1.1 Types of sensory impairments: Single (Hearing Impairment & Visual Impairment) & Dual sensory impairment (Deaf-blindness)

Sensory impairment is when one of the senses; sight, hearing, smell, touch, taste and spatial awareness, is no longer normal. Communication is the greatest challenge.

 ‘Sensory impairment’ or ‘sensory loss’ are umbrella terms used to describe loss of the distance senses i.e. sight and hearing.

You will find that the term ‘sensory impairment’ is commonly used by professionals rather than ‘sensory impaired’ individuals themselves who may be more likely to use the terms below.

There are three very distinct groups within sensory impairment:

Visually impairment or blindness

As the term indicates, a visual impairment involves an issue with sight which interferes with a student’s academic pursuits. The Individuals with Disabilities Education Act (IDEA) officially defines the category as “an impairment in vision that, even with correction, adversely affects a child’s educational performance. The term includes both partial sight and blindness.”

Hearing impairment or deafness

Hearing impairment as a disability category is similar to the category of deafness, but it is not the same. The official definition of a hearing impairment by the Individuals with Disabilities Education Act (IDEA) is “an impairment in hearing, whether permanent or fluctuating, that adversely affects a child’s educational performance but is not included under the definition of ‘deafness.'” Thus, knowing the definition of deafness is necessary to understand what sort of disabilities are considered hearing impairments. A hearing loss above 90 decibels is generally considered deafness, which means that a hearing loss below 90 decibels is classified as a hearing impairment.

An inability to comprehend verbal language due to an inability to hear characterizes deafness. The official definition of deafness from the Individuals with Disabilities Education Act (IDEA) is “a hearing impairment that is so severe that the child is impaired in processing linguistic information through hearing, with or without amplification.” The phrase “with or without amplification” is significant as it indicates that a hearing aid will not provide sufficient accommodation so that the student can succeed in the classroom.

Deaf-blind people

Deaf-blindness refers to a child with both hearing and visual disabilities. The Individual with Disabilities Education Act (IDEA) officially defines the term as “concomitant [simultaneous] hearing and visual impairments, the combination of which causes such severe communication and other developmental and educational needs that they cannot be accommodated in special education programs solely for children with deafness or children with blindness.”


1.2 Importance of hearing

Hearing (or audition) is the sense of detecting sound, that is, receiving information about the environment from vibratory movement communicated through a medium such as air, water, or ground. It is one of the traditional five senses, along with sight, touch, smell, and taste.

Both vertebrates and arthropods have a sense of hearing. In humans and other vertebrates, hearing is performed primarily by the auditory system: Sound is detected by the ear and transduces into nerve impulses that are perceived by the brain.

Hearing is a sense—that is, a mechanism or faculty by which a living organism receives information about its external or internal environment. In other words, it is an inherent capability or power to receive and process stimuli from outside and inside the body, similar to the sense of sight. The term, "sense," is often more narrowly defined as related to higher animals. In this case, a sense is considered a system involving sensory cells that respond to a specific kind of physical energy (both internal and external stimuli), which are converted into nerve impulses that travel to the brain (typically a specialized area), where the signals are received and analyzed.

Although school children are routinely taught that there are five senses (sight, hearing, touch, smell, taste; a classification first devised by Aristotle), a broader schema presents these five external senses as being complemented by four internal senses (pain, balance, thirst, and hunger), with a minimum of two more senses being observed in some other organisms.

Hearing is the ability to perceive sound from a source outside the body through an environmental medium. The cause of sound is vibratory movement from a disturbance, communicated to the hearing apparatus through an environmental medium, such as air. Scientists group all such vibratory phenomena under the general category of "sound," even when they lie outside the range of human hearing.

Hearing functions to detect the presence of sound, as well as to identify the location and type of sound, and its characteristics (whether it is getting louder or softer, for instance). Humans and many animals use their ears to hear sound, but loud sounds and low-frequency sounds can be perceived by other parts of the body as well, through the sense of touch.


1.3 Process of hearing & its impediment leading to different types of hearing loss


The process of Hearing

The process of hearing begins with the occurrence of a sound. Sound is initiated when an event moves and causes a motion or vibration in air. When this air movement stimulates the ear, a sound is heard and the human ear can hear from 20 Hz to 20,000 Hz. 

In the human ear, a sound wave is transmitted through four separate mediums along the auditory system before a sound is perceived: in the outer ear—air, in the middle ear— mechanical, in the inner ear liquid and to the brain—neural.

Sound Transmission through the Outer Ear - Air transmitted sound waves are directed toward the delicate hearing mechanisms with the help of the outer ear, first by the pinna, which gently funnels sound waves into the ear canal, then by the ear canal.

Sound Transmission through the Middle Ear- When air movement strikes the tympanic membrane, the tympanic membrane or eardrum moves. At this point, the energy generated through a sound wave is transferred from a medium of air to that which is solid in the middle ear. The ossicular chain of the middle ear connects to the eardrum via the malleus, so that any motion of the eardrum sets the three little bones of the ossicular chain into motion.

Sound Transmission through the Inner Ear- The ossicular chain transfers energy from a solid medium to the fluid medium of the inner ear via the stapes. The stapes is attached to the oval window. Movement of the oval window creates motion in the cochlear fluid and along the Basilar membrane. Motion along the basilar membrane excites frequency specific areas of the Organ of Corti, which in turn stimulates a series of nerve endings.

Sound Transmission to the Brain- With the initiation of the nerve impulses, another change in medium occurs: from fluid to neural. Nerve impulses are relayed through the central nervous, through various nuclei along the auditory pathway to areas to the brain. It is the brain that interprets the neural impulses and creates a thought, picture, or other recognized symbol.

Types of Hearing Loss according to place of impairment

Conductive hearing loss – hearing loss due to the interference in the transmission of sound to and through the sense organ (outer or middle ear)


·         Malformation of outer ear, ear canal, or middle ear structures

·         Fluid in the middle ear from colds

·         Ear infection (otitis media - an infection of the middle ear in which an accumulation of fluid may interfere with the movement of the eardrum and ossicles

·         Allergies

·         Poor Eustachian tube function

·         Perforated eardrum

·         Benign tumors

·         Impacted earwax

·         Infection in the ear canal

·         Foreign body in the ear

·         Otosclerosis

Sensory-neural hearing loss – due to the abnormality of the inner ear or the auditory nerve, or both


·         Exposure to loud noise

·         Head trauma

·         Virus or disease

·         Autoimmune inner ear disease

·         Hearing loss that runs in the family

·         Aging (presbycusis)

·         Malformation of the inner ear

·         Meniere’s Disease

·         Otosclerosis - a hereditary disorder in which a bony growth forms around a small bone in the middle ear, preventing it from vibrating when stimulated by sound.

·         Tumors


Mixed hearing loss - combination of both; sometimes called a flat loss


1.4 Definition of hearing loss, demographics & associated terminologies: deaf/ Deaf/ deafness/ hearing impaired/ disability/ handicapped

Definitions of Hearing Impairment

Person with disability act- (PWD, 1995)

·        Definition of disability in pwd act includes hearing impairment

Hearing impairment means loss of 60 decibel or more in the better ear in speech conversation frequencies.

·        Chapter 5 education have point for restructuring the curriculum for benefit of students with hearing impairment , to facilitate them to take only one language as part of their curriculum.

Centre for diseases control and prevention (CDC)

·        Refers to hearing impairment as conditions that affect the frequency and or intensity of one’s hearing. Individuals with mild to moderate hearing impairments may be “hard of hearing” but are not “deaf” these individuals differ from deaf individuals as they use their hearing to assist in communication with others

According to degree of hearing loss

WHO- Grades of hearing impairment-

Grade-of impairment

Audiometric    ISO value


0-No impairment

25db/ better

No or very slight hearing problems

Can hear whispers

1-slight impairment


Able to hear and repeat words spoken in normal voice at 1 meter

2-moderate impairment

41-60 db

Able to hear and repeat words spoken in raised voice at 1 meter

3-severe impairment

61-80 db

Able to hear some words when shouted into better ear

4-profound impairment

81 db or greater

Unable to hear and understand even a shouted voice


National institute for the hearing handicapped-


Type of


DB level

Word recognition score

% of



Mild hearing


26- 40


80-100 % in better


Less than 40%

    II.            a

Moderate hearing




50-80 % in better




Severe hearing




40-50 % in better




a)profound hearing




Less than 40% in better ear



b) total loss

91 and


Very poor


According to place of impairment

       conductive hearing loss – hearing loss due to the interference in the transmission of sound to and through the sense organ (outer or middle ear)

      Sensory-neural hearing loss – due to the abnormality of the inner ear or the auditory nerve, or both

       mixed hearing loss - combination of both; sometimes called a flat loss

According to the age at onset of deafness

      Congenitally deaf – born deaf

      Adventitiously deaf – born with normal hearing and became deaf through accident/illness

According to language development-

      Pre-lingually deaf – born deaf or lost hearing before speech and language were developed

      Post-lingually deaf- lost hearing after development of spontaneous speech and language


According to WHO over 5% of the world’s population – or 466 million people – has disabling hearing loss (432 million adults and 34 million children). It is estimated that by 2050 over 900 million people – or one in every ten people – will have disabling hearing loss.

Disabling hearing loss refers to hearing loss greater than 40 decibels (dB) in the better hearing ear in adults and a hearing loss greater than 30 dB in the better hearing ear in children. The majority of people with disabling hearing loss live in low- and middle-income countries.

Approximately one third of people over 65 years of age are affected by disabling hearing loss. The prevalence in this age group is greatest in South Asia, Asia Pacific and sub-Saharan Africa.

The Census 2011 revealed that, In India, 20% of the disabled persons are having disability in movement, 19% are with disability in seeing, and another 19 % are with disability in hearing. 8% has multiple disabilities.

      Out of the total disabled in the age group 0-19 years, 20% are having disability in hearing followed by 18% with disability in seeing. 9% has multiple disabilities. 

      Among the disabled in the age group 20-39 years, 22% are having disability in movement and 18% has disability in hearing. 6% has multiple disabilities. 

      Among the disabled in the age group 40-59 years, 23% are having disability in movement and 19% has disability in seeing. 5% has multiple disabilities. 

      Among the elderly disabled persons, the disabilities in movement (25%), in seeing (25%) and hearing (12%) are prominent. 12% has multiple disabilities.

1.5 Challenges arising due to congenital and acquired hearing loss

Congenital causes

Congenital causes may lead to hearing loss being present at or acquired soon after birth. Hearing loss can be caused by hereditary and non-hereditary genetic factors or by certain complications during pregnancy and childbirth, including:

Acquired causes

Acquired causes may lead to hearing loss at any age, such as:

Among children, chronic otitis media is a common cause of hearing loss.


      Language: Delayed language development with unclear speech and incorrect pronunciation.

      Emotion and behavior:  Easy to have emotional and behavioral problems as a result of difficulties in verbally expressing himself/ herself

      Self-confidence:  Lack of self-confidence with poor self-image for being always mistaken to be slow in response

      Social interaction:  Socially excluded by peers due to poor comprehension and expression, or actively avoid social contact and communication

      Academic performance: Academic performance being affected due to difficulty in receiving the correct messages

      It causes delay in the development of receptive and expressive communication skills (speech and language).

      The language deficit causes learning problems that result in reduced academic achievement.

      Communication difficulties often lead to social isolation and poor self-concept.

      It may have an impact on vocational choices.