Measuring device for auditory organ

Abstract

A measurement device (1) for an auditory organ includes: a signal output unit (52) configured to output a stimulation sound signal for stimulation sound in order to output, into an external auditory canal of a subject, a stimulation sound, in which sound pressure amplitude and frequency change in a temporally discontinuous manner and which includes at least each frequency component of a frequency band to be measured; a signal acquisition unit (54) configured to acquire, as a measurement signal, a signal indicating a pressure fluctuation in the external auditory canal when the stimulation sound is output toward inside of the external auditory canal of the subject; and an analyzing device (93) configured to analyze frequency characteristics of the auditory organ of the subject on the basis of the stimulation sound signal and the measurement signal.

Description

Measuring devices for the hearing organ

[0001] The present invention relates to measurements for the hearing organ, and in particular to non-invasive measurements of the frequency characteristics of the hearing organ.

[0002] Various methods for non-invasively examining the condition of the hearing organ are known. For example, Japanese Patent Publication No. 2023-108617 discloses technology relating to an ear probe that can be used in tympanometry and impedance audiometry. Tympanometry and impedance audiometry are methods for non-invasively examining the condition of the middle ear. In such hearing tests, a stimulus sound of a predetermined frequency is input into the ear canal. Japanese Patent Publication No. 2023-108617 discloses that a single-frequency sound or a click sound is used as the stimulus sound. Such mechanical stimulus sounds are not pleasant to the subject. Furthermore, for example, when the subject is a child, measurements may be required in a sedated state to ensure accuracy, but mechanical stimulus sounds may awaken or excite the subject. There is a demand for accurate measurements of the hearing organ that are medically quality and precise without causing discomfort.

[0003] Japanese Patent Application Publication No. 2023-108617

[0004] The present invention aims to improve medical quality and accuracy by reducing discomfort or arousal of the subject in non-invasive measurement of the characteristics of the hearing organ.

[0005] According to one aspect of the present invention, a measuring device for the auditory organ comprises a signal output unit configured to output a stimulus sound signal for the stimulus sound, in order to output a stimulus sound that includes at least each frequency component of a frequency band to be measured and whose sound pressure amplitude and frequency change discontinuously over time into a subject's ear canal; a signal acquisition unit configured to acquire, as a measurement signal, a signal that indicates pressure fluctuations in the ear canal when the stimulus sound is output into the subject's ear canal; and an analysis device configured to analyze the frequency characteristics of the subject's auditory organ based on the stimulus sound signal and the measurement signal.

[0006] According to one aspect of the present invention, a method for measuring characteristics of the auditory organ includes outputting a stimulus sound into a subject's ear canal based on a stimulus sound signal, the stimulus sound including at least each frequency component of a frequency band to be measured and having a sound pressure amplitude and frequency that change discontinuously over time; acquiring, as a measurement signal, a signal that indicates pressure fluctuations in the ear canal when the stimulus sound is output into the subject's ear canal; and analyzing the frequency characteristics of the subject's ear canal based on the stimulus sound signal and the measurement signal.

[0007] According to the present invention, in the non-invasive measurement of the characteristics of the auditory organ, the quality and accuracy of medical care can be improved by improving the stimulus sound to reduce discomfort or arousal of the subject.

[0008] FIG. 1 is a schematic diagram showing an outline of an exemplary configuration of a measurement device according to an embodiment. FIG. 2 is a functional block diagram showing an outline of an exemplary configuration of a measurement device according to an embodiment. FIG. 3A is a diagram for explaining sound pressure in the ear canal. FIG. 3B is a diagram for explaining sound pressure in the ear canal. FIG. 4 is an example of measurement results of frequency characteristics of sound pressure level acquired using a microphone when a frequency sweep sound is used as a stimulus sound for an adult subject. FIG. 5 is a flowchart showing an example of an outline of an operation of a computer of a measurement device according to an embodiment. FIG. 6 is a diagram showing characteristics of music played on a music box used as an example of a stimulus sound. FIG. 7 is a diagram showing an example of measurement results when music is used as the stimulus sound in a measurement according to an embodiment. FIG. 8 is a diagram showing an example of measurement results when the duration of the stimulus sound is different in a measurement according to an embodiment.

[0009] An embodiment will be described with reference to the drawings. This embodiment relates to a device for measuring characteristics of the auditory organ. The measurement device of this embodiment can perform measurements non-invasively. As an example, this measurement device outputs a stimulus sound into a subject's ear canal and acquires pressure fluctuations within the ear canal at the time. The measurement device is configured to analyze the characteristics of the subject's auditory organ by analyzing the pressure fluctuations. The measurement device can acquire information related to the impedance of the middle ear, in particular. This impedance reflects the dynamic characteristics of the middle ear system, in particular. Based on the acquired information related to the impedance, the condition of the auditory organ, particularly the middle ear, can be evaluated. For example, an evaluation of the sound conduction characteristics of the middle ear can be obtained. Furthermore, for example, the presence or absence of fixation or disruption of the ossicular chain, the presence or absence of otitis media including serous otitis media, the presence or absence of thinning or adhesion of the tympanic membrane, and the presence or absence of a middle ear malformation can be determined. The acquired information can be used to diagnose middle ear diseases and conductive hearing loss. In other words, this measurement device can function as a diagnostic device for the auditory organ.

[0010] [Device Configuration] Fig. 1 is a schematic diagram showing an outline of an example configuration of a measurement device 1 according to this embodiment. Fig. 2 is a functional block diagram showing an outline of an example configuration of the measurement device 1 according to this embodiment. As shown in Fig. 1, the measurement device 1 includes a computer 10, an AD / DA converter 60, an amplifier system 70, and a probe 80.

[0011] The probe 80 is configured so that its tip is inserted into the ear canal 210 of the subject 200. The probe 80 includes an earphone 82 for outputting a stimulating sound toward the ear canal 210, and a microphone 84 for acquiring pressure fluctuations within the ear canal 210.

[0012] The computer 10 is a general-purpose computer, and may be, for example, a personal computer. The computer 10 includes, for example, a central processing unit (CPU) 11, various integrated circuits such as a memory 12 and a storage 13, and various interfaces 14. The computer 10 may further include a field programmable gate array (FPGA) or the like prepared according to the processing of the measurement device 1. The computer 10 performs processing such as controlling the operation of each part of the measurement device 1, generating signals related to the stimulus sound, and analyzing pressure fluctuations in the ear canal. The operation of the computer 10 is performed according to a program recorded in the computer 10 as software or hardware or provided from outside the computer 10. The program may be recorded on various recording media.

[0013] The AD / DA converter 60 has a DA converter 62 and an AD converter 64. The amplifier system 70 has an earphone amplifier 72 and a microphone amplifier 74. The DA converter 62 of the AD / DA converter 60 converts the digital signal related to the stimulus sound output from the computer 10 into an analog signal and outputs it to the earphone amplifier 72 of the amplifier system 70. The earphone amplifier 72 amplifies the analog signal related to the stimulus sound input from the DA converter 62 and outputs the stimulus sound from the earphone 82 of the probe 80. The microphone amplifier 74 of the amplifier system 70 amplifies an analog signal related to pressure fluctuations in the ear canal 210 acquired by the microphone 84 of the probe 80 and outputs it to the AD converter 64 of the AD / DA converter 60. The AD converter 64 converts the analog signal acquired from the microphone amplifier 74 into a digital signal and inputs it to the computer 10.

[0014] The computer 10 has functions as a control unit 22, a stimulation sound signal generation unit 32, a signal output unit 52, a signal acquisition unit 54, an analysis device 93, etc. The control unit 22 controls each operation of the computer 10.

[0015] The stimulation sound signal generating unit 32 generates a stimulation sound signal related to the stimulation sound to be output. The generated stimulation sound signal related to the stimulation sound is output to the DA converter 62 via the signal output unit 52. The stimulation sound signal generating unit 32 may prepare and output a stimulation sound signal based on, for example, audio data recorded in the storage 13, or may synthesize and output a stimulation sound signal based on, for example, a program recorded in the storage 13.

[0016] In this embodiment, the stimulation sound is configured to include each frequency component in the measurement target frequency band. For example, if the measurement target frequency band is from 100 Hz to 2000 Hz, the stimulation sound may include at least frequency components from 100 Hz to 2000 Hz.

[0017] The stimulation sound is preferably not mechanical and does not cause discomfort to the subject 200. For example, it is preferable that the stimulation sound includes at least each frequency component in the frequency band to be measured and that the frequency changes rhythmically over time. The stimulation sound may be, for example, music, i.e., a combination of pitch, volume, duration, tone, chord, etc., selected and selected in a certain manner. Using music or other stimulation sounds can reduce discomfort to the subject 200 during measurement or provide comfort to the subject 200 during measurement. The stimulation sound may particularly be a lullaby. For example, when the subject 200 is an infant, using a lullaby as the stimulation sound can be expected to relax the subject 200 and allow for appropriate measurement. In pediatric disease examinations, multiple measurements may be performed under sedation. In such cases, it is particularly important not to awaken or excite the subject 200. Using lullabies or other stimulation sounds rather than mechanical sounds can be expected to reduce the risk of waking or exciting a sleeping or calm child.

[0018] The stimulation sound may not have a constant sound pressure amplitude, and the frequency and sound pressure amplitude of the sound waves may not change monotonically. The sound pressure amplitude and frequency of the stimulation sound may change discontinuously over time. Therefore, the energy of each frequency of the stimulation sound may be non-uniform. The stimulation sound may include, for example, a series of high and low tones that unfold with a certain rhythm. It is preferable that the stimulation sound includes a chord, or a series of multiple chords, so as to include each frequency component in the frequency band to be measured.

[0019] Even when the stimulus sound is music, it may generally contain various frequency components due to harmonics, distorted waves, etc. In order to include each frequency component in the measurement target frequency band, the stimulus sound is preferably a recording of music played by a musical instrument, for example. The musical instrument may include an automatic playing instrument such as a music box, an electric instrument, etc.

[0020] When a stimulus sound is output from earphones 82 inserted into the ear canal 210 of the subject 200, pressure fluctuations occur in the ear canal 210 as a result of the stimulus sound acting on the subject 200. The microphone 84 acquires this pressure fluctuation in the ear canal 210. The analysis device 93 acquires a measurement signal related to the pressure fluctuations in the ear canal acquired by the microphone 84 from the AD converter 64 via the signal acquisition unit 54. The analysis device 93 analyzes the acquired signal. The analysis device 93 analyzes the frequency characteristics of the auditory organ of the subject 200 based on the stimulus sound signal and the measurement signal. More specifically, the analysis device 93 analyzes the frequency characteristics of the auditory organ of the subject 200, particularly the middle ear, based on the stimulus sound input to the ear canal 210 and the acquired pressure fluctuations in the ear canal 210.

[0021] As described above, the signal output unit 52, DA converter 62, earphone amplifier 72, earphone 82, etc. collectively function as a stimulation sound output unit 91 configured to output a stimulation sound based on a stimulation sound signal toward the ear canal 210 of the subject 200. Furthermore, the signal acquisition unit 54, AD converter 64, microphone amplifier 74, microphone 84, etc. collectively function as a sound receiving unit 92 configured to acquire a signal indicating pressure fluctuations in the ear canal 210 when the stimulation sound output unit 91 is outputting the stimulation sound.

[0022] The configuration of the measuring device 1 shown here is an example, and can be modified as appropriate as long as it performs the same functions. Here, an example is shown in which the computer 10 performs all of the various controls and data analysis related to the operation of the measuring device 1, but this is not limited to this. The functions of the computer 10 may be realized by any number of devices. Furthermore, some of the functions of the computer 10 may be performed by other devices located in remote locations and connected to the computer 10 via a network. For example, the operation of each component of the measuring device 1 may be controlled from a remote location, or acquired data may be analyzed by a server located in a remote location. While various physical configurations are possible, the measuring device 1 performs functions such as a stimulation sound output unit 91, a sound receiving unit 92, and an analysis unit 93.

[0023] [Measurement Principle] The principles of measurement and analysis of auditory organ characteristics using the measuring device 1 will now be described. As shown in FIG. 1 , in the human auditory organ, the eardrum 222 at the end of the external auditory canal 210 and the cochlea 232 of the inner ear are connected via ossicles 224, including the malleus 225, incus 226, and stapes 227. The middle ear consists of the eardrum 222, the ossicles 224, and the tympanic cavity, a small, air-filled space in which the ossicles 224 are located. Vibrations from the eardrum 222 are transmitted via the chain of ossicles 224 to the cochlea 232, where sensory cells reside. Middle ear diseases, such as lesions, can cause conductive hearing loss. For example, there are known middle ear diseases in which vibrations from the eardrum 222 cannot be properly transmitted to the cochlea 232 due to a partial disconnection of the chain of ossicles 224 or partial fixation of the ossicles 224. Other known middle ear diseases include various types of otitis media, including serous otitis media, thinning and adhesion of the tympanic membrane, and middle ear malformations.

[0024] The sound pressure inside the ear canal 210 will now be described. During measurement using the measuring device 1, the diaphragm 83 of the earphone 82 vibrates at one end of the ear canal 210, and the eardrum 222 vibrates at the other end of the ear canal 210. Figures 3A and 3B are diagrams that schematically show this state.

[0025] When the frequency of the stimulation sound output from the earphone 82 is lower than the resonance frequency of the middle ear, the vibration membrane 83 of the earphone 82 and the eardrum 222 are displaced in phase, as shown in FIG. 3A. Therefore, the pressure P in the ear canal 210 is expressed as follows: P=K(ΔV−ΔV ＴＭ ) / V, where K is the bulk modulus of air, ΔV is the volume change caused by the diaphragm 83 of the earphone 82, and ΔV ＴＭ is the volume change caused by the eardrum 222, and V is the volume of the ear canal 210. At this time, the more the eardrum 222 vibrates, the smaller the volume change becomes, and the smaller the sound pressure becomes.

[0026] When the frequency of the stimulation sound output from the earphone 82 reaches the resonant frequency of the middle ear, the phase of the eardrum 222 is inverted, as shown in FIG. 3B. Therefore, the pressure P in the ear canal 210 is expressed as follows: P=K(ΔV+ΔV ＴＭ ) / V. At this time, the more the eardrum 222 vibrates, the greater the volume change and the greater the sound pressure.

[0027] FIG. 4 shows an example of measurement results using an adult subject 200 and a device having the same hardware configuration as the measurement device 1. The measurement results shown in FIG. 4 were performed using a conventionally known method, different from the method according to the present embodiment. Specifically, the measurement was performed by outputting a frequency sweep sound, whose frequency varied from 100 Hz to 2000 Hz over 10 seconds, from the earphone 82. When this frequency sweep sound was output, the sound pressure in the ear canal 210 was measured using the microphone 84. The solid line in FIG. 4 shows the sound pressure level (SPL) acquired using the microphone 84 versus the frequency of the stimulus sound. Here, SPL is expressed as follows: SPL = 20 log | P / P REF |, P is the sound pressure measured by microphone 84, and P REF is the reference sound pressure, 2.0×10 -5 The curve showing the frequency characteristics of the sound pressure level shown by the solid line in Fig. 4 is referred to as the SPL curve. In Fig. 4, the dashed line shows the volume change caused by the eardrum 222 at this time with respect to the frequency of the stimulus sound.

[0028] The SPL curve indicates the characteristics of the auditory organs of the subject 200, including the outer ear, middle ear, and inner ear. In particular, the SPL curve is known to primarily indicate the characteristics of the middle ear of the subject 200. It is known that large changes in SPL observed in the SPL curve indicate resonance in the middle ear. In FIG. 4, the intermediate value between the frequency at which the SPL curve shows a minimum value and the frequency at which the SPL curve shows a maximum value is indicated by a dashed-dotted arrow as the resonance frequency (RF) of the middle ear. It is also known that ΔSPL, which is the difference between the minimum value and the maximum value of the SPL curve, indicates the mobility of the eardrum 222.

[0029] For example, it is known that evaluating the resonant frequency (RF) and ΔSPL can provide information such as whether the middle ear is normal or whether there is a middle ear disease due to a lesion or the like. For example, when the ossicles 224 are fixed and difficult to move, ΔSPL is smaller and RF is slightly higher than in a normal ear. It is also known that when the ossicles 224 are detached and unable to transmit sound to the inner ear, ΔSPL is larger and RF is slightly lower than in a normal ear. In this way, feature quantities such as RF and ΔSPL can be identified from the SPL curve, and the characteristics of the auditory organ, particularly the characteristics of the middle ear, can be identified based on these feature quantities. The feature quantities used to identify the characteristics of the auditory organ are not limited to the RF and ΔSPL of the SPL curve. Various feature quantities, such as the maximum and minimum values ​​of the SPL curve, can also be used. For example, the condition of the auditory organ of the subject 200 can be evaluated based on the characteristics of the auditory organ. Based on the evaluated state of the hearing organs, for example, the sound conduction characteristics of the middle ear of the subject 200 are evaluated, which can be used for diagnosis, etc.

[0030] The effectiveness of conventional measurement methods using frequency sweep sounds as the stimulus sound has been confirmed. However, mechanical sounds such as frequency sweep sounds tend to cause discomfort to the subject 200. In particular, when the subject 200 is an infant, if the subject 200 finds the stimulus sound unpleasant, the sleeping subject 200 may wake up or move, preventing stable measurement. Furthermore, when frequency sweep sounds are used as the stimulus sound, the measurement takes a relatively long time, such as 10 seconds in the above example. For the subject 200, a shorter measurement time is preferable. Furthermore, this measurement method is susceptible to adverse effects from noise and other factors. Therefore, unlike the conventional method described above, the measurement device 1 of this embodiment performs measurements to determine the SPL curve as follows.

[0031] It is assumed that the auditory organ of the subject 200 is a linear system. In this case, the relationship between the stimulus sound, i.e., the sound x(t) input to the ear canal 210 using the earphone 82, and the acquired sound, i.e., the sound y(t) acquired from the ear canal using the microphone 84, can be expressed by the following equation using the impulse response h(t) of the auditory organ system.

[0032] Here, let us consider the audio x(t) related to the stimulating sound as the stimulating sound signal x(t) output from the signal output unit 52, and the audio y(t) related to the acquired sound as the measurement signal y(t) acquired by the signal acquisition unit 54, and estimate the impulse response h(t) from these.

[0033] The least squares method is used to obtain the optimum impulse response h(t) of the system in the above equation, i.e.,

[0034] From the above equation, it can be seen that the auditory system can be identified regardless of the type and length of the stimulus sound signal x(t).

[0035] In this embodiment, the stimulation sound may include at least each frequency component of the measurement target frequency band. Accordingly, the stimulation sound signal x(t) may be any signal as long as it includes at least each frequency component of the measurement target frequency band. Furthermore, the sound pressure amplitude and frequency of the stimulation sound vary discontinuously over time. Accordingly, the amplitude and frequency of the stimulation sound signal x(t) may vary discontinuously over time. Therefore, the sound generated by the stimulation sound signal x(t) may be a sound that is pleasant to the subject 200, rather than a mechanical sound. For example, the stimulation sound signal x(t) may be music such as a lullaby.

[0036] The duration of the stimulus sound signal x(t) may be any length based on the measurement principle described above. Therefore, as long as conditions for stable measurement are met, the duration of the stimulus sound signal x(t) may be relatively long, such as a single phrase of a song. By increasing the measurement time and increasing the amount of information acquired, improvement in measurement accuracy can be expected. On the other hand, when a shorter measurement time is required, the duration of the stimulus sound signal x(t) can be shortened, for example, to less than 3 seconds or less than 2 seconds. Furthermore, the duration of such a stimulus sound signal x(t) can be further shortened, for example, to approximately 1 second, 0.2 seconds, 0.1 seconds, or 0.01 seconds. Depending on the hardware performance and measurement accuracy, the duration of the stimulus sound signal x(t) may be extremely short, as long as it is longer than 0 seconds. Reducing the measurement time reduces the burden on the subject. Furthermore, reducing the time required for a single measurement allows multiple measurements, such as repeated measurements or measurements under multiple conditions, to be performed in a short period of time. The duration of the stimulus sound signal x(t) can be set appropriately depending on various conditions.

[0037] The measuring device 1 inputs a stimulus sound using such a stimulus sound signal x(t) into the ear canal 210 of the subject 200 as described above, and obtains the response of the middle ear system, which is the object of observation, as a measurement signal y(t) using the microphone 84.

[0038] The analysis device 93 has functions such as a system identification unit 41, a Fourier transform unit 42, a feature identification unit 43, and an auditory organ characteristic analysis unit 44. The system identification unit 41 performs the above-mentioned calculation based on the stimulus sound signal x(t) and the measurement signal y(t) to perform system identification processing, estimating the impulse response h(t) of the auditory organ system. The Fourier transform unit 42 uses an algorithm such as a fast Fourier transform (FFT) to Fourier transform a function related to the impulse response h(t) obtained by the system identification unit 41, thereby obtaining the frequency response of the auditory organ including the middle ear system being observed, i.e., the above-mentioned SPL curve.

[0039] The feature specifying unit 43 specifies feature quantities, such as the above-mentioned resonant frequency (RF) and ΔSPL, based on the obtained SPL curve. The auditory organ property analyzing unit 44 analyzes the properties of the auditory organs of the subject 200 based on these feature quantities.

[0040] [Operation of the Apparatus] The operation of the measurement apparatus 1 will be described. During measurement, the probe 80 is inserted into the ear canal 210 of the subject 200. Fig. 5 is a flowchart showing an outline of an example of the operation of the computer 10. The description will be made with reference to this flowchart.

[0041] In step S1, the computer 10 generates a stimulation sound signal x(t) based on, for example, audio data recorded on a recording device. In step S2, the computer 10 outputs the generated stimulation sound signal x(t) to the DA converter 62. Based on this stimulation sound signal x(t), the stimulation sound is output from the earphone 82 toward the ear canal 210 of the subject 200 via the DA converter 62 and the earphone amplifier 72.

[0042] At this time, as a result of the stimulus sound acting on the subject 200, a pressure fluctuation occurs in the ear canal 210. A signal indicating this sound pressure in the ear canal 210 is generated by the microphone 84. The signal generated by the microphone 84 is input to the computer 10 via the microphone amplifier 74 and the AD converter 64. In step S3, the computer 10 acquires the sound pressure signal from the microphone 84 as a measurement signal y(t).

[0043] In step S4, the computer 10 performs a process for identifying the auditory system based on the stimulus sound signal x(t) and the measurement signal y(t) as described above. That is, the computer 10 estimates a function corresponding to the impulse response h(t) of the auditory system. In step S5, the computer 10 performs a Fourier transform on the estimated impulse response h(t) to obtain an SPL curve that indicates the frequency characteristics of the auditory system.

[0044] Based on the SPL curve, the computer 10 analyzes the characteristics of the hearing organs of the subject 200. For example, in step S6, the computer 10 identifies, based on the SPL curve, feature quantities such as the resonant frequency of the middle ear and / or the ΔSPL value indicating the mobility of the eardrum 222. In step S7, based on the identified feature quantities, the computer 10 evaluates the characteristics of the hearing organs, such as the sound conduction characteristics of the middle ear, to determine, for example, whether the hearing organs of the subject 200 are normal or whether they have a middle ear disease, and if so, what type of disease they have.

[0045] Note that the measurement need not be performed only once, but may be performed repeatedly. For example, measurements may be performed repeatedly while adjusting the insertion of the probe 80 into the ear canal 210, and the measurement may be terminated when an appropriate measurement is obtained. Furthermore, the analysis device 93 may perform system identification by processing a group of results from multiple measurements in the same manner as results obtained from a single series of measurements. This processing also obtains a function corresponding to the impulse response h(t) of the auditory organ system, and an SPL curve is obtained based on this function. For example, multiple measurements may be performed, and measurement results that satisfy predetermined conditions may be used as a group of results for system identification. The output time of the stimulus sound corresponding to one measurement among the multiple measurements may be, for example, less than two seconds. In this case, the total time required for the multiple measurements may be, for example, several seconds to several tens of seconds.

[0046] [Measurement Example] <First Measurement Example> A measurement example using the measurement device 1 of this embodiment will be described. An adult male was used as the subject, and measurements were performed using the method of this embodiment and a conventional method as a comparative example. In the measurement of this embodiment, the stimulus sound was a recording of music played on a music box, and measurements were performed using the analysis method of this embodiment. The characteristics of the stimulus sound used are shown in Figure 6. In this figure, (a) shows the relationship between normalized sound pressure amplitude and elapsed time, (b) shows the relationship between sound pressure level and frequency, and (c) shows the relationship between frequency, elapsed time, and sound pressure amplitude. Music used as a stimulus sound has a limited number of fundamental waves, but because it is played on a music box, it contains many harmonics and the like, and it can be seen that it contains each frequency component of the frequency band to be measured. It can also be seen that music used as a stimulus sound has discontinuous changes in both sound pressure amplitude and frequency over time, and the energy at each frequency is non-uniform.

[0047] In the analysis method according to this embodiment, a measurement signal was obtained using a microphone 84 while a stimulus sound, which was music played by a music box, was input into the ear canal 210 through an earphone 82. System identification was performed based on the stimulus sound signal and the measurement signal, and an impulse response was estimated. An FFT process was performed on a function corresponding to the obtained impulse response, and an SPL curve was obtained.

[0048] On the other hand, in the conventional measurement according to the comparative example, the stimulus sound signal used for the stimulus sound was a frequency sweep signal whose frequency changed from 100 Hz to 2000 Hz over 10 seconds. In the method of the comparative example, the sound pressure acquired using the microphone 84 was directly converted to a sound pressure level, and the SPL curve was acquired by plotting it in correspondence with the frequency of the input stimulus sound at the time of sound pressure acquisition.

[0049] An example of the measurement results is shown in FIG. 7 . The solid line indicates the SPL curve obtained for a certain subject (subject 1) using the analysis method according to this embodiment. The dashed line indicates the SPL curve obtained for the same subject (subject 1) using a conventional method as a comparative example. As shown in FIG. 7 , the solid and dashed lines closely match. This demonstrates that the analysis method according to this embodiment can obtain an SPL curve similar to that obtained using conventional methods whose effectiveness has been confirmed. It was also demonstrated that the analysis method according to this embodiment can obtain an appropriate SPL curve even when using a stimulus sound such as music, in which the energy at each frequency is non-uniform and both the sound pressure amplitude and frequency change discontinuously over time.

[0050] Furthermore, a different adult male subject (subject 2) was used as the subject, and measurements were similarly conducted using the measurement device 1 of this embodiment, with music played on a music box as the stimulus sound. The results are shown by the dashed dotted line in Figure 7. In this case as well, an appropriate SPL curve was obtained. It was also revealed that differences in SPL curves due to individual differences could be obtained.

[0051] Second Measurement Example: The effect of the duration of the stimulus sound on the resulting SPL curve was investigated. The same adult male (Subject 1) as in the first measurement example was used as the subject. As in the comparative example of the first measurement example, the stimulus sound signal used for the stimulus sound was a frequency sweep signal whose frequency changed from 100 Hz to 2000 Hz, and by varying the frequency sweep speed, the duration of the stimulus sound was set to 10 seconds, 1 second, 0.5 seconds, 0.4 seconds, 0.3 seconds, 0.2 seconds, and 0.1 seconds. In both cases, the system identification and FFT analysis method of this embodiment was used.

[0052] The obtained SPL curves are shown in Figure 8. Even when the stimulus sound was a frequency sweep sound, similar results were obtained as when the stimulus sound was music. As shown in Figure 8, the obtained SPL curves were in good agreement when the stimulus sound duration was 10 seconds, 1 second, 0.5 seconds, 0.4 seconds, 0.3 seconds, and 0.2 seconds. When the stimulus sound duration was 0.1 seconds, the measurement results were different from the measurement results for other cases. Therefore, it was revealed that, using the measurement device and the analysis method of this embodiment, good measurements can be obtained even when the stimulus sound duration is shortened to approximately 0.2 seconds. The reason for the different measurement results when the stimulus sound duration was 0.1 seconds was thought to be due to hardware performance, such as the slow startup time of the microphone 84. By improving hardware performance, it is possible to shorten the stimulus sound duration to less than 0.2 seconds, for example, to approximately 0.1 or 0.01 seconds.

[0053] [About the Measuring Device] With the measuring device 1 according to this embodiment, the stimulus sound may vary discontinuously over time in both sound pressure amplitude and frequency, or the energy at each frequency may be non-uniform. It is sufficient for the stimulus sound to provide some energy input for each frequency component in the measurement frequency range. Therefore, the stimulus sound may be a rhythmically varying sound with time-varying frequency, such as music. In non-invasive measurement of auditory organ characteristics, mechanical stimulus sounds are not pleasant to the subject 200. Using music or other such stimulus sounds can reduce the subject 200's discomfort during measurement, thereby improving the medical quality of the measurement. In particular, when the subject 200 is an infant, the stimulus sound may be music such as a lullaby. Using a lullaby or other such music can keep the infant subject 200 calm and relaxed during measurement, which is expected to result in accurate measurements. For example, in pediatric disease examinations, where multiple measurements may be performed under sedation, it may be necessary to avoid waking or agitating the subject during measurement. By using lullabies or other sounds as stimuli, measurements can be performed while maintaining a calm state, enabling accurate measurements to be achieved. These factors contribute to improving the medical quality and accuracy of this measurement.

[0054] The measurement device 1 according to this embodiment can perform highly accurate measurements while shortening the measurement time compared to conventional methods. Furthermore, the measurement device 1 according to this embodiment obtains an SPL curve by first obtaining a function equivalent to the impulse response and then performing a Fourier transform. This allows for a good SPL curve to be obtained despite noise. Therefore, appropriate measurements can be performed even with a relatively low energy input, for example, by shortening the duration of the stimulus sound while keeping the sound pressure of the stimulus sound below 80 dB SPL.

[0055] The measurement device 1 according to this embodiment performs measurements on a living body, namely the auditory organ. A living body generates various noises, such as those caused by the movement of the subject 200 and blood flow. The method and device according to this embodiment, which can detect a slight signal with high sensitivity even in the presence of noise, are particularly effective in measurements on a living body.

[0056] Measurement requires inputting a stimulus sound into the ear canal 210 of the subject 200. However, in order to avoid damaging the hearing organ, it is undesirable to input a high volume, such as 90 dB SPL or more. Furthermore, inputting a high volume may cause the acoustic reflex, which may prevent accurate measurement for acquiring the characteristics of the hearing organ. Therefore, it is important to be able to perform measurements at relatively low sound pressures. For example, in this embodiment, the maximum sound pressure of the stimulus sound can be set to less than 90 dB SPL, such as 80 dB SPL or 70 dB SPL.

[0057] Furthermore, the longer the measurement time, the more susceptible the measurement is to noise, such as the movement of the subject 200. In particular, when measuring small children, such as infants, babies, and newborns, the movement of the subject 200 becomes a major problem. Therefore, it is important to input a stimulus sound at a relatively low sound pressure while keeping the measurement time relatively short.

[0058] It is of great significance that measurements can be taken not only on adults but also on small children, including infants, newborns, etc. Early detection and treatment of hearing disorders, especially at a young age such as in newborns, can greatly contribute to the subsequent development of language and other abilities.

[0059] Furthermore, since the measurement time can be relatively short, the total measurement time can be shortened even when measurements are performed under various conditions while changing various conditions. For example, in the above-described embodiment, the pressure in the ear canal 210 is measured as atmospheric pressure, but even when measurements are performed while changing the pressure in the ear canal 210 in various ways, the measurement can be completed in a short time.

[0060] [Modification] In the above embodiment, an analysis related to system identification assuming that the auditory organs of the subject 200 are a linear system has been illustrated. However, this is not a limitation. For example, system identification assuming a nonlinear system may also be performed. Furthermore, in the above embodiment, a signal related to pressure fluctuations in the ear canal is used as a measurement signal obtained as a result of a stimulus sound acting on the subject. However, this is not a limitation. The measurement signal may be, for example, a signal related to an electroencephalogram obtained as a result of a stimulus sound acting on the subject.

[0061] Therefore, the technology according to the above-described embodiment can also be applied to measurements related to, for example, auditory steady-state evoked responses (ASSR) and distortion product otoacoustic emissions (DPOAE). Generally, in ASSR measurements, sinusoidal amplitude modulated sounds (SAM sounds) with frequencies ranging from 250 Hz to 8 kHz are used as stimulus sounds, and electroencephalograms (EEG) are used as measurement signals. By applying the technology according to the present embodiment, for example, music is used as stimulus sounds, and measurement signals of EEG are used to obtain results similar to those of ASSR measurements based on system identification of a nonlinear system. Furthermore, in DPOAE measurements, generally, two pure tones with f2 between 1 and 10 kHz, satisfying the relationship f2 = 1.2f1, are used as stimulus sounds, and the 2f1 - f2 component of the sound measured by a microphone is used as measurement signals. By applying the technology according to the present embodiment, for example, music is used as stimulus sounds, and measurement signals obtained by a microphone are used to obtain results similar to those of DPOAE measurements based on system identification of a nonlinear system.

[0062] The present invention has been described above by showing preferred embodiments, etc., but it goes without saying that the present invention is not limited to the above-described embodiments, etc., and various modifications can be made within the scope of the present invention.

Claims

1. A measuring device for the auditory organs, comprising: a signal output unit configured to output a stimulus sound signal for the stimulus sound, in order to output a stimulus sound that includes at least each frequency component of a frequency band to be measured and whose sound pressure amplitude and frequency change discontinuously over time into the ear canal of a subject; a signal acquisition unit configured to acquire, as a measurement signal, a signal that indicates pressure fluctuations in the ear canal when the stimulus sound is output into the ear canal of the subject; and an analysis device configured to analyze the frequency characteristics of the auditory organs of the subject based on the stimulus sound signal and the measurement signal.

2. The measuring device described in claim 1, further comprising: a stimulation sound output unit including an earphone configured to output the stimulation sound toward the subject's ear canal based on the stimulation sound signal; and a sound receiving unit including a microphone configured to acquire a signal indicating pressure fluctuations in the ear canal when the stimulation sound is being output.

3. The measuring device according to claim 1 or 2, wherein the analysis device is configured to estimate the impulse response of the auditory organ by system identification based on the stimulus sound signal and the measurement signal, assuming that the auditory organ of the subject is a linear system or a nonlinear system, and to derive a function indicating the sound pressure level in the ear canal versus frequency as the frequency characteristic of the auditory organ by Fourier transforming the estimated impulse response.

4. The measurement device according to claim 3, wherein the analysis device is configured to identify a feature of the function and evaluate the sound conduction characteristics of the subject's middle ear based on the feature.

5. A measuring device according to any one of claims 1 to 4, wherein the stimulus sound is music.

6. The measuring device of claim 5, wherein the stimulus sound is a recording of music played on a musical instrument.

7. A measuring device according to any one of claims 1 to 6, wherein the output time of the stimulus sound for one measurement is less than 2 seconds.

8. A method for measuring characteristics of the auditory organs, comprising: outputting, into the ear canal of a subject, a stimulus sound that includes at least each frequency component of a frequency band to be measured based on a stimulus sound signal and whose sound pressure amplitude and frequency change discontinuously over time; acquiring, as a measurement signal, a signal that indicates pressure fluctuations in the ear canal when the stimulus sound is output into the ear canal of the subject; and analyzing the frequency characteristics of the auditory organs of the subject based on the stimulus sound signal and the measurement signal.

9. The measurement method of claim 8, wherein analyzing the frequency characteristics of the hearing organ includes: estimating an impulse response of the hearing organ by system identification based on the stimulus sound signal and the measurement signal, assuming that the hearing organ of the subject is a linear system or a nonlinear system; and deriving a function indicating the sound pressure level in the ear canal versus frequency as the frequency characteristic of the hearing organ by Fourier transforming the estimated impulse response.

10. The measurement method according to claim 9, wherein analyzing the frequency characteristics of the auditory organ further includes: identifying a feature of the function; and evaluating the sound conduction characteristics of the subject's middle ear based on the feature.

11. A measurement method according to any one of claims 8 to 10, wherein the stimulus sound is music.

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