Portuguese Version

Year:  2000  Vol. 66   Ed. 5 - (1º)

Artigos Originais

Pages: 426 to 431

Intelligibility of Monosyllables In Quiet and in Noise.

Author(s): Ari de Paula*,
José A. Oliveira**,
Natália M. Godoy***,
Marilis B. A. Canovas***.

Keywords: audiometric threshold, word recognition, noise induced hearing loss, presbiacusy, back noise, intelligibility

Abstract:
Introduction: In a conventional audiometric evaluation it is usually used a cabin. However, several studies show that in a competitive environment the comprehension of the words decreases for all the individuals. Aim: With the target of evaluating it closer to reality, a study with fourteen normal and ten presbyacusic patients was idealized to develop a methodology of evaluation of the hearing discrimination in both silent and noisy environment, and also to observe the speech recognition in competitive atmosphere. Material and method: It was used the white noise as it is easily picked up in a common audiometric cabin with loudspeakers, amplifier and a recorder to reproduce a female voice that mentioned the Geraldo de Sá's list of phonetically balanced monosyllables. The evaluations took place in a free field without the use of earphones. Results: At the and of the evaluations we observed that the methodology was efficient and trustful and we could also assure that the presbyacusic patients have an audiologic level of discrimination not up to young patients with regular hearing in a competitive environment. Conclusion: The sounding source for the understanding of monosyllables must be higher than the environmental noise to the presbyacusic patients while to the youngs the sounding pressure levels might be lower than the environmental noise.

INTRODUCTION

In our days, noise is a constant element in the life of people in urban areas: Many patients, especially the elderly, report that they do not have difficulties to talk to one person in a silence setting; however. communication in the presence of constant noise becomes very impaired. Audiological exams normally employed (pure tone and speech audiometry, speech discrimination) are carried out in a sound proof booth, producing results that are not compatible with the hearing environment of patients. Simonton (1953), in his study of hearing discrimination in noise, concluded that severity of presbyacusis influences hearing discrimination in competitive noise. Cooper (1971) captured the noise of cafeterias at the university he used to work with normal patients and sensorineural loss patients and reproduced the noise while conducting hearing exams in the sound booth; he concluded that the second group had more difficulty to discriminate and stated that "it would be necessary to measure both discrimination situations, in noise and in quiet, to understand the problem the subject has". Jokinen (1973) demonstrated that subjects who are over 50 years of age start to present significant difficulties in understanding words in competitive noisy environment. Aniansson (1979) suggested that 2000 Hz would be a significant frequency for understanding words in noise. Dirks (1982) noticed that in presbyacusis patients levels of speech discrimination are worse than in normal patients specially if the noise reproduced that of parties, pubs and gathering of people. Dubno (1984) observed that the effects of word understanding gets worse with aging and are independent of hearing loss, which would be an aggravating factor, and in a "simple interpretation", according to the author, it is suggested that there is a central lesion of the auditory system in the elderly that would be responsible for a bad performance in word understanding in noise. Middelweerd (1990) concluded that in subjects considered audiologically normal; it is possible to find an abnormal curve if we conduct a more precise hearing test for discrimination in competitive noise. Elbaz (1992) Studied normal subjects and noticed that the level of word understanding decreases as competitive noise increases, up to a zero value when signal-to-noise ratio is 30dB, in free field with competitive noise. In the study of children with central auditory dysfunction Pereira and Shochat (1997) addressed the topic of tests that compare speech recognition in quiet and in the presence of competitive noise. In these tests, the function "performance-intensity" is measured for monosyllable words or sentences at different levels of intensity, adding a competitive noise to the test and offering a more realistic perspective of the dysfunction.

1 - Recorder / Reproducer Sony Stereo.
2 - Amplifier Sony Stereo.
3 - CD-10 distributor to loudspeakers.
4 - Frontal loudspeaker reproducing a female voice.
5 - Posterior loudspeaker reproducing white noise (buzzing).
6 - Patient.
7 - Distance between patient and loudspeakers: 30 centimeters.
8 - Audiometric booth.
Figure 1. Diagram of sound distribution system.

OBJECTIVES

1- Normalization: to study in normal subjects (control group) speech discrimination in competitive noise to produce a curve of normal hearing;

2 - To study hearing discrimination in competivive noise in subjects who have mild presbyacusis.

3 - To propose a simple methodology to assess hearing discrimination in noise.

MATERIAL AND METHOD

In an audiometric booth, we adapted a loudspeaker that produced white noise (buzzing) in free field, represented by letter R, placed 30cm from the back of patient (Figure 1). We adapted an amplifier model LBT-35WB to an audiometer brand Qualitone model WRC, used to produce the noise.

In another loudspeaker, placed 30cm in front of the patient, the sound of a female voice was produced, identified as signal and represented by the letter S. We used vhe table by Geraldo de Sá (1952), comprising 5 lists of 44 phonetically balanced monosyllables each.

Equipment used

1 - a) Recording, reproduction and distribution systems of amplified sound to loudspeakers model LBT-35WB, brand Sony, 110 volts.

1- b) Device for distribution of sound to loudspeakers, according to the need of studies, model CD-10, especially manufactured for this purpose.

2 - Sound proof booth, made of Sonex foam, measuring 1.38m wide by 1.42m long by 1.80m high, installed in a room measuring 3.34m wide by 3.40m long by 2.80m high, in a office on the 12th floor, not acoustically treated and furnished with tables, chairs and pictures.

3 - Equipment used for planned measures:

o Meter for sound pressure level, brand Bruel & Kjaer, model 2235.

o Filter of frequency octaves, brand Bruel & Kajer, model 1624.

o Microphone 1/2", brand Bruel & Kajer, model 4176.

o Temperature and humidity meter, brand Radio Shack, model 6A5.

In Figure 1 we present the diagram of the sound distribution system.

Procedure

To assess hearing discrimination, we recorded in a cassette a female voice reading the lists of Geraldo de Sá, with an interval of 3 to 5 seconds between each word, so that the examined patient could repeat them. The words were reproduced by the frontal loudspeaker at a fixed intensity throughout the exam and calculated for each patient based on the mean of thresholds of 500 to 2000 Hz of the best ear plus 40 dB.

We selected as control group a group of 14 subjects considered audiologically normal, with audiometric curve lower than 25dB, normal impedanciometry, no history of otological complaints, normal otoscopy and no history of exposure to intense noise.

Our target study group consisted of 10 elderly subjects, with mild sensorineural presbyacusis, normal impedanciometry, without history of otological complaints, normal otoscopy and no history of exposure to intense noise.

All subjects were submitted to exams in the adapted booth. We assessed hearing discrimination in quiet using the first list of 44 words by Geraldo de Sa (1952), 40 dB above the mean of pure tone thresholds of 500,1.000 and 2.000 Hz in the best ear (because this is the frequency range classically considered the speech range). Next, we conducted the test of speech discrimination in noise playing the noise in the booth at 50dB sound pressure level, without varying the intensity of produced signal and using the second list of words of Geraldo de Sá. Later, noise intensity was increased in 5 dB steps, up to 80dB of noise, using a list of words for each incremental step. Since there are only 5 lists of words, when we came to the last one, we restarted using the first one, until we reached zero discrimination. In the next step, we found the signal-to-noise ratio (S-R) for each patient, because there was an mean of frequencies 500, 1000 and 2000Hz for each patient added by 40dB of signal. The subtraction of the produced signal for each patient (fix signal) from the produced noise in that moment is S-R ratio, a necessary measure to enable standardization of obtained results.

RESULTS

We studied a total of 32 subjects, divided into two groups: the normal group with 14 subjects, mean age of 24.5 years and 11.07dB among 500, 1000 and 2000 Hz; and the group with presbyacusis, mean age of 72.7 years and 30 dB among 500, 1.000 a 2.000. Therefore, by adding 40 dB, the average of the signal produced in the exam for normal group was 51.07 dB, and 70 dB for the group of presbyacusis patients. The .mean of hearing discrimination in quiet for normal group was 100% in all subjects; in the other group, the mean was 91.6%, within the ranges of 84 and 100%. The mean hearing discrimination found for each group for each difference in dB between signal (40 dB above mean of 500,1.000 and 2.000 Hz in the best ear) and noise is showed Table 1 (S-R ratio); upon analyzing it, we noticed that in the normal group, the discrimination was 50% in -10 to -15 dB of S-R ratio, that is to say, even with noise 10 to 15 dB higher than the signal produced, the subjects of the group identified 50% of the words. In a situation of zero S-R ratio the group of normal patients understood 98.2% of the words in average, whereas the group of presbyacusis patients understood only 29.6%. Moreover, in order to have zero discrimination, the normal group required noise 25 to 30dB higher than the signal, whereas in the other group, 10 to 15dB higher level was enough to have them lose the ability of discrimination, showing that the ability was not proportional between the two groups. In Graph 1, we found the average position of normal and presbyacusis subjects, showed as lines 1 and 2, respectively.

DISCUSSION

In our days, especially in large cities, noise is an aggravating factor in the poor quality of communication among people; some patients, especially the elderly, frequently report difficulties to understand words in noise settings. This intense background noise is a constant in the life of people, which is not harmful enough to lead to destruction of Corti's organ cells; however, for subjects who already have some degree of hearing deficit, the noise may impair understanding of words and compromise social communication. Cooper (1971) stated that normal subjects, as well as cochlear pathologic subjects, have a considerable loss in hearing discrimination under such situations. One example is the family environment, normally consisting of people from different age ranges, sometimes with TV sets and radios switched on, and people concomitantly talk; in this kind of situation, the elderly suffer more than the children to understand what is being discussed, that is, noise is highly deleterious for this kind of patient, and the present study intended to assess this difference and compare it to younger adults, in order to determine how much background noise a presbyacusis patient bears in discriminating words.

TABLE 1 - Presentation of hearing discrimination with corresponding S-R ratio. We observed in each column a reduction in the ability to distribute as noise increases; however, in group "P" = presbyacusis patients, hearing discrimination is deteriorated faster if compared to group "N" = normal hearing patients. We highlight that in the same level of noise, hearing discrimination of presbyacusis patients is much worse.

Hearing discrimination was chosen because it represents a need every subject has. On the other hand, existing routine audiological assessments do not take these facts into account, because they are conducted in quiet and without competitive noise; in fact, it is exactly the contrary, because the more the booth isolates external noise, the better will be the quality of exams. Therefore, we may say that in order to have a more precise hearing assessment, we should include competitive noise in the routine, a statement already made by Cooper (1971). Similarly to Jokinen (1973) and Elbaz (1992), we chose white noise as competitive noise, because it is easy to be reproduced by the audiometer and it has a wide spectrum and reaches the range of 500 to 2000Hz, that is, the range of frequency for word understanding. Therefore, according to Jokinen (1973), the use of masking in a audiometric booth to assess hearing discrimination in noise is a complex procedure if compared to the regular audiological battery we do as routine; in the future, we will have to review the diagnostic validity of these tests when applying them to some specific age ranges.

In the vertical axis, we can see hearing discrimination and in horizontal axis, the difference between signal and noise during performance of exam. The dot on the "silence" vertical line represents the discrimination found in this situation for normal hearing patients, whereas the small white square represents it for presbyacusis patients. Line 1 represents the decrease of mean in hearing discrimination for normal subjects; as S-R ratio decreases, increases noise. Line 2, representing presbyacusis patients, it shows how discrimination deterioration is hindered by the increase in level of background noise (reduction of difference S-R).
Graph 1. Performance of hearing discrimination in competitive noise.

The table by Geraldo de Sá was chosen as source of signal because it has already been validated for use in the Portuguese language. We decided to record the list of words in order to deal with the smallest number of variables; in addition, we used a female voice because it is more pleasant to hear it and it is closer to the range of 500 to 2000Hz used as basis for the calculation of the mean. We left an interval of 3 to 5 seconds between the words for the patient to repeat each word. Each exam lasted from 10\ to 20 minutes. Elbaz (1992) stated that this kind of assessment requires proper installation of sound free field setting, in appropriate dimensions and conditions. In our study, we marked on the floor the area for the booth and the position in which the patient would sit, and the patient was instructed not to move his or her head towards the loudspeaker, because measures from loudspeakers to the head of patients were standardized (30 cm). According to Dirks (1982), it is necessary to conduct a "biological calibration" of this kind of booth, that is, each booth should have its own normal range values. Therefore, we standardized our equipment in a control group of 14 patients considered normal hearing people. Their speech discrimination was 100% in quiet. We conducted the assessment according to the specifications described in Material and Methods and we found an average loss of discrimination as we increased intensity of competitive white noise in the booth, reaching the "biological calibration" reported by Dirks. We noticed a descending curve, with slight losses of discrimination in the begin (noise intensity still low) that progressed to a larger loss in intermediary position and flatness again at the end, with high noise intensity (curve 1 in Graph 1). This pattern found in our study is compatible with values found by Elbaz (1992). The target study group of 10 presbyacusis patients had a mean discrimination in quiet of 91.6%, a value expected for this type of pathology. Based on the results obtained in noise for the patients, we noticed the same pattern of curve, but it was somewhat flatter (curve 2 in Graph 1). It shows the clear hearing difficulty of these patients in noise environment, when compared to normal subjects. Whereas normal subjects reached 50% discrimination with noise 10 to 15dB higher than signal, presbyacusis patients needed a signal 10 to 15 dB higher than background noise to reach the same level of discrimination. Therefore, normal subjects required 25 to 30dB background noise to reach zero discrimination, whereas presbyacusis patients reached this zero level at 10 to 15dB of background noise. It is interesting to notice that closeness of values between the two groups in quiet is not repeated under noisy conditions. Therefore, it has been clearly shown why elderly patients, even those with a mild hearing loss caused by presbyacusis, frequently report hearing difficulties in their daily routine. The same analysis was made by Simonton (1953), Jokinen (1973) and Dubno (1984), and the latter attributed the difficulty to a central origin, explaining the loss of ability to understand words in noisy-environment.

CONCLUSION

1. The ability presbyacusis patients have to understand words in noise is considerably worse than that of normal hearing subjects.

2. Normal hearing subjects can understand 50% of the words even when noise is higher than signal, whereas presbyacusis patients require the signal to be higher than the noise in order to achieve 50% discrimination.

3. Hearing discrimination in quiet does not reflect hearing discrimination in competitive noise.

4. Among existing audiological tests we should include an audiological assessment in competitive noise, to determine with precision the difficulties patients go through when discriminating words, especially the elderly patients.

5. The methodology employed proved to be efficient because it provided important information that helped understand hearing difficulties of people in noisy environments.

ACKNOWLEDGEMENT

To José J. Orlandi.

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* Professor and Preceptor of Medical Residence at Santa Casa and Hospital Irmãos Penteado de Campinas/ SP.
** Ph.D. Professor and Head of the Department of Otorhinolaryngology, Universidade de São Paulo - Ribeirão Preto/ SP.
*** Speech and Hearing Therapist of the Department of Otorhinolaryngology at Santa Casa and Hospital Irmãos Penteado de Campinas/ SP.

Affiliation: Universicade de São Paulo - Ribeirão Preto - Departamento de Oftalmologia a Otorrinolaringologia da Faculdade de Medicina de Ribeirão Preto /SP.
Address for correspondence: Ari de Paula - Avenida Julio de Mesquita, 960 - 18° andar - Bairro Cambuí - 13025-061 Campinas/ SP.
Tel: (55 19) 236-8972 - Fax: (55 19) 232-4478.
Article submitted on January 17. 2000. Article accepted on August 10, 2000.

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