Subjective audiometric measurements

The precise evaluation of subjective hearing tests depends on the cooperation, the reactions and the interpretations of the examinee. These tests form the basis of any diagnosis of hearing and any further medical examination (Thiel 2000). The result of subjective tests is an audiogram, which shows the auditory threshold for pure tones.

The wave of a pure tone consists of only a single frequency, thus pure tones can be considered as demonstrating the range of pitches. In fact, the human ear can hear pure tones that are much lower or higher, than those presented in an audiogram. For an audiogram though, pure tones, which are found in human speech, are selected and used for testing the hearing. When analyzed electronically ‘each speech sound has been found to be an unique and complex combination of these pure tones’ (English 2004, 44). An audiogram hence demonstrates within which range of frequencies a hearing loss occurs and tests the performance of the inner ear. It thus facilitates a quantitative assessment of the hearing loss.

7 For a Decibel (Loudness) Comparison Chart see: http://www.gcaudio.com/resources/howtos/loudness.html

The test is done in a sound room where the examinee’s ear is tested by providing him or her with sounds, which come from a so-called audiometer. The audiometer also automatically interprets the examinee’s reactions. The sounds are transmitted through loudspeakers or headphones. Pure tones are used for the test in a range from 10 Hertz to 125 Hertz. The loudness of the sounds is varied between 0 dB and 120 dB.

Putting the above information together we gain three components an audiogram (see figure 2) consists of:

1. The range of pitches presented in the hearing test.

The pitches (or pure tones) can be seen as lined up in the horizontal part of the audiogram (measured in Hertz (Hz), see figure 2). An audiologist will use the term

‘frequency’ (see 1.3) to describe in which area the hearing is disturbed, for example, high frequency hearing loss or low frequency loss.

2. The Loudness of each pitch, or how loud a pitch has to be, to be heard by the examinee.

The loudness can be seen in the vertical part of the audiogram (see figure 2). It is measured in Decibel (dB). There are various degrees of hearing loss (see 1.5), which can be deciphered in an audiogram.

Component 1 and 2 combined give us the ‘hearing threshold’ (English 2004, 45), which tells us how loud each frequency has to be in order that the examinee can hear it.

The audiologist records the threshold of an examinee in circles. In figure two, for example, the hearing threshold for 125 Hz is 40 dB, for 250 Hz it is 50 dB, for 500 Hz it is 80 dB, etc. (see figure 2, upper left). Figure 2 shows how the hearing level starts for frequencies at 125 Hz as moderate hearing loss (at 40 dB) and further becomes a severe-to-profound hearing loss from the frequencies of 250 Hz and further.

3. The hearing in each ear.

Usually, the hearing is tested in both ears and presented in different audiograms. In figure 2, for instance, we can see the tested hearing of the right ear (see upper left

‘Rechtes Ohr’/right ear). The hearing thresholds of both ears as recorded in the audiograms can then be presented in one audiogram together.

Figure 2 shows the audiogram and speech audiogram of a profoundly hard of hearing person. The audiogram is the author’s audiogram. With courtesy to the university hospital Munich.

In addition to a conventional audiogram, some audiologists generate a speech-audiogram, which tests the speech comprehension. For this purpose, special tests are used, which vary from country to country. These tests assess either the perception of single words, or of whole sentences. Both tests together provide a clear picture of the type and degree of hearing loss. Once an audiologist has tested the hearing and identified the type of hearing loss, an otorhinolaryngologist can initiate further steps for the treatment of the hearing loss.

1.3.2 Objective audiometric measurements

The evaluation of objective audiometric measurements does not require the collaboration of the patient. These measurements test the mechanical changes relating to the transmission of sound within the ear and the reactions of the nervous system (including the hearing nerve) to acoustic stimuli. Electric Response Audiometry (ERA), impedance measurement, tests that provoke otoacoustic emissions,⁸ or the nowadays implemented new-born hearing screening (Gross 2005) are some of the objective tests used in audiometry. These tests are made with the help of special instruments, which interpret the reactions of the nerves of the examinee. Usually the results of the objective tests confirm the results of the subjective tests and thus allow the control of the overall test results. Particularly for patients whose collaboration is not always given, e.g. children, these tests are an important means of diagnosis to detect a hearing loss at an early age.

1.4 Types of hearing loss and their consequence for communication⁹

Observation has shown that the general public has very limited and biased information concerning the issue of hearing loss. The assumption that there is only one type of hearing loss and that hearing loss occurs mainly in elderly people is still pervasive. The notion of the term hearing loss is difficult to comprehend, as hearing loss occurs in various forms and in different degrees. The effect of it is experienced differently from person to person,¹⁰ as many other factors play a distinctive role as well.

In medicine and its related fields as e.g. audiology, the type of hearing loss is categorized according to the location of the damage in the auditory system.

8 Otoacoustic emissions are sounds, which are produced from within the ear and can be provoked by an external stimulation (Kemp 1978).

9 Article 1 of this thesis provides a further and more detailed description concerning the issues discussed in this section.

10 For further reading see: Craggs-Hinton (2007), Rezen and Hausman (2000).