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Basics of Hearing Loss
This page is provided to help you understand the basics of hearing loss as well as basic terminology often used in the field of audiology.
This information should be used for informational purposes only. If you are experiencing hearing loss, please consult a physician.
Degrees of hearing loss
- Normal hearing (0-25 dB) At this level, hearing is within normal limits.
- Mild hearing loss (26-40 dB): Mild hearing loss may cause inattention, difficulty suppressing background noises and increased listening efforts. Patients with this degree of loss may not hear soft speech. Children may be fatigued after listening for long periods.
- Moderate hearing loss (41-55 dB): Moderate hearing loss may affect language development, syntax and articulation, interaction with peers and self-esteem. Patients with this degree of loss have trouble hearing some conversational speech.
- Moderate-severe hearing loss (56-70 dB): Moderate-severe hearing loss may cause difficulty with speech and decreased speech intelligibility. Patients with this degree of loss do not hear most conversational-level speech.
- Severe hearing loss (71-90 dB): Severe hearing loss may affect voice quality.
- Profound hearing loss (>90 dB): With profound hearing loss (deafness), speech and language deteriorate.
Types of hearing loss
Conductive Hearing Loss: a temporary or permanent hearing loss typically due to abnormal conditions of the outer and/or middle ear.
Sensorineural Hearing Loss: typically a permanent hearing loss due to disease, trauma or inherited conditions affecting the nerve cells in the cochlea, the inner ear or the eighth cranial nerve.
Mixed Hearing Loss: a combination of conductive and sensorineural
Central Auditory Processing Disorder: a condition where the brain has difficulty processing auditory signals that are heard.
Terminology
Audiogram
The audiogram is a chart of hearing sensitivity.
Intensity is the level of sound power measured in decibels.
Loudness is the perceived correlation of intensity.
Frequency
Frequency is cycles per unit of time and is measured in hertz, i.e., cycles per second.
Pitch is the perceived correlation of frequency.
Usually frequencies of 250-8000 Hz are used in testing because this range represents most of the speech spectrum, although the human ear can detect frequencies from 20-20,000 Hz. Some children can detect even higher frequencies.
Pure-tone average
Pure-tone average (PTA) is the average of hearing sensitivity at 500, 1000, and 2000. This average should approximate the speech reception threshold (SRT) within 5 dB and the speech detection threshold (SDT) within 6-8 dB.
Speech reception threshold
The SRT is the softest intensity spondee words that an individual can repeat at least 50% of the time.
Spondees are bisyllabic words equally emphasizing both syllables. In some cases (i.e., patients with poor word recognition), a limited set of words may be used.
Speech detection threshold
The speech detection threshold (SDT), also termed the speech awareness threshold (SAT), is the lowest intensity speech stimulus that an individual can detect at least 50% of the time.
Word recognition
Word recognition (formerly called speech discrimination) is the ability to repeat correctly an open set of monosyllabic words at suprathreshold intensity. Word lists are phonetically balanced (PB), meaning that the speech sounds used occur with the same frequency as in the whole language.
The score represents the percent of words correct for most word recognition tests.
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