Understanding Spatial and Asymmetrical Hearing Loss: Causes, Symptoms, and Treatment

Hearing loss affects millions of people, with varying degrees and types of impairment. Among these, spatial hearing loss and asymmetrical hearing loss present unique challenges. This article delves into the specifics of these conditions, exploring their causes, symptoms, and available treatment options. Understanding these nuances is crucial for timely diagnosis and effective management, ultimately improving the quality of life for those affected.

Defining Hearing Loss

Before discussing asymmetrical hearing loss, it's important to understand some terms commonly used to describe a patient’s hearing thresholds.

Hearing Threshold: The quietest level of sound a person can hear at least 50% of the time.
Degree of Hearing Loss: Categorizes the severity of hearing impairment based on decibel (dB) levels measured during pure tone audiometry.
Unilateral Hearing Loss: Occurs in one ear.
Bilateral Hearing Loss: Affects both ears.
Sensorineural Hearing Loss: Results from damage to the inner ear or the auditory nerve, often caused by aging, noise exposure, or certain medical conditions. Tiny receptors in your inner ear called hair cells are damaged. These hair cells are responsible for converting sound waves into signals that your brain interprets as sound. Unfortunately, these cells can’t repair themselves, making SNHL a permanent condition in most cases. But wearing hearing aids or other hearing devices can greatly improve your hearing and quality of life.
Conductive Hearing Loss: Occurs when there is a problem with the outer or middle ear that prevents sound from being conducted to the inner ear, which might be due to ear infections, fluid in the middle ear, or earwax buildup.

Asymmetrical Hearing Loss

An asymmetrical hearing loss is noted when the degree of hearing loss differs between ears. The degree of difference at which to note an asymmetrical hearing loss was first defined by the AAO-HNS (1993, 1994), as a difference of 15 dB or more in air-conduction pure-tone average (PTA) at frequencies of 500, 1000, 2000, and 3000 Hz between the ears. The AAO-HNS reaffirmed this definition in 2015, but without specifying test frequencies. Should any of the above be noted, audiologists may refer the patient to an ENT or ear, nose, and throat doctor.

Recognizing Symptoms

Recognizing the symptoms of asymmetrical hearing loss is crucial for timely diagnosis and treatment. This condition is characterized by a noticeable difference in hearing ability between the two ears. Key signs to watch for include a noticeable decrease in hearing in one ear, difficulty understanding speech on one side, and a sudden need to increase the volume of audio devices. Other symptoms may include tinnitus (ringing in the ears), dizziness, or a feeling of fullness in the affected ear.

Additional symptoms include:

Difficulty Locating Sounds: Individuals may struggle to determine the direction from which sounds are coming.
Uneven Hearing Perception: One ear may hear sounds more clearly than the other, leading to an unbalanced auditory experience.
Speech Understanding Issues: People with asymmetrical hearing loss often have difficulty understanding speech, especially in environments with background noise.
Tinnitus: Ringing, buzzing, or other phantom sounds in one ear can be a symptom of asymmetrical hearing loss.

Individuals with asymmetrical hearing loss often face significant challenges when trying to hear in environments with background noise, even when one ear has normal hearing. This difficulty arises because the disparity in hearing ability between the ears affects the brain’s ability to process sounds effectively.

As noted above, individuals with asymmetrical hearing loss often exhibit difficulty with sound localization. In a noisy environment, determining where a sound is coming from relies on both ears working together to provide spatial cues. Additionally, background noise can mask speech, making it harder to understand conversations, especially in social settings, restaurants, or crowded places where multiple conversations and ambient noises occur simultaneously. The brain struggles to filter out the background noise and focus on the speech, leading to frustration and communication difficulties.

People with asymmetrical hearing loss may subconsciously or consciously rely more on their better-hearing ear, turning their head to favor the stronger ear. In noisy environments, the poorer-hearing ear may contribute little to no useful auditory input, especially for individuals with poor speech understanding (measured by WRS) in that ear. This can lead to a reduction in overall sound quality and speech intelligibility.

In some individuals a process known as “binaural interference” may occur. Binaural interference is defined as worse speech understanding with both ears than with just the better ear alone. This reduced ability to integrate sound from both ears means that even with amplification, understanding speech in noise remains difficult.

These challenges highlight the importance of seeking professional help for asymmetrical hearing loss. Audiologists can recommend hearing aids, assistive listening devices, or auditory training programs designed to improve hearing in noisy environments.

Asymmetrical sensorineural hearing loss affects both ears, but hearing loss is worse in one ear.

Audiograms and Asymmetrical Hearing Loss

An audiogram is a visual tool used to represent an individual's hearing thresholds across different frequencies, typically measured in Hertz (Hz). For those with asymmetrical hearing loss, an audiogram provides clear insights into the disparity between the ears. In cases of asymmetrical hearing loss, the audiogram will show a noticeable difference in the hearing thresholds between the two ears. For example, one ear may show mild hearing loss while the other shows severe hearing loss at various frequencies. Understanding the audiogram allows patients to see the specific frequencies where their hearing differs between ears, providing a clearer picture of their condition. It also aids in discussing potential interventions, such as hearing aids or cochlear implants, which can be tailored to address the unique needs of each ear.

Example of an Audiogram

Common Causes

Asymmetrical hearing loss can arise from various factors, each impacting the ears differently. While some common causes of asymmetrical hearing loss are listed below, this list Is not complete.

Ear Infections: Particularly otitis media, are a common cause of temporary asymmetrical hearing loss. These infections can lead to fluid accumulation in one ear, affecting its ability to transmit sound properly. Symptoms often include a sudden decrease in hearing, pain, and sometimes fever.
Noise-Induced Hearing Loss (NIHL): Exposure to loud sounds, whether through occupational noise or recreational activities, can cause damage to the hair cells in the cochlea. If one ear is exposed to louder noises or is more susceptible to damage, it may exhibit a greater hearing loss compared to the other ear.
Genetic Factors: Some individuals may inherit conditions that affect hearing differently in each ear, leading to a disparity in hearing ability. Congenital causes, such as malformations of the ear or auditory pathway abnormalities, can contribute to this condition as well.
Sudden Idiopathic Sensorineural Hearing Loss (SISNHL): Any hearing loss that occurs rapidly, unexpectedly, and without obvious cause is described as sudden idiopathic sensorineural hearing loss (SISNHL). While SISNHL may occur bilaterally and symmetrically, it often presents as a hearing loss in only one ear developing within a 72-hour period. The exact cause of SISNHL is usually unknown, or “idiopathic,” but it can result from viral infections, vascular issues, or autoimmune responses. This condition typically affects one ear and can lead to significant hearing loss, sometimes accompanied by tinnitus or a feeling of fullness in the ear.

Treatment Options

Effective management of asymmetrical hearing loss involves a range of treatment options tailored to individual needs.

Hearing Aids: For those with asymmetrical hearing loss and good or fair WRS, hearing aids are a common and effective solution. These devices amplify sounds to compensate for hearing deficits in one or both ears. Depending on the degree of hearing loss, audiologists can recommend different styles and models of hearing aids, including behind-the-ear (BTE) and in-the-ear (ITE) options.
CROS/Bi-CROS Hearing Aids: For individuals with unusable hearing in their poorer ear, CROS (contralateral routing of signals) or Bi-CROS hearing aids may be an option. CROS hearing aids are used when one ear has normal hearing while the other has significant hearing loss; they capture sound from the poorer ear and transmit it to the better ear, allowing for a more balanced hearing experience. On the other hand, Bi-CROS hearing aids are intended for those who have hearing loss in both ears, but one ear has a greater degree of impairment. In this case, the Bi-CROS system transmits sound from the poorer ear to the better ear, while also amplifying sounds for the better ear. CROS and Bi-CROS devices serve as effective non-surgical solutions for individuals with asymmetrical hearing loss, providing enhanced sound awareness and comfort. However, for many users, these devices may not significantly improve sound localization or speech understanding in noisy environments.
Cochlear Implants and Bone-Anchored Devices: For individuals with more severe asymmetrical hearing loss, advanced solutions like cochlear implants and bone-anchored devices may be appropriate. Cochlear implants are surgically implanted devices that directly stimulate the auditory nerve, providing a sense of sound to individuals with profound hearing loss in one ear. The cochlear implant system consists of two main components: an external processor that captures sounds and converts them into digital signals, and an internal implant that is surgically placed under the skin behind the ear.
Auditory Therapy and Rehabilitation: In addition to amplification devices, customized auditory therapy and rehabilitation play a crucial role in managing asymmetrical hearing loss. Audiologists often develop individualized therapy plans that may include auditory training, speechreading, and counseling to help patients improve their listening skills and cope with hearing challenges.

CROS and BiCROS Hearing Aids: How They Work and Who They Can Help

Spatial Hearing Loss

Spatial hearing loss means you can hear sounds but struggle to tell where they're coming from. This can affect daily life, safety, and social situations, even if your overall hearing seems fine. Causes include hearing loss in one ear, brain processing issues, or ageing.Treatment options like directional hearing aids, auditory training, and simple communication strategies can help. If you're finding it harder to locate sounds, a hearing assessment is recommended.

Many people associate hearing loss with difficulty detecting sounds or understanding speech. However, there's another type of hearing challenge that often goes unrecognised, which is being unable to determine where sounds are coming from. This condition, known as spatial hearing loss or auditory localisation disorder, can significantly impact daily life even when hearing sensitivity remains normal.

What is spatial hearing loss?

This refers to difficulty localising sounds in your environment. People with this condition can often hear sounds clearly but struggle to identify their direction or distance. This means you might hear a car horn but be unable to determine which direction the vehicle is approaching from, or hear someone calling your name in a crowded room without knowing where to look. Unlike traditional hearing loss, which affects the ability to detect sounds, spatial hearing loss specifically impacts how the brain processes directional audio information. This can occur on its own or alongside other hearing problems.

How sound localisation works

Understanding spatial hearing requires knowing how our auditory system normally processes directional information. When a sound occurs, several things help us determine its location. When any part of this system fails, spatial hearing becomes compromised.

Interaural time differences: Sounds reach the ear closest to the source slightly earlier than the far ear. This time difference, measured in microseconds, provides important directional information.
Interaural level differences: Your head acts as a natural barrier, creating subtle volume differences between ears. Sounds are typically louder in the ear closer to the source.
Spectral cues: Your outer ear or pinna naturally filters sound frequencies differently based on direction, creating unique acoustic signatures for various locations.
Binaural processing: Your brain combines information from both ears to create a three-dimensional sound map of your environment.

Common symptoms of spatial hearing loss

People with spatial hearing loss may experience:

Difficulty locating ringing phones, alarms, or other electronic devices
Inability to determine which direction traffic is coming from
Trouble following conversations in noisy environments
Feeling disoriented in crowded spaces
Needing to rely heavily on visual cues during conversations
Experiencing anxiety in unfamiliar acoustic environments
Difficulty separating speech from background noise

Causes

Several factors can contribute to spatial hearing problems:

Hearing loss in one ear: Unilateral hearing loss eliminates the ability to compare sounds between ears, making localisation difficult.
Auditory processing disorders: Central auditory processing problems can affect how the brain interprets spatial information, even when hearing sensitivity is normal.
Neurological conditions: Stroke, traumatic brain injury, or other neurological issues can damage brain areas responsible for sound localisation.
Age-related changes: Natural ageing can affect both hearing sensitivity and spatial processing abilities.
Ear infections or blockages: Temporary conditions that affect one ear more than the other can disrupt spatial hearing.
Certain medications: Some drugs can affect inner ear function or auditory processing.

Impact on daily life

Spatial hearing loss affects more than just sound localisation. It can impact safety, as it is difficult to determine vehicle direction while walking or driving, which poses safety risks. Social interactions are also challenging when you can't identify who's speaking in group settings, and jobs requiring good spatial awareness may become more difficult. Constant spatial confusion can create anxiety and social withdrawal, and make independence limited with simple tasks like finding a ringing phone or responding to someone calling your name become complicated.

Diagnosis and testing

If you suspect spatial hearing problems, you would need to consult an audiologist who will perform various diagnostic tests, such as: A comprehensive hearing evaluation, speech-in-noise testing, sound localisation assessments, auditory processing disorder testing and a medical evaluation to rule out underlying conditions.

Treatments

Treatment approaches vary depending on the underlying cause:

Hearing aids: For those with accompanying hearing loss, modern hearing aids with directional microphones can help with spatial processing.
Auditory training: Specialised therapy can help improve sound localisation skills through targeted exercises.
Environmental modifications: Reducing background noise and improving lighting can make social situations more manageable.
Communication strategies: Learning to use visual cues and positioning yourself strategically in conversations.

When to seek help

Consult a healthcare professional if you experience:

Persistent difficulty locating sounds
Increased anxiety in noisy environments
Safety concerns related to spatial awareness
Social isolation due to communication challenges
Sudden onset of spatial hearing problems

Prevalence of Hearing Loss

13% of people (30 million in 2016) have hearing loss in one or both ears. While a standard definition of asymmetrical hearing loss has been suggested (AAO-NHS, 2015), it is not universally utilized. This makes it difficult to determine the exact prevalence of asymmetrical hearing loss. A study in 2021, however, noted a prevalence of 9.46% among adults.

Year	Percentage of Adults with Hearing Loss
2016	13%
2021	9.46%

Conclusion

Asymmetrical hearing loss can be serious, depending on its cause and severity. It can impact daily life by making it difficult to locate sounds, understand speech in noisy environments, and communicate effectively. In some cases, it may indicate underlying health issues such as acoustic neuromas or other medical conditions that require attention. It can also be a result of easily treated conditions like excessive earwax or ear infections. Therefore, it is important to seek professional evaluation and treatment to address any potential risks and improve hearing health.