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8 " , ' , ~ g' C {" ; ' 50 ~ 60 0> C 70 .~ rn 80 Q) I 90 100 110 120 Figure 8.2 Diagram of simple audiogram with normal pure tone thresholds. Parts of the audiogram 1. Frequency (pitch): (a) measured on the horizontal axis in hertz (250 - 8000 Hz) (b) the higher the number, the higher the pitch (c) can be pure tones or bands of tone 2. Intensity (loudness): (a) measured on the vertical axis in decibels (b) measured in 5 dB steps (c) the bigger the number, the louder the sound 84 Communication Disorders 3. Symbols: (a) left ear = x (b) right ear= 0 (c) bone conduction = or v (d) aided = A or D Air conduction measures the whole system; bone conduction measures the inner ear (by-passing the middle car). Differences represent types of loss. Speech audiogram 1. Speech reception threshold is: (a) measured with words (b) recorded at level of intensity just understood (c) expected to agree with pure tone audiogram 2. Speech discrimination is: (a) measured with words (b) scored by percentage of correct words (total 50 words) (c) scored at a variety of intensities (d) carried out with different conditions (e.g., speech and noise) in the same ear (e) needed to help decisions about use of hearing aids 3. Tests can be free-field measures within a sound booth (using visual reinforcement with young children) or direct input measures from headphones. Results can be determined from spontaneous behavioural responses (head turning to sound source) or conditioned and learned responses (raised finger or pressed button to activate light on audiometer.) Understanding the audiogram in terms of speech and language Each audiogram has to be understood and interpreted in detail. In the case of young children, bear in mind that the audiogram may not be reliable. Results may differ due to examiner and examinee attitudes and behaviours and other factors such as fatigue and anxiety. It is important to replicate results. Audiometers need to be carefully calibrated to en-sure reliability. Children's hearing may appear to improve as they become better listeners with hearing aids and more experienced at tests. It is also important to ascertain that amplification is optimum and frequency specific, i.e., the greater the loss at a specific frequency, the greater the amplification. Some frequencies may not need amplification at all; hearing aids should be adjusted accordingly. Levels of hearing loss related to intensity Hearing is often referred to in the following terms: Hearing Disability 85 • normal hearing (0 - 25 dB) • mild loss (25 - 40 dB) • moderate loss (40 - 60 dB) • severe loss (60 - 80 dB) • profound loss (80 dB plus) The levels depicted on the audiogram below describe the effects of the above losses in terms of intensity. Note that the capacity of the audiometer is important. If a person does not have apparent hearing at 110 dB, it may be due to the limits of the audiometer. Therefore a patient's unaided chart may show 'no hearing' at 110 dB and 2000 Hz, but aided thresholds at the same frequency at 90 dB. en ~ C/) Q) 15·u Q) -0 C >- +-'·00 c Q) +-' ~ 125 -10 250 0 20 Whisper Speech 40 65 Cars 80 Plane 90 100 Frequency in hertz (Hz) 500 1K 2K 4K 8K I I N°Tal I Mild I I Moderate marked handicap I I Severe 1 I Profound I Figure 8.3 Levels of loss related to dB and still-audible sound sources. Levels of hearing loss related to frequency and language The following chart shows that hearing loss related to specific frequencies will affect particular components of language more than others. This is a critical factor to understand in relation to the rehabilitation of young, profoundly hearing-impaired children acquiring language. Even minimal hearing is very useful particularly if well aided (Ling, 1976). Figure 8.4 demonstrates the following: 1. Hearing between 250-500 Hz allows the patient to hear and use intonation, tonal and prosodic markers if they are made available to the patient through normal speech; such a patient also has access to most of the pragmatic cues of language. 86 Communication Disorders 125 o en 1J en Q) .0 co·u .0 Q) lo.... 1J Q) > c c >- 0 +-' Z·00 c Q) +-' c 100 en Q) c 0 +-' .......... c 0 :;::; co C 0 +-' c .......... en u =0 0 en e a.. Frequency in hertz (Hz) 1K 8K . s • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • .................................. 01 c·c co Q) E .......... en u +=i c co E...

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