Author: Dolly Bhargava, M. Spec. Ed.

Hearing impairment can be classified into four categories depending on the site of the problem in the ear - conductive, sensorineural, mixed, and central auditory processing disorder.

A. Conductive Hearing Impairment

A conductive hearing impairment results from a blockage or damage to the outer or middle ear structures.  This problem interferes with the transmission of sound through the outer and middle ear to the inner ear, resulting in reduced loudness of the sound (quantity of sound). A conductive hearing loss can fluctuate according to the presence or severity of the blockage. During these periods of reduced hearing the student may miss out on learning, negatively affecting all aspects of development (Pagliano, 2005). Some of the common causes of conductive hearing impairment include excessive earwax (cerumen); middle ear infections (such as Otitis Media, where there is pus or fluid build-up or inflammation which causes pain and reduces the ability of the eardrum to vibrate); a hole or perforation of the ear drum;and otosclerosis (the eardrum and the ossicles have decreased mobility) (Scheetz, 2000). In many cases, a conductive hearing impairment can be corrected with medication, hearing aids or surgery.

B. Sensorineural Hearing Impairment

A sensorineural hearing loss results from damage to the inner ear or the auditory nerve.  A sensorineural hearing loss can range from mild to profound and often affects the student’s ability to hear certain frequencies more than others.  Thus, even with amplification to increase the sound level, a student with sensorineural hearing loss may perceive distorted speech sounds, resulting in difficulty with understanding speech and interpreting various sounds (quantity and quality of sound). Some of its causes include genetic disorders (which can interfere with proper development of inner ear structures); injuries; complications during pregnancy or birth; infections or illnesses (such as mumps, measles, chickenpox) and medication side effects (Lysons, 1996). This type of hearing impairment is usually permanent and irreversible.  Sensorineural hearing impairments are frequently not medically or surgically treatable.  However, most people with a sensorineural loss find wearing hearing aids and using sound amplification technology to be of significant benefit (Dugan, 2003). 

C. Mixed Hearing Impairment

A mixed hearing loss refers to a combination of conductive and sensorineural hearing loss, indicating that there may be damage in the outer or middle ear and the cochlea or auditory nerve.  Treatment depends on the severity of the conductive (i.e. hearing aid, medical or surgical intervention) and sensorineural (i.e. hearing aid) portions of the hearing impairment (Dugan, 2003).  

D. Central Auditory Processing Disorder

This form of hearing impairment occurs when the auditory centers of the brain are affected by injury, disease, tumor, heredity, birth trauma, head trauma or unknown causes. Although the outer, middle and inner parts of the ear deliver sound signals, these signals are unable to be processed and interpreted by the brain.  Thus, even though the person’s hearing may be normal, there are difficulties with understanding what is being said, resulting in learning problems.  Central auditory processing involves a variety of skills such as localizing the sound, attending to it, perceiving it accurately through auditory discrimination and auditory recognition to make sense of the sound (ASHA Task Force on Central Auditory Processing Consensus Development, 1996).  Difficulties in one or more of the above-listed behaviors may constitute a central auditory processing disorder. The use of assistive technology and environmental modifications to the listening environment can provide acoustic enhancement by amplifying the incoming speech signal, thereby improving the auditory signal to noise ratio, that is, the ratio between the signal and any unwanted background noise (Pagliano, 2005).  According to the ASHA Task Force on Central Auditory Consensus Development (1996) audiologists are best qualified to understand breakdowns in central auditory processing and to guide management of the condition.

Understanding these four categories of hearing impairment will be helpful to you as a teacher, as they suggest the teaching and learning frameworks that must be set in place so that each student can properly access the curriculum.