研究 Binaural Fusion Test

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研究

Binaural Fusion Test: A Diagnostic Approach to the Central Auditory Disorders.

RITsu Hayashi, M. D.

Chapter 1: Review of the Literatures on the Clinical Application of Binaural Sum- mation, Integration or Fusion. Two principal methods utilizing binaural hearing phenomenon have been recently developed for the diagnostics of disturbances in the central auditory system: 1) a directional audiometry and 2) a test of binaural fusion or summation with speech or pure tones. A number of papers have been published as to the directional audiometry but will not be reviewed in this article. Hirshl summarized the research works on binaural summating effect during the last hundred years. According to his review, Seebeck2 first discoveredthe binaural summating effect during the experiment on binaural beat. Since then, many investigators have experimented on that subject and some of them have made attempts to study the central auditory dysfunction by means of binaural hearing test with distorted speech. Bocca3)developed a diagnostic method to examine the efficiency of central mechanism in hearing. The Italian PB words were delivered simultaneously to both the ears through two independent channels. The non-distorted speech, of which the average discrimination score did not exceed 30 percent, was presented to one ear through Channel 1. The distorted speech (500 cps low pass) was presented to the other at 45 db above the threshold through Channel 2. The results revealed that the discrimination score in binaural presentation was nearly equal to the addition of each monaural score. Calearo4 applied this technique to the diagnostics of central auditory function. He was the first who used the binaural integration for the diagnostic purpose. Ten patients with lesions of the temporal lobe or of the surrounding regions were examined. In most of the cases, the binaural integration was absent when the signals through the Channel 2 were delivered to the ear opposite to the affected lobe. Several years later, Jerger6) used the same technique and ascertained Calearo's result. Matzker67 used binaural fusion of two coherent distorted speech materials as a test index. In Test 1, one ear received the words filtered through the frequency band of 500-800 cps, and the other received simultaneously the band of 1500-2400 cps of the same verbal message. In normal subjects, each band alone yielded poor discrimination, but binaural presentation of the two bands resulted in a good fusion of them and a high discrimination score. In Test 2, the two bands of verbal message were mixed electrically and then presented binaurally, i. e. each ear received the mixed information of the two bands simultaneously. In Test 3, the same procedure as Test 1 was repeated. Then, the numbers of unidentified words in Test 1 or 3 were compared with the numbers in Test 2. Normal subjects showed no remarkable difference between these two kinds of presentation, but some of the cases of presbycusis and diseases of the central nervous system showed very poor discrimination in Test 1 or 3 in spite of good discrimination in Test 2. On the basis of more than one thousand cases examined, Matzker considered that the poor binaural fusion is attributable to the impairment of the brain stem, especially the medial geniculatebodies. Modifying the Matzker's method, Lindens used the Swedish spondaic words filtered through the bands of 560-715 cps and of 1800-2200 cps. Comparison of discrimination scores was made between monau- * Department of Otolaryngology Faculty of Medicine Kyoto University (Director: MASANORI MORIMOTO, M. D. Instruction: FUMIHIKO OHTA, M. D.)

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ral and binaural presentations of each band. In the cases of unilateral temporal lobe legion, monau - ral distorted speech yielded poor discrimination in the contralateral ear. The discrimination score in the binaural presentation usually ranged between each monaural score. His results were different from those of Matzker in that poor binaural fusion was not demonstrated in the cases of expand- ing intracranial lesion. Groen and Hellema9 classified sensorineural deafness into two groups according to the steepness of monaural and binaural speech audiograms; 1) if the binaural curve was steeper than each monaural one, the lesion might be located somewhere between the cochlea and the superior olivary nucleus and 2) if the binaural curve was parallel to each monaural one, the lesion might be located centrally beyond the superior olivary nucleus. Cherry and Taylor10) studied on the periodical switching of verbal messages. Normal subjects were able to obtain more than 90 percent of intelligibility when the periodically switched speech materials were delivered alternately to both the ears keeping 50 percent on-off ratio at any frequency of switching. Using this tehnique, Calearo11 obtained a good result in detecting a malingering. Bocca12 suggested the possibility that this test could be effective for the differential diagnosis of brain stem pathology vs. corticel or peripheral lesions. Kirikae et a113 tested the aged persons by using a similar procedure and reported that the aged subjects showed poor discrimination in monaural and binaurally switched presentations of interrupted speech. They attributed the results to senile changes in the auditory nervous system from the level of the spiral ganglion to the auditory cortex.

Many researchers listed above have contributed to the establishment of the diagnostics of im- pairments in the central auditory nervous system with their own methods which were elaborated by utilizing binaural interaction. As to their methods, Calearo used the binaural presentation of distorted speech and non-distorted one of low intensity. In the studies of Matzker and Linden, the speech was filtered through two frequency bands and presented binaurally. The comparison of discrimination score was made by Matzker between the diotic presentation of the signals through the two bands and the dichotic presentation of the signals through the high band and those through the low band, but Linden compared the discrimination scores between the binaural presentation and the monaural presentation of the signals through each frequency band. Groen and Hellema compared the steepness of binaural and monaural speech audiograms. In the study of Kirikae et al, the interrupted speech was presented in binaural switching. As to the diseases which were treated by them, Calearo and Linden tested lesions of the brain tumor, especially of the temporal lobe. Matzker, and Groen and Hellema examined the cases of some diseases of the central nervous system and deafness due to many kinds of origin, and the aged persons were tested by Kirikae et al. There are some divergencies among their opinions on the site of binaural interaction, but most of them supposed that the site might be the brain stem at which both auditory pathways crossed each other and that a message might be integrated in the brain stem before being transmitted to the auditory cortices. However, they appear to have no sufficient evidences to make such an explanation and it is doubtful that a binaural fusion test could reveal so many disorders as shown by Matzker. The purpose of this paper is to examine the feasibility of the Matzker's method as a diagnostic procedure for the central auditory dysfunction, to modify the method if necessary, and to obtain some information which may give the cue regarding the site of binaural fusion.

Chapter 2 Speech as Test Material.

What kind of speech is best to be used as the material of binaural test? The language, of

58 耳鼻臨床 58: 8 Binaural Fusion Test: ADiagnostic ApProach to the Central Auditory Disorders. 559 course, must be native or familiar to the test subjects. Bocca, Calearo, Matzker and Linden used disyllabic words in their tests, but Jerger used PB words. Short sentences were employed by Calearo in his study on switched speech. For the binaural speech audiometry with non-distorted material, monosyllables were used by Groen and Hellema. Most of these investigators used meaningful materials besides some of the Bocca's works. On the other hand, Kirikae et al used Japanese nonsense monosyllables as the test material. Horiguti14) made a comparative study of materials in speech audiometry between Japanese and other languages, and emphasized that nonsense monosyllables were best to be used in Japan. Non- sense monosyllables, as he pointed out, are not so unfamiliar to Japanese people. Listener's know- Table 1. The phonetic symbols of Japanese ledge of vocabularies and dialectic difference have 67 monosyllables. less influence on the discrimination if nonsense monosyllables are used, than when meaningful speech materials are used. This shows the reason why they have been actually used as the standard material of the conventional speech audiometry in Japan. They consist of 100 monosyllables, of which 5 are vowels, 62 are consonant-vowel (CV) type and 33 are consonant-semivowel-vowel (CJV) type. Vowels and CV syllables, of which phonetic symbols are shown in Table 1, are more familiar and more frequently used than CJV syllables. The 67 monosyllables (5 vowels and 62 CV syllables) cover 90.2 percent in the rate of occurence in con- versation. 14 For these reasons, the 67 monosyllables were used as the test material in the author's study.

Chapter 3 Selection of Frequency Bands for the Binaural Fusion Test.

Matzker's method is based on the binaural fusion of two coherent distorted speech signals of which each alone is unintelligible, but of which simultaneous hearing obtains a good discrimination. The purpose of study in this chapter is to select the frequency bands and the test-syllables which are appropriate to such distortion. The vowels play very important roles in the phonetic structure of the Japanese 67 nonsense monosyllables. All the monosyllables have vowel components which occupy large portions of time sequence. An analysis of the Japanese five vowels is essential for determining what frequency band-pass filter should be used for the binaural fusion test. Since the details of acoustical analysis of Japanese five vowels were already published by the author15>, they are summarized in this paper. The Japanese five vowels, 〔a〕, 〔i〕,〔u〕, 〔e〕and〔o〕, pronounced by three normal males(pitch ca. 130 cps) and three normal females (pitch ca. 260 cps), were recorded on a magnetic tape with Tape Recorder FT-1 (Sony). The recorded vowels reproduced with Tape Recorder KP-3 (Sony) were filtered through Audiofilter SA-2701 (Rion) and recorded again with FT-1. This electric filter has the characteristics of rejecting at a rate of more than 60 db per octave. By the filtering, the frequency range, 106-4800 cps, of the male voices was divided into 11 bands with the cut off frequencies 106, 150, 212, 300, 425, 600, 850, 1200, 1700, 2400, 3400 and 4800 cps. The range, 212-4800 cps, of the female voices was divided into 9 bands. The obtained materials were presented to 16 normal subjects at medium level through a loudspeaker. Most of the subjects identified (425_600 cps) and (600-850 cps) as 〔o〕, (850-1200 cps) and (1200-1700 cps) as 〔a〕, and

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(2400-3400 cps) and (3400-4800 cps) as 〔i〕 regardless of the kind and sex of the pronounced vowels. Very few subjects identified these filtered vowels as〔u〕or〔e〕. This means that the

principal formant of〔o〕, 〔a〕or〔i〕exists in the range of 425-850 cps, 850-1700 cps or 2400-4800 cps respectively and that vowels〔u〕and〔e〕are not able to be constructed with such narrow

band as obtained by dividing the range of 106-4800 cps into ll bands. In other words, 〔u〕and

〔e〕are more. appropriate to be used in the binaural fusion test than〔o〕, 〔a〕and〔i〕, because it is necessary for the test to select two frequency bands that the signals filtered through both of

them are identified in spite of poor discrimination for the signals filtered through each of gthem.

In the second experiment, the recorded vowels〔u〕and〔e〕phonated by two normal males

and two normal females were filtered through two different frequency bands and the articulation

score was examined. As the first formants of〔u〕and〔e〕were estimated around (300-425 cps)

and about 600 cps respectively from the articulation curves of high-pass and low-pass filterings,

(300-425cps)was selected as the lower band of〔u〕, and(425-600 cps)and(600-850 cps)were selected as the lower band of〔e〕. The combination of the bands, 425-600 cps and 1700-2400 cps,

yielded greatest score of〔e〕. For〔u〕, good identification was 6btained at the combination of(300- 425cps)and either of(600-850 cps), (850-1200 cps)or(1200-1700 cps). Accordingly, it is sup-

posed that the combination of(300-600 cps)as a lower band and(1200-2400 cps)as a higher one is. satisfactgry for the binaural fusion test when〔u〕and〔e〕are used as the key-vowels.

In the third experiment, binaural fusion of the 67 monosyllables was studied. The outline of

the experilnental set up is shown in the block diagram of Fig. 1, which indicates Tape Recorder

Fig. 1. The block diagram of the experimental set up of binaural fusion test using the 67 Japanese monosyllables.

Channel 1

Tape Recorder Channel 2 KP-3

KP-3, Audiofilters SA-2701 and Amplifiers SQ-63 (LUX) in use. The 67 monosyllables pronounced by a 25-year-old female who spoke standard Japanese were filtered through a band-pass of 1200-2400 cps in Channel 1 and 300-600 cps in Channel 2. Ten subjects with normal hearing were selected for the test. Signals through the Channel 1 were presented to one ear at 30 db above the threshold of detectability and those through the Channel 2 were presented to the other at 40 db. After each monaural presentation, the signals through the two channels were presented to both the ears simultaneously. Then, a comparison was made between the articulation scores in the monaural

and binaural presentations. Generally speaking, the syllables which had succeeding vowels〔u〕and

〔e〕showed good binaural fusion, i. e. high articulation score in binaural presentation and low articulation score in each monaural presentaion, and the syllables which contained the vowels〔a〕and

〔i〕showed poor binaural usion. However, the syllables containing〔o〕showed much better fusion than expected from the results of the first experiment. This appeared to occur because the rejection of filter at low-pass 600 cps and high-pass 1200 cps covered the lower and upper frequency boun- daries of the first formant of〔o〕respectively.

The frequency bands of 300-600 cps and of 1200-2400 cps were originally selected so that a good identification could be obtained for the vowels〔u〕and〔e〕. However, the combination of these bands sometime yielded good fusion for not only the syllables containing〔o〕but the syllables containing〔a〕or〔i〕. It follows that not only the syllables containing〔u〕and〔e〕but also those

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containing other vowels could be used as the test materials. From this point of view, 29 monosyllables which showed better fusion than the average value, were selected for the next experiment. They are〔ru〕, 〔so〕, 〔ba〕, 〔se〕, 〔re〕, 〔go〕, 〔zo〕, 〔bo〕, 〔da〕, 〔bi〕, 〔su〕, 〔pu〕, 〔he〕, 〔to〕, 〔ra〕,

〔pi〕, 〔tsu〕, 〔bu〕, 〔ze〕, 〔de〕, 〔po〕, 〔sa〕, 〔za〕, 〔ha〕, 〔fl〕, 〔hi〕, 〔ke〕, 〔pe〕 and 〔no〕.

In the study of this chapter, the Japanese five vowels, 〔a〕, 〔i〕, 〔u〕, 〔e〕and〔o〕, were divided

into narrow frequency bands by electric filtering and their articulation scores were examined. The

scores for〔u〕and〔e〕were so small that those for the filtering through two bands were exa-

mined. From the results, it was found that the range of 300-600 cps as a lower band and the

range of 1200-2400 cps as a higher one were satisfactory for the binaural fusion test when〔u〕

and〔e〕were used as the key-vowels. The combination of those ranges proved to be valid for the syllables containing〔u〕and〔e〕and some syllables containing other vowels.

Chapter 4: Examination of Matzker's Method.

The method developed by Matzker consists of three test procedures. Test 1 is a binaural hearing of 41 disyllabic words filtered through (500-800 cps) and (1500-2400 cps), i. e. the signals passed through the low band is delivered to one ear and the signals passed through the high band is delivered to the other simultaneously. In Test 2, the signals passed through both the bands are presented to both the ears, i. e. each ear receives same information simultaneously. Test 3 is a repetition of Test 1. Same word materials are used during these thress tests, which are listened at medium level. This method is based on his own hypothesis on the central auditory mechanism of binaural fusion. There is, accoding to him, a fourfold protecting system of hearing in the brain stem, i. e. the right medial geniculate body receives impulses from both the ears (doublef old), the left medial geniculate body receives impulses from both the ears (doublef old) and both the medial geniculate bodies receive impulses from both the ears (fourfold). Even in a patient with complete unilateral deafness, the impulses can be transmitted to both the medial geniculate bodies and auditory cortices through the system. Matzker considered that it was owing to the compensation by the fourfold protection that conventional audiometry would not detect any hearing loss even if more than 30 percent of synapses in the brain stem were destructed. According to him, Tests 1 and 3 transform the system to doublef old one by making the information in each ear unintelligible. The fourfold protection is preserved in Test 2. If there are some dysfunction of auditory synapses in the brain stem, poor intelligibility must be shown in Tests 1 and 3. Matzker selected 41 disyllabic words as the test material and numbers of the unidentified words were checked. The results were evaluated by the criteria described below;

Positive: The numbers of the unidentified words are more than 15 in Test 1 and the numbers in Test 3 exceed those in Test 2.

Negative: The numbers are less than 10 in Test 1.

Most of the brain tumor cases and some cases with any other lesions in the central nervous system showed positive results. Most of the responses shown by the aged persons were positive. These positive responses were attributed to some dysf unctions of auditory synapses in the brain stem. Matzker's tempting hypothesis on the central auditory mechanism led the author to engage in this kind of experimental work. The 29 monosyllables as shown in the Chapter 3, were reproduced with Tape Recorder DN-72R (DENON), of which the output was divided into two channels so that the signals filtered by two Audiofilters SA-2701 could be recorded again on Stereotype Tape Recorder DN-55R (DEMON). Fig. 2 shows the outline of the experimental procedure by a block

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Fig. 2. The block diagram of two-channel filtering.

Channel 1

DN- 72R Channel 2 DN-55R

Fig. 3. The block diagram of binaural fusion test.

Channel 1

Tape Recorder 700 Channel 2

diagram. The obtained tape was used in Tests 1 and 3. This tape was reproduced with DN-72R and recorded with DN-55R without passing through filters. The procedure allowed the informa- tions passed through each filter to be mixed and recorded on each single track. The obtained tape was used in Test 2. All reproduction in the actual tests, of which a block diagram is shown in Fig. 3, was performed with Stereotype Tape Recorder 700 (DENON). In Tests 1 and 3, the Channel 1 in which the syllables were filtered through (1200-2400 cps) was connected to the right ear and the Channel 2 with a filter of (300-600 cps) was connected to the left simultaneously. The signals through the Channel 1 were given at 30 db above the threshold of 1500 cps and those through the Channel 2 were given at 40 db above the threshold of 500 cps. In Test 2, the level at which the signals were given to each ear was 30 db above the average threshold among 500, 1000 and 2000 cps. The syllables were presented at intervals of four seconds and the same syllables were used through Test 1, 2 and 3. The subjects were asked to note or repeat orally their answers. Differently from Matzker, the binaural function was evaluated from the difference in the discrimination score between Test 2 and either Test 1 or Test 3 whichever showed better discrimination. Before the clinical use, ten normal subjects were examined and the rejection limit at one percent level of statistical significance was adopted as a tentative standard. The average value of the difference was 0. 6 syllables and the limit was 2.4 syllables, with the normal value ranging from -1 to 3 syllables. The results of the test on 18 patients are shown in Table 2. Recruitment was measured by Fowler's binaural balance test or Li sher's difference limen test. Only the patients who had hearing loss of less than 40 db in speech area were selected for the test. They were classified into three groups according to the value of the rejection limit, i. e. positive, normal and negative. The word "normal" means the range between the positive and negative rejection limits, "positive" means the range above the positive limit and "negative" means the range below the negative limit. This classification is of course quite different from Matzker's criteria and the difference will be discussed in the end of this chapter. Two cases were positive, fifteen were normal and only one was negative. The positive cases are summarized.

Case 1, a 41-year-old book salesman,was first seen on January 6, 1964,complaining of deafnessprogressive

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Table. 2. The results of binaural fusion test following Matzker's method. The signals through the high band, 1200～2400 cps, was delivered to the right ear at 30 db above the threshold

of 1500 cps and those through the low band, 300～600 cps, was delivered to the left ear at 40 db above the threshold of 500 cps. Cases 1 and 2 are positive and others are normal except Case 18 which is negative.

for two years, mild fulness in the right ear, tinnitus Fig. 4. The pure tone audiogram of Case 1. and occasional vertigo. Conventional audiometry revealed symmetric sensorineural deafness in which recruitment was positive (Fig. 4). Among the 29 syllables, the numbers of correct answer in Test 1, 2 and 3 were 11, 20 and 10 respectively (expressed as 11-20-10.). Caloric test revealed mild hypof unction of the right vestibulum. The hearing loss in this case appeared to be due to some impairment of the inner ears, judged from the results of those examinations besides the binaural fusion test. Case 2, a 52-year-old merchant, was first seen on December 21, 1963. He complained of hearing loss in the right ear, but of no tinnitus or vertigo, The pure tone audiogram is shown in Fig. 5. The recruitment of the ears was negative by the DL test. The score obtained on the binaural fusion test was 8-16-12, positive. However, Case 7, a right temporal lobe tumor (glioma), showed normal pattern of binaural fusion. The score was 13-14-10. Craniotomy ascertained that the tumor had not affected the cortical auditory area.

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Fig. 5. The pure tone audiogram of Case 2. In the next study, in which the singals through the Channel 2 were given at 30 db instead of 40 db in Tests 1 and 3, the average value of the difference among ten normal subjects was 1.4 syllables and the rejection limit at one percent level of significance was 6.7 syllables, with the normal value ranging from -5 to 8 syllables. Table 3 summarizes the results on twelve patients. Only one case was positive, eleven were within the normal range and no case was negative. The positive case is summarized.

Case 19, a 31-year-old businessman, was sent to our clinic for audiometry on January 24, 1964. The patient had been treated of pulmonary tuber- culosis with 50 g of Streptomycin for the last 25 Fig. 6. The pure tone audiogram of Case 19. weeks. He had complained of tinnitus since several weeks after the beginning of SM-administration. The audiogram revealed slight symmetric sensorineural deafness in which recruitment was between positive and negative (Fig. 6). This case was diagnosed as SM-intoxication and the score in the binaural fusion test was 15-26-16, positive.

Matzker's binaural fusion test was examined on 30 patients by the author's modifications in several points which are described below. 1) Twenty nine Japanese nonsense monosyllables instead of 41 German disyllabic words were used. 2) As to the frequency bands, (300- 600 cps) and (1200-2400 cps) instead of (500- 800 cps) and (1500-2400 cps) were selected. 3) Matzker established the criteria for evaluation of the function of binaural fusion based on the experience in his study. However, in the author's study, the rejection limit at one percent level of significance in 10 normal subjects for the score difference between Test 2 and either Test 1 or 3 whichever showed better discrimination, was adopted as a tentative standard for the evaluation. Matzker's assessment of the test result appeared so subjective, especially at the management of the unidentified words in Test 3, that the author classified the patterns of binaural fusion according to the rejection limit in ten normal subjects as the standard for evaluation. It is extremely difficult to draw a boundary between normal and abnormal in binaural function. In the author's study, the number of the subjects as a control group was so small that the rejection limit was calculated not at five percent level of significance but at one percent, for one percent significance seemed to conceal the defect of a small number of the subjects. Case. 18 showed a negative response. This kind of response will be discussed in Chapter 7.

Among the 30 patients tested, three cases (two sensorineural deafness due to unknown cause and one SM-intoxication) showed positive response, i. e. poor binaural fusion. According to the

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Table 3. The results of binaural fusion test following Matzker's method. The signals through the high band, 1200 - 2400 cps, was deliveredto the right ear at 30 db above the threshold of 1500 cps and those through the low band, 300 - 600 cps, was delivered to the left ear at 30 db above the thresholdof 500 cps. Case 19 is positiveand others are normal.

Matzker's hypothesis, an organic lesion in the central auditory pathways, especially in the brain stem, was suspected in those cases (No. 1, 2 and 19). This suspicion would be correct to some extent, for the purpose of the binaural fusion test is to evaluate a phenomenon which undoubtedly occurs in the central auditory nervous system, and the rate of rejection limit was strictly selected. However, the data obtained in this study seemed too simple to evaluate the binaural function and to avoid a chance response. It appeared to be better for Matzker's binaural fusion test to be modified in several points which are described below. 1) Matzker used only one intensity level for the presentation of the signals. As stated before, the value of rejection limit in the control subjects was much greater at 30 db of the low band than at 40 db. This means that discrimination score is easily infuenced by the level of signals presented. The test, therefore, must be performed at several different levels. 2) In accordance with his own hypothesis on the mechanism of binaural integration, Matzker examined only the score difference between the diotic presentation of the signals through both the high and low bands, and the dichotic presentation of the signals through the high band and those through the low band. However, it also seemed to be necessary to compare the score difference between the dichotic presentation of the signals through the high band and those through the low band, and the monaural hearing of the signals through each band. 3) In Matzker's study, the side of ear to receive each band appeared to have been decided without sufficient consideration on the patterns of audiogram and the case histories. More exact appreciation of binaural function will be expected by changing the side each other.

With these points taken into consideration, an attempt was made for a modification of the original Matzker's method as described in the next chapter.

Chapter 5 Binaural Fusion Test Using Four Intensity Levels.

Fig. 7 shows the mean discrimination curves with the distorted 67 Japanese monosyllables in

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the diotic presentation of the signals through both the high and low bands at which both the ears receive the same signals (A), the binaural presentation of the two bands at which the high band - pass signals were given to the right ear and the low band-pass signals were given to the left ear (B), and the monaural presentation of the high band (C) or low band (D). Six normal subjects were tested for this study. The apparatus used are shown in Figs. 2 and 3, and the same speech material was used as mentioned in Chapter 3. The high band-pass signals were given to the right ear in C, and the low band-pass signals were given to the left ear in D. The numbers in the ab- scissa are the presented levels above the mean threshold of detectability in the monaural presentations. For Curve B, each band was delivered at same intensity level. For Curve A, the monaural threshold was measured for the mixed mate- Fig. 7. The mean discrimination curves for six normal rial of the two bands and same level was subjects with the 67 Japanese monosyllables. given to each ear. No large difference in the discrimination score was noted between Cur- ves A and B, but a marked difference was noted between Curve B and Curve C or D. For most of the syllables, Curve C obtained on each subject was much higher than the Curve D of the same subject. Therefore, the discrimination score difference between Curves B and C can be utilized as an index of binaural function. This difference and the score difference between A and B, based on Ma- tzker's hypothesis as mentioned already, were studied as the indexes in the next experiment. Generally speaking, every hearing test must be performed as shortly as possible. From this point of view, four levels from 10 db to 40 db appeared to be enough to make the. new binaural fusion test so effective, for those curves in Fig. 7 reach in nearly flat shape at 40 db. Only 10 syllables li3ted below, which showed good binaural fusion, were selected for each level. (Goad binaunil fusion means a large discrimination score difference between the binaural and monaural presentations. ) A: Binaural presentation of two electrically mixed bands (1200 - 2400 cps and 300 - 600 cps). 10 db:〔o〕〔ru〕〔yo〕〔ka〕〔u〕〔ro〕 B: Binaural presentation of the two bands. 〔ke〕〔me〕〔pi〕〔ga〕 C: Monaural presentation of the high band. 20db: 〔ge〕〔ru〕〔ni〕〔u〕. 〔fu〕〔be〕 D: Monaural presentation of the low band. 〔re〕〔ko〕〔go〕〔pu〕

30db: 〔ba〕〔t∫i〕〔be〕〔po〕〔za〕〔ra〕〔bo〕〔o〕〔re〕〔bu〕 40 db: 〔ra〕〔re〕〔za〕〔ru〕〔o〕〔bo〕〔go〕〔gu〕〔bi〕〔pa〕

The syllables were produced by the same speaker as in Chapters 3 and 4, and they were presented at intervals of four seconds and in random order in each of six test procedures. (1) Binaural presentation of non-distorted syllables (diotic). (2) Binaural presentation of the signals through both the high and low bands (diotic). (3) Binaural presentation (dichotic). The high band is given to the left ear and the low one is given to the right ear.

66 耳鼻臨床 58: 8 Binaural Fusion Test: A Diagnostic Approach to the Cent, al Auditory Disorders. 567

(4) Monaural presentation of the high band to the left ear. (5) Binaural presentation (dichotic). The high band is given to the right ear and the low one is given to the left ear. Fig. 8. Average pattern of binaural fusion obtained (6) Monaural presentation of the high for 10 normal subjects in the four-level method. band to the right ear. The series of the test procedures take about 20 minutes to be finished. The first procedure has two purposes. One is practice for binaural hearing in which a subject hears the test material at the center of head. The other is a comparison of the discrimination score with that in the distorted materials.

Results. Fig. 8 shows the curves of average values obtained for 10 normal' subjects. As a typical pattern, Curve (2) was located between Curves (3) and (4) or Curves (5) and (6) except at 40 db. Binaural function can be discussed on four kinds of score difference: (2) - (3), (2) - (5), (3) - (4) and (5) - (6). The ranges within the rejection limits at one percent level of significance are shown in Table 4.

Table 4. The normal range of binaural fusion for 10 normal subjects in the four-level method (unit: syllables; rejection limit: one percent).

Twenty nine patients were tested with these procedures. All the cases who showed abnormal results at one level or more were regarded as poor in their binaural function. From this criterion, two cases (No. 31 and No. 32) were classified as positive and twenty seven cases from No. 33 to No. 59 were classified as normal (Table 5). The positive cases are summarized.

Case 31, a 13-year-old junior high schoolboy, was first seen on April 28, 1964, complaining of hearing loss. Difficulty in movement of the right upper extremity had been apparent since September, 1963 and his family had suspected of some hearing loss in the October. The patient had walked with dragging the right foot since January, 1964. As these troubles and occasional headache in the left temporal to occipital area had been gradually developed, he was admitted in the department of neurosurgery of Kyoto University, early in April, 1964. The pure tone audiometry revealed nearly normal hearing ability, but the discrimination scores in an ordinary speech audiometry were poorer than expected from the pure tone audiogram (Fig. 9). Fig. 10 shows the result of the binaural fusion test. All the discrimination scores were lower than those of the normal subjects. Curve (2) was close to Curve (1), but fairly above Curves (3) and (5). The difference between (3) and (4) was hold relatively wide, but the difference between (5) and (6) was narrow. The score differences, (2) - (3) at 10 and 30 db and (5) - (6) at 40 db, were significant, which meant poor binaural function. Neurological examinations revealed no abnormal findings in the ocular f undi and the field of vision or in the cerebrospinal fluid. Some cortical sensory disturbances were found in the right extremities and the EEG-finding suggested a subcortical

67 568 Ritsu Hayashi 耳鼻臨床 58: 8

Table. 5. The results of four-level method. Cases 31 and 32 are positive and others are normal.

organic lesion in the left supratentorial area. There were, however, no abnormal findings in the cerebral angio- graphy and pneumoventriculography. As no such pathognomonic findings were obtained as to decide the diagnosis of brain tumor, this patient is still under observatioi. Case 32, a 50-year-old merchant, was first examined on May 14, 1964, complaining of headache and occasional tinnitus in the left ear. He had received a bullet-lodge by a piece of hand grenade in the left temporal area in China on September 20, 1939 and he had been in coma for about 40 days after the injury. The piece had been removed by craniotomy at the Tokyo Army Hospital in January, 1941. The site has been uncertain because of unavailability of the operation record. Mild articulation disorder, occasional unconsciousness of short duration and occasional cramp in the right upper extremity had been developed since then. The pure tone audiogram is shown in Fig. 11 in which C5-dip is apparent in the left ear. Fowler's binaural balance test was positive at 4000 cps. Maximal discrimination score of the left ear was more than 90 percent and no abnormal threshold adaptation was revealed by BekEsy audiometry. Fig. 12 shows the result of the binaural fusion test. The score difference, (5) -

68 耳鼻臨床 58: 8 Binaural Fusicn Test: A Diagnostic Approach to the Central Auditory Disorders. 569

Fig. 9. The pure tone and speech audiogrom of Case 31.

Fig. 10. The pattern of binaural fusion of Case 31. Fig. 11. The pure tone audiogram of Case 32. Curve (2) is fairly above Curves (3) and (5).

Fig. 12. The pattern of binaural fusion of Case 32. (6), was smaller than (3) - (4) and it was signi- The score difference, (5) - (6), is small at 20 and ficant at 40 db. This patient was diagnosed as a 40 db. temporal lobe epilepsy at the department of psychi- atry, Kyoto University.

The above-mentioned modifications seemed to be more satisfactory for the evaluation of binaural fusion than the Matzker's original test. For case 31, a subcortical lesion of left side was suspicious, but poor binaural fusion was apparent regardless of the side of ear to receive the high or low band. However, there was a tendency that the fusion was poorer when the high band was connected to the ear contralateral to the suspected side of lesion than to the homolateral. For

69 570 Ritsu Hayashi 耳鼻臨床 58: 8

Case 32, a cortical lesion in the left temporal lobe was suspicious and the function of binaural fusion was poor when the high band was connected to the contralateral ear. Those modifications thus allowed to evaluate the function of binaural fusion from more collec- tive judgement than Matzker's. However, the four-level method appeared to have a shortcoming that the number of syllables presented in each intensity level was too small to make the test results consistent.

Chapter 6 Binaural Fusion Test Using Two Intensity Levels.

Two levels with 20 syllables instead of four levels with 10 syllables seemed to be so sufficient to examine the discrimination score as a func- Fig. 13. The average pattern of binaural fusion tion of intensity level that 20 db and 40 db obtained for 10 normal subjects in the two-level were employed in the next experiment. As method. the test materials, 10 syllables listed below were added to each group of the 10 syllables used at 20 db and 40 db in the four-level method. 20 db: 〔o〕〔su〕〔no〕〔ne〕〔po〕〔ri〕

〔gu〕〔bi〕〔te〕〔bo〕 40 db: 〔a〕〔be〕〔tfi〕〔zi〕〔no〕〔ba〕

〔ri〕〔zu〕〔po〕〔ze〕 These syllables were pronounced by the same person as in the four-level method. Fig. 13 shows the lines of average values obtained for 10 normal subjects. As a typical pattern, Line (2) was located between Lines (3) and (4) or between Lines (5) and (6). The ranges within the rejection limit at one percent level are shown in Table 6. The values of standard deviation in the two-level method were smaller than those in the four-level method, but there was no significant difference between both the methods. Fifty nine patients were tested with this method. Three cases, No. 60, 61 and 62, were classified as positive and fifty three cases from No. 63 to No. 115 were classified as normal. Case 116 showed a negative pattern (Table 7). The three positive cases are described below in detail.

Table 6. The normal range of binaural fusion for 10 normal subjects in the two-level method (unit: syllables; rejection limit one percent).

70 耳鼻臨床 58: 8 Binaural Fusion Test: A Diagnostic ApProach to the Central Auditory Disorders. 571

Table 7. The results of two-level method. Cases 60, 61 and 62 are positive and others are normal except Case 116 which is negative. 572 Ritsu Hayashi 耳鼻臨床 58: 8

Fig. 14. The pure tone and speech audiogram of Case 60.

Fig. 15. The pattern of binaural fusion of Case 60. Case 60, a 26-year-old mechanic, complaining Line (3) is below Line (2) and no difference is of tinnitus in the right ear, was first seen on June detectable between Line (3) and Line (4). 2, 1964. He had a head injury at the right temporal area in a traffic accident on September 11, 1960. His consciousness had been lost for three days after the injury. Fracture of the base of skull was de- tected on X-ray film. This patient had been doing fairly fine besides mild dull headache until the summer in 1962. Tinnitus and deafness in the right ear had gradually developed and attacks of dizziness had occured occasionally since then. Fig. 14 shows the pure tone and speech audiograms. Recruitment of the right ear was positive at 4000 cps with Fowler's balance test and no abnormal threshold adaptation was revealed in the ears. The pattern of binaural fusion is shown in Fig. 15. Line (3) was below Line (2) and nearly no difference was detectable between Line (3) and Line (4). The score diffefence, (3) - (4) at 40 db, was significantly small. When the high and low bands were presented to the right and left ears respectively, binaural effect was normal. Caloric test revealed hypof unction of the right vestibulum, but some neurological examinations did not reveal any disturbances. This patient showed a normal binaural summation at threshold for short tone burst16. Case 61, a 26-year-old mechanic, was first seen on August 28, 1964. He had felt his ears full since the head injury at the parietal to right temporal area with short duration of unconsciousness in July, 1964. Patency of eustachian tubes was normal. Fig. 16 shows the pure tone audiogram. Recruiment of the ears was negative with Li sher's DL test and no abnormal threshold adaptation was found. The binaural fusion test, as shown in Fig. 17, revealed that the patient had poor binaural function. Line (3) and Line (5) were below Line (2), and differences, (3) - (4) and (5) - (6), were relatively small. The score difference, (2) - (5) at 40 db, was significant.

72 耳鼻臨床 58: 8 Binaural Fusion Test: A Diagnostic Approach to the Central Auditory Disorders. 573

Case 62, a 53-year-old cleaning woman, was Fig. 16. The pure tone audiogram of Case 61. first seen on July 22, 1964, complaining of mild vertigo. Ataxic walking, speech disorder (rhinolalia aparta) and intention tremor had gradually developed with her since the mid-fall in 1963, and she was admitted in the department of internal medicine, Kyoto University on July 15, 1964 under the diagnosis cf cerebellar ataxia. Pneumoventriculography showed normal finding, but EEG suggested some diffuse organic change in the cerebrum. Fig. 18 shows the pure tone audiogram. Recruitment of the ears was negative and no abnormal threshold adaptation was found. Fig. 19 revels that the binaural function is poor. The differences, (2) - (5) at 40 db and (5) - (6) at 20 db, are significant. Case 75 was a left temporal lobe tumor (gl ioblastoma) which infiltrated the cortical auditory area. The pure tone audiogram showed nearly normal hearing of the ears. The pattern of binaural Fig. 17. The pattern of binaural fusion of Case, 61. fusion is shown in Fig. 20, in which the discrimi- Line (3) and Line (5) are below Line (2). nation of distorted syllables is poor, especially when the signals through the high band is given to the right ear. It was, however, statistically clessificd into a normal pattern.

Cases 60 and 61, the cases of head injury, showed poor binaural fusion in spite of the lack of neurological findings. However, both the cases showed quite different pattern each other, that is to say, the binaural function of Case 60 was poor only when the signals through the high band were presented to the left ear and the signals through the low band were presented to the right, but that of Case 61 was poor regardless of the side of ear to which the signals through each of the bands were presented. This suggested that both the cases had the lesions which were different each other in their extension or level in the central auditory nervous system. For Case 62, a cerebellar lesion was suspicious, but EEG-finding seemed to show some diffuse organic change in the cerebrum. The pattern of binaural fusion shown by this case resembled that of Case 61, but the binaural function was lower when the signals through the high band were presented to the right ear than to the left. The binaural function shown by those cases described in Chapter 5 and 6 will be discussed in Chapter 7 especially on the site of lesions.

73 574 Ritsu Hayashi 耳鼻臨床 58: 8

Fig. 18. The pure tone audiogram of Case 62. Chapter 7 Discussion.

1. Site of lesion. From a theoretical point of view, cases with impairment of the inner ear only, must have a normal binaural function. In the above-mentioned study, all the cases of Me- nier's disease and acoustic trauma showed a normal pattern of binaural fusion. This would support the explanation that the poor binaural fusion is indicative not of the inner ear impairment but of a lesion in the central auditory nervous system. It is a very interesting and important problem where the binaural fusion takes place in the central auditory nervous system. Many investigators, as described in Chapter 1, seem Fig. 19. The pattern of binaural fusion of Case 62. to have thought that it occurs in the brain Line (3) and Line (5) are below Line (2) and stem. However, the data obtained in this stu- negative difference is detectable at 20 db between Line (5) and Line (6). dy are so complicated that such an inference seems to be impossible. The most interesting result in this study was that some cases showed a marked discrepancy between the patterns of binaural fusion when the signals through the high band were delivered to the right ear and when they were delivered to the left. In Case 32 (a bullet lodge in the left temporal area. The pattern of binaural fusion was shown in Fig. 12.) and Case 60 (a head injury at the right temporal area. The pattern of binaural fusion was shown in Fig. 15.), the pattern of binaural fusion became quite different depending o.n the side of ear to receive the signals through the high or low band. In Case 61 (a head injury at the parietal to the right temporal area. The pattern of binaural fusion was shown in Fig. 17.), such a difference was not found. I n Case 31 (a suspicious temporal lobe tumor case who showed a marked discrepancy in hearing between pure tones and speech. The pattern of binaural fusion was shown in Fig. 10.) and Case 62 (a cerebellar ataxia. The pattern of binaural fusion was shown in Fig. 19.), poor binaural function was detectable regarldess of the side, but the function was lower when the signals through the high band were presented to the right ear than to the left. An unilateral lesion in the central auditory pathway is conceivable for Cases 32 and 60, and the fusing pattern of Case 61 seemed to indicate some diffusely extending change over both sides. For Case 31, some diffuse extension of degenerative

74 耳鼻臨床 58: 8 Binaural Fusion Test: A Diagnostic Approach to the Central Auditory Disorders. 575

change would be greater in the left side of Fig. 20. The pattern of binaural fusion of Case 75. central auditory nervous system than in the right side. The author believes that the side dominance in Cases 32 and 60 might be difficult to explain from a lesion in the brain stem, in which the auditory pathways are closely gathered in a narrow place, or that the binaural function of a lesion of the brain stem would be poor regardless of the side of ear to receive the signals passed through each of the high and low frequency bands. Within the limit set by a small number of cases in this study, an unilateral lesion in the cortical or subcortical auditory area would explain the patterns of binaural fusion of Cases 32 and 60. The Calearo's study on temporal lobe tumors would support this explanation. For Cases 32 and 75 (a left temporal lobe tumor. The pattern of binaural fusion was shown in Fig. 20.), it is obvious that the lesion exists in the left cerebral hemisphere. A lesion in the right hemisphere is conceivable for Case 60. For Case 31, principal disturbance would be evident in the left hemisphere. These considerations lead to the following suggestion: binaural function might be poor when the signals passed through the high band is delivered to the ear opposite to the side of affected cerebral area. Case 60 was examined regarding the binaural summation at threshold for short tone burst. 16) The patient showed nearly normal summation, which would suggest that the site of binaural summation for pure tones is different from the site of binaural fusion of two coherent band-passed speech signals. Binaural summation of pure tones may occur in the brain stem, especially in the superior olivary nuclei. 2. Relation between binaural function and recruitment. Many investigators reported that the recruitment in most of the retrocochlear deafness was negative, but few papers have been published on the relation between binaural function and recruitment of the ears. Groen and Hellema9 reported that 30 percent of the cases of poor binaural integration showed positive recruitment. Morimoto17 stated in the paper "Otological study of brain tumor" that some of the cases of retrocochlear deafness showed a positive recruitment. Those investigators considered that the positive recruitment in a central auditory disturbance originated from an accompanied or secondary imapirment of the inner ear. Recruitment, as they pointed out, is not necessarily an absolute index for the differential diagnosis between the inner ear deafness and the retrocochlear deafness. In the author's study, some of the cases of poor binaural function such as Cases 32 and 60 showed a positive recruitment, of which the primary origin (head injury for those cases) might be same as of the poor binaural function. However, recruitment appeared to have no special relation to the binaural function according to the assessment of the data shown in Tables 5 and 7. 3. Method of binaural fusion test. Matzker seemed to be correct in his hypothesis that a comparison of discrimination score be-

75 576 Ritsu Hayashi 耳鼻臨床 58: 8 tween the diotic presentation of the signals through both the high and low bands and the dichotic presentation of the signals through the high band and those through the low band was almost sufficient to evaluate the binaural function. However, the evaluation seemed to be reliable and comprehensive by adding the comparison of the score between the dichotic presentation of the signals through the high band and those through the low band, and the monaural presentation of the signals through the high band as the author did. Furthermore, the monaural presentation allowed to examine the intelligibility of each ear for distorted speech. As to the two kinds of methods which were used by the author, no statistial difference in the variability of the test results was found between the two-level method using 20 syllables at a level and the four-level method using 10 syllables at a level. However, the two-level method seemed to be more reliable than the four-level method, because, in normal subjects, the rejection limit in the former was relatively narrower than in the latter. 4. Treatment of the experimental data. The Matzker's assessment on his data was so uncomprehensive that the data obtained in this study was treated statistically at one percent level of significance, but this proved to be not necessarily satisfactory. The rejection limit at one percent level was adopted for practical convenience. However, this limit, of course, does not mean the real boundary between normal and abnormal functions. Therefore, it is possibly considered that positive group may include some cases with unimpaired central auditory pathway and normal group may include some impaired cases. How- ever, most of the cases classified into positive group by the author's test were suspectable of some disturbances in the central nervous system. It should be decided by composite judgement with other audiological findings whether the pattern of binaural fusion indicates any organic neurological disorders or not. A few cases showed negative pattern, i. e. too large score difference between binaural presentations of the two bands and of the two electrically mixed bands or between the binaural presentation of the two bands and the monaural presentation of the high band. This kind of pattern would not mean any organic change but poor sensitivity to the simultaneous reception of the same signals from both the ears or to the monaurally delivered band-passed speech.

Chapter 8: Summary and Conclusion.

From the results of acoustic analysis of the Japanese five vowels, two frequency bands (300 cps-600 cps and 1200 cps-2400 cps) were selected for the binaural fusion test in this study. With the use of Japanese nonsense monosyllables as the test signal, 30 patients with hearing loss were examined according to the Matzker's method. Following several modifications were made to cover the drawbacks which was found in the original Matzker's method. 1) To evaluate the binaural function, comparisons of the score difference were made not only between the Biotic presentation of the signals through both the high and low bands, and the dichotic presentation of the signals through the high band and those through the low band, but also between the latter and the monaural presentation of the high band. 2) In the binaural presentation, the side of ear to receive the signals through the high or low band was not fixed but was alternated each other, i. e. the signals through the high and low bands were presented to the left and the right ear respectively, then those through the high band were presented to the right ear and those through the low band were presented to the left. 3) Four or two intensity levels instead of only one were used. Five cases among 86 patients tested by these modified methods were judged as abnormally poor in binaural fusion. They showed a tendency that binaural function was poor when the high band was connected to the ear opposite to the side of affected cerebral area. Some of them induced the author to consider that the site of binaural fusion of coherent distorted speech singals is not

76 耳鼻臨床 58: 8 Binaural Fusion Test: A Diagnostic Approach to the Central Auditory Disorders. 577 the brain stem but the cortical or subcortical area. Most of the cases of Menier's disease and acoustic trauma. showed a normal pattern and this certified the diagnostic values of the binaural fusion test for deficiencies in the central auditory pathway. Acknowledgement

I wish to express my sincere gratitude to Professor Masanori Morimoto and Emeritus Professor Mitsuharu Goto for their guidance during this study. To Dr. Fumihiko Ohta, my sincere and warm thanks are due for his valuable advice and help throughout my work. I am deeply indebted to Dr. Hiroaki Takahashi and Mr. Yoshio Takeuchi for their helpful advice. I greatly appreciate the kind co-operation of Drs. Hosoda, Sugiyama, Monju, Ishijima and Yamamoto, and all the doctors of the department of otolaryngology, Kyoto University. I wish to thank Dr. Nobuhiko Isshiki for his kind correction of my English and Miss Date for her assistance with the manuscript. This investigation was supported by a grant in aid for Fundamental Scientific Research from the Education Ministry, and presented in part at the Seventh Annual Meeting of the Japan Society of Logopedics and Phoniatrics (November 24, 1962), the Eighth Annual Meeting of the Japan Audiological Society (October, 29, 1963), the 65th Annual Session of the Oto-rhino-laryngological Society of Japan (May 5, 1964) and the Nineth Annual Meeting of the Japan Audiological Society (September 24, 1964).

References

1) Hirsh, I. J., Binaural Summation - A Century of Investigation, Psychological Bulletin 45: 3; 193, May, 1948. 2) Seebeck, A.: Beitrage zur Psychologie des Geoor- and Gesichtsinnes, Abschn. A. Pogg. Ann., 68: 449, 1846. 3) Bocca, E.: Binaural Hearing: Another Approach, Laryngoscope 65: 12; 1164, 1955. 4) Calearo, C.: Binaural Summation in Lesions of the Temporal Lobe, Acta oto-laryng. (Stockh.) 47: 392, 1957. 5) Jerger, J. F.: Observations on Auditory Behavior in Lesions of the Central Auditory Pathways, Arch. Otolaryng. 71: 797, May 1960. 6) Matzker, J.: Emn Binauraler Horsynthese-Test zum Nachweis Zerebraler Horstorungen, Georg Thieme Verlag, Stuttgart, 1958. 7) Matzker, J.: Two New Methods for the Assessment of Central Auditory Functions in Cases of Brain Disease, Ann. Otol. (St. Louis), 68: 1185, 1959. 8) Linden, A.: Distorted Speech and Binaural Speech Resynthesis Tests, Acta oto-laryng. (Stockh.) 58: 33, 1964. 9) Groen, J. J., and Hellema, C. M.: Binaural Speech Audiometry, Acta oto-laryng. (Stockh.) 52: 397, 1960. 10) Cherry, E. C., and Taylor, W. K.: Some Further Experiments upon the Recognition of Speech with One and with Two Ears, J. Acoust. Soc. Amer. 26: 4; 554, 1954. 11) Calearo, C.: Detection of Malingering by Periodically Switched Speech, Laryngoscope 67: 130, 1957. 12) Bocca, E. Factors Influencing Binaural Integration of Periodically Switched Messages, Acta oto-laryng. (Stockh.) 53: 142, 1961. 13) Kirikae et al.: A Study of Hearing in Advanced Age, Laryngoscope, 74: 2; 205, 1964. 14) Horiguti, S.: Do Phonemic and Linguistic Differences among Languages Interfere with Speech Audiometry ?, International Audiology, 3: 2; 237, 1964. 15) Ohta, F., Takahashi, H. and Hayashi, R.: Binaural Fusion Test with Band-Pats Filters (in Japanese), Audiology, 7: 2, 1964. 16) Ohta, F., et al.: Binaural Summation at Threshold for Short Tone Burst, Japan Otolaryng., 1, 1965 (in press). 17) Morimoto, M.: Otological Study of Brain Tumor (in Japanese). 1955.

研 究 Binaural Fusion Test

研究 Binaural Fusion Test