There are various types of hearing loss, but generally speaking there are two main categories: conductive and sensorineural hearing loss. Whether a hearing impairment is categorized as conductive or sensorineural depends on the origin of the loss.
Conductive Hearing Loss
If the loss can be localized to the outer or middle ear, the hearing loss is conductive. The specific hearing loss can originate at the pinna (visible ear), ear canal, eardrum, middle ear bones or any combination of these.
Sensorineural Hearing Loss
When the loss is caused by a problem involving the inner ear (cochlea/auditory nerve), it is considered a sensorineural hearing loss. This type of loss occurs when the hair cells, neural fibers or their connections to the cochlea are damaged or do not function optimally.
It is possible for hearing loss to be of both a conductive and sensorineural nature which is then referred to as a mixed loss.
Understanding the Hearing Evaluation
Determination of the origin of hearing loss is accomplished during audiological testing, which includes completion of an audiogram (or graph of one’s hearing). The audiogram is a grid with two scales – frequency and intensity.
The horizontal scale is the “frequency parameter”. Frequency, which we perceive as pitch, can be described as the different notes on a musical scale and is measured in Hertz (abbreviated as Hz). The audiogram typically shows test results for 6 to 10 frequencies from 250 (left on the scale) to 8000 (right on the scale) Hz.
The vertical scale is the “intensity parameter”. Intensity, which we perceive as loudness, can be described as how loud or soft a sound is. Intensity is measured in decibels (abbreviated as dB or dBHL).
During the hearing test, each test frequency is varied by intensity to determine the softest sound that can be heard. This is referred to as determining hearing threshold. Thresholds for each ear are plotted as markings on an audiogram, or sometimes recorded numerically in a table. When plotted, markings for the left ear will often be written with blue ink and/or indicated by an “X” while those obtained for the right ear will often be written with red ink and/or indicated by an “O”. The more the intensity level has to be raised (i.e. appearing more towards the bottom of the audiogram), the more diminished the hearing at that particular test frequency.