"One of the greatest mysteries in medicine is undoubtedly the brain, and how it develops and evolves. Even when given the best possible information about the sounds in our environment, our minds can play tricks on us. For some of my patients, the best strategy is simply teaching them to avoid the pitfalls, as understanding sound and language is the real magic, much more so than whether or not you heard it." - Drew Sutton, MD, Board-Certified Otolaryngologist
Diagnostic tools have advanced enormously in recent decades, as research and efforts have focused on early intervention. This trend is evident in schools, where there is growing interest in screening for common learning disorders so that no student is left behind due to an undiagnosed condition.
A good example of this is the recently implemented dyslexia screening in the Washington State education system. This early reading screening offers those who would otherwise struggle with undiagnosed dyslexia the opportunity to benefit from tailored support that is easier to live with and more effectively managed.
Another disorder that has gained visibility in recent years is Central Auditory Processing Disorder (CAPD). While many cases are now detected very early, in childhood or adolescence, several people have slipped through the cracks and live with CAPD without even knowing it.
The bulk of research and resources dedicated to CAPD focuses on pediatrics, as early detection improves the prognosis; however, adults diagnosed with CAPD lack information, support, and appropriate screening.
Here is an overview of CAPD: what it is, how it affects listening ability, and what tools and strategies affected individuals can use to make their daily lives easier.
Anatomy of Hearing
Hearing is a highly complex process involving moving parts, nerve impulses, and a whole network of neurons to make sense of it all. We don't notice all this behind-the-scenes work, but it's a true feat that the body accomplishes with apparent ease.
As with any well-oiled machine, a single grain of sand can derail the entire process. The same applies to hearing: hearing impairment can occur at any stage. Here is a detailed examination of each stage of hearing and the associated hearing impairments. Understanding how hearing works and what can go wrong is essential to grasping the difference between hearing impairment and auditory processing disorder.
The Outer Ear
The outer ear consists of the parts of the ear visible to the naked eye. It includes the external structures of the ear and the ear canal. Both of these channel sound waves towards the structure called the eardrum.
From a hearing loss perspective, little can go wrong with the outer ear, as it mainly consists of fixed structures. The only thing that can reduce hearing ability is a buildup of earwax in the ear canal.
Over time, earwax can accumulate to the point where it prevents sound from properly reaching the eardrum. Fortunately, thorough earwax cleaning usually restores normal hearing.
The Middle Ear
The middle ear is a distinct compartment from the outer ear, separated from it by the tympanic membrane, also known as the eardrum. It includes the tympanic membrane, the ossicles, the tympanic cavity, and the Eustachian tubes.
The middle ear acts as an intermediary, converting sound vibrations into the movement of tiny ossicles. This process, called conduction, is an essential aspect of hearing. When sound enters the ear canal, it reaches a dead end: the eardrum. When sound waves strike the tympanic membrane, it oscillates back and forth.
The inner ear can contribute significantly to conductive hearing loss. In this type of hearing loss, any of the above structures can be affected. The most common case is an ear infection, where the tympanic cavity fills with fluid: sound conduction becomes poor, sounds appear muffled and more difficult to hear.
Other forms of conductive hearing loss exist, such as a perforated eardrum, but their commonality is that they always stem from a dysfunction of the middle or outer ear.
The Inner Ear
The inner ear is where sound is converted into nerve impulses. The ossicles are connected to the cochlea, an essentially hollow structure lined internally with specialized hair cells.
When the stapes vibrates the cochlea, a wave travels through it. The hair cells corresponding to the characteristics of this precise wave transmit the message to the auditory nerve. The cochlea has thousands of different hair cells, allowing the human body to perceive a wide range of sounds.
Inner ear problems cause what is known as sensorineural hearing loss. This is due to damage to the hair cells in the cochlea or the auditory nerve leaving the ear. Sensorineural hearing loss is often permanent and results from overstimulation and deterioration of the cochlear hair cells.
A typical case is people who work for long periods in noisy environments without hearing protection. The result is constant stimulation of the cochlear hair cells, which eventually cannot cope and stop functioning correctly.
Brain Processing
It is at the level of brain processing that all the work of converting sound waves into nerve impulses pays off. Once the signal is sent out of the cochlea, it travels along the auditory nerve to the brainstem, where the first stages of information processing take place.
The signal then passes through other regions of the brain, where it is successively processed until it reaches the auditory cortex.
One of the main problems related to brain processing abilities is central auditory processing disorder. Unlike other hearing impairments, CAPD has almost nothing to do with hearing a sound: it concerns understanding and distinguishing one sound from another.
Central Auditory Processing
Central auditory processing refers to all the refining and processing operations that the brain performs to interpret sound. This processing includes several stages: determining which sounds are important, recognizing sound patterns, and much more. Correct central auditory processing allows you to hold a conversation in a noisy crowd, locate the source of a sound, and understand verbal communication.
Central Auditory Processing Disorder
CAPD is a condition in which one aspect of this processing does not occur as it should. Affected individuals may therefore have more difficulty recognizing certain sounds, locating the origin of a sound, or understanding speech.
In adults, CAPD can easily impact quality of life. Constantly having to ask others to repeat themselves, struggling to understand someone in a noisy environment, and regularly misunderstanding what has been said are all sources of annoyance.
All these symptoms stem from processing errors, not from typical hearing loss. With CAPD, the sense of hearing may be perfectly intact; it is the ability to perceive sound that is impaired.
Tools for CAPD
CAPD is a persistent problem, and learning to cope with it can reduce its daily impact. Here are some tools useful for people who struggle to process sounds.
Subtitles
Subtitles have existed for decades: basically, they are a written transcription of what is being said. Today, software converts speech to text in real-time. People with CAPD understand their interlocutors, but words that sound similar can sometimes make it difficult for them to keep up with the pace of a conversation.
Real-time subtitles help them considerably not to miss anything in the exchange.
Hearing Aids
Another useful tool is a quality hearing aid. While hearing aids are generally used to compensate for hearing loss, some can also be helpful for CAPD. Devices like the CLARIA EV3 incorporate technologies that reduce background noise while amplifying speech sounds.
For people with CAPD, reducing ambient noise and amplifying the voice greatly facilitates understanding and processing incoming speech. The EV3's clear sound + technology significantly improves sound quality and offers a listening experience more isolated from disturbances.
Conclusion
In summary, central auditory processing disorder is a hearing impairment that concerns the processing of sounds. Although its symptoms may resemble those of conventional hearing loss, it is a distinct impairment that has nothing to do with auditory acuity but everything to do with how information is processed and perceived by the brain.
CAPD can be diagnosed at any time in life, but it is often detected early, allowing for earlier therapeutic intervention. Adult CAPD diagnoses remain uncommon. Nevertheless, there are several tools that facilitate the perception of the sound world around you.
Sources:
Screening Tools and Best Practices | K12
Central Auditory Processing Disorder | ASHA
Anatomy and Physiology of the Ear | University of Rochester Medical Center
