Unit 2: Definition, types, characteristics and educational needs of children with

2.1. Hearing Impairment: Definition and types

2.2. Visual Impairment: Definition and types

2.3. Mental Retardation: Definition and types

2.4. Neuro–muscular: Definition and types

2.5. Autism Spectrum Disorder: Definition and types













2.1. Hearing Impairment: Definition and types


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 VIII C.N., 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.


       A person who is not able to hear as well as someone with normal hearing – hearing thresholds of 25dB or better in both ears – is said to have hearing loss.

       ‘Hard of hearing’ refers to people with hearing loss ranging from mild to severe.

       ‘Deaf’ people mostly have profound hearing loss, which implies very little or no hearing

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.

Idea- individual with disability education act, 2004

·        Defines hearing impairment as impairment in hearing, whether permanent or fluctuating that adversely affects a chill’s educational performance but is not included under the definition of deafness.

World health organization (WHO) -

·        Defines – A person who is not able to hear as well as someone with normal hearing – hearing threshold of 25db or better in both ears is said to have 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)

      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 degree of hearing loss –

       Loss Slight 27-40 dB

      Mild 41-55 dB

      Moderate 56-70 dB

      Severe 71-90 dB

      Profound 91 dB or more

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-

• Prelingually deaf – born deaf oer lost hearing before speech and language were developed

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

Ø National institute for the hearing handicapped-

Various types of impairments


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



2.2. Visual Impairment: Definition and types

How We See: The eye functions like a camera. Vision is a complex function. The act of seeing requires light to see by and the brain to interpret what is seen. The light rays reflected from an object in a person’s field of vision fall on the eyes.

The rays pass through the cornea, aqueous humour, and through pupil which dilates or contracts to control light in accordance to the brightness of the object. The rays then pass through crystal lineless and the rays of light are focussed on the retina. The process of focusing is called accommodation. The cornea and the lens combine to bend the light rays as they pass through. The rays pass through the vitreous body and penetrate on retina, where they set up a photo-chemical response in the outermost layers, stimulating the rods & cones.

The impulse is picked by retinal nerve fibres and passes along the optic nerve to the brain where an upside down image is formed. Based on experience, the inverted image is psychologically transposed.

Definition of visual impairment as adopted in the persons with Disabilities (Equal opportunities, Protection of Right & Full Participation) Act 1995 as well as National Programme for control of Blindness (NPCB).

Blindness: refers to a condition where a person suffers from any of the following conditions, namely:

1.     Total absence of sight; or

2.      Visual acuity not exceeding 6/60 or 20/200 (snellen) in the better eye even with the correction lenses, or

3.     Limitation of the field of vision subtending an angle of 20 degree or worse

For deciding blindness visual acuity and / or field of vision are considered.

Low vision: As per PWD Act, 1995 also recognises low vision as a category of disability and defines it as follows:- “Person with low vision,” means a person with impairment of visual functioning even after treatment or standard refractive correction but who uses or is potentially capable of using vision for the planning or execution of a task with appropriate assistive device.

For teachers this definition is of no use as it does not give the range of visual acuity as well as field of vision. Practitioners therefore follow the WHO working definition of low vision- “A person with low vision is one who has impairment of visual functioning even after treatment and/or standard refractive correction, and has a visual acuity of less than 6/18 to light perception or a visual field of less than 10 degrees.”

The World Health Organization uses the following classifications of visual impairment. When the vision in the better eye with BEST POSSIBLE glasses correction is:

The International Classification of Diseases 11 (2018) classifies vision impairment into two groups, distance and near presenting vision impairment.

Distance vision impairment:

Near vision impairment:

2.3. Mental Retardation: Definition and types

There are many definitions of mental retardation, the most comprehensive among them is the one given by the American Association on Mental Retardation (AAMR) 1983 restated till 2004.

The Mental Deficiency Act of 1921 in England considered “ Mental defectiveness as a condition of arrested or in complete development of mind existing before the age of eighteen years, whether arising from inherent causes or induced by disease or injury.

According to American Association on Mental Dediciency (AAMD), 1956....

   “Mental retardation refers to sub-average general intellectual functioning, which originates during the developmental period and is associated with impairments in adaptive behaviour.”

This definition refers to sub-average intelligence, which is explained as one SD below the mean (approximately 85 and below 100-15=85). This developmental period was described as birth to 16years. Using this definition for legal purposes, it was observed that a number of persons who were close to normal (IQ 70 to 85) were receiving support. By incidence too they are more in number and as the severity increases the number of persons affected reduces. As it was not serving the purposes and the right population, the definition was revised in 1973.

AAMR, 1992....

  “Mental retardation refers to substantial limitation in present functioning. It is characterized by significantly sub-average intellectual functioning, existing concurrently and with related limitations in two or more of the applicable adaptive areas: communication, self care, home living, social skills, community use, self direction, health and safety, functional academics, leisure and work. Mental retardation manifest before age 18.”

q Limited Functioning

The first part of this definition establishes mental Retardation as a category of concern for people whose current levels of functioning are limted. Mental Retardation is difficulty in learning and performing certain daily life skills as a esult of substantial limitations in conceptual, practical and social intelligence.

q Intellectual Functioning

The second part of the definition “significantly sub- average intellectual functioning” usually translated as a score of 70 to 75 or below on one or more individually administered general intelligence tests. Tests scores and other information are reviewed and evaluated by teams of professionals as a part of the process of diagnosing Mental Retardation.

q Adaptive Skills

The third part that the individual must also demonstrate lilted adaptive skills in key areas- is an important part od=f the definition. First, adaptive skill limitations must occur at the same time as intellectual limitations; intellectual functionong alone is insufficient basis for a diagnosis of mental retardation. Second, more than one area of adaptive skills must be limited to reduce the chnces of making a mistake in diagnosing Mental Retardation.

AAMR, 2002...

“Mental retardation is a disability characterized by significant limitations both in intellectual functioning and in adaptive behavior as expressed in conceptual, social, and practical adaptive skills.  This disability originates before age 18.”




Ø     130+        Very Superior (Gifted)

Ø     120-129   Superior

Ø     110-119   High Average

Ø     90-119     Average

Ø     80-89       Low Average

Ø     70-79       Borderline

Ø     69 and below   Mental impairment

q AAMD/AAMR Classification Systems

Heber (1961)      

Borderline   68-84

Mild             52-67

Moderate    36-51

Severe        20-35

Profound     <20

q Profiles of Intellectual Disability


Ø Mild ID Profile

Minor delays in the preschool period

Evaluation often only after school entry

2-3 word sentences used in early primary grades

Expressive language improvement with time

Reading/math skills – 1st to 6th grade levels

Social interests typically age appropriate

Mental age range of 8-11 years of age

Persistent low academic skill attainment can limit vocational possibilities


Ø Moderate ID Profile

More evident and consistent delays in milestones

At school entry may communicate with single words and gestures

Functional language is the goal

School entry self-care skills – 2-3 year range

By age 14:  basic self-care skills, simple conversations, and cooperative social interactions

Mental age of 6-8 years of age

Vocational opportunities limited to unskilled work with direct supervision and assistance


Ø Severe ID Profile

Identification in infancy to two years

Often co-occurring with biological anomalies

Increased risk for motor disorders and epilepsy

By age 12:  may use 2-3 word phrases

Mental age typically 4-6 years of age

As adults assistance typically required for even self-care activities

Close supervision needed for all vocational tasks


Ø Profound ID Profile

Identification in infancy

Marked delays and biological anomalies

Preschool age range may function as a 1-year-old

High rate of early mortality

By age 10:  some walk/acquire some self-care skills with assistance

Gesture communication

Recognizes some familiar people

Mental age range from birth to 4 years of age

Functional skill acquisition not likely


2.4. Neuro–muscular: Definition and types


Cerebral palsy (commonly referred to as CP) affects normal movement in different parts of the body and has many degrees of severity.

CP causes problems with posture, gait, muscle tone and coordination of movement.

The word “cerebral” refers to the brain’s cerebrum, which is the part of the brain that regulates motor function. “Palsy” describes the paralysis of voluntary movement in certain parts of the body.

Cerebral Palsy is a group of conditions that are characterized by chronic disorders of movement or postures; it is cortical in origin, manifests itself early in life and is not the outcome of a progressive disease.





These developmental movement disorders can be limited to: one side of the body, the legs, the arms, all four limbs or just one limb.



Poliomyelitis, also called polio or infantile paralysis, is a highly infectious viral disease that may attack the central nervous system and is characterized by symptoms that range from a mild nonparalytic infection to total paralysis in a matter of hours.


The reason it is called poliomyelitis is because the prefix polio means 'grey' in ancient Greek, myelo refers to the spinal cord, and itis refers to the inflammation of something. Therefore, when we combine all of these terms together we get the inflammation of the spinal cord's grey matter, or poliomyelitis.

Poliomyelitis or infantile paralysis is a viral infection that affects the nerves of the spinal cord, located inside the spinal bones (vertebrae) at the back of the body. This infection can cause permanent paralysis of muscles. Poliomyelitis mostly affects children up to 15 years of age, but can affect adults too. After the acute phase, the disease is not communicable to others. Since poliomyelitis does not affect the brain, the intellectual ability of children with poliomyelitis remains intact.



A spinal cord injury — damage to any part of the spinal cord or nerves at the end of the spinal canal — often causes permanent changes in strength, sensation and other body functions below the site of the injury.

Medical providers divide the spinal cord into four distinct regions. Knowing the region in which the injury is located is often the key to understanding diagnosis and treatment. The four spinal cord regions are:

Types of spinal cord injuries

All spinal cord injuries are divided into two broad categories: incomplete and complete.

Incomplete spinal cord injuries are increasingly common, thanks in part to better treatment and increased knowledge about how to respond—and how not to respond—to a suspected spinal cord injury. These injuries now account for more than 60% of spinal cord injuries, which means we're making real progress toward better treatment and better outcomes.

Some of the most common types of incomplete or partial spinal cord injuries include:

Knowing the location of your injury and whether or not the injury is complete can help you begin researching your prognosis and asking your doctor intelligent questions. Doctors assign different labels to spinal cord injuries depending upon the nature of those injuries.


 Spina bifida literally means ‘split spine’

A fault in the development of the spinal cord and surrounding bones (vertebrae) leaves a gap or split in the spine. The spinal cord has not formed properly, and may also be damaged. To help understand what it is, it is useful to explain the composition of the nervous system.


The three main types of spina bifida always present at birth are:

Spina Bifida Cystica (cyst-like)

The visible signs are a sac or cyst, rather like a large blister on the back, covered by a thin layer of skin. There are two forms:

1)   Myelomeningocele (meningomyelocele)

Myelomeningocele is the most serious and more common of the two forms of cystic spina bifida. Here the cyst not only contains tissue and cerebro-spinal fluid but also nerves and part of the spinal cord. The spinal cord is damaged or not properly developed. As a result, there is always some paralysis and loss of sensation below the damaged region.

The amount of disability depends very much on where the spina bifida is, and the amount of affected nerve tissue involved. Bladder and bowel problems occur in most people with myelomeningocele, as the nerves come from the bottom of the spinal cord, so are always below the lesion. It is also necessary to have intact nerve pathways to the brain for complete control and sensation.

The outer part of the vertebrae is split. The spinal cord and meninges are damaged and pushed out through the opening. Hydrocephalus is usually associated with this form.

2)   Meningocele

In this form, the sac contains meninges (tissues which cover the brain and spinal cord) and cerebro-spinal fluid, which bathes the central nervous system. Development of the spinal cord may be affected, but impairment is usually less severe than myelomeningocele. Meningocele is the least common form of spina bifida.

The outer part of the vertebrae is split. The spinal cord is normal. The meninges are damaged and pushed out through the opening.

3)Spina Bifida Occulta (hidden form)

This is a mild form of spina bifida which is very common. Estimates vary but between 5% and 10% of people may have spina bifida occulta. It must be emphasised that, for the vast majority of those affected, having spina bifida occulta is of no consequence whatsoever. Often people only become aware that they have spina bifida occulta after having a back x-ray for an unrelated problem.

The outer part of the vertebrae is not completely joined. The spinal cord and its covering (the meninges) are undamaged Encephalocele.

·        Encephalocele

This is a sac which is formed when the bones of the skull fail to develop. It may contain only cerebro-spinal fluid or part of the brain may also be present in the sac, resulting in brain damage.

·        Anencephaly

This is where the brain does not develop properly or is absent, and the baby is either still born or dies shortly after birth.

·        Hydrocephalus Most babies born with myelomeningocele also have hydrocephalus (from the Greek hydro, meaning water, and cephalie meaning brain). This is an accumulation of cerebro-spinal fluid which arises from an imbalance in the production and drainage of that fluid.


¡  Muscular Dystrophy (MD) is a group of inherited diseases in which the voluntary muscles progressively weaken overtime.

¡  Heart and other organs can also be affected.

¡  9 major types:

§  Duchenne, Myotonic, Becker, Limb-girdle, Facioscapulohumeral, Congenital, Oculopharyngeal, Distal, and Emery-Dreifuss

§  Can occur at any age

§  Most common in young males.

§  Type is based on what age the individual is when muscular dystrophy appears

§  Also depends on how severe the disease is, which muscles it affects, rate of progression, and the way it appears.

§  Some types of muscular dystrophy only affect males.

§  Some individuals with this disease experience mild symptoms, while others suffer from severe muscle weakness, dying at an early age.


¡  Multiple sclerosis (MS) is a potentially disabling disease of the brain and spinal cord (central nervous system).

¡  In MS, the immune system attacks the protective sheath (myelin) that covers nerve fibers and causes communication problems between your brain and the rest of your body. Eventually, the disease can cause the nerves themselves to deteriorate or become permanently damaged.

¡  Signs and symptoms of MS vary widely and depend on the amount of nerve damage and which nerves are affected. Some people with severe MS may lose the ability to walk independently or at all, while others may experience long periods of remission without any new symptoms.

¡  There's no cure for multiple sclerosis. However, treatments can help speed recovery from attacks, modify the course of the disease and manage symptoms.

¡  The cause of multiple sclerosis is unknown. It's considered an autoimmune disease in which the body's immune system attacks its own tissues. In the case of MS, this immune system malfunction destroys myelin (the fatty substance that coats and protects nerve fibers in the brain and spinal cord).

¡  Myelin can be compared to the insulation coating on electrical wires. When the protective myelin is damaged and nerve fiber is exposed, the messages that travel along that nerve may be slowed or blocked. The nerve may also become damaged itself. It isn't clear why MS develops in some people and not others. A combination of genetics and environmental factors appears to be responsible.

2.5. Autism Spectrum Disorder: Definition and types


World Health Organisation (WHO) 2013

      Core symptoms: Mixture of impaired capacity for reciprocal socio-communicative interaction and a restricted, stereotyped repetitive repertoire of interests. Individuals with ASD may have decreased general intellectual ability.

      Neuro-developmental impairments in communication, social interaction and unusual ways of perceiving and processing information hinders daily functioning of people with ASDs and  impede their educational and social attainments.

The Individuals with Disabilities Education Act (IDEA)

      A developmental disability affecting verbal and non-verbal communication and social interaction,(Age<3).

       Engagement in repetitive activities and stereotyped movements, resistance to environmental change or change in daily routines, and unusual responses to sensory experiences.

Rehabilitation Council of India (RCI)

      Autism is one of five developmental disorders included under the umbrella of the Pervasive Developmental Disorders.

      Autism is characterized by deficits in social interaction and communication, and unusual and repetitive behaviour. autism manifests at birth or within the first two-and-a-half years of life.

The Americans with Disabilities Act of 1990 (ADA)

      Autism is defined as a developmental disability significantly affecting verbal and non- verbal communication and social interaction, generally (< age 3), which adversely affects a child's educational performance

Types of ASD

The most recent and updated version of the Diagnostic and Statistical Manual of Mental Disorders version 5 (DSM -5) of American Psychiatric Association has just a single category for the diagnosis of an autistic disorder – autism spectrum disorders, which include the following disorders that were previously discussed separately:

      Autism or Autistic Disorder: Children who seem to have met most of the rigid criteria of a diagnosis of Autism are said to have Autism or Autistic Disorder. They have moderate to severe impairments in Social and Language skills, possess Repetitive Behaviors and Restricted Interests. Often the children and individuals with Autistic Disorder also have mental retardation and seizures.

      Asperger’s Syndrome: Asperger Syndrome ~ AS, is the mildest form of Autism. It is found to have affected boys three times more in comparison with girls.

The most common symptoms of Asperger Syndrome are the children affected become excessively interested in a single subject or topic. They tend to find out and learn everything about their preferred subject and talk about it all the time. As compared with other form of Autism, children with Asperger have extremely good vocabulary however their social skills are markedly impaired and they are often awkward and uncoordinated.

It is also found that the children with Asperger’s Syndrome very often have normal or above normal IQ (Intelligence Quotient). As a result, many doctors address it as High-Functioning Autism. As children with AS enter into Childhood, they are at a high risk of developing Anxiety and Depression.

      PDD-NOS (Pervasive Development Disorder, Not Otherwise Specified) : PDD-NOS is a little complex syndrome to diagnose amongst children on the Autism Spectrum. Commonly children & individuals whose behavioral symptoms are more severe than Asperger’s Syndrome but less severe than Autistic Disorder are diagnosed as PDD-NOS.

No two children/individuals with PDD-NOS exhibit similar symptoms. This makes generalizing the disorder rather more complex. Commonly, children with PDD-NOS exhibit following symptoms:

Impaired social communication/interaction (similar to Autistic Disorder)

Better language/communication skills as compared to children with Autistic Disorder however these skills are not as good as of children with Asperger’s Syndrome

Lesser sensory dysfunction as a result fewer repetitive behaviors

      Rett Syndrome : Rett Syndrome is severe form of Autism and it mostly occurs in girls. It is mostly caused by a genetic mutation wherein the mutation occurs randomly and has no inherited significance. It is a rare syndrome affecting about one in 10,000-15,000 girls.

In this syndrome, girls aging between 6 to 18 months of age regress marginally and lose linguistic and social skills. They habitually wring hands and develop coordination problems. Head growth slows down significantly and by the age of two their head appears to be far below normal. The treatment of Rett Syndrome focuses mostly on physical therapy and speech therapy to improve function.

      Child Disintegrative Disorder : It is the least common and most severe form of Autism Spectrum Disorder. In CDD, the child rapidly loses multiple areas of function between the ages of 2 to 4 years of age. This regression takes place in social skills, linguistic skills as well as in intellectual abilities.

Very often the child develops a seizure disorder. The children with CDD – Childhood Disintegrative Disorder are severely impaired and don’t recover their lost function.

The number of children affecting CDD is lesser than 2 children per 100,000 children with Autism Spectrum Disorder. Boys are more commonly affected by CDD than girls.