2.4 CLINICAL FEATURES OF DEAFNESS
2.4.2 Levels of hearing loss
Knowledge of the levels or degrees of hearing loss will help enhance the understanding of the nature of deafness, and is especially relevant for parents raising deaf children so that appropriate decisions can be made regarding their deaf children’s learning and development. There are different degrees of hearing loss, and the level of hearing loss that children experience can have a profound impact on their overall learning and development. Ideally babies should be tested by an audiologist as early as possible soon after birth so that appropriate interventions can be implemented timeously in the event that deafness is detected. Based on the results of the audiological tests, a child who is suspected of experiencing a hearing loss is then identified as deaf or hard of hearing.
Kapp (1991: 322) maintains that although measurement of the degree of hearing loss is important for educational purposes, care should be taken not to be too rigid in this regard, as it may compromise the individual child’s specific educational needs.
Classification according to the degree of hearing loss should not be regarded as
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absolute, since it is not the only criterion for determining the child’s placement in a particular type of school.
The intensity or loudness of sounds is measured on the vertical axis of the audiogram in decibels (dB), while the frequency (high or low pitch of the sound) is plotted on the horizontal axis, and is measured in hertz (Hz) (Storbeck, 2005: 351; Northern &
Downs, 2002: 6-7). A decibel (named after Alexander Graham Bell) is defined as a unit of measure which is “one tenth of a bel”, an “arbitrary unit that expresses the ratio of a measured power or pressure to a specified reference value” (Northern & Downs, 2002: 7).
The levels of hearing loss are shown in Table 2.2 which has been adapted from Marschark et al. and Schirmer (in Storbeck, 2005: 352).
Table 2.2 Levels of hearing loss
Hearing person 0 – 25dB
Mild hearing loss 26 – 40dB
Hard of hearing
Moderate hearing loss 41 – 55dB Moderately severe hearing loss 56 – 70dB
Severe hearing loss 71 – 90dB
Deaf
Profound hearing loss 91dB+
The levels of hearing loss can be explained as follows (Storbeck, 2005: 352; Schirmer, 2001: 13-14):
Normal hearing sensitivity (0-25dB)
A hearing person’s level of hearing falls within this category.
Mild hearing loss (25-40dB)
A person who falls into this category is hard of hearing. Schirmer (2001: 18) states that a person with mild hearing loss has no difficulty in communicating in quiet
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environments in which the topic is familiar and the vocabulary is limited. However, faint or distant speech presents a problem even in a quiet environment, and classroom discussions are difficult to follow. Without the use of hearing aids and assistive listening devices a child who has a 35-40% hearing loss can miss up to 50% of class discussion, when voices are soft or far away (Flexer, 1994: 38). A child with an unmanaged mild hearing loss is likely to lag behind at least one grade (Northern &
Downs, 2002: 14).
Moderate hearing loss (41 – 55dB): Anyone who fits into this category would also be regarded as hard of hearing. The person can hear conversational speech only at close proximity. Group work such as class discussions can be challenging (Schirmer, 2001:
18). Several authors state that learners with moderate hearing loss who have not received appropriate early intervention are likely to fall behind by at least two grades by fourth grade (Flexer, 1994: 39).
Moderately severe hearing loss (56 – 70dB): According to Schirmer (2001: 18), a moderately severe deaf person can only hear conversational speech if it is loud and clear, and has much difficulty in group discussions. Although the person’s speech is intelligible, it is noticeably impaired. Matkin (in Flexer, 1994: 39) holds the view that a child with a 56dB hearing loss can miss 100% of class discussion, and without appropriate early and continuing intervention, is likely to have marked difficulty in school, as well as experience social behaviour problems.
Severe hearing loss (71 – 90dB): A severely deaf person is unable to hear conversational speech unless it is loud, and even then many of the words cannot be recognised. The person’s speech is not quite clear. Even though environmental sounds can be detected, these are not always identified (Schirmer, 2001: 18). Various authors believe that with appropriate amplification and auditory intervention strategies, a child with severe hearing loss can be hard of hearing and not deaf. With the help of some support services, the child will be able to learn and live in a mainstreamed environment (Flexer, 1994: 39).
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Profound hearing loss (91dB +): Schirmer (2001: 18) states that a profoundly deaf person may hear loud sounds but simply cannot hear conversational speech. The person’s own speech, if developed at all, is not easy to understand. The chief modality of communication is vision. The person cannot hear sounds without amplification.
However, the vast majority of persons in this category do have some residual hearing.
Nonetheless, the ability of a profoundly deaf child to benefit from amplified sound will depend on several factors.
It is clear from the above discussion that the degree of hearing loss varies and does not on its own determine communicative function. It will therefore impact differently on the developing child (Flexer, 1994: 39).