Arch. Oto-Rhino-Laryng. 209, 277--290 (1975) 9 by Springer-Verlag 1975
Some Thoughts on the Perception of Ultrasonics by Man H. G. Dieroff a n d H. E r t e l Clinic of E.N.T., Friedrich-Schiller-University of Jena (Director: Prof. Dr. med. habil. R. Albrecht) Received, January 21, 1975
Summary. After a short specification of the ultrasonic transmitter device by which the test frequencies of 20, 40, 60 and 100 kHz could be emitted by means of a transmitter fixed to the forehead of the subject with constant pressure, the mean perception threshold for ultrasonics is described, which had been recorded by using the wide-band noise of the audiometer MA 30. Both curves do not differ considerably so that ultrasonic investigations can be carried out in the presence of working noise without producing wrong measurement results. A comparison of perception between ultrasonic frequencies and audio frequencies in the hearing range showed that ultrasonics produce, independent of the stimulation frequency, the same sensory impression as a sound at a frequency of about 12 or 13 kHz. Applying this method to hard of hearing subjects with noise induced hearing damages and deaf subjects had the following results: 1. Subjects with noise induced hearing damages very early have a raised perception threshold for ultrasonics. There was no correlation between the extent of the auditory threshold (the shift of the threshold) and the perception threshold of ultrasonics. 2. Deaf people almost without exception are not able to perceive ultrasonics. 3. With hard of hearing of the inner ear of different genesis ultrasonic perception is varying. There was no particular raise of the ultrasonic perception threshold with hereditary hard of hearing of the inner ear. 4. On the basis of the results the question is discussed in which section of the auditory system ultrasonic perception occurs. In the opinion of the authors the origin of perception might be in the organ of Corti itself. An unambiguous proof, however, could not be found so far. At present the procedure of investigation does not yet allow an application in practical diagnostics of ear specialists. Zusammen/assung. Nach kurzer Beschreibung der Ultraschallgeberapparatur mit der die Testfrequenzen 20, 40, 60, 80 und 100 kHz fiber einen an der Stirn der Versuchsperson mit konst~ntem Aufdruck befestigten Geber verabfolgt werden konnten, wird die gemittelte Wahrnehmungsschwelle fiir Ultraschall normalhSriger Personen beschrieben. Anschliel]end wird eine zweite gemittelte Wahrnehmungsschwelle ffir Ultrasehall vorgestellt, die bei Anwesenheit des Verti~uberger~usches des Audiometers MA 30 aufgenommen worden war. Beide Kurven weichen nicht nennenswert voneinander ab, so da$ Ultraschallprfifungen bei Anwesenheit yon Arbeitsgeri~uschen gemaeht werden k6nnen, ohne zu falschen Mel~ergebnissen zu fiihren. Ein Wahrnehmungsvergleieh zwischen Ultraschallfrequenzen und Tonfrequenzen im H6rbereieh erbrachte, dab der Ultraschall unabh~ngig vonder Reizfrequenz den gleichen Sinneseindruek wie ein Ton yon einer Frequenz yon etwa 12 oder 13 kHz erzeugt. Eine Anwendung der Methode bei l~rmhSrgeseh~digten SchwerhSrigen und tauben Personen ffihrte zu folgenden Ergebnissen: 1. L/irmhSrgeseh/idigte haben sehr friihzeitig eine erhShte Schwelle ffir Ultraschall. Eine Korrelation zwisehen dem AusmaB der ttSrschwellenverschiebung und der Lage der Wahrnehmungsschwelle ffir Ultraschall bestand nieht. 2. GehSrlose sind fast ausnahmslos nicht in der Lage, Ultraschall wahrzunehmen. 3. Bei InnenohrschwerhSrigkeiten unterschiedlicher Genese verhiilt sieh die Ultrasehallwahrnehmung sehr weehselhaft, eine bevorzugte ErhShung der Schwelle fiir Ultrasehall ergab sieh bei der heredit/~ren InnenohrsehwvrhSrigkeit nicht.
278
It. G. Dieroff and H. Ertel
4. Auf Grund der Ergebnisse wird diskutiert, in welchem Abschnitt des HSrsystems die Ultraschallwahrnehmung erfolgen kSnnte. Nach Meinung der Autoren diirfte die Perzeption im Cortiorgan selbst stattfinden, wobei ein sicherer Beweis sieh bisher nicht ermitteln lieB. Das Untersuchungsverfahren bringt zur Zeit fiir die Diagnostik der ohren~rztlichen Praxis noeh keine Erweiterung. 1. I n t r o d u c t i o n Seeking for a n a p p r o p r i a t e s c r e e n i n g - s y s t e m for t h e quick d e t e c t i o n of noise i n d u c e d h e a r i n g d a m a g e s a n d p r o c e e d i n g from t h e i n v e s t i g a t i o n s done b y Sagalovieh [9--11 ] we also m a d e t e s t s w i t h ultrasonics in t h e f r e q u e n c y r a n g e b e t w e e n 20 a n d 100 k H z . Our i n v e s t i g a t i o n s were b a s e d on t h e p h e n o m e n o n of " u l t r a s o n i c h e a r i n g " , which h o w e v e r can no longer be e x p l a i n e d b y our h i t h e r t o existing k n o w l e d g e of t h e p e r c e p t i o n of i n f o r m a t i o n b y hearing. I n this w o r k results a n d o b s e r v a t i o n s on t h e p h e n o m e n o n of t h e p e r c e p t i o n of ultrasonics o b t a i n e d b y u l t r a s o n i c p e r c e p t i o n t e s t s in t h e l a b o r a t o r y a n d b y series e x a m i n a t i o n s of subjects w i t h h e a r i n g d a m a g e s are p r e s e n t e d a n d discussed. A discussion on h y p o t h e s i s for u l t r a s o n i c p e r c e p t i o n follows t a k i n g into special c o n s i d e r a t i o n t h e conceptions h i t h e r t o discussed in t h e l i t e r a t u r e . T h e p r a c t i c a l a p p l i c a t i o n is also r e f e r r e d to. 2. Description of the Ultrasonic T r a n s m i t t e r
2.2. Structure o/the Transmitter The total structures of the ultrasonic transmitter used for investigations is shown in Fig. 1. Oscillator generation is caused by a thickness vibrator as Seignette salt (Rochelle salt) consisting of 16 vibratory units (dimensions for one unit: 1.25 mm • 20 mm• 20 mm). The vibrator is placed on the front surface (radiation surface) of the aluminium transmitter capsule and is fixed to it by an epoxy resin sealing. By means of this a strong attenuation of the vibrator and an enlargement of the bandwidth is achieved. The resonance frequency of the complex transmitter is/0 ~ (45--50) kHz, its maximum power output when emitted in water near the resonance frequency and with the maximum input voltage at the transmitter (U~ = 25 V) Pmax ~ 50 mW (measured by an ultrasonic power measuring instrument USL I produced by VEB Transformatoren- und RSntgenwerk Dresden). The excitation of the trans-
I
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_
Fig. 1. Total structure of the ultrasonic transmitter (radiation surface: F = 8,5 cm ~)
Some Throughts on the Perception of Ultrasonics by Man
279
mitger is achieved by sinusoidM signals at the measuring frequency of/M = 20 kHz--100 kI-Iz connected in 10 kHz steps and the amplitude of which could be adjusted continuously up to lJ ~ 25 V. For each measuring frequency a sufficient linearity between the sound pressure measured above the centre of the radiation surface and applied voltage is given. On condition that the transmitter is vibrating unloaded as a whole after being put on the head the value of the input voltage can be considered in approximation as the degree of the sound pressure on the head. To control the input voltage a high-resistance voltmeter was used.
2.2. Investigations on the Ultrasonic Emission o/the Transmitter In connection with the observation of ultrasonic perception the question has to be answered whether the aural impression is due to sound portions possibly emitted by the transmitter in the upper frequency range of hearing. These are all sound portions belonging to the frequency range of 12.5 kHz ~ ] < 20 kHz for the excitation of the receiver at all measuring frequencies. The measurement was carried out with a 1/8 inch microphone (model 4138, manufacturers: Briiel & Kjaer) which is placed directly in front of the radiation surface. With regard to the sound portions measurable at ]~ = 20 kttz the portions already diminish a t / ~ = 40 kHz by more than 20 dB and are no longer detectable at 50 kHz. Taking into consideration the investigation results of Plunder [8] on the increase of the attenuation of the bone conduction at higher frequencies (ultrasonic power is reduced to half at / = 175 kHz with a bone path length of 1 = (4--5) mm and at / ~ 800 kHz with 1 ~ (2.2--2.4) mm respectively) it is unlikely that the measured sound portions result in the observed sensory impression, especially as the voltage applied to the transmitter was regulated in such a way that the perception threshold of ultrasonics at ]~ = 20 kI-Iz had just been exceeded. For further control a third octave band analysis of the sound emitted at a receiver excitation of/M = 20 kHz was carried ou~. It becomes evident that the sound pressure portions belonging to the upper audio frequency range (of the third octave medium frequency band /m = 16 kHz) are about 20 dB lower than the maximum sound pressure occurring at the excitation frequency. The sound emission of the transmitter occurs at the narrow band for the respective measuring frequency. As the two results of the investigation show ultrasonic perception is not due to the sound emissions of the ultrasonic transmitter in the upper audio frequency range, but must be connected with the direct ultrasonic influence on the head.
3. Experimental Procedure and Results T h e results a n d o b s e r v a t i o n s p r e s e n t e d below w e r e o b t a i n e d b y using t h e u l t r a . sonic t r a n s m i t t e r described a b o v e a t l a b o r a t o r y t est s a n d a t s c r e e n i n g - h e a r i n g tests. T h e ultrasonic t r a n s m i t t e r was always p u t on t h e c e n t r e of tile f o r e h e a d of th e s u b j e c t a n d h a d close c o n t a c t w i t h t h e head, especially w i t h t h e sm'face r o u n d t h e c e n t r e of t h e emission surface. T h e n e c e s s ar y pressure of t h e t r a n s m i t t e r on t h e h e a d was a t t a i n e d b y a special a d a p t e r w i t h c o n s t a n t pressure to which t h e transm i t t e r was fixed. To i m p r o v e th e coupling b e t w e e n t h e t r a n s m i t t e r a n d t h e scalp a t h i n l ay er of grease (boro glycerin) was a p p li e d t o t h e emission surface in addition.
3.1. Investigation o/the Pitch o] the "Ultrasonic Sound" T h e ai m of t h e i n v e s t i g a t i o n was to find o u t in which f r e q u e n c y r a n g e t h e " u l t r a s o n i c s o u n d " occurs, w h i c h was specified b y t h e subjects as being cl ear l y p e r c e p t i b l e d u r i n g h e a r i n g tests (comp. p a r a g r a p h 3.2). F o r this a s u b j e c t i v e f r e q u e n c y c o m p a r i s o n was c a r r i e d o u t in t h e l a b o r a t o r y . I t w a s t h e t a s k of t h e subjects to increase t h e u l t r a s o n i c i n t e n s i t y b y increasing t h e i n p u t v o l t a g e so m u c h t h a t a " s o u n d " w a s clearly p e r c e p t i b l e a n d t h e n to a d a p t a s o u n d v a r i a b l e in f r e q u e n c y a n d s o u n d level t o t h e f r e q u e n c y of this " u l t r a s o n i c s o u n d " . T h e 20 Arch. O~o-l~hino-Laryn~..Vol. 209
280
H.G. Dieroff ~nd H. Ertel
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emission to the reference tone from an audio frequency oscillator occurred by means of an earphone (model DT 48, manufacturers: Beyer, FRG). The experimental set-up is shown in Fig.2. The measuring frequencies were/M --~ 20 kHz, 60, 80 and 100 kHz. Seven normal hearing assistants of audiometry took part in the tests (experience in the frequency comparison of different sounds was available). The upper limit of audibility was 16 to 17 k I t z on an average. The age of the subjects was between 20 and 30 years. The subjects reported unanimously t h a t when being exposed to ultrasonics a continuous and distinct sound was perceptible after having exceeded a perceptible threshold, which announces itself by a "crackling" in the head (also sec paragraph 3.2.4). As the test result in Fig. 3 shows this "ultrasonic sound" is always determined in the frequency range of 13 kHz ~-- ] --~ 16 kHz independent of the measuring frequency. A significant dependence of the perceptible sound upon the measurin~ frequency is not detectable. In addition an orientating measurement was carried out on three subjects tc fihd out the subjective frequency impression with the measuring frequency bein~ continuously increased from 20 kHz to 80 kHz. The transmitter coupling to the forehead remained unchanged during measurements.
Some Thoughts on the Perception of Ultrasonics by Man
281
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Fig. 4. Ultrasonic perception threshold (given in volts) for the frequencies of 20, 40, 60 and 80 kHz; . - - - - . Values for normal hearing subjects; . . . . . . Values for normal hearing subjects during the exposure of both ears to wide-band noise (masking noise of the:audiometer MA30) . - .... 9 Values for noise hearing damaged subjects
The frequency change resulted in insignificant frequency changes of the perceptible ultrasonic sound, which, however, were kept within the limits of the frequency range shown in Fig. 3. On the other hand the sound level impression of the ultrasonic sound in the same ear was clearly changed. Thereby it could be found that the sound level maximum repeated itself regularly at the frequency of 1N (11--13) kHz. As to the localization of the sound perception in the head the subjects in most eases specified the back half of the skull or the skull directly behind the ears as the "scene" of perception. About one third of the subjects unambiguously specified a localization in the ear. Whether the sound impression was perceived on the right or left depended to a large extent on the place of attachment of the receiver to the forehead as well as on the tested frequency as already described by Kunze and Kietz [6].
3,2. Observations at Screening-Hearing Tests 3.2.1. Test Results with Noise Workers After having presented ultrasonic perception with normal hearing persons above we are going to describe our observations obtained by series examinations 20*
282
H.G. Oieroff and H. Ertel (2
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Fig. 5. Sample results of ultrasonic tests with 361 noise workers in a press room; N ~ number of subjects; variable a: threshold value of ultrasonics; feature az: normal threshold; teature a~: increased threshold; variable b: threshold value with audible sound; feature bz: normal threshold of audibility; feature b~: increased threshold of audibility
with ultrasonics on noise workers, deaf subjects and subjects with damages of the inner ear of our outpatients department (also comp. Dieroff [2, 3]. As the basis for systematic series examinations we found out the perception threshold of 23 normal hearing subjects aged between 18 and 25 years and recorded it in voltage (Fig.4). As the standard values v a r y at about 3 - - 5 volts with the transmitter coupling described we consider ourselves to be entitled to assume 5 volts as the threshold value for normal ultrasonic perception. As can be seen in Fig. 4 different ultrasonic perception thresholds were ascertained for normal hearing and noise h e a r i n g damaged subjects (noise workers). The mean perception threshold of noise workers is clearly above t h a t of normal hearing subjects. Through an additional experiment we got information on whether there is an influence on the ultrasonic perception threshold b y masking both ears of normal hearing subjects with the wide-band noise of the audiometer MA 30 of VEB Pr~citronic Dresden. Fig.4 shows that there is a slight raising of the threshold by masking. Obviously the ultrasonic perception threshold is not masked by masking with. the applied wide-band noise, ~ ~,- A further test on 361 workers who were greatly exposed to industrial impulse noise resulted in a correlation between the probability of the occurrence of noise working induced damages of the inner ear and the increased ultrasonic perception threshold according to a statistical evaluation b y Schubert [13]. For evaluation the results of the samples (Fig. 5) of the variables a: threshold value with ultrasonics and the variables b: thresh01d value With audible sound were collected first a n d then the confidence intervals of conditi0nal probabilities w (b~/aj) were specified with an error probability of 5 ~ The numerical results are presented in Fig. 6: The data of the conditional probability w (b~/aj) supply information on the probability of the occurrence of the properties bi of hearing in the range of audibility, if the properties a I were specified in the range of ultrasonic (for specification of the characteristics see legend of Fig.5). According to Fig.6 the hypothesis is possible t h a t most probably a normal perception threshold in the range of ultrasonics also suggests a normal threshold in the range of audibility and vice versa that an increased ultrasonic perception threshold suggests an increased hearing threshold.
Some Thoughts on the Perception of Ultrasonics by Man
400
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I n pursuance of these studies of noise workers we carried out investigations in another four factories. Subjects exposed to noise were tested in a weaving mill, a cement mill, a shipyard and an iron mill (press room). Thereby the essential problem was to find out if it is possible to utilize the ability of ultrasonic perception for the selection of noise hearing damaged subjects. The results of the samples provided an informative picture because 66 out of 69 selected subjects in the shipyard with noise hearing damage also had an increased ultrasonic threshold. I n comparison we found 20 subjects out of a total of 78 in the press room of the iron mill and 22 subjects out of 201 in the weaving mill who had an increased threshold for ultrasonic perception with a normal threshold of audibility in the range of audio frequency. Concerning the weaving mill this observation suggests an early drift of the ultrasonic perception threshold as the first symptoms: of
284
H.G. Dieroff and H. Ertel
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Cause Hereditary
Unknown
Acquired
8 8 4
10 8 5
11 17 9
Total
20
23
37
In per cent related to i06 subjects
19
22
35
Completely deaf Residual hearing Continuous curve
noise damage, because none of the weavers was tested before the third working year under noise. The same is true for the 20 subjects of the iron mill, because the average working time under noise in this "normal hearing" group was as much as 5.3 years at an average age of 27.5 years. I n the group of heard of hearing subjects in this factory an average working time of 17.2 years at an average age of 44.05 years could be calculated. The sample result of these four groups is shown in Fig. 7. According to that only 9 subjects out of 334 with existing hearing damage would not have been detected by the application of ultrasonic as a screening procedure. But 45 subjects would have been detected by an increased ultrasonic threshold, although they have a normal threshold for the range of audio frequency. On the other hand, however, the sample result of 361 workers in a pressing room (Fig.5) shows an essential deviation of proportions, as 56 subjects showed an increased threshold for normal sound, although the perception threshold for ultrasonics had not been increased. This discrepancy cannot be explained at present. 3.2.2. Investigations at a School for the Deaf 106 children an~ youngsters of a school for the deaf were tested as to their ability of ultrasonic perception. They were at an age at which it was possible to
Some Thoughts on the Perception of Ultrasonics by Man
285
Table 2. Survey of ultrasonic perception, causes and hearing damages (HL) of pupils at a school for hard of hearing children (from Dieroff [3]) Cause
20 kHz normal threshold
Hereditary Unknown Acquired
1 8 3
Total Mean value of HL (dB) 2, 3, 4 and 6 kHz Mean value of HL (dB) 3, 4, 6 and 8 kHz
20 kHz raised threshold
20 kHz no perception
20, 40, 60 and 80 kHz no perception
2 12 19
1 2 6
-2 7
12 (19%)
33 (53%)
9(14% )
68
79
74
93
70
81
77
97
9(14% )
make them understand the method of investigation and the response to be expected. Ultrasonics was offered at the frequencies of 20, 40, 60 and 80 kHz. Out of 106 children a total of 80 could not specify ultrasonic perception. A survey of the causes and the extent of the hearing damage of these 80 subjects is given in Table i. Most of those who could n o t perceive ultrasonics were c o m p l e t e l y d e a f p u p i l s a n d p u p i l s w i t h r e s i d u a l hearing.
3.2.3. Investigation Results at a School for Hard of Hearing Pupils We tested 63 subjects at a school for hard of hearing pupils, who were also able to clearly specify a perceived response to ultrasonics correctly. The test frequencies were again 20, 40, 60 and 80 kI-Iz. It was remarkable that these pupils were able to perceive ultrasonics relatively well and that no dependence of ultrasonic perception on the cause of the hearing damage could be found. The results are to be found in Table 2. Despite a considerable mean hearing damage of 68 dB 12 subjects have a normal perception threshold at the test frequency of 20 kHz. A correlation between the size of the mean hearing loss and the increase of the ultrasonic perception threshold could not be found. It was remarkable that contrary to the observations by Sagalovich [9] no uniform absence of ultrasonic perception could be registered.
3.2.4. T e s t R e s u l t s of S u b j e c t s w i t h D a m a g e s of t h e I n n e r E a r f r o m t h e E.N.T. O u t p a t i e n t s D e p a r t m e n t W e t e s t e d t h e a b i l i t y of' u l t r a s o n i c p e r c e p t i o n on 40 s u b j e c t s of different ages w i t h e x p a n d e d d a m a g e s of t h e i n n e r ear. T h e r e s u l t s are shown in T a b l e 3. There is a c o r r e l a t i o n b e t w e e n t h e size of t h e m e a n h e a r i n g loss a n d t h e p e r c e p t i o n o f ultrasonics. W i t h increasing m e a n h e a r i n g loss t h e p e r c e p t i o n t h r e s h o l d for u l t r a sonics also increases. I n m a n y cases a n u l t r a s o n i c p e r c e p t i o n was n o t d e t e c t a b l e a t a b r u p t slopes in t h e h i g h - f r e q u e n c y range.
286
H.G. Dieroff and H. Ertel
Table 3. Survey of ultrasonic perception, causes and hearing damages of outpatients who had to be diagnosed for hard of hearing of thd inn~r ear (from Dieroff [3]) Cause
20 kHz normal threshold
Hereditary Unknown Acquired
1 6 --
Total Mean value of HL (dB) 2, 3, 4 and 6 kHz Mean value of HL (dB) 3, 4, 6 and 8 kHz
20 kHz raised threshold 1 4 6
20 kHz no perception 1 5 2
20, 40, 60 and 80 kHz no perception 4 8 2
7(17.5% )
11(27,5% )
8(20% )
14(35% )
46
51
59
86
48
54
63
89
3.3. Special Observations in Connexion with Ultrasonic Perception I n the course of our investigations inadequate responses occasionally occurred with subjects when being exposed to ultrasonics. I n addition to the clear perception of the "ultrasonic sound" several subjects also mentioned having felt a pressure and crackling in the head immediately before sound perception, whereby the feeling of pressure frequently did not even disappear after sound exposure. Kunze and Kietz [6] also refer to similar side effects when they write : "Real pain sensation did not occur at strong excitement either; the sensation at strong excitement, however, was felt as markedly unpleasant and often resulted in aftereffects similar to tinnitus aurium which lasted for many hours." These authors, however, used a higher sound intensity in each case. According to the data given by Sagalovich [9] the maximum ultrasonic pressure occurring at our investigation was only about 1/10 of the minimum therapeutic ultrasonic intensities of (0.2--0.4) Wcm -2 which is usually applied in medicine. Thus the ultrasonic intensities applied by us are with certainty harmless from what we know so far. However, the subjective inadequate response observed by us makes us point out that only low and limited ultrasonic intensities should be applied.
4. Discussing Hypotheses on Ultrasonic Perception Answering the question for the localization of ultrasonic perception within the hearing system is of decisive importance for the diagnostic evaluation of "ultrasonic hearing". Unfortunately no satisfactory answer could be found so far. But on the basis of the observations of ultrasonic perception presented in this paper the following hypotheses can be made (without an evaluation of the sequence) whereby it can only be a discussion using our own results and the references in the literature : 1. Ultrasonic perception as a result of inadequate stimulation of particular sections of the hearing system
Some Thoughts on the Perception of Ultrasonic by Man
287 5cha//druck
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Fig. 8. Curves of the threshold of audibility for bone conduction sound with one normal hearing (curve 0) and 2 hard of hearing subjects (curves I and II); curve N: curve of the threshold value for bone conduction according to v. B~k~sy for comparison (Fig. 8 was plotted according to specifications by Kunze and Kietz [6]
2. Ultrasonic perception as a result of adequate stimulation of the inner ear 2.1. The existence of rudimentary ultrasonic receptors 2.2. The generation of subharmonic vibrations in the range of audio frequency through non-linearities in the transmission p a t h of ultrasonics. Ad 1: An adequate stimulation of the fibers of the auditory nerve by avoiding the real r e c e p t o r - - t h e cochlea--has been discussed several times. As to the localization of stimulus coupling there are only guesses. Most likely perception can be localized where the l~Tervus acustieus leaves the internal acoustic meatus (Porus acusticus internus). The perception of the high pitched tone is explained by the fact t h a t the outer sheet of the auditory nerve is formed b y the nerve fibers of the basal turn of the cochlea [6, 9]. Sagalovieh [9] furthermore specifies "sensitive nerve elements of the Modiolus" as the place of perception. I f such an inadequate stimulation took place, the stimulating effect would still have to occur in the internal petrous portion of the temporal bone, because, as Pfander [8] stated, the attenuation of ultrasonics in the bone was quite remarkable. According to Pfander the sound energy reaching the inner ear is only about 1 ~ of the emitted total energy at / = 175 kHz when sound is emitted from the mastoid process. I n our opinion the observations described below also indicate the existence of an inadequate stimulation of the fibers of the auditory nerve: According to investigations b y Kunze and Kietz [6] as well as b y Sagalovich [10] a distinct break of the perception threshold occurs at the point of transition from the range of audio frequency to the range of ultrasonics. The results of investigation obtained from individual subjects b y Kunzc and Kietz [6] also show t h a t the perception threshold in the range of ultrasonics is nearly independent of frequency (Fig. 8). Possibly the threshold curve, which is ascending slightly with
288
H.G. Dieroff and H. Ertel
increasing frequency, can be explained by the attenuation of bone conduction which depends on the frequency (see Pfander [8]). The curves of the hearing threshold of hard of hearing subjects run into the ultrasonic perception thresholds of normal hearing subjects, if the perception threshold is prolonged in a straight line in the hearing range. However, our own results of investigation (paragraph 3.2.1), which we obtained from nearly 100C subjects with hearing damages, do not confirm this latter result according to [6]. With hard of hearing subjects, especially with noise workers, we found out a shifting of the perception threshold towards higher intensities as hard of hearin~ increases. The curves of the perception threshold which are expected by us are plotted in Fig. 8 (curve I' and II'). A dependence of "audible" ultrasonic sound on the presented ultrasonic frequency cannot be specified according to [10, 6] and our own observations (eomp. paragraph 3.1). However, the perception of loudness of the ultrasonic sound clearly depends on the ultrasonic intensity. A masking of the ultrasonic sound by sound in the audio frequency range cannot be observed (comp. paragraph 3.2.1 and [9]). Ad 2: Contrary to the hitherto discussed perception of ultrasonics by inadequate stimulation Kunze and Kietz [6], Pfander [8] and Sagalovieh [9,12] think it possible that perception takes place in the organ of Corti. Pfander presents results of hearing tests with unilaterally deafened (labyrinth eetomered) patients. Ultrasonics were only perceived by the sound ear. Sagalovich [12] considers the organ ot corti to be the place of perception after having found out that the perception ot ultrasonic failed when the auditory nerve of experimental animals (guinea pigs) was cut. Ad 2.1: From this point of view the existence of residual hearing of ultra-high frequencies must be taken into consideration. Kunze and Kietz [6] also discussed the hypothesis of some sort of residual hearing at ultra-high frequencies. According tc the structure of the basilar membrane this was to be expected in the immediate vicinity of the oval window. Schwarzkopf, too [14], does not exclude such a possibility owing to the development of the auditory organ with mammalia. Small mammalia can perceive ultrasonics and also have special receptors in the cochlea. A perception of ultrasonics in the organ of corti is also indicated by our measurement results representing the correlation between ultrasonic perception and the working years under noise or the age. With advancing age an ascending degeneration of the auditory nerves of workers who had been exposed to noise foi many years can be proved in a suitable way by the Langenbeck Test, the speech audiogram, the measurement of impedance change, the directional andiometry and the dichotic intelligibility test (Dieroff [4]). If the perception of ultrasonics occurred in the auditory nerve, the perception of ultrasonics would have to disappear without exception with advancing age or growing noise exposure respectively. Such a behaviour, however, could not be observed with our material ot investigation. For the correlation between the working years under noise and the ultrasonic perception threshold as well as between the age of the subjects and the
Some Thoughts on the Perception of Ultrasonic by Man
289
Table 4
4]2.
"I/3
Some Thoughts on the Perception of Ultrasonics by Man H. G. Dieroff a n d H. E r t e l Clinic of E.N.T., Friedrich-Schiller-University of Jena (Director: Prof. Dr. med. habil. R. Albrecht) Received, January 21, 1975
Summary. After a short specification of the ultrasonic transmitter device by which the test frequencies of 20, 40, 60 and 100 kHz could be emitted by means of a transmitter fixed to the forehead of the subject with constant pressure, the mean perception threshold for ultrasonics is described, which had been recorded by using the wide-band noise of the audiometer MA 30. Both curves do not differ considerably so that ultrasonic investigations can be carried out in the presence of working noise without producing wrong measurement results. A comparison of perception between ultrasonic frequencies and audio frequencies in the hearing range showed that ultrasonics produce, independent of the stimulation frequency, the same sensory impression as a sound at a frequency of about 12 or 13 kHz. Applying this method to hard of hearing subjects with noise induced hearing damages and deaf subjects had the following results: 1. Subjects with noise induced hearing damages very early have a raised perception threshold for ultrasonics. There was no correlation between the extent of the auditory threshold (the shift of the threshold) and the perception threshold of ultrasonics. 2. Deaf people almost without exception are not able to perceive ultrasonics. 3. With hard of hearing of the inner ear of different genesis ultrasonic perception is varying. There was no particular raise of the ultrasonic perception threshold with hereditary hard of hearing of the inner ear. 4. On the basis of the results the question is discussed in which section of the auditory system ultrasonic perception occurs. In the opinion of the authors the origin of perception might be in the organ of Corti itself. An unambiguous proof, however, could not be found so far. At present the procedure of investigation does not yet allow an application in practical diagnostics of ear specialists. Zusammen/assung. Nach kurzer Beschreibung der Ultraschallgeberapparatur mit der die Testfrequenzen 20, 40, 60, 80 und 100 kHz fiber einen an der Stirn der Versuchsperson mit konst~ntem Aufdruck befestigten Geber verabfolgt werden konnten, wird die gemittelte Wahrnehmungsschwelle fiir Ultraschall normalhSriger Personen beschrieben. Anschliel]end wird eine zweite gemittelte Wahrnehmungsschwelle ffir Ultrasehall vorgestellt, die bei Anwesenheit des Verti~uberger~usches des Audiometers MA 30 aufgenommen worden war. Beide Kurven weichen nicht nennenswert voneinander ab, so da$ Ultraschallprfifungen bei Anwesenheit yon Arbeitsgeri~uschen gemaeht werden k6nnen, ohne zu falschen Mel~ergebnissen zu fiihren. Ein Wahrnehmungsvergleieh zwischen Ultraschallfrequenzen und Tonfrequenzen im H6rbereieh erbrachte, dab der Ultraschall unabh~ngig vonder Reizfrequenz den gleichen Sinneseindruek wie ein Ton yon einer Frequenz yon etwa 12 oder 13 kHz erzeugt. Eine Anwendung der Methode bei l~rmhSrgeseh~digten SchwerhSrigen und tauben Personen ffihrte zu folgenden Ergebnissen: 1. L/irmhSrgeseh/idigte haben sehr friihzeitig eine erhShte Schwelle ffir Ultraschall. Eine Korrelation zwisehen dem AusmaB der ttSrschwellenverschiebung und der Lage der Wahrnehmungsschwelle ffir Ultraschall bestand nieht. 2. GehSrlose sind fast ausnahmslos nicht in der Lage, Ultraschall wahrzunehmen. 3. Bei InnenohrschwerhSrigkeiten unterschiedlicher Genese verhiilt sieh die Ultrasehallwahrnehmung sehr weehselhaft, eine bevorzugte ErhShung der Schwelle fiir Ultrasehall ergab sieh bei der heredit/~ren InnenohrsehwvrhSrigkeit nicht.
278
It. G. Dieroff and H. Ertel
4. Auf Grund der Ergebnisse wird diskutiert, in welchem Abschnitt des HSrsystems die Ultraschallwahrnehmung erfolgen kSnnte. Nach Meinung der Autoren diirfte die Perzeption im Cortiorgan selbst stattfinden, wobei ein sicherer Beweis sieh bisher nicht ermitteln lieB. Das Untersuchungsverfahren bringt zur Zeit fiir die Diagnostik der ohren~rztlichen Praxis noeh keine Erweiterung. 1. I n t r o d u c t i o n Seeking for a n a p p r o p r i a t e s c r e e n i n g - s y s t e m for t h e quick d e t e c t i o n of noise i n d u c e d h e a r i n g d a m a g e s a n d p r o c e e d i n g from t h e i n v e s t i g a t i o n s done b y Sagalovieh [9--11 ] we also m a d e t e s t s w i t h ultrasonics in t h e f r e q u e n c y r a n g e b e t w e e n 20 a n d 100 k H z . Our i n v e s t i g a t i o n s were b a s e d on t h e p h e n o m e n o n of " u l t r a s o n i c h e a r i n g " , which h o w e v e r can no longer be e x p l a i n e d b y our h i t h e r t o existing k n o w l e d g e of t h e p e r c e p t i o n of i n f o r m a t i o n b y hearing. I n this w o r k results a n d o b s e r v a t i o n s on t h e p h e n o m e n o n of t h e p e r c e p t i o n of ultrasonics o b t a i n e d b y u l t r a s o n i c p e r c e p t i o n t e s t s in t h e l a b o r a t o r y a n d b y series e x a m i n a t i o n s of subjects w i t h h e a r i n g d a m a g e s are p r e s e n t e d a n d discussed. A discussion on h y p o t h e s i s for u l t r a s o n i c p e r c e p t i o n follows t a k i n g into special c o n s i d e r a t i o n t h e conceptions h i t h e r t o discussed in t h e l i t e r a t u r e . T h e p r a c t i c a l a p p l i c a t i o n is also r e f e r r e d to. 2. Description of the Ultrasonic T r a n s m i t t e r
2.2. Structure o/the Transmitter The total structures of the ultrasonic transmitter used for investigations is shown in Fig. 1. Oscillator generation is caused by a thickness vibrator as Seignette salt (Rochelle salt) consisting of 16 vibratory units (dimensions for one unit: 1.25 mm • 20 mm• 20 mm). The vibrator is placed on the front surface (radiation surface) of the aluminium transmitter capsule and is fixed to it by an epoxy resin sealing. By means of this a strong attenuation of the vibrator and an enlargement of the bandwidth is achieved. The resonance frequency of the complex transmitter is/0 ~ (45--50) kHz, its maximum power output when emitted in water near the resonance frequency and with the maximum input voltage at the transmitter (U~ = 25 V) Pmax ~ 50 mW (measured by an ultrasonic power measuring instrument USL I produced by VEB Transformatoren- und RSntgenwerk Dresden). The excitation of the trans-
I
Epoxydhurzve=gu~ Geberkupsel--
~chwtn~er I 1~33~m
_
Fig. 1. Total structure of the ultrasonic transmitter (radiation surface: F = 8,5 cm ~)
Some Throughts on the Perception of Ultrasonics by Man
279
mitger is achieved by sinusoidM signals at the measuring frequency of/M = 20 kHz--100 kI-Iz connected in 10 kHz steps and the amplitude of which could be adjusted continuously up to lJ ~ 25 V. For each measuring frequency a sufficient linearity between the sound pressure measured above the centre of the radiation surface and applied voltage is given. On condition that the transmitter is vibrating unloaded as a whole after being put on the head the value of the input voltage can be considered in approximation as the degree of the sound pressure on the head. To control the input voltage a high-resistance voltmeter was used.
2.2. Investigations on the Ultrasonic Emission o/the Transmitter In connection with the observation of ultrasonic perception the question has to be answered whether the aural impression is due to sound portions possibly emitted by the transmitter in the upper frequency range of hearing. These are all sound portions belonging to the frequency range of 12.5 kHz ~ ] < 20 kHz for the excitation of the receiver at all measuring frequencies. The measurement was carried out with a 1/8 inch microphone (model 4138, manufacturers: Briiel & Kjaer) which is placed directly in front of the radiation surface. With regard to the sound portions measurable at ]~ = 20 kttz the portions already diminish a t / ~ = 40 kHz by more than 20 dB and are no longer detectable at 50 kHz. Taking into consideration the investigation results of Plunder [8] on the increase of the attenuation of the bone conduction at higher frequencies (ultrasonic power is reduced to half at / = 175 kHz with a bone path length of 1 = (4--5) mm and at / ~ 800 kHz with 1 ~ (2.2--2.4) mm respectively) it is unlikely that the measured sound portions result in the observed sensory impression, especially as the voltage applied to the transmitter was regulated in such a way that the perception threshold of ultrasonics at ]~ = 20 kI-Iz had just been exceeded. For further control a third octave band analysis of the sound emitted at a receiver excitation of/M = 20 kHz was carried ou~. It becomes evident that the sound pressure portions belonging to the upper audio frequency range (of the third octave medium frequency band /m = 16 kHz) are about 20 dB lower than the maximum sound pressure occurring at the excitation frequency. The sound emission of the transmitter occurs at the narrow band for the respective measuring frequency. As the two results of the investigation show ultrasonic perception is not due to the sound emissions of the ultrasonic transmitter in the upper audio frequency range, but must be connected with the direct ultrasonic influence on the head.
3. Experimental Procedure and Results T h e results a n d o b s e r v a t i o n s p r e s e n t e d below w e r e o b t a i n e d b y using t h e u l t r a . sonic t r a n s m i t t e r described a b o v e a t l a b o r a t o r y t est s a n d a t s c r e e n i n g - h e a r i n g tests. T h e ultrasonic t r a n s m i t t e r was always p u t on t h e c e n t r e of tile f o r e h e a d of th e s u b j e c t a n d h a d close c o n t a c t w i t h t h e head, especially w i t h t h e sm'face r o u n d t h e c e n t r e of t h e emission surface. T h e n e c e s s ar y pressure of t h e t r a n s m i t t e r on t h e h e a d was a t t a i n e d b y a special a d a p t e r w i t h c o n s t a n t pressure to which t h e transm i t t e r was fixed. To i m p r o v e th e coupling b e t w e e n t h e t r a n s m i t t e r a n d t h e scalp a t h i n l ay er of grease (boro glycerin) was a p p li e d t o t h e emission surface in addition.
3.1. Investigation o/the Pitch o] the "Ultrasonic Sound" T h e ai m of t h e i n v e s t i g a t i o n was to find o u t in which f r e q u e n c y r a n g e t h e " u l t r a s o n i c s o u n d " occurs, w h i c h was specified b y t h e subjects as being cl ear l y p e r c e p t i b l e d u r i n g h e a r i n g tests (comp. p a r a g r a p h 3.2). F o r this a s u b j e c t i v e f r e q u e n c y c o m p a r i s o n was c a r r i e d o u t in t h e l a b o r a t o r y . I t w a s t h e t a s k of t h e subjects to increase t h e u l t r a s o n i c i n t e n s i t y b y increasing t h e i n p u t v o l t a g e so m u c h t h a t a " s o u n d " w a s clearly p e r c e p t i b l e a n d t h e n to a d a p t a s o u n d v a r i a b l e in f r e q u e n c y a n d s o u n d level t o t h e f r e q u e n c y of this " u l t r a s o n i c s o u n d " . T h e 20 Arch. O~o-l~hino-Laryn~..Vol. 209
280
H.G. Dieroff ~nd H. Ertel
tlltraschall -
Tongenerafo/,"
9ene~'a2or
Fig. 2. Illustration of the experimental set-up of "subjective hearing comparison"
f d6
kHz / f
r
d~ / '
,/
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J
J
45
J
/
/
jf j717
///fr
~2
20
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60
80
,.~l-/z
1oo
fH
Fig. 3. Dependence of the "ultrasonic sound" / on the measuring frequency/~ (with specification of the standard deviation)
emission to the reference tone from an audio frequency oscillator occurred by means of an earphone (model DT 48, manufacturers: Beyer, FRG). The experimental set-up is shown in Fig.2. The measuring frequencies were/M --~ 20 kHz, 60, 80 and 100 kHz. Seven normal hearing assistants of audiometry took part in the tests (experience in the frequency comparison of different sounds was available). The upper limit of audibility was 16 to 17 k I t z on an average. The age of the subjects was between 20 and 30 years. The subjects reported unanimously t h a t when being exposed to ultrasonics a continuous and distinct sound was perceptible after having exceeded a perceptible threshold, which announces itself by a "crackling" in the head (also sec paragraph 3.2.4). As the test result in Fig. 3 shows this "ultrasonic sound" is always determined in the frequency range of 13 kHz ~-- ] --~ 16 kHz independent of the measuring frequency. A significant dependence of the perceptible sound upon the measurin~ frequency is not detectable. In addition an orientating measurement was carried out on three subjects tc fihd out the subjective frequency impression with the measuring frequency bein~ continuously increased from 20 kHz to 80 kHz. The transmitter coupling to the forehead remained unchanged during measurements.
Some Thoughts on the Perception of Ultrasonics by Man
281
u, ~0
V ,Y
"\ \
8
\
7
~q
/
/
/
/
/
/
/
6 5
S
43
4
20
40
60
k~z
8o
f
Fig. 4. Ultrasonic perception threshold (given in volts) for the frequencies of 20, 40, 60 and 80 kHz; . - - - - . Values for normal hearing subjects; . . . . . . Values for normal hearing subjects during the exposure of both ears to wide-band noise (masking noise of the:audiometer MA30) . - .... 9 Values for noise hearing damaged subjects
The frequency change resulted in insignificant frequency changes of the perceptible ultrasonic sound, which, however, were kept within the limits of the frequency range shown in Fig. 3. On the other hand the sound level impression of the ultrasonic sound in the same ear was clearly changed. Thereby it could be found that the sound level maximum repeated itself regularly at the frequency of 1N (11--13) kHz. As to the localization of the sound perception in the head the subjects in most eases specified the back half of the skull or the skull directly behind the ears as the "scene" of perception. About one third of the subjects unambiguously specified a localization in the ear. Whether the sound impression was perceived on the right or left depended to a large extent on the place of attachment of the receiver to the forehead as well as on the tested frequency as already described by Kunze and Kietz [6].
3,2. Observations at Screening-Hearing Tests 3.2.1. Test Results with Noise Workers After having presented ultrasonic perception with normal hearing persons above we are going to describe our observations obtained by series examinations 20*
282
H.G. Oieroff and H. Ertel (2
at
4y
s N - 36r
a,
17
56 ----~ b
Fig. 5. Sample results of ultrasonic tests with 361 noise workers in a press room; N ~ number of subjects; variable a: threshold value of ultrasonics; feature az: normal threshold; teature a~: increased threshold; variable b: threshold value with audible sound; feature bz: normal threshold of audibility; feature b~: increased threshold of audibility
with ultrasonics on noise workers, deaf subjects and subjects with damages of the inner ear of our outpatients department (also comp. Dieroff [2, 3]. As the basis for systematic series examinations we found out the perception threshold of 23 normal hearing subjects aged between 18 and 25 years and recorded it in voltage (Fig.4). As the standard values v a r y at about 3 - - 5 volts with the transmitter coupling described we consider ourselves to be entitled to assume 5 volts as the threshold value for normal ultrasonic perception. As can be seen in Fig. 4 different ultrasonic perception thresholds were ascertained for normal hearing and noise h e a r i n g damaged subjects (noise workers). The mean perception threshold of noise workers is clearly above t h a t of normal hearing subjects. Through an additional experiment we got information on whether there is an influence on the ultrasonic perception threshold b y masking both ears of normal hearing subjects with the wide-band noise of the audiometer MA 30 of VEB Pr~citronic Dresden. Fig.4 shows that there is a slight raising of the threshold by masking. Obviously the ultrasonic perception threshold is not masked by masking with. the applied wide-band noise, ~ ~,- A further test on 361 workers who were greatly exposed to industrial impulse noise resulted in a correlation between the probability of the occurrence of noise working induced damages of the inner ear and the increased ultrasonic perception threshold according to a statistical evaluation b y Schubert [13]. For evaluation the results of the samples (Fig. 5) of the variables a: threshold value with ultrasonics and the variables b: thresh01d value With audible sound were collected first a n d then the confidence intervals of conditi0nal probabilities w (b~/aj) were specified with an error probability of 5 ~ The numerical results are presented in Fig. 6: The data of the conditional probability w (b~/aj) supply information on the probability of the occurrence of the properties bi of hearing in the range of audibility, if the properties a I were specified in the range of ultrasonic (for specification of the characteristics see legend of Fig.5). According to Fig.6 the hypothesis is possible t h a t most probably a normal perception threshold in the range of ultrasonics also suggests a normal threshold in the range of audibility and vice versa that an increased ultrasonic perception threshold suggests an increased hearing threshold.
Some Thoughts on the Perception of Ultrasonics by Man
400
283
W(b,/ ~.,)
% :%
W(
9O
80
~0
5O
4.O
w(~r162 aO
2O
WCb~la, )
40
gZ~
1.1[
~::Z2
P l e r k m o I clef UltrQ~chaH - WQhrnehrnunqaschwelle
Fig. 6. Illustration of the statistical evidence of the relations between raising the ultrasonic perception threshold and the noise induced hearing damage (specification of the variables as in Fig. 5)
I n pursuance of these studies of noise workers we carried out investigations in another four factories. Subjects exposed to noise were tested in a weaving mill, a cement mill, a shipyard and an iron mill (press room). Thereby the essential problem was to find out if it is possible to utilize the ability of ultrasonic perception for the selection of noise hearing damaged subjects. The results of the samples provided an informative picture because 66 out of 69 selected subjects in the shipyard with noise hearing damage also had an increased ultrasonic threshold. I n comparison we found 20 subjects out of a total of 78 in the press room of the iron mill and 22 subjects out of 201 in the weaving mill who had an increased threshold for ultrasonic perception with a normal threshold of audibility in the range of audio frequency. Concerning the weaving mill this observation suggests an early drift of the ultrasonic perception threshold as the first symptoms: of
284
H.G. Dieroff and H. Ertel
a~
45
334
3
,o
N = Jg"l
ot
---~b Fig. 7. Sample results of ultrasonic tests with 361 noise workers from 4 different places of noise exposure (specification of the variables analogous to Fig. 5) Table 1. Survey of the distribution of the causes of seriously hearing damaged subjects who did not perceive ultrasonics (from Dieroff [3]) Hearing situation
Cause Hereditary
Unknown
Acquired
8 8 4
10 8 5
11 17 9
Total
20
23
37
In per cent related to i06 subjects
19
22
35
Completely deaf Residual hearing Continuous curve
noise damage, because none of the weavers was tested before the third working year under noise. The same is true for the 20 subjects of the iron mill, because the average working time under noise in this "normal hearing" group was as much as 5.3 years at an average age of 27.5 years. I n the group of heard of hearing subjects in this factory an average working time of 17.2 years at an average age of 44.05 years could be calculated. The sample result of these four groups is shown in Fig. 7. According to that only 9 subjects out of 334 with existing hearing damage would not have been detected by the application of ultrasonic as a screening procedure. But 45 subjects would have been detected by an increased ultrasonic threshold, although they have a normal threshold for the range of audio frequency. On the other hand, however, the sample result of 361 workers in a pressing room (Fig.5) shows an essential deviation of proportions, as 56 subjects showed an increased threshold for normal sound, although the perception threshold for ultrasonics had not been increased. This discrepancy cannot be explained at present. 3.2.2. Investigations at a School for the Deaf 106 children an~ youngsters of a school for the deaf were tested as to their ability of ultrasonic perception. They were at an age at which it was possible to
Some Thoughts on the Perception of Ultrasonics by Man
285
Table 2. Survey of ultrasonic perception, causes and hearing damages (HL) of pupils at a school for hard of hearing children (from Dieroff [3]) Cause
20 kHz normal threshold
Hereditary Unknown Acquired
1 8 3
Total Mean value of HL (dB) 2, 3, 4 and 6 kHz Mean value of HL (dB) 3, 4, 6 and 8 kHz
20 kHz raised threshold
20 kHz no perception
20, 40, 60 and 80 kHz no perception
2 12 19
1 2 6
-2 7
12 (19%)
33 (53%)
9(14% )
68
79
74
93
70
81
77
97
9(14% )
make them understand the method of investigation and the response to be expected. Ultrasonics was offered at the frequencies of 20, 40, 60 and 80 kHz. Out of 106 children a total of 80 could not specify ultrasonic perception. A survey of the causes and the extent of the hearing damage of these 80 subjects is given in Table i. Most of those who could n o t perceive ultrasonics were c o m p l e t e l y d e a f p u p i l s a n d p u p i l s w i t h r e s i d u a l hearing.
3.2.3. Investigation Results at a School for Hard of Hearing Pupils We tested 63 subjects at a school for hard of hearing pupils, who were also able to clearly specify a perceived response to ultrasonics correctly. The test frequencies were again 20, 40, 60 and 80 kI-Iz. It was remarkable that these pupils were able to perceive ultrasonics relatively well and that no dependence of ultrasonic perception on the cause of the hearing damage could be found. The results are to be found in Table 2. Despite a considerable mean hearing damage of 68 dB 12 subjects have a normal perception threshold at the test frequency of 20 kHz. A correlation between the size of the mean hearing loss and the increase of the ultrasonic perception threshold could not be found. It was remarkable that contrary to the observations by Sagalovich [9] no uniform absence of ultrasonic perception could be registered.
3.2.4. T e s t R e s u l t s of S u b j e c t s w i t h D a m a g e s of t h e I n n e r E a r f r o m t h e E.N.T. O u t p a t i e n t s D e p a r t m e n t W e t e s t e d t h e a b i l i t y of' u l t r a s o n i c p e r c e p t i o n on 40 s u b j e c t s of different ages w i t h e x p a n d e d d a m a g e s of t h e i n n e r ear. T h e r e s u l t s are shown in T a b l e 3. There is a c o r r e l a t i o n b e t w e e n t h e size of t h e m e a n h e a r i n g loss a n d t h e p e r c e p t i o n o f ultrasonics. W i t h increasing m e a n h e a r i n g loss t h e p e r c e p t i o n t h r e s h o l d for u l t r a sonics also increases. I n m a n y cases a n u l t r a s o n i c p e r c e p t i o n was n o t d e t e c t a b l e a t a b r u p t slopes in t h e h i g h - f r e q u e n c y range.
286
H.G. Dieroff and H. Ertel
Table 3. Survey of ultrasonic perception, causes and hearing damages of outpatients who had to be diagnosed for hard of hearing of thd inn~r ear (from Dieroff [3]) Cause
20 kHz normal threshold
Hereditary Unknown Acquired
1 6 --
Total Mean value of HL (dB) 2, 3, 4 and 6 kHz Mean value of HL (dB) 3, 4, 6 and 8 kHz
20 kHz raised threshold 1 4 6
20 kHz no perception 1 5 2
20, 40, 60 and 80 kHz no perception 4 8 2
7(17.5% )
11(27,5% )
8(20% )
14(35% )
46
51
59
86
48
54
63
89
3.3. Special Observations in Connexion with Ultrasonic Perception I n the course of our investigations inadequate responses occasionally occurred with subjects when being exposed to ultrasonics. I n addition to the clear perception of the "ultrasonic sound" several subjects also mentioned having felt a pressure and crackling in the head immediately before sound perception, whereby the feeling of pressure frequently did not even disappear after sound exposure. Kunze and Kietz [6] also refer to similar side effects when they write : "Real pain sensation did not occur at strong excitement either; the sensation at strong excitement, however, was felt as markedly unpleasant and often resulted in aftereffects similar to tinnitus aurium which lasted for many hours." These authors, however, used a higher sound intensity in each case. According to the data given by Sagalovich [9] the maximum ultrasonic pressure occurring at our investigation was only about 1/10 of the minimum therapeutic ultrasonic intensities of (0.2--0.4) Wcm -2 which is usually applied in medicine. Thus the ultrasonic intensities applied by us are with certainty harmless from what we know so far. However, the subjective inadequate response observed by us makes us point out that only low and limited ultrasonic intensities should be applied.
4. Discussing Hypotheses on Ultrasonic Perception Answering the question for the localization of ultrasonic perception within the hearing system is of decisive importance for the diagnostic evaluation of "ultrasonic hearing". Unfortunately no satisfactory answer could be found so far. But on the basis of the observations of ultrasonic perception presented in this paper the following hypotheses can be made (without an evaluation of the sequence) whereby it can only be a discussion using our own results and the references in the literature : 1. Ultrasonic perception as a result of inadequate stimulation of particular sections of the hearing system
Some Thoughts on the Perception of Ultrasonic by Man
287 5cha//druck
elehfr 2,pctnnung.. UE
i r
v
i 403
"I
I I
14o
qo~
I q oo'l
I I _ q063
q425
0,2~0
q,F
1
2
~P
0
~8
32
6~ kHz 424
Fre~enz
Fig. 8. Curves of the threshold of audibility for bone conduction sound with one normal hearing (curve 0) and 2 hard of hearing subjects (curves I and II); curve N: curve of the threshold value for bone conduction according to v. B~k~sy for comparison (Fig. 8 was plotted according to specifications by Kunze and Kietz [6]
2. Ultrasonic perception as a result of adequate stimulation of the inner ear 2.1. The existence of rudimentary ultrasonic receptors 2.2. The generation of subharmonic vibrations in the range of audio frequency through non-linearities in the transmission p a t h of ultrasonics. Ad 1: An adequate stimulation of the fibers of the auditory nerve by avoiding the real r e c e p t o r - - t h e cochlea--has been discussed several times. As to the localization of stimulus coupling there are only guesses. Most likely perception can be localized where the l~Tervus acustieus leaves the internal acoustic meatus (Porus acusticus internus). The perception of the high pitched tone is explained by the fact t h a t the outer sheet of the auditory nerve is formed b y the nerve fibers of the basal turn of the cochlea [6, 9]. Sagalovieh [9] furthermore specifies "sensitive nerve elements of the Modiolus" as the place of perception. I f such an inadequate stimulation took place, the stimulating effect would still have to occur in the internal petrous portion of the temporal bone, because, as Pfander [8] stated, the attenuation of ultrasonics in the bone was quite remarkable. According to Pfander the sound energy reaching the inner ear is only about 1 ~ of the emitted total energy at / = 175 kHz when sound is emitted from the mastoid process. I n our opinion the observations described below also indicate the existence of an inadequate stimulation of the fibers of the auditory nerve: According to investigations b y Kunze and Kietz [6] as well as b y Sagalovich [10] a distinct break of the perception threshold occurs at the point of transition from the range of audio frequency to the range of ultrasonics. The results of investigation obtained from individual subjects b y Kunzc and Kietz [6] also show t h a t the perception threshold in the range of ultrasonics is nearly independent of frequency (Fig. 8). Possibly the threshold curve, which is ascending slightly with
288
H.G. Dieroff and H. Ertel
increasing frequency, can be explained by the attenuation of bone conduction which depends on the frequency (see Pfander [8]). The curves of the hearing threshold of hard of hearing subjects run into the ultrasonic perception thresholds of normal hearing subjects, if the perception threshold is prolonged in a straight line in the hearing range. However, our own results of investigation (paragraph 3.2.1), which we obtained from nearly 100C subjects with hearing damages, do not confirm this latter result according to [6]. With hard of hearing subjects, especially with noise workers, we found out a shifting of the perception threshold towards higher intensities as hard of hearin~ increases. The curves of the perception threshold which are expected by us are plotted in Fig. 8 (curve I' and II'). A dependence of "audible" ultrasonic sound on the presented ultrasonic frequency cannot be specified according to [10, 6] and our own observations (eomp. paragraph 3.1). However, the perception of loudness of the ultrasonic sound clearly depends on the ultrasonic intensity. A masking of the ultrasonic sound by sound in the audio frequency range cannot be observed (comp. paragraph 3.2.1 and [9]). Ad 2: Contrary to the hitherto discussed perception of ultrasonics by inadequate stimulation Kunze and Kietz [6], Pfander [8] and Sagalovieh [9,12] think it possible that perception takes place in the organ of Corti. Pfander presents results of hearing tests with unilaterally deafened (labyrinth eetomered) patients. Ultrasonics were only perceived by the sound ear. Sagalovich [12] considers the organ ot corti to be the place of perception after having found out that the perception ot ultrasonic failed when the auditory nerve of experimental animals (guinea pigs) was cut. Ad 2.1: From this point of view the existence of residual hearing of ultra-high frequencies must be taken into consideration. Kunze and Kietz [6] also discussed the hypothesis of some sort of residual hearing at ultra-high frequencies. According tc the structure of the basilar membrane this was to be expected in the immediate vicinity of the oval window. Schwarzkopf, too [14], does not exclude such a possibility owing to the development of the auditory organ with mammalia. Small mammalia can perceive ultrasonics and also have special receptors in the cochlea. A perception of ultrasonics in the organ of corti is also indicated by our measurement results representing the correlation between ultrasonic perception and the working years under noise or the age. With advancing age an ascending degeneration of the auditory nerves of workers who had been exposed to noise foi many years can be proved in a suitable way by the Langenbeck Test, the speech audiogram, the measurement of impedance change, the directional andiometry and the dichotic intelligibility test (Dieroff [4]). If the perception of ultrasonics occurred in the auditory nerve, the perception of ultrasonics would have to disappear without exception with advancing age or growing noise exposure respectively. Such a behaviour, however, could not be observed with our material ot investigation. For the correlation between the working years under noise and the ultrasonic perception threshold as well as between the age of the subjects and the
Some Thoughts on the Perception of Ultrasonic by Man
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Table 4
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