The afferent auditory pathway transmits acoustic information from the inner ear via the auditory nerve to various brainstem nuclei and on to the auditory cortex. It comprises the vestibulocochlear nerve (VIII cranial nerve), the cochlear nucleus, and higher central structures. Disruptions in this pathway lead to sensorineural hearing loss and central auditory processing disorders. Objective measurement methods such as brainstem response (ABR) test the integrity of the afferent auditory pathway. An intact afferent auditory pathway is a prerequisite for speech comprehension and localization of sound sources.

Ageusia refers to the complete loss of taste and occasionally occurs in combination with hearing and balance disorders. It can be caused by damage to the chorda tympani nerve, which transmits taste signals from the tongue to the brain. Patients also complain of reduced saliva production and loss of appetite. In ENT diagnostics, ageusia is often examined in conjunction with olfactory tests. Treatment depends on the underlying cause, such as infection or trauma.

Air conduction describes the transmission of sound waves through the air via the outer ear and middle ear to the inner ear. It is the primary hearing pathway for normal everyday sounds and is represented as an air conduction curve on audiograms. Deviations between air conduction and bone conduction indicate conductive hearing loss. Air conduction measurements allow a distinction to be made between middle ear and inner ear disorders. Clinically, air conduction is measured using headphone audiometry.

In an auditory context, accommodation refers to the adjustment of hearing to changing sound pressure levels through muscular tension in the ossicles. This mechanism protects the inner ear from loud stimuli and optimizes sensitivity to quiet signals. Accommodation occurs within milliseconds and is controlled by the stapedius and tensor muscles. Lesions of the muscles or nerves can cause this protective reflex to fail, increasing the risk of noise-induced hearing loss. Audiometrically, impaired accommodation is reflected in altered reflex thresholds.

Active listening training involves targeted exercises to improve auditory perception and speech intelligibility, especially in difficult listening situations. Various sound patterns and speech signals are presented to strengthen central processing processes. Studies show that regular training promotes neural plasticity in the auditory cortex. Areas of application include tinnitus therapy, rehabilitation after sudden hearing loss, and support for central hearing disorders. Modern programs use computer-assisted tasks and biofeedback.

Acoustics is the study of the generation, propagation, and perception of sound. It forms the basis for all audiological measurement methods and the development of hearing aids. Within acoustics, a distinction is made between airborne, bone, and structure-borne sound. Applied acoustics deals with room acoustics, noise protection, and sound insulation measures. In hearing aid technology, acoustic principles are incorporated into filter design and amplifier technology.

Auditory hallucinations are the perception of voices or sounds without an external sound source. They can have psychological causes (e.g., schizophrenia) or neurological lesions. In audiology, they are distinguished from tinnitus because hallucinations can carry linguistic content. Diagnosis involves neuropsychological tests and imaging procedures. Psychotherapy and medication are used for treatment.

Acoustic reflex testing measures the stapedius reflex, which responds to loud sounds by contracting the stapedius muscle. This reflex protects the inner ear from overload and can provide clues about middle ear or brainstem lesions. Unilateral and bilateral reflex loss provide differentiated diagnoses for conductive and sensorineural hearing loss. The test is performed using tympanometry devices that record reflex thresholds and latencies. It is clinically important in cases of neural hearing disorders and otosclerosis.

In hearing aids, acoustic signal processing refers to the conversion of microphone signals into optimized sound signals for the wearer. Digital chips filter out background noise, amplify speech, and dynamically adapt to the environment. Techniques such as feedback suppression and adaptive directional microphones improve hearing quality in noisy environments. Advanced systems use AI to learn hearing preferences and automatically recognize scenes. Signal processing is crucial for natural hearing with hearing aids.

The stapedius reflex is an involuntary contraction of the stapedius muscle in response to intense sound stimulation. Raising the stirrup footplate reduces sound transmission to the inner ear, protecting it. Reflex measurements provide information about the function of the middle ear, facial nerve, and brain stem. A missing or asymmetrical reflex response may indicate otosclerosis or cranial nerve damage. The reflex is part of standard tympanometry in audiological diagnostics.

Acoustic trauma is caused by sudden, extremely loud sound events such as explosions or blast trauma. It leads to damage to the hair cells in the inner ear, which is often accompanied by tinnitus and permanent hearing loss. Immediate measures include corticosteroids to reduce inflammation and high-pressure oxygenation. Long-term consequences can include speech comprehension difficulties and hyperacusis. Prevention through hearing protection is crucial to avoid acoustic trauma.

Age-related hearing loss (presbycusis) is the gradual, physiological loss of hearing in older age. It mainly affects the hair cells in the inner ear and neural connections, leading to reduced speech comprehension. Symptoms are particularly noticeable in the high frequency range and when there is background noise. Hearing aids and auditory training can significantly improve quality of life and communication. Preventive measures such as noise protection and nutrition play a supporting role.

The alveolar membrane in the inner ear is a thin layer that supports hair cells in the organ of Corti and converts vibrations into neural signals. It ensures precise frequency separation along the cochlea. Changes or damage to the membrane impair pitch recognition and volume perception. Histological studies show that age and noise exposure reduce the elasticity of the membrane. Biological research is focused on regenerative therapies to restore this membrane.

The incus is the middle of the three ossicles in the middle ear and transmits vibrations from the malleus to the stapes. It acts as a lever that increases sound pressure before the vibrations are transmitted to the inner ear. This amplification ensures that the incus efficiently converts air sound into bone sound. Functional disorders such as ossification (otosclerosis) can cause conductive hearing loss. For detailed information on the sound conduction chain and testing procedures, see Rinne and Weber tests.

Amplitude describes the deflection of a sound wave and determines the perceived volume. It is measured as sound pressure level in decibels and correlates directly with auditory perception. High amplitudes can cause damage to hair cells, while low amplitudes are close to the hearing threshold. In audiometry, amplitude indicates the dynamic range of a person's hearing. Technical applications regulate amplitudes to minimize distortion in hearing aids.

Amplitude modulation (AM) refers to the change in sound amplitude following a modulation signal, such as speech or music signals. AM is used in hearing tests to check the modulation sensitivity of the ear. Reduced perception of AM can indicate central auditory processing disorders. In hearing aids, AM detection helps to separate speech from background noise. Psychoacoustic experiments with AM provide insights into neural coding mechanisms in the auditory system.

Anacusis refers to the complete loss of hearing, in which neither air nor bone conduction nor the slightest acoustic stimuli can be perceived. It can be congenital or caused by severe damage to the inner ear, the auditory nerve, or central auditory pathways. Those affected are completely dependent on visual and tactile aids such as sign language or vibro-alerts for communication. Medically, anakusis is tested using tone and speech audiometry as well as otoacoustic emissions and evoked potentials to determine the extent and location of the damage.

Analog hearing aids continuously amplify acoustic signals without digital signal processing. They work with simple amplifier stages and filters, are inexpensive, but less flexible than digital models. Adjustments are made mechanically or via potentiometers, which makes fine tuning difficult. Today, analog devices are rarely used, mainly in simple applications or as backup. Their sound quality is considered less natural than digital systems.

Anisoacusis describes a difference in hearing threshold between the two ears, often caused by unilateral damage to the middle or inner ear. Audiometrically, this manifests as asymmetry between air conduction and bone conduction curves. Clinically, anisoacusis can indicate otosclerosis, Meniere's disease, or neural lesions. Treatment depends on the cause and may include surgical intervention or hearing aids. Monitoring anisoacusis helps to assess the progression of the disease and the success of treatment.

Antiemetics relieve nausea and vomiting associated with vestibular disorders such as inner ear inflammation. They usually act on histamine or dopamine receptors in the vomiting center. By reducing accompanying symptoms, they improve the tolerability of vestibular training. Long-term use requires monitoring, as side effects such as fatigue may occur. In ENT practice, antiemetics are combined with vestibular rehabilitation for optimal results.

Vestibular dysfunction affects areas of the brain that control appetite and nausea. Impaired balance perception often leads to eating disorders and weight loss. Therapies include vestibular training and pharmacological support to normalize eating behavior. Dietary recommendations with easily digestible foods reduce accompanying symptoms. Interdisciplinary care by ENT, neurology, and nutrition therapists improves quality of life.

Arbitrary sound sources are unpredictable, random noises in the environment that do not belong to speech patterns. They make speech comprehension more difficult and increase the cognitive load when listening. Hearing aid algorithms must recognize and filter out such background noise. Laboratory tests with arbitrary signals test the robustness of hearing systems. Psychoacoustic studies investigate how the brain separates arbitrary noises from relevant signals.

Arterial pressure in the inner ear ensures sufficient blood supply to the hair cells and neural structures. If the pressure drops, ischemia and hearing loss can occur. Vascular medicine examinations measure blood flow parameters to detect vascular constrictions. Treatment options range from drug-induced dilation to microsurgical procedures. Stable perfusion is crucial for hearing health and sensory cell regeneration.

The articulation index (AI) indicates the proportion of speech sounds that are correctly reproduced for a hearing aid user. It is measured in speech audiometry and represented as a value between 0 and 1. A high AI (> 0.7) means good speech intelligibility, while low values indicate a need for adjustment. AI measurements help to optimize hearing aid programs and document rehabilitation progress. The index correlates closely with subjective hearing comfort in everyday life.

In cases of ear canal atresia, the external ear canal is congenitally absent, leading to complete sound conduction blockage. Those affected suffer from unilateral or bilateral conductive hearing loss. Surgical opening (atresiaplasty) can partially restore hearing. Audiological care includes bone conduction hearing aids until surgery. Long-term follow-up checks for scarring and hearing gain.

An audiogram is a graph that shows hearing thresholds across different frequencies. Air conduction and bone conduction are measured separately to distinguish between conductive and sensorineural hearing loss. Normal values range from 0 to 20 dB; deviations indicate degrees of loss. Audiograms form the basis of all hearing medicine diagnoses and therapy planning. Modern digital audiometers automatically store and compare curve progressions.

An audiologist is a medical specialist or scientist who specializes in the diagnosis and treatment of hearing and balance disorders. They perform complex tests such as AEP, OAE, and speech audiometry. Audiologists work in an interdisciplinary manner with ENT doctors, neurologists, and hearing aid acousticians. They develop individual rehabilitation plans and provide long-term support to patients. Their training covers medicine, neuroscience, and technology.

Audiology is the interdisciplinary field that deals with hearing, balance, and auditory processing. It combines aspects of medicine, physics, psychology, and technology. Audiologists research hearing mechanisms, develop diagnostic procedures, and optimize hearing aids. Clinical audiology includes screening, differential diagnosis, and therapy. The goal is to maintain and improve hearing and communication abilities.

Audiometry refers to all measurement methods used to determine hearing thresholds and speech intelligibility. These include tone, speech, and objective measurements such as OAE and AEP. The results are used in hearing aid fitting and therapy monitoring. Modern audiometry devices use computer-assisted procedures and automated protocols. Regular audiometry is used to monitor progress in noisy work environments or when ototoxic medication is being taken.

Auditory evoked potentials are electrical signals in the brain that are measured in response to sound stimuli. They allow objective assessment of the auditory pathway from the ear to the cortex. AEPs are used in newborn screening, when brain stem lesions are suspected, and in neurological diseases. Different wave components provide information about individual stages of the auditory pathway. The examination is performed using scalp electrodes, without the active participation of the patient.

Auditory feedback occurs when hearing aid microphones pick up the amplified sound from the receiver and enter a feedback loop. This manifests itself as whistling or humming and can severely impair the listening experience. Modern hearing systems use adaptive algorithms to detect and suppress feedback in real time. Acoustic adjustments such as tight earmolds further reduce the risk. An optimal microphone-receiver distance design minimizes feedback mechanically.

Auditory processing encompasses the central processes involved in analyzing and interpreting sound signals in the brain. It includes feature extraction, speech comprehension, and sound localization. Auditory processing disorders manifest themselves in difficulties understanding speech in the presence of background noise. Neuropsychological tests and central audiometry procedures aid in diagnosis. Rehabilitation through auditory training targets the plasticity of the auditory cortex.

The auditory cortex in the upper temporal lobe is the central processing station for sound information. This is where the frequency, volume, rhythm, and direction of sound are evaluated. Plastic changes in the cortex enable learning processes such as auditory training and tinnitus management. Lesions lead to central hearing disorders and speech comprehension deficits. Imaging techniques (fMRI, PET) examine activity patterns during acoustic stimuli.

ABR measures waves of electrical activity along the auditory pathway in the brainstem after click stimuli. It is used for the objective diagnosis of hearing thresholds and neural conduction disorders. ABR is standard in newborn screening and when acoustic neuroma is suspected. Analysis of wave latencies allows conclusions to be drawn about the location of lesions from the ear to the brainstem. The examination is painless and is performed using scalp electrodes.

Auricular stimulation uses electrical or mechanical stimuli on the outer ear to influence neural networks. It is used in pain therapy, tinnitus treatment, and vestibular rehabilitation programs. Stimulation can promote blood circulation and stimulate neural plasticity. Clinical studies are investigating its effects on chronic tinnitus and vertigo. The safety profile is considered good, and side effects are rare.

Auriculotherapy is a form of ear acupuncture in which specific points on the auricle are treated to achieve systemic effects. It is used as a complementary treatment for tinnitus, dizziness, and stress. Its effectiveness is scientifically controversial, but patients report subjective improvement. Points corresponding to specific organs and nerve reflex zones are treated. Auriculotherapy is part of integrative ENT and pain therapy concepts.

The outer ear comprises the auricle and external auditory canal and conducts sound waves to the eardrum. The shape of the auricle amplifies certain frequencies and aids directional perception. Conditions such as exostoses or otitis externa impair sound reception. Audiological examinations check the patency and resonance of the outer ear. Surgical procedures can restore shape and function in cases of malformation.

Autophony refers to the perception of one's own voice via bone conduction, which results in a duller sound. This effect occurs because vibrations are transmitted directly to the inner ear via the skull bones. When we speak, we perceive our voice as louder and fuller than others do. Autophony can be more pronounced in cases of Eustachian tube dysfunction or after middle ear surgery. Audiometric tests separate air conduction from bone conduction to diagnose autophony.