A professional hearing assessment is formally known as Audiometry, which is the measurement of a person’s ability to hear different sounds. This comprehensive evaluation is performed by a licensed audiologist, a specialist in hearing, balance, and related disorders. The process involves a battery of tests designed to measure the softest sounds an individual can hear across various pitches, assess the function of the middle and inner ear structures, and determine how clearly speech is understood. These procedures provide a complete picture of auditory health, identifying the type, degree, and configuration of any potential hearing loss.
The Standard Behavioral Assessment
The behavioral assessment requires active patient participation and is the most common part of a hearing test. Pure-Tone Audiometry is the foundational test, determining the quietest sound a person can hear at specific frequencies. The patient sits in a sound-treated booth and signals when they hear a tone presented through headphones or ear inserts. The audiologist records the softest level heard, known as the hearing threshold.
This procedure uses two methods for delivering sound: air conduction and bone conduction. Air conduction tests the entire auditory pathway, from the outer ear through the middle ear to the inner ear, using headphones. Bone conduction bypasses the outer and middle ear by placing a small vibrator on the mastoid bone behind the ear, directly stimulating the cochlea. Comparing these two sets of results allows the audiologist to determine if a hearing loss is conductive (outer or middle ear issue), sensorineural (inner ear or nerve issue), or mixed.
Speech Audiometry evaluates the ability to hear and understand spoken words. This includes the Speech Recognition Threshold (SRT), the lowest volume level at which a person can correctly repeat simple words, often two-syllable spondees. It also includes the Word Recognition Score (WRS), where single-syllable words are presented at a comfortable volume to measure the percentage correctly understood, providing insight into speech clarity. Speech testing offers a practical, real-world measure of communication ability that pure-tone testing alone cannot provide.
Evaluating Middle Ear Function
Tests assessing the middle ear cavity focus on physical function and mechanics rather than the perception of sound. Tympanometry is a quick, objective test that measures the movement, or compliance, of the eardrum in response to air pressure changes in the ear canal. A small probe changes the pressure, and the resulting graph, called a tympanogram, reveals how well the eardrum and middle ear bones are working. This test detects issues like fluid behind the eardrum, a perforation, or Eustachian tube dysfunction.
This assessment is often paired with Acoustic Reflex Testing, which measures the involuntary contraction of the stapedius muscle in the middle ear in response to a loud sound. This reflex causes a slight stiffening of the middle ear system, monitored by the same probe used for tympanometry. The presence or absence of this acoustic reflex, and the sound level required to elicit it, provides information about the integrity of the middle ear, the inner ear, and the auditory nerve pathway through the brainstem.
Objective Measures of Inner Ear Response
Objective tests measure the auditory system’s physiological responses for individuals who cannot provide reliable behavioral responses, such as infants or young children. Otoacoustic Emissions (OAEs) testing assesses the function of the cochlea, specifically the outer hair cells. When healthy outer hair cells are stimulated by sound, they produce a faint echo or emission that travels back out and is recorded by a tiny microphone in the ear canal. The presence of OAEs suggests hearing sensitivity is better than a mild loss, while their absence indicates cochlear damage.
The Auditory Brainstem Response (ABR) test measures the electrical activity generated by the auditory nerve and the brainstem in response to sound. Small electrodes placed on the scalp and earlobes record these neural signals as clicks or tones are presented through headphones. The resulting waveforms indicate how well sound travels from the ear to the brain. ABR is important for screening newborns and diagnosing conditions like auditory neuropathy, providing a comprehensive view of the auditory pathway up to the brainstem.
Decoding the Hearing Test Results
All measured hearing thresholds from the pure-tone test are plotted on a graph called an Audiogram, the central document for interpreting the assessment. The audiogram visually represents a person’s hearing sensitivity across the key frequencies for speech and environmental sounds. The horizontal axis (X-axis) represents the frequency (pitch), ranging from low (250 Hertz) to high (8000 Hertz).
The vertical axis (Y-axis) represents the intensity (loudness) in decibels (dB), with softest sounds at the top and loudest at the bottom. The results are plotted using specific symbols for air and bone conduction thresholds. Hearing loss severity is determined by where the symbols fall on the vertical axis; thresholds below 25 dB are considered normal, while greater losses are classified as mild, moderate, severe, or profound.