To explore if there is a relationship between hearing aid feature settings and a patient’s speech-in-noise (SIN) score.
o To analyze how advanced hearing aid features, such as directionality and digital noise reduction (DNR), are applied in clinical practice and their effectiveness.
Why the Study Was Done
1. Current Challenges:
o Speech-in-noise recognition is a major challenge for hearing aid users.
o Lack of standardized protocols for assigning hearing aid features based on SIN scores.
2. Specific Gaps:
o No published guidelines for using features like DNR or hearing assistive technologies (HAT) tailored to SIN difficulties.
Main Findings
1. Directionality and SIN Difficulty:
o A statistically significant relationship was found between directionality settings and SIN difficulty:
§ Fixed directionality was associated with severe and moderate SIN difficulty.
§ Adaptive directionality was more beneficial for mild SIN difficulty.
o Omnidirectional settings did not align with SIN severity for effective outcomes.
2. Digital Noise Reduction (DNR):
o No significant relationship was detected between DNR settings and SIN difficulty.
o The lack of significance may be due to high usage rates of DNR across all patients, regardless of SIN difficulty:
§ 89% for normal, mild, and moderate difficulty.
§ 77% for severe difficulty.
3. Hearing Assistive Technologies (HAT):
o No statistical relationship found between HAT use and SIN scores.
o Likely due to low adoption rates among patients.
Clinical Implications
1. Standardization Needs:
o Clear protocols for fitting hearing aids based on SIN scores are lacking.
o The study highlights the need to tailor hearing aid settings more systematically.
2. Feature-Specific Recommendations:
o Directionality:
§ Fixed directionality may benefit those with severe SIN difficulty.
§ Adaptive settings are preferable for mild SIN difficulty.
o DNR and HAT:
§ Their impact needs further investigation to establish practical recommendations.
3. Audiologist Practices:
o Insights into how audiologists make fitting decisions could improve patient outcomes.
Future Research Directions
1. Digital Noise Reduction (DNR):
o Explore how different DNR settings affect SIN outcomes.
o Investigate why high DNR usage did not correlate with improved SIN scores.
2. Hearing Assistive Technologies (HAT):
o Study barriers to adoption and their potential benefits in SIN scenarios.
3. QuickSIN and AAA Recommendations:
o Compare fitting outcomes when based on:
§ QuickSIN score-driven recommendations.
§ Audiologist-patient interaction outcomes.
4. Audiologist Decision-Making:
o Conduct surveys to understand how audiologists decide which advanced features to activate.
o Include notes on individual fitting practices and their alignment with clinical recommendations.