Previous chapter

Chapter 5: Impairment, Disability, and Handicap

John Frederiksen, Mike Martin, Leonor Moniz Pereira, Ramxa2n Puig de la Bellacasa and Stephen von Tetzchner

"Although there is clearly a biological difference between the disabled and the able-bodied, this is not the decisive difference between the two groups. Handicap is a social construct. There is a biological sub-stratum, but what it means to be handicapped to others and to oneself is overwhelmingly social and decisively political" (Roth, 1983, p. 56). Many different types of impairments and disabilities may have an impact on the use of telecommunications. Knowledge about impairments and disabilities is important to understand possible consequences for the use of telecommunications. It is also a prerequisite for designing and producing standard telecommunications equipment and services that can be used by as many people as possible, and for developing specialised equipment designed to alleviate the negative consequences of a disability. The present chapter reviews some common impairments and disabilities. (Chapter 21 reviews some specific consequences of impairments and disabilities for telecommunication use in relation to standardisation activities).

The World Health Organization (WHO) suggested the following definitions in 1980:

Impairment: a loss or abnormality of psychological, physiological, or anatomical structure or function.

Disability: any restriction or lack (resulting from an impairment) of the ability to perform an activity in the manner or within the range considered normal for a human being.

Handicap: a disadvantage for a given individual, resulting from an impairment or a disability, that limits or prevents the fulfilment of a role that is normal (depending on age, sex, and social and culture factors) for that individual.

Impairments and disabilities may be temporary or permanent, reversible or irreversible, and progressive or regressive. The situation people find themselves in may determine to what degree a disability is handicapping for them. It is evident from the definitions above that a handicap is the result both of an impairment and of environmental conditions (cf. Figure 5.1). If environmental barriers are taken away, the person will still be impaired, but not necessarily handicapped. It should also be noted that the definition of disability as distinct from handicap is not without problems, in particular the formulation "considered normal for a human being", and many people with disabilities do not distinguish their use.

The functional ability of people who are diagnosed as having the same impairment or disability may vary widely. For example, some people who are legally blind may be able to utilize differences in light intensity, while others are unable to perceive such differences. People who have clinically similar hearing impairments, as shown on audiograms, may use quite different aspects of the acoustic information available to them. The degree of handicap may vary significantly and may be specific to certain situations.

In this brief review of impairment and disability, differences in degree are dealt with only in a very general manner. The emphasis is on typical features rather than variations. However, when assessing the needs of a single individual, variation that may influence the handicapping effects of the condition must be taken into account.

1.0 Visual Impairment

In medical terms, visual impairment can be defined as a total loss of, or reduced ability to, perceive light and colour. The classic definition of blindness is a visual acuity of 6/60 or less in the better eye with optimum correction, or visual acuity of better than 6/60 if the widest diameter of field of vision subtends an angle no larger than 20 degrees. This means that a blind person must be at 6 metres in order to see something that a person with normal sight can see at 60 metres, or that the field of vision is so restricted that only a very limited area can be seen at one time (see Figure 5.2). Within this legal definition, a wide variety of visual impairments can be found. Bauman (1969) distinguishes between a visual impairment where vision is of no practical use in a testing or working situation; a visual impairment where vision is of some help in a testing or working situation, but where effective reading of even moderately enlarged print is not possible, and a visual impairment where print may be used effectively, although it may have to be large type, held very close to the eyes, or used with special visual aids and under special lighting conditions.

Blindness implies a total or near total loss of the ability to perceive form. Partial sight implies an ability to utilize some aspects of visual perception, but with a great dependency on information from other modalities, in particular touch and hearing. Reduced vision may handicap a person in situations which put great demands on the use of vision, but in most situations the person will not be handicapped by the visual impairment; they will, for example, be able to read large type print with glasses.

The incidence of all kind of visual impairment increases considerably with age. Less than 10 percent of blind people are under 20 years of age while nearly 50 percent are 65 years or older (Bauman, 1969). In addition, people older than 40 need higher light intensity and contrast than 20-year-olds, and the difference increases dramatically between age 40 and 60.

Problems with orientation and mobility are one of the typical consequences of failing sight. In the case of elderly people, difficulties in orientation and mobility may be intensified by other cognitive impairments.

2.0 Hearing Impairment

Hearing impairment implies a total or partial loss of the ability to perceive acoustic information. The impairment may affect the full range of hearing, or be limited to only parts of the auditory spectrum, which for speech perception is the region between 250 and 4000 Hz (see Figure 3.x in chapter 3).

The term deaf is used to describe people with profound hearing losses while hard of hearing is used for those with mild to severe hearing losses. Hearing loss is expressed in decibel (Db) relative to an audiometric cero which is a standardized normal threshold of hearing. Deafness is usually defined as an average hearing loss of more than 92 Db in the speech area. A person with a hearing loss of 70-90 Db is severely hard of hearing. A person with a hearing loss of 50-60 Db is considered moderately hard of hearing (Davis, 1970). Measured losses of less than 20 Db is considered normal acuity.

The onset of the hearing impairment is important for language development and for identification with the deaf community. A person who was born profoundly deaf or has become deaf at a very early age, i.e. prelingual deafness, is dependent mainly on visual communication for speech and language development, and often uses sign language. A person who becomes deaf later in life usually has a good mastery of both spoken and written language before the onset of deafness. Some deaf people may fall between these two groups. For example, they may become deaf at an early age, but after they have learned to speak, say at 3-4 years of age, and therefore may not have a full mastery of spoken or written language.

For a discussion of telecommunication devices, it is useful to distinguish between deaf people with and without intelligible speech; and between those who can and those who cannot understand speech with amplification. Although some people with prelingual deafness have intelligible speech, this is more typical of those deaf persons who acquired speech and language skills before the onset of the hearing impairment. For people with profound deafness, speech discrimination may be very limited without lip-reading even when they can hear some sound with the help of a hearing aid.

Written text is closely related to spoken language, and the function of writing is to mirror speech (Saussure, 1916). Thus, although mastery of spoken language may not be a prerequisite for learning to read, it greatly facilitates the acquisition of reading and writing. Thus, due to the limited knowledge of spoken language, the written language skills of many prelingually deaf people may often be limited as well (cf., Conrad, 1979).

Post-lingually deafened people usually have intelligible speech, but because they cannot hear their own voice, their control of volume may be erratic, and they may therefore speak too softly or too loudly. While they typically have no special problems in the use of written language for, if their hearing impairment was acquired in childhood, vocabulary and other aspects of both spoken and written language use may be adversary influenced, due to more limited experience with spoken language.

People of any age may have a mild to severe hearing loss, but the majority will be elderly. For people who are hard of hearing, speech and hearing remain the main mode of communication, often with the help of a hearing aid. In the case of a severe hearing impairment, however, the person may be dependent on lip reading in addition to using a hearing aid, and for some types of hearing impairment, a hearing aid is of limited help. Furthermore, although many hard-of-hearing people hear speech with the help of amplification, their ability to understand speech may be hindered due to the effect of hearing loss. The ability to hear is not necessarily equal with the ability to understand what is said.

3.0 Impairment of Speech Production

Speech impairment refers to any reduction in a person's ability to use speech in a functional and intelligible way. The impairment may influence speech in a general way, or only certain aspects of it, such as fluency or voice volume. Speech impairment may be due to a number of different factors. It may or may not be linked with difficulties in speech perception or comprehension. Speech impairment may be caused by developmental problems as in the case of moderate to severe developmental language disorder (dysphasia), or by distorted speech due to lack of muscular control (dysarthria). It may be an acquired impairment, for example loss of expressive language skills (expressive aphasia) caused by a stroke or brain tumour, or speech impairment after removal of the larynx (laryngectomy). Acquired disorders are more prevalent with advancing age. When speech impairment is caused by reduced muscular control (apraxia), it is often accompanied by reduced muscular control of the arms. Low volume is often apparent in people who have had laryngectomy and who must speak in a "whispering" voice.

The intelligibility of speech may be reduced by varying degrees: speech may be lacking totally or it may be unintelligible even to people who are familiar with the speaker. In other cases, the speaker may be intelligible to familiar persons, while difficult to understand for others. There may also be situational variation: for example, people who stutter do so in some situations and not in others, depending upon whom they talk to and the communicative load of the situation.

4.0 Impairment of Language Comprehension

This category contains a loss of, or a reduction in, the ability to understand language. The disability may imply only an impairment of language, or it may be associated with a more general intellectual impairment.

Several disorders of the central nervous system may include impairment of language comprehension. In some conditions, like severe developmental language disorder (receptive dysphasia), only the language function is affected, while other conditions may influence most intellectual functions. This may, for example, be the case for people with autism.

Impaired language comprehension may be developmental or acquired. In developmental disorders, the impairment of comprehension will also have consequences for the ability of people to express themselves. In some acquired conditions, it is mainly comprehension that is affected while the people are able to express themselves. Aphasia, a language disorder caused by stroke or trauma, may affect language comprehension and/or use.

Many people with limited comprehension may be able to communicate better through the visual modality than through speech. They may use manual signs or special symbol systems (e.g. Bliss, Rebus), but the vocabulary may be severely limited (cf. Kiernan, Reid & Jones, 1982; von Tetzchner & Martinsen, in press).

In the case of people with intellectual impairment, non-verbal modes of instruction may also be affected. Thus, not only communication in itself, but also instruction in the use of different kinds of equipment may be severely hindered.

People with language disorders and a more general intellectual handicap may have some understanding of language but a limited vocabulary and reduced comprehension of sentence structure. The understanding of language may be strongly related to context, which means that comprehension is very dependent on non-linguistic cues, such as the presence of persons or objects, or limited to a small number of well known situations. Most forms of telecommunication will be hindered because of the limitation in non-linguistic contextual cues.

5.0 Intellectual Impairment

People with reduced intellectual ability constitute a very diverse group with a range of sensory, motor and cognitive impairments; most impairments, including visual and auditory impairment, have a higher incidence in the group that is called intellectually impaired. One common trait is that they tend to do things slower than other people, another that they have reduced comprehension of instructions and language in general. For the purpose of adapting telecommunication equipment and services, the best strategy may be to consider intellectual impaired people as having multiple impairments (see below).

6.0 Reading Impairment

Dyslexia is a disorder manifested by difficulty in learning to read despite conventional instruction, adequate intelligence, and socio-cultural opportunity. It is dependent on fundamental cognitive disabilities, which are frequently of constitutional origin (Critchley, 1970). The reading impairment may or may not be associated with other language disorders, such as developmental dysphasia and anarthria due to cerebral palsy. Severe reading disorder may also be an acquired condition similar to aphasia, and is then usually called alexia.

A lack of reading skills will be a handicap in a wide range of social and professional situations. In particular, it will influence the person's ability to obtain information.

7.0 Reduced Function of Legs and Feet

A reduced function of legs and feet implies dependency on a wheelchair or other mobility aid to help walking (e.g. crutch or stick). People with this disability are usually able to communicate normally on the telephone, but may have problems getting to the equipment.

The mobility of a wheelchair user depends largely on the dimensions of the wheelchair. The length of a wheelchair is usually less than 1.25 meters, including the footboard, and its width is in most cases less than 0.75 meters. This gives a necessary turning radius of 1.4-1.5 meters. Electric wheelchairs may be somewhat wider, but the hands of the user do not extend beyond the arm rests. Thus, the radius of manual and electric wheelchairs will be approximately the same.

In general, a wheelchair user is dependent on an even surface without any significant change of elevation. The maximum abrupt change of level to be managed by somebody driving the wheelchair himself is about 2.5-3 centimetres. Some users may manage an uneven road surface, but it will be most unpleasant, and the wheelchair may break down. For example, it is quite painful for wheelchair users to drive in areas with uneven paving stones. Entering or leaving a sidewalk may be difficult, and even dangerous. Long-distance travel in a hand propelled wheelchair is tiring and may cause cramp in the hands.

A person in a wheelchair with a normal arm function will usually be able to reach 0,4-1,2 m. Thus, for installations to be within reach, they should be placed at not more than 0,4 m from the nearest place a wheelchair user can access, for example, not more than 0.4 meters from the side of a table. People who use walking aids, such as crutches and sticks, are mobile over short distances, but will have difficulties moving longer distances. Therefore, it is essential that they do not have to travel long distances and that suitable resting places are provided. Snow and ice are particularly troublesome for people with difficulties in walking. Even rainy weather may cause considerable problems, as many kinds of surface, such as stripes in pedestrian crossings, woodfloors and paving stones, become very slippery when they are wet. In a telephone booth, it may, for example, cause problems to hold the receiver and dial while holding the balance.

8.0 Reduced Function of Arms and Hands

Reduced function of arms and hands includes the lack of arms or hands, or reduced ability to use them due to reduced strength or co-ordination. For a person who lacks both arms, or the functional use of both arms, activities related to moving, turning or pressing objects are often impossible, or may have to be replaced by other methods, for example, a mouth stick. This does not influence speech communication itself, but implies great difficulty in using a wide range of technical and non-technical equipment.

A person who lacks one arm or who has lost the ability to use one arm in a functional way, will typically be handicapped in manipulating equipment that demands the simultaneous use of both hands. This includes a large range of equipment, and especially the simultaneous pressing of two or three keys on computer or terminal keyboards.

For people who cannot move their fingers independently, all fine motor skills will be affected. They may not be able to use keyboards or keypads, ticket automats, etc. Turning of pages, and inserting paper into printing devices, may also be difficult.

Lack of strength is a problem in actions that demands strength when lifting, pressing, pushing etc. People with muscular dystrophy, or other conditions that affect the muscles or muscle control, often have reduced strength.

People with severely reduced strength may be unable to use the keyboard of a typewriter or computer, and the keypad of a telephone. They may not be able to press down the handle to open a door, or to lift a book or a telephone receiver.

People with moderate loss of strength may be able to lift and move only very small objects, and to hold them for only a limited time. They may not be able to push open heavy doors, or to open drawers.

Reduced function of arms and hands due to reduced co-ordination is usually a result of neurological damage, e.g. cerebral palsy, or disease, e.g Parkinsonism.

Reduced ability to coordinate the movements of the arms and hands will influence all activities that demand manipulation of objects or equipment. Impaired coordination may also increase the probability of hitting and breaking things, and to make errors when operating equipment. For example, a person with cerebral palsy or Parkinson's disease may be unable to drive a car, pour a glass of water, write a message, or dial a telephone number.

9.0 Impairment of Growth

Impairment of growth primarily includes adults who are significantly shorter than the population mean. This condition is typically caused by malfunctioning of the hormone system.

In general, shortness adversely influences one's access to equipment. Installations that are positioned high up may be difficult to use unless some form of step is provided. Short people also tend to have short arms, which makes manipulation of some types of equipment awkward or difficult.

It should be noted, however, that also people who are significantly taller than the average of the population may have some problems in using equipment that is mounted at a low level, or where the ceiling, for example of a telephone booth, is too low.

10.0 Other Impairments and Disabilities

The above categories cover a wide range of impairments and disabilities. There are, however, individuals who do not readily fit into any of these categories. For instance, people who have to spend most of their time in bed cannot readily be included in the category of wheelchair-dependent users. Their lack of mobility is a significant difference in function, and it is necessary to consider the possible problems this more special situation of being bedridden creates. British studies indicate that at any given time, 0.5 percent of the population are in bed for a limited period, due to disease or accident. This is only one example of a common temporary disability.

Some people have multiple impairments; for example, combined visual and hearing impairment, or hearing impairment and problems in controlling the movement of their arms and hands. People with intellectual impairment typically have several impairments. Within the scope of the present chapter, it has not been possible to discuss such multiple impairments. When assessing the needs of people with multiple impairments, it may be difficult to distinguish the effect that the different impairments have on the use of telecommunication equipment, and the impact of multiple impairments may be greater than the added sum of the individual impairments. For example, most people with reading disorders have no problems with the use of ordinary telephones, although their inability to use the telephone directory may prove an obstacle for them. However, if a person with severe reading disorders acquires a profound hearing loss, text transmission via the telephone network is impossible, and the person is excluded from a form of telecommunications ordinarily used by people with hearing impairment.

The impact of each impairment may also vary according to the situation. For example, for a person with moderate hearing impairment and cerebral palsy, manipulating the equipment may be the most difficult task at home where the telephone has augmented amplification. In a public telephone, the low sound intensity may be a relatively greater problem than handling the equipment.


Bauman, M.K. (1969). Dimensions of blindness. In M.H. Goldberg & J.R. Swinton (Eds.), Blindness research: the expanding frontiers. London: Pennsylvania State University Press.

Conrad, R. (1979). The deaf school child. London: Harper & Row.

Critchley, M. (1970). The dyslexic child. London: Heinemann.

Davis, H. (1970). Abnormal hearing and deafness. In H. Davis & S.R. Silverman (Eds.), Hearing and deafness. New York: Holt, Rinehart and Winston, pp. 83-139.

Kiernan, C., Reid, B., & Jones, L. (1982). Signs and symbols. London: Heinemann.

Roth, W. Handicap as a social construct. (1983). Society, 58, 56-61.

Saussure, F. de (1916). Cours de linguistique gCnCrale. Paris: Payot.

von Tetzchner, S. & Martinsen, H. (in press). Introduction to sign teaching and use of communication aids. London: Whurr.

World Health Organization (1980). International classification of impairments, disabilities, and handicaps. Geneva: WHO.

Next chapter