Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R29/00—Monitoring arrangements; Testing arrangements
  • H04R29/001—Monitoring arrangements; Testing arrangements for loudspeakers
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/12—Audiometering
  • A61B5/121—Audiometering evaluating hearing capacity
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
  • A61B5/6801—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
  • A61B5/6813—Specially adapted to be attached to a specific body part
  • A61B5/6814—Head
  • A61B5/6815—Ear
  • A61B5/6817—Ear canal
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
  • A61B5/6887—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient mounted on external non-worn devices, e.g. non-medical devices
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
  • H04R25/70—Adaptation of deaf aid to hearing loss, e.g. initial electronic fitting

Definitions

• the present invention relates to hearing evaluation and hearing aid fitting More particularly, the present invention relates to virtual electroacoustic audiometry for unaided, simulated aided, and aided hearing evaluation
• the human auditory system processes sounds from a complex three- dimensional space via the extemal, middle, and inner ear, as well as via the complex neural pathways that lead to the auditory cortex within the brain
• a measurable hearing loss due to various conductive, se ⁇ so ⁇ neural, or central auditory disorders, affects a significant percentage of the human population, particularly elderly persons Rehabilitation via hearing aids remains the only viable option for those types of hearing impairments that cannot otherwise be medically treated or surgically alleviated
• the hearing aid prescription process involves translating the diagnostic data into target hearing aid electroacoustic parameters that are used in the selection of the hearing aid
• Traditional hearing evaluation methods and instruments employ a variety of air-conduction transducers for coupling acoustic signals into the ear
• Commonly used transducers include supra- aural earphones, such as TDH-39, TDH-49, TDH-50, insert earphones, such as ER-3A, and free-field speakers (see Specification of Audiometers, ANSI- S3 6-1989, American Standards National institute)
• a threshold measurement obtained with such transducers is referenced to a mean threshold obtained by testing a group of otologically normal individuals This mean threshold, by definition, is referred to as the zero decibel hearing-level or 0 dB HL With this zero reference concept, threshold measurements of otologically normal persons can vary by 20 dB or more These variations can be attributed to following factors-
• audiomet ⁇ c signals such as speech and/or noise are delivered to the ear via a conventional audiometers and associated transducers
• the sound perception by the test subject is not localized to any particular point in space (see Specification of Audiometers, ANSI-S3.6-1989, American Standards National Institute).
• speech audiometry evaluation the speech stimuli level is adjusted for one ear and speech noise level is separately adjusted in the opposite ear.
• the test subject perceives sounds to be within the head and localization is limited to left/right direction
• This type of signal presentation and perception is referred to as intracranial and is unlike the way humans normally perceive natural sounds
• Bronkhorst and Plomp and Begault expanded on previous binaural interaction advantage studies by employing headphone localization techniques (see Bronkhorst, A W , Plomp, R , The Effects of Head-Induced Interaural Time and Level Differences on Speech Intelligibility in Noise, Journal of the Acoustical Society of America, vol. 83, no 4, 1988, pp 1508- 1516; Bronkhorst, A.
• REM real ear measurement
• Target hearing aid characteristics are then calculated based on the natural ear canal response characteristics, as well as other criteria (see Mueller, H. G., Hawkins, D. B., Northern, J. L, Probe Micro p hone Measurements Hearing Aid Selection and Assessment. 1992, Ch 5)
• the hearing aid is prescribed, ordered, and received during a subsequent visit, the aid is inserted over the probe tube and adjusted to match the prescribed target hearing aid characteristics.
• REM evaluation and REM-based prescriptive methods provide considerable improvements over previous fitting methods which relied on the combination of audiomet ⁇ c data and hearing aid 2-cc coupler specifications
• REM offers insight into the in situ performance of the hearing aid, it suffers from several fundamental problems, as described below
• a hearing aid may be optimized for a specific listening condition while compromising the performance under other conditions that may be more important to the hearing-impaired individual
• a significant factor that contributes to the results of a hearing aid fitting is the problem of adequately correlating diagnostic data with fitting needs of the hearing-impaired individual Diagnostic measurements are typically taken in dB HL with transducers that are calibrated in 6-cc couplers
• Hearing aid specification and performance measurements employ 2-cc couplers which do not represent the real-ear Fitting involves the use of one of several prescriptive formulae, with results that are known to vary as much as 15 dB for the same diagnostic data across standard audiomet ⁇ c frequencies (see Mueller, H G , Hawkins, D B , Northern, J L , Probe Microphone Measurements Hearing Aid Selection and Assessment, 1992, p 107).
• These fitting formulae incorporate statistically based conversion factors that simplify the correlation of hearing aid requirements to a particular hearing impairment However, averaged conversion factors are known to vary considerably with respect to objectively measured individual conversion factors
• a full audiomet ⁇ c evaluation is a required first step prior to fitting a hearing aid. Pure tones and one or more speech perception tests are typically involved in the basic audiometric test battery Suprathreshold measurements may also be taken to establish a hearing dynamic range profile, in addition to the frequency response profile obtained in the threshold audiogram test . Following the audiometric evaluation, a hearing aid is then prescribed, selected, ordered, and subsequently tried and adjusted after being received from the manufacturer or assembled in the clinic.
• the fitting or determination of the electroacoustic parameters of a hearing aid typically involve a combination of objective measurements to achieve a desired target characteristics based on one of many prescriptive formulae and subjective measures based on the individual's subjective response to speech and other sounds at various loudness levels.
• Conventional audiometry methods employing headphones, inserts, or sound-field speakers, rely on presenting acoustic energy to the ear of the individual in a manner which is not representative of sound delivery under realistic listening conditions.
• Conventional audiometers present various tones, speech, and noise stimuli to each ear individually and thus are not capable of investigating the individual's binaural integration advantage, or of assessing the hearing function in a three-dimensional sound environment.
• Hearing aid characteristics are determined by a tournament process of elimination, while the hearing-impaired person is presented with real-word sounds played back from tape decks via a set of speakers located around the hearing- impaired person's head.
• the system's fitting process is based on subjective responses of the hearing-impaired who must continuously decide on an alternative signal processing option, and supposedly eventually arrive at an optimal fitting.
• the fitting process via the Veroba system does not involve any objective measurements or calculations for selecting and fitting of the hearing aid.
• the entire fitting process is based on the subjective response of the hearing impaired person.
• most hearing impaired individuals, on their own, cannot explore in a timely and efficient manner the spectrum of various complex and interrelated electroacoustic parameters of a hearing aid under various listening environments.
• a serious limitation of Veroba is that it does not teach how to assess objectively the performance of the simulated hearing aid, nor does it teach how the aided performance is related to the individual's unaided response determined previously during the audiometric evaluation process.
• a major unsubstantiated claim in Veroba's system is the simulation of a realistic acoustical environment via tape-deck playback and speakers located around the head of the hearing-impaired individual.
• recorded acoustic signals that are played back are further subjected to acoustic modifications due to speaker characte ⁇ stics, speaker position with respect to ear/head, and acoustic characteristics of the room, i.e. wall reflections and acoustic absorption.
• a realistic listening condition cannot be achieved with Veroba or any such system.
• Veroba is not capable of manipulati ⁇ g the acoustic condition from its recorded form, e.g by projecting an audio source in a specific location within a three-dimensional acoustic space with a specific acoustic boundary condition
• ITS-hea ⁇ ng aid simulator developed by Breakthrough, Inc offers computer digital audio playback of digital recordings obtained from the output of various hearing aids (see ITS- Hearmg Aid Simulator, Product brochure, Breakthrough, Inc., 1993) Each recording segment represents a specific acoustic input, listening scenario, hearing aid model, and hearing aid electroacoustic setting.
• the recording segments require memory space either on a hard disk or other known forms of memory storage devices, such as compact-disk read-only-memory
• This digital-recordmg-based approach renders impractical the arbitrary selection of a hearing aid, hearing aid setting, and input stimulus for a hea ⁇ ng- impaired individual, when considering all the possible combinations
• the effects of hearing aid vent sizes, and associated occlusion effect, insertion depth, and individual external ears cannot be simulated with the proposed hearing aid simulator because it relies on conventional transducers, / e headphones and insert earphones.
• State-of-the-art REM equipment allows for m-the-ear-canai acoustic response measurements
• the acoustic stimuli are typically generated by the REM equipment itself and delivered via a speaker, typically positioned at 0° azimuth, or with two speakers positioned at 45° azimuth, with the respect to the transverse plane of the head
• the response measurements, / e free-field to real-ear transfer function are essentially one-dimensional since they only provide a single transfer function per ear in a particular speaker-ear relationship, and are thus not capable of establishing a multi-dimensional profiie of the real-ear response
• Another disadvantage of conventional REM equipment and methods is the lack of real speech stimuli presentation because most REM equipment only offer pure-tone, pure-tone sweep, speech-noise and other speech-like stimuli These stimuli do not explore responses to particular speech segments that may be important to the hearing-impaired individual during unaided and aided conditions
• the invention provides a virtual electroacoustic audiometer (VEA), which is a system used in the assessment of human hearing function in the unaided, simulated aided, and aided conditions.
• VOA virtual electroacoustic audiometer
• ICP intra-canal prostheses
• a probe measurement system partially inserted in the ICP, measures the in- the-ear-canal response conditions near the tympanic membrane during all hearing evaluation, thus providing a common reference point for correlating responses in the unaided, simulated aided, and aided evaluation conditions.
• a unique modular hearing aid defined in accordance with the results of such hearing assessment is also provided that includes highly configurable electroacoustic and electronic signal processing elements.
• the system performs audiometric tests, such as pure tone thresholds, uncomfortable loudness levels (UCL), speech reception threshold, and speech discrimination.
• audiometric tests such as pure tone thresholds, uncomfortable loudness levels (UCL), speech reception threshold, and speech discrimination.
• peripheral hearing tests as well as other central auditory processing (CAP) tests, evaluate the hearing function of the human in response to acoustic stimuli measured near the tympanic membrane in absolute sound pressure level (SPL) terms, unlike conventional stimuli which are presented in relative hearing level (HL) terms.
• SPL absolute sound pressure level
• VEA Another significant feature of the VEA is its ability to synthesize, or create, acoustic signals that are representative of signals received in real listening environments in a three-dimensional space. This is achieved by incorporating the various filtering effects of room acoustics, atmospheric absorption, spreading loss, interaural delay, and spectral shaping of external ear, and other body effects.
• a listening condition representing a teacher-talker in classroom is digitally synthesized and acoustically delivered via the ICP to a child to assess his/her unaided and aided listening ability in a classroom environment.
• Spatialized competing signals representing school children noise is optionally presented in addition to the spatialized primary speech signal, i.e. the teacher, to assess further the child's speech discrimination ability in the presence of background noise.
• the unaided evaluation method involves both ears in the listening experience similar to the way humans normally hear sounds, with each ear receiving a portion of the acoustic energy according to the relationship between each ear and the various virtual audio sources.
• conventional audiometry methods present intracranial acoustic stimuli to each ear individually, for example, speech to one ear, and competing noise in the opposite ear.
• the simulated aided assessment of the VEA system is accomplished by incorporating the electroacoustic performance of a desired hearing aid into the unaided digital synthesis of acoustic signals.
• the simulated hearing aid electroacoustic parameters include microphone and receiver transfer functions, and amplifier and filter characteristics.
• Specific or generalized acoustic models are digitally presented to the input of the simulated hearing aid process.
• Specific acoustic models represent listening scenarios that are important to the individual under evaluation and that may be selected and manipulated by the operating ciinician, for example a teacher-talker source model in a classroom environment model with a specific source-ear relationship. A typical goal in such a specific scenario is to maximize speech intelligibility by optimizing the electroacoustic characteristics of the simulated hearing aid.
• Generalized acoustic conditions represent listening scenarios that are associated with -15- normative response data
• An example of a generalized model is an audiologic word list, such as W-22, having a specific spatialized background noise Test scores are compared with general model normative data stored in the system's memory
• the VEA system also simulates other hearing aid effects that can not be simulated by the digital synthesis process due to the unique effects of the individual ear These include the occlusion effect, venting size, and oscillatory feedback potential
• the occlusion effect is a phenomenon that results in changes to the perceived characteristics of the individual's own voice when the ear canal is occluded with a hearing aid
• the VEA system offers a method of measuring various individualized acoustic transfer functions in a three-dimensional space, which are incorporated during the various synthesis processes to create virtual acoustic conditions for an individual
• Fig 1 is a block level schematic diagram showing the major components of the VEA system, including dual ICP prostheses inserted in the ear canal of an individual, a probe microphone system, and a computer system including a digital audio synthesizer module, a digital audiometer module, and a virtual acoustic space measurement module according to the invention,
• Fig 2 is a block level schematic diagram of a digital audio synthesizer module according to the invention.
• Fig. 3 is a block level schematic diagram of a digital audiometer module according to the invention.
• Fig 4 is a block level schematic diagram of a virtual acoustic space measurement module according to the invention.
• Fig. 5 is a block level schematic diagram of a virtual acoustic space measurement system according to the invention.
• Fig 6 is a perspective view of an adjustable chair used for positioning a patient's head du ⁇ ng virtual acoustic space testing
• Fig. 7 is a schematic diagram showing speaker arrangement in a virtual acoustic space measurement system, including transverse plane speakers, and sagittal plane speakers according to the invention
• Fig 8 is a schematic diagram showing an example of transfer function interpolation at a point /3 from transfer functions, measured at points m- ⁇ an ⁇ /772 in a two-dimensional transverse plane according to the invention
• Fig. 9 is a schematic diagram showing an example of realization of a realistic listening scenario for unaided hearing evaluation conditions, and in particular showing a teacher-talker/child-listener scenario including direct acoustic paths PR I and PL I and early reflection paths PR2 and PL2 to the right and left ears of the child-listener according to the invention,
• Fig. 10 is a block level schematic diagram showing an example of realization of a realistic listening scenario for unaided hearing evaluation conditions, and in particular showing a process representation of a teacher-talker/child- listener scenario during unaided evaluation according to the invention
• Fig. 1 1 is a partially sectioned, perspective view showing an intra-canal prosthesis (ICP) for an ICP-ITE representing hearing aids for shallow ear canal placement according to the invention
• Fig 12 is a partially sectioned, perspective view showing an intra-canal prosthesis (ICP) for an ICP-ITC representing hearing aids for deep ear canal placement according to the invention
• Fig. 13 is a perspective view showing an intra-canal prosthesis (ICP) face- plate end, including face-plate probe tube holders and probe tube placement according to the invention;
• ICP intra-canal prosthesis
• Fig. 14 is a partially sectioned, side view showing an ICP core module for a two-part ICP configuration according to the invention
• Fig. 15 is a partially sectioned, side view showing adjustable vent inserts and an ICP-ITE sleeve for an ICP-ITE configuration according to the invention
• Fig 16 is a partially sectioned, side view showing an ICP-ITC sleeve for a two-part ICP configuration according to the invention
• Fig 17 is a partially sectioned, side view showing a complete two-part ICP- ITC assembly according to the invention
• Fig 18 is a partially sectioned, side view showing an ICP having a programmable vent according to the invention
• Fig 19 is a partially sectioned, side view showing a hearing aid and direct acoustic coupling method to an ICP, including direct acoustic coupling via a magnetic attraction method according to the invention;
• Fig 20 is a partially sectioned, side view showing a hearing aid and direct acoustic coupling method to an ICP, including direct acoustic coupling via an acoustic coupler method according to the invention
• Fig 21 is a partially sectioned, side view showing a hearing aid and direct acoustic coupling method to an ICP, including a programming and acoustic coupling interface according to the invention
• Fig 22 is a partially sectioned, side view showing a hearing aid and acoustic coupling to an ICP via an acoustic coupler tip according to the invention
• Fig 23 is a block level schematic diagram showing an example of a fitting process provided by the virtual electroacoustic audiometer system according to the invention.
• Fig. 24 is a graphic computer generated display showing a reference measurements module according to the invention.
• Fig 25 is a graphic computer generated display showing an unaided evaluation module according to the invention.
• Fig 26 is a graphic computer generated display showing a predicted aided module according to the invention.
• Fig 27 is a graphic computer generated display showing a simulated aided evaluation module according to the invention
• Fig. 28 is a graphic computer generated display showing an aided evaluation module according to the invention
• Fig 29 is a line graph plotting the variability of measured SPL versus distance of probe tip from tympanic membrane for 5 kHz and 15 kHz tones for an individual according to the invention
• Fig. 30 is a bar graph plotting the measured SPL for 5 kHz and 15 kHz during probe advancing at 6 mm from tympanic membrane according to the invention
• Fig. 31 is a bar graph plotting the measured SPL for 5 kHz and 15 kHz during probe advancing at 5 mm from tympanic membrane according to the invention
• Fig. 32 is a bar graph plotting the measured SPL for 5 kHz and 15 kHz during probe advancing at 4 mm from tympanic membrane according to the invention
• Fig. 33 is a block level schematic diagram showing an example of a teacher- talker/child-listener scenario using predicted aided evaluation for the right ear according to the invention
• Fig 34 is a block level schematic diagram showing an example of a teacher- talker/child-listener scenario using simulated aided evaluation for the right ear according to the invention
• Fig. 35 is a block level schematic diagram showing a simulated hearing aid with directional microphone according to the invention.
• Fig 36 is a block level schematic diagram showing an example of the realization of realistic listening scenarios for aided hearing evaluation conditions according to the invention.
• Fig 37 is a block level schematic diagram showing an example if the prediction and simulation of oscillatory feedback of a simulated hea ⁇ ng aid DETAILED DESCRIPTION OF THE INVENTION
• Window refers to a graphical area displayed on a computer screen, that represents a collection of controls, objects, entry fields, and plots, that are grouped together according to a iogical functional manner.
• Iconized Refers to an active window that is shown as an icon. Its display is disabled but may be enabled by clicking on the icon on the computer screen
• the virtual electroacoustic audiometer (VEA) described herein is a unitary instrument that is used in the hearing assessment in the unaided, simulated aided, and aided conditions
• the VEA also offers new methods for hearing aid fitting and analysis using a combination of digital synthesis of realistic acoustic stimuli and in-the-ear-canal response measurements throughout the assessment and fitting processes.
• Fig. 1 shows the main components of the preferred embodiment of the VEA system 15
• a pair of intra-canal prostheses (ICP) 22 is inserted in the ear canal 21 of an individual for delivering acoustic stimuli 25 in a manner similar to that of a hearing aid.
• Each ICP contains a receiver, i.e. a speaker, for transmitting acoustic signals to the tympanic membrane 26
• the ICP also contains a probe tube 24 for measu ⁇ ng the acoustic response that results from the unique interaction of the receiver-produced acoustic stimuli and the ear-canal characteristics of the individual.
• a probe microphone system consisting of a probe tube 24 and probe microphone 23 measures acoustic signals from the ear canal 21 and provides electrical signals representative of the acoustic signals
• a response keyboard 27 is provided to register a response from the test subject 20 during va ⁇ ous hearing evaluation tests
• Each ICP receiver 22 is electrically connected to a digital audiometer module 19 that provides an interface to various audiometric transducers including the ICP receiver 22 and probe measurement system 23
• the digital audiometer module is connected to a digital audio synthesizer module 18 and a virtual acoustic space measurement module 14 via various inter ⁇ module cables
• the virtual acoustic space measurement module includes an output terminal 16 for connection to a plurality of test speakers
• These modules may be contained at or within a standard personal computer (PC) 1 1 that also contains standard computer accessories such as memory storage devices 17, a display monitor 10, a keyboard 12, and a mouse 13 Memory storage devices are collectively referred to as system memory 17
• the digital audio synthesizer, digital audiometer, and virtual acoustic space measurement modules are connected to the personal computer system via the Industry Standard Architecture (ISA)-bus interface 34 and ISA-bus 39 of the personal computer (see, for example Fig. 2).
• Digital data representing audio sources are retrieved from the system memory via the bus interface 34, and are oigitally processed by a digital signal processor 33 within the digital audio synthesizer module 18
• the digitally processed data are then converted to analog form using an digital-to-analog converter 35 that typically operates at conversion rate of 44 1 kHz, or at another rate depending on the desired signal bandwidth required.
• the digital audio synthesizer module also receives analog signals representing audio signals via its input connector 31 from extemal audio sources such as tape or CD players (not shown) Received analog signals are converted to digital signals by the analog-to-digital converter 32 for signal processing via digital signal processor 33.
• Multiple digital audio synthesizer modules may be used to enhance the system's digital signal processing capability. This is particularly useful for parallel real-time binaural signal synthesis
• Multiple digital audio synthesizer modules are cascaded by connecting the output 38 of one digital audio synthesizer module to the auxiliary input 30, or input 31 of another digital audio synthesizer module.
• the internal and auxiliary signals are combined within the module at a summing node 36 prior to output
• two digital audio synthesizer modules are used.
• Each module employs a Motorola DSP56001 digital signal processor clocked at 40 MHz.
• the analog output 38 from the digital audio synthesizer module 18 is routed to the mixer 45 of the digital audiometer module 19 (Fig.
• Audiometric transducer interface circuit 49 Outputs to audiometric transducers include ICPs 50 (discussed above, and in further detail below), bone vibrators 51 (not shown), a headphone 52 (not shown), and other conventional methods of delivering sounds to the ear of an individual
• Amplified signals from the audio amplifier 46 are also sent to the digital audio synthesizer module input 31 from an audio buffer circuit 47 output connection 48.
• the mixer circuit 45 also includes connections for receiving audio signals from ICP microphones 55, an operating clinician microphone 56 (not shown), and a patient microphone 57 (not shown), via a microphone amplifier 58
• Extemal line-level signals received at input connectors 53 are also amplified via an amplifier 54 and sent to mixer circuit 45.
• a response keypad interface circuit 60 is employed to interface the system to the response keypad via a connector 59 to register an individual's response to acoustic stimuli during various audiometric evaluation processes.
• the operating clinician microphone connected to the digital audiometer module, allows the operating clinician to communicate with the patient via the ICP pair
• the patient microphone allows the patient to communicate back to the operating clinician during certain audiometric tests that require verbal responses from the patient.
• the patient microphone is also used in occlusion effect measurements, as are described in more detail below.
• the digital audiometer module also includes a PC-BUS connection 43 and PC-BUS interface circuit 44 that link the digital audiometer module to the VEA to coordinate module operation at the system level.
• the VEA also includes a virtual acoustic space measurement system (Fig. 5) that is used to evaluate the individual's acoustic transfer function set.
• a block diagram of the virtual acoustic space measurement module 14 is shown in Fig. 4.
• the virtual acoustic space measurement module receives electrical signals, representing various acoustic signals, from the digital audio synthesizer module output connectors 38 via a set of input connectors 64. Input signal level adjustment and routing is accomplished via a mixer circuit 65, an audio amplifier circuit 66, and a speaker routing and interface circuit 71.
• the output of the virtual acoustic space measurement module is thence coupled to various test speakers in a speaker array 16.
• the virtual acoustic space measurement module also includes a PC-BUS connection 68 and PC-BUS interface circuit 67 that link the virtual acoustic space measurement module to the VEA to coordinate module operation at the system level.
• Such coordination includes processing information indicative of patient head position connected to the module from a patient head positioning sensor via a connector 70 and a positioning sensor interface circuit 69.
• An adjustable chair 78 is preferably used to ensure proper ear positioning within the measurement space, as shown in Fig 6.
• a vertical adjustment lever 79 adjusts the vertical position of the individual on the chair.
• a back adjustment knob 81 adjusts a chair back support 80.
• the head support 82 is adjustable to support the head of the individual seated on the chair.
• An ear position reference arm 84 provides a target reference by pointing a set of ear canal opening pointers 83 to the individual's ear canal openings.
• the ear position reference arm 84 is preferably removable from the ear area via a reference arm vertical adjustment knob 85 to minimize acoustic reflections into the ear area during transfer function measurements.
• An infrared tracking method may also be used to position and maintain the head in the proper position with respect to the speaker array 16, Fig. 5; 89-94, Fig. 7).
• a light- reflective target object (not shown) placed just below the ear lobe of the individual, may be used to reflect the infrared light from the incident infrared light emitter. Proper ear placement is indicated by reflected light which is detected by the positioning sensor interface 69 (Fig. 4).
• the virtual acoustic space measurement system generates various sets of transfer functions that are used during the hearing evaluation process.
• a transfer function of a linear system defines a complex function H(jw) having magnitude and phase characteristics that are dependent on frequency (w).
• the transfer function set in the virtual acoustic space measurement system is obtained from a set of acoustic sources, such as speakers, positioned in a three-dimensional space
• the preferred speaker setup is an array of six speakers 89-94 positioned at an equal distance (d) from a patient head reference point 88, as shown in Figs 5 and 7
• the head reference point 88 is defined as the point bisecting the line joining the centers of the openings of the ear canal 21
• / e #1 (89), #2 (90), #3 (91 ), and #4 (92) are located in the transverse plane 95 containing the head reference point 88 Speakers 1 through 4 are positioned at azimuth angles 0°, 45°, 315°, and 270°, respectively, as shown in Fig 7 at A
• Three of the speakers, / e #1 (89), #5 (93), and #6 (94) are located in the sagittal plane 96 containing the head reference point 88 Speakers #1 , #5, and #6 are positioned at altitude angles of 0°, 45°, and -45° respectively, as shown in Fig 7 at B
• a set of transfer functions for the six-speaker configuration shown in Fig. 7 allows six pairs, / e right and left ear measurements, of frontal measurements where the head is facing speaker #1 An additional six pairs of back measurements are preferably taken where the head is facing opposite (not shown) to speaker #1 Accordingly, a complete transfer function set consists of 12 pairs of measurements that represent finite points in a sphere of a radius (d) Of the twelve paired measurements, eight paired measurements are in the transverse plane and six paired measurements are in the sagittal plane Two paired measurements are common to both planes Paired measurements contain not only individual transfer ru ⁇ ctions for each ear, but also contain the interaural phase relationship with respect to each speaker
• H U a (Pn ⁇ J w where pn is the location of speaker n defined by polar coordinates d, ⁇ , and ⁇ , where d is the distance between the speaker and the head reference point as shown in Fig 7 at A , ⁇ is the azimuth angle of sound incidence with the respect to transverse plane as shown in Fig 7 at A ; and ⁇ is the altitude angle with respect to the sagittal plane as shown in Fig 7 at B
• H ua (p n , jw ) represents the acoustic transfer function that results from sound propagation from a speaker #n to the tympanic membrane when various acoustic factors are considered, including atmosphe ⁇ c propagation losses, effects of head, torso, neck, pinna concha, ear canal, tympanic membrane,
• Transfer function measurements with a probe tube placed on the face-plate of the ICP may also be made These measurements are referred to herein as Hfp n, jw), which represent the transfer function from a speaker #n to a face-plate (fp) of the ICP (discussed in more detail below), at a location representative of the microphone position on a face-plate of a simulated hearing aid
• a transfer function H(p(d, ⁇ , ), jw) at an arbitrary point pd, ⁇ , in space at coordinates d, ⁇ , and can be interpolated from the set of measured transfer functions as shown in Fig 8
• a transfer function of a point in space can be approximated by the weighted average of the two nearest measured transfer functions
• Fig 8 shows an example of an approximate transfer function H(i3 ,jw) interpolated in the transverse plane at point 13 from transfer functions H (n , jw) and H (12 , jw), which are also interpolated from transfer functions H(m ⁇ , jw) and H (m ⁇ , jw) measured with speakers #1 (89) and #2 (90)
• H ( ⁇ 3 , j w) [ H (m ⁇ , jw) + H (m2 , ]w) ]/[2 * L at Qw) ] [1]
• L a t (jw) is the atmospheric loss transfer function due to atmospheric absorption and spreading roll-off of sound.
• interpolation can be used to approximate any transfer function at an arbitrary point in a three-dimensional space from the weighted average of the nearest set of measured transfer functions
• the accuracy of interpolated functions can be improved if additional measurements are made with additional speakers and/or speaker-head orientations
• the preferred embodiment of the invention employs a practical compromise between the number of speakers, e g six in the embodiment of the invention desc ⁇ bed herein, and individual orientations, e g two a front and a back orientation
• non-linear weighting for transfer function interpolation may be more appropriate if determined from statistical data obtained from transfer function measurements of large number of individuals
• the Hicp-rec (jw) transfer function which represents the ICP receiver to m-the-ear-canal electroacoustic transfer function, as measured by a probe when the ICP is positioned in the ear canal of the individual
• H ua (p n , jw), Hf p (p n , jw), H, C p-rec (jw), H, C p-m ⁇ c (w), and H ⁇ cp-fb(jw) are employed in various combinations to digitally synthesize acoustic signals, representing unaided, simulated aided, or aided listening conditions, with realism that is not possible with conventional evaluation and fitting methods
• a teacher-talker 101 and a child-listener 102 acoustic environment 100 is created as follows- direct acoustic paths R j and PL I , and reflection paths pR2 and PL2 > tor right and left ears of the child-listener 102 are represented by transfer functions interpolated from previously measured transfer functions of the child.
• a digital audio file 107 that represents teacher-talker speech is retrieved from a system memory 106 and digitally processed by digital signal processor 114
• the digital signal processor performs signal processes H ua (PR1 - jw) 108, H ua (pL 1 , jw) 110, H ua (pR2 , jw) 109 and H ua (pi2 , jw) 111 , which represent the paths P 1, PL 1 . PR2 .
• Right and left ear path processes are summed at summing nodes 1 12 and 113 and are further processed with inverse transfer functions, 1 / H ⁇ C ⁇ -rec-R ⁇ (jw) (116) and 1/H IC p-rec- ⁇ -t (jw) (104), for ⁇ ght and left ICP receivers 119/120, respectively
• Th e inverse transfer functions are provided to cancel the acoustic transfer function that occurs between the ICP receiver and the residual volume of the ear canal as the sound is delivered
• the processed right and left digital signals are then converted to analog signals via a digital-to-analog converter 1 15 and routed to right and left ICPs via an audiometric interface circuit 1 17
• the process of projecting a virtual audio image to a listener at a particular point in a three-dimensional space, such as teacher-talker speech to a child- listener, is referred to as spatialization
• live-voice signals from the operating clinician via the operating clinician microphone can be used, instead of digital audio data, for spatialization and delivery to the listener wearing the ICP pair
• the virtual position and volume of the spatialized audio source are under the control of the virtual audiometer system of the present invention, as is explained in more detail below
• Transfer function measurements of linear time-invariant systems such as the transfer functions H U a (Pn, jw), Hfp (Pn, jw), H IC p-rec (jw), ⁇ cp-m ⁇ c Qw). and H ⁇ cp-fb(w), typically employs discrete or swept pure tone acoustic stimulus.
• Other stimuli include speech-noise, white-noise, and other speech-like noise signals.
• VEA's probe microphones are calibrated at the head reference point when the VEA is first installed in its clinical setup
• These calibration data stored in the system memory, are subsequently used during transfer function measurements to correct for the unique frequency response characteristics of each probe microphone used and the unique characteristics of room acoustics
• Fig 1 1 is a partially sectioned, perspective view showing an intra-canal prosthesis (ICP) for an ICP-ITE representing hearing aids for shallow ear canal placement
• Fig 12 is a partially sectioned, perspective view showing an ICP for an ICP-ITC representing hearing aids for deep ear canal placement
• Fig 13 is a perspective view showing an ICP face-plate end, including face-plate probe tube holders and probe tube placement
• Fig 14 is a partially sectioned, side view showing an ICP core module for a two-part ICP configuration
• Fig 15 is a partially sectioned, side view showing adjustable vent inserts for an ICP-ITE
• Fig 16 is a partially sectioned, side view showing an
• the ICP of Figs 11 and 12 each have a receiver 136, while the housing 129 in the embodiment of Fig 1 1 is different from the housing 152 of the embodiment of Fig. 12
• the mtra-canal-prosthesis shown in Figs 11-22, consists mainly of a receiver 136, a receiver port 199, a probe tube 133 inserted in probe tube canal 134, vent inserts 128 inserted in vent canal 130, a probe microphone 131 , a face plate 122, and a housing made of a flexible mate ⁇ al, such as an acrylic
• the ICP is generally designed to represent physical and electroacoustic characteristics of a desired type of hearing aid with the exception of the signal processing and generation, which is performed by the audio synthesizer board of the computerized virtual electroacoustic audiometer system
• Figs 1 1 and 12 show ITE and ITC ICPs that represent hearing aids having shallow and deep canal placement, respectively
• the receiver 136 used in the preferred embodiment of the present invention manufactured by the Knowles Corp.
• the probe tube 133 preferably made of a silicone rubber material and having a diameter of approximately 1 mm, is inserted in the probe tube canal 134 of the ICP as shown in Figs 11-22
• a vent canal 130 is preferably provided for pressure equalization in the ICP- ITC versions that have deep canal insertion depths (Figs 12 and 17), and to accommodate vent inserts for the ICP-ITE version having shallow canal insertion depths (Figs 1 1 and 15)
• a vent canal allows the insertion of various vent inserts into the vent canal to achieve desired in situ acoustic characteristics.
• a vent insert of relatively large diameter may be used to reduce the occlusion effect that results from increased perceived volume of the individual's own voice
• a smaller vent insert may be used to eliminate acoustic leakage from the receiver via the vent insert.
• a miniature connector socket 138 and connector plug 123 electrically connects the ICP to the VEA system via attached connector cable 125
• the VEA system in conjunction with the probe microphone system, permits measurements of the occlusion effects versus ICPs and vent types, as is explained later
• the ICP also contains two probe tube holders 124 and a placement handle 126 for placement of the probe tube, as shown in Figs. 11 , 12, and 17
• Fig 13 shows a more detailed illustration of a face plate 122, including the face plate tube holders 124.
• a ICP/ITC sleeve 156, and a hearing aid microphone position 132 are also shown This configuration is used when measuring acoustic leakage feedback and face ⁇ plate transfer functions
• the ICP housing (129, Fig. 1 1 ; 152, Fig 12) is preferably made of a soft flexible material with acoustic baffimg effects to provide comfort and acoustic sealing
• a small housing version is more suitable for pediat ⁇ c populations, while a larger version is suitable for adults who have large ear canals.
• the ICP, shown in Figs. 1 1 and 12 is preferably disposable to avoid contamination from individuals who have infected ear canals.
• An alternate embodiment of the invention provides a two-part ICP configuration, as shown in Figs. 14-17.
• a core part 169 (Fig. 14) is inserted in a variety of disposable sleeves 177, as shown in Figs. 15 and 16. This option provides an economical alternative to the configuration shown in Figs. 1 1-13 because only the sleeve component is disposable.
• the core part 169 is encapsulated in a protective material, preferably having semi-flexible properties.
• a decoupling capacitor 167 may be used to filter extraneous electromagnetic signals that cause audible noise.
• the sieeve part shown in Figs. 15 and 16 is typically made of flexible material, such as a soft acryiic, such that the ICP fits comfortably into a variety of ear shapes and sizes.
• Fig. 16 shows a sleeve suitable for deep canal insertions, representing ITC and CIC hearing aid types.
• an acoustic baffle system 186 that provides an acoustic seal while the ICP is inserted in the ear canal.
• Fig. 15 shows an ICP sleeve for shallow canal insertions representing ITE hearing aid types.
• the ICP core is inserted in the sleeve cavity 179 of any ICP, including those shown in Figs. 15 and 16.
• the specific size of the ICP sleeve selected by the operating clinician depends upon the test performed, individual canal size, and hearing aid simulation requirements.
• An example of the combined parts of a core ICP and an ICP sleeve are shown in Fig. 17, which represents an ICP-ITC assembly.
• Fig. 18 shows a variation of the vent mechanism where the size of the vent is electronically controlled and adjusted (see Zdeblick, K., A Revolutionary Actuator For Microstructures, Sensors Magazine, eb. 1993).
• This is accomplished by employing programmable micro-valve 193 (such as the NO-300 manufactured by Redwood Microsystems of Redwood City, California) which contains a silicon diaphragm 194 which is to regulate the size of the vent attached to the vent canal 197 via the micro-valve port 195.
• Typical vent size range is between .032 and 1.5 mm, according to the voltage level supplied from the virtual electroacoustic audiometer module in response to operating clinician test selections.
• the ICP of the present invention presents acoustic signals directly to the microphone 211 of the hearing aid 214.
• the acoustic coupling of the present invention spans a minimal distance typically less than 15 mm.
• Figs. 19 and 21 show an embodiment of the invention in which acoustic coupling is accomplished via a magnetic attraction method.
• the ICP receiver 136 is coupled to the hearing aid microphone 21 1 via magnetic attraction between a magnet disk 206 on the receiver end of the ICP and another magnet disk 209 near the hearing aid microphone port 210, and which is part of the face-plate 218 of a hearing aid 214, as shown in Fig. 19.
• a sealing ring 205 provides acoustic sealing to minimize leakage in the coupling.
• a hearing aid battery holder 221 a hearing aid volume control 219, a hearing aid circuit 212, and a hearing aid vent canal 217, all representing conventional components of a hearing aid device.
• Fig. 21 provides a programmable hearing aid circuit 253 that allows dynamic ITE testing via control signals routed from the VEA over a programming cable 257.
• Fig. 21 shows an electrically programmable hearing aid with a programming cable 257 connecting the hearing aid circuit to the VEA of the present invention.
• These hearing aids contain circuits that are programmable or adjustable, typically via electrical signals.
• the shown programming interface at the face ⁇ plate is via the battery holder which is adapted to route programming elect ⁇ cal signals to the hearing aid circuit.
• the programming signals and interface methods are typically unique to the hearing aid model as provided by the specification of the hearing aid circuit used. These programming signals and interface methods are known to persons skilled in the art of hearing aid design.
• Other programmable hearing aids currently commercially available employ ultrasonic or infra-red signals with the appropriate signal interface circuits within the hearing aid.
• An alternative acoustic coupling method couples the ICP receiver 136 to the hearing aid microphone 211 via a acoustic coupler 243, as shown in Fig. 20.
• the extended microphone port 242 unique to the present invention, also acts as a handle to facilitate insertion and removal of hearing aid 214 during its normal use.
• FIG. 22 Another embodiment of the invention, shown in Fig. 22, employs an acoustic coupler 290 adapted for insertion into a microphone port 299 of the hearing aid 214.
• the microphone port 299 is recessed to accommodate an acoustic coupler tip 291.
• Another acoustic coupling method employees a suction-cup ring to couple the ICP receiver to existing conventional hearing aids that are not equipped with special interface parts.
• One major advantage of the direct acoustic coupling of the present invention is to improve the signal-to-noise ratio at the microphone of the hearing aid while the aid is being adjusted or evaluated. This is primarily accomplished by acoustically isolating the microphone of the hearing aid from ambient room noise via its coupling to the ICP.
• Hearing aids of the present invention also employ a probe tube canal to allow for probe tube insertion and subsequent in-the-ear-canal acoustic measurements via the probe measurement system as shown in Figs. 19-22.
• the conventional method of in-the-ear-canal measurements with hearing aids involve probe placements beneath the hearing aid which subjects the probe to pinching effects, thus affecting the accuracy of the measurement.
• placing the probe tube beneath the hearing aid creates an acoustic leakage path which causes oscillatory feedback.
• the probe tube canal of the present invention also provides an improved method of advancing the probe while the hearing aid is placed in the ear canal.
• the sequence of these phases as outlined in Fig. 23 represents a typical fitting process unique to the system of the present invention.
• the fitting process offered by the virtual electroacoustic audiometer system in the preferred embodiment of the present invention is implemented in five phases: (1 ) reference measurements 264, (2) unaided hearing evaluation 265, (3) predicted aided evaluation 266, (4) simulated aided evaluation 267, and (5) aided evaluation 268.
• individual phases or a components of each phase can be administered individually, or in other sequence as suitable for the individual under hearing evaluation.
• Each process phase is implemented in a graphical module, as shown in Figs. 24-28.
• the first phase, i.e. reference measurements is implemented by a reference measurements module (Fig. 24) that contains a reference measurement window (shown open in Fig 24) and a signal model window (shown iconized in Fig. 24).
• the reference measurement window allows for measurements of various transfer functions that are used later throughout the fitting process.
• the unaided transfer function Hua (Pn • W) described above, is measured when the 3D-REUR (3 Dimensional Real-Ear Unaided Response) option is selected Measurements are obtained from the frontal (facing speaker #1 ) or back (facing opposite speaker #1 ) orientations, depending on the Front/Back option selected Plots of right and left ear transfer functions can be displayed in either transverse or sagittal plane depending on the Transverse/Sagittal option selection Fig. 24 shows a set of 8-pa ⁇ red H ua (p n , jw) transfer functions in the transverse plane. The measurement is performed by positioning the individual centrally to the speaker array (discussed above) and placing right and left probe tubes in their respective unoccluded ear canal.
• 3D-REUR 3 Dimensional Real-Ear Unaided Response
• Another novel feature of the invention is the ability to measure and quantify the occlusion effect of the simulated hearing aid, as well as the fitted hearing aid.
• a reference measurement with the ear canal unocciuded must be taken. The procedure, briefly described here, is to request the individual to utter a vowel, preferably a vowel with high energy contents in its low frequency spectrum, such as "ee.”
• a measurement is taken with the probe positioned near the tympanic membrane.
• the occlusion effect reference measurement i.e. unoccluded, is saved for occlusion effect measurement with the ear canal occluded using either the ICP or the hearing aid, as is explained below.
• the occlusion effect reference measurement is performed when the occlusion reference option is selected
• the face-plate transfer function Hf p (pp, jw ) (plots not shown) is measured when the Face-Plate Response option is selected.
• the ICP is placed in the ear and the probe tube tip is placed in the microphone position 132 of the face-plate as shown in Fig. 13
• the ICP-receiver to real ear transfer function, H, C p-rec (jw) is measured when ICP Calibrate option is selected This requires the probe tube to be inserted in the probe tube canal of the ICP, and the tip of the tube near the tympanic membrane
• a novel method is employed to optimize such probe placement within the ear canal, and specifically to minimize the effects of standing waves present in the ear canal due to wave reflections from the tympanic membrane.
• the frequency dependent standing wave patterns are well characterized and known to persons skilled in the art of acoustics and particularly real ear acoustic measurements
• the new method of the invention involves acoustic presentation of a dual tone, one at a low frequency in the range of 1 kHz to 5 kHz, and a second at a range of 15 kHz to 20 kHz.
• the acoustic response to tone signals delivered either via a speaker or the ICP receiver, depending on measurement is continuously measured by microphone probe system and displayed on the monitor, as shown in Figs. 30-32.
• a plot of the acoustic response in an ear of an individual for each tone, shown in Fig. 29, indicates a characteristic rise in the low frequency response and a notch in the high frequency response as the probe is advanced closer to the tympanic membrane. This notch occurs at approximately 5 mm from the tympanic membrane for the 15 kHz tone
• Monitoring of the relative response characteristics during probe insertion provides a visual and computer-assisted method to indicate proper probe positioning as shown in the spectrum plots of Figs 30-32 The end of this procedure is generally indicated when a significant notch, typically exceeding 15 dB as shown in Fig 31 , followed by a significant rise in the high frequency, i.e. second tone, response.
• the low frequency, i.e. second tone, response shows only a small increase, within 3 dB, as the probe is inserted closer to the tympanic membrane
• the object of this procedure is to position the probe such that minimal standing waves are present at frequencies of interest during transfer function measurements.
• probe reference point The appropriate probe position is referred to hereafter as the probe reference point
• the second phase, unaided evaluation is implemented by an unaided evaluation module, shown in Fig 25 which consists of an unaided analysis window, shown open in the figure, a spatialization window, also shown open, a signal model window, shown iconized, and an audiometric evaluation window, also shown iconized
• the unaided analysis window allows for various in-the-ear-canal measurements and displays for hearing evaluation in the unaided condition while the ICP is inserted in the ear canal Measurements and plots include Audiogram spectrum, Distortion, Time Analysis, Spectrogram, and 2-CC curves Acoustic stimuli, measurement methods, and associated plots for these tests are known to persons skilled in the arts of audiology and signal analysis However, the Audibility Spectrogram is a new feature that is unique to the present invention as described below.
• the Audibility Spectrogram is a spectral plot showing the audibility of a signal with respect to the hearing profile of the individual and the critical audibility features of an acoustic signal
• the audibility spectrogram is essentially a three-dimensional matrix represented in a two-dimensional plot that indicates signal dynamics (time) and Critical Audibility Regions (CAR) versus frequency, as shown in Fig. 25.
• CARs shown as the outer contours, are specific to each signal segment that is selected from the signal model window CARs of a speech segment are defined by the critical sound features, such as the energy of significant formats in vowels, the energy of fundamental frequency of voicing, the energy of aperiodic frequency sounds, and other criteria known to effect intelligibility, detection, or identification, depending on the signal model selected.
• the Audibility Spectrogram plots are derived by combining spectrograms of analyzed signals and defined CARs, and probe measured spectrograms computed and compared with the measured hearing profile of the individual at the CARs. Measured spectrogram values that fall below the threshold of hearing for the individual are assigned to Below Threshold (B-Thresh) values which define the outer contour region, within the CAR; while measured spectrogram values that exceed the threshold of hearing within CAR are assigned Above Threshold (A-Thresh) values which define a region within the Below Threshold region; and measured spectrograms values that exceed the uncomfortable loudness level (UCL) of the individual are assigned Above-UnComfortable Loudness level (A-UCL) vaiues which define the inner-most contour regions.
• B-Thresh Below Threshold
• A-Thresh Above Threshold
• measured spectrograms values that exceed the uncomfortable loudness level (UCL) of the individual
• the resulting color-coded plot is typically contour shaped for speech signals.
• any type of acoustic signal can be assigned CARs and a corresponding audibility spectrogram based on the individual's measured hearing profile.
• the objective of the Audibility Spectrogram plot is to provide a quick graphical means of indicating the audibility of dynamically received acoustic signals by taking in consideration the individual's hearing profile and the critical audibility features of a signal model. This plot is particularly important in hearing aid fitting optimization processes during predicted aided, simulated aided . and aided evaluation.
• the spatialization window permits selection of signal presentation mode, either in Spatialized or Intracranial modes.
• Spatialized mode presents selected sources and background signals to be delivered to both ears via inserted ICPs according to the selected spatial relationship of head, sources, background, and boundaries, as shown in Fig. 25.
• Spatial relationships include the distance between the audio source and the head reference point (d), azimuth angle ( ⁇ ), and altitude angle ( ⁇ ).
• Intracranial mode offers the conventional sound presentation method where selected signals and corresponding levels are delivered without spatialization to one or both ears.
• the Signal Model window permits the selection of source and background signals and corresponding level Source selection may be of pure tone type, speech, music, or any signal of audiological significance. Background signals are typically competing speech, environmental noise, and other signals of audiological significance.
• the level of signals selected in the spatialized mode is preferably in dB SPL calibrated to 1 meter from the source in free field.
• the measured in-the-ear-canal acoustic response is preferably displayed in dB SPL as measured by the probe microphone system
• source and background signals are routed to right, left, or booth ears as in conventional audiometry.
• the level of signals selected in the intracranial mode is preferably in dB SPL.
• the H !CD . rec (jw) transfer function measurement via the ICP calibration procedure described above permits level selection in dB SPL.
• measurements via the probe microphone system can be made as needed to ensure that the probe and the ICP remain properly positioned in the ear canal.
• a specific selection of source and background signal type, levels, and spatialization mode is defined as a signal model
• One or more signal models can be selected, saved, and retrieved by the system for presentation and analysis purposes.
• a signal model can represent any individual or a combination of acoustic signals/scenarios, including speech, background noise, music, pure tone, masking noise, composite signals, and other audioiogically significant signals.
• the audiometric evaluation window allows for various conventional audiometric measurements to be taken This includes threshold audiogram, most comfortable level (MCL), uncomfortable loudness level (UCL), speech reception threshold (SRT), and various other audiometric measures known to persons skilled in the art of audiology.
• MCL most comfortable level
• UDL uncomfortable loudness level
• SRT speech reception threshold
• SPL absolute sound pressure level
• Another feature of the invention relates to the modes of audiometric signal presentation
• spatialized or intracranial listening modes selected from the Spatialization window not only affect the presentation selected from the Signal Model window, but also the Audiometric Evaluation window as well
• a standard audiological word list such as NU- 6 or W-22 commonly used in conventional speech audiometry, can be presented in the conventional intracranial mode, or alternatively, in the spatialized mode unique to the invention
• the signal process of a spatialized unaided evaluation involves the unaided transfer function H ua (p n , jw), interpolated based on selections of the spatialization window, and the H icp-rec 0 W ) transfer function
• H ua p n , jw
• H icp-rec 0 W H icp-rec 0 W
• the third phase, the predicated aided evaluation, is implemented by the predicated aided evaluation module
• This module shown in Fig. 26, allows the operating clinician to select a hearing aid and predict its performance without the involvement of the hearing-impaired individual
• the module consists of a Hearing Aid Select/Adjust window, shown open, a Predicated Analysis window, shown open), a Signal Model window, shown iconized, a Spatialization window, shown iconized, and the Audiometric Evaluation module
• the Signal Model, Spatialization, and Audiometric Evaluation windows are essentially identical to those described in the Unaided Evaluation phase
• the Hearing Aid Select/Adjust window permits hea ⁇ ng aid selection and subsequent adjustment
• the predicated results of the selection/adjustment are shown on the selected plots of the adjacent Predicted Analysis window
• Hearing aid selection can be automatic or manual, depending on the hearing aid selection
• Automatic/Manual option selected involves selecting one or more hearing aids based on the fitting algorithm selected, and various other criteria selected by the hearing-impaired and the operating clinician
• Conventional fitting formulae and methods such as POGO, Berger, and NAL-II, are provided
• the preferred fitting method is the dynamic audibility method which employs a rational such that Audibility Spectrogram is optimized This corresponds to plots that maximize the Above-Threshold (A-Thresh) contour areas while minimizing Bellow-Threshold (B-Thresh) and Above-UnComfortable loudness Level (A-UCL) contour areas. Hearing aid models that best match the selected criteria are automatically retrieved from the system memory.
• a hearing aid model contains ali of the necessary electroacoustic parameters that are used for signal processing of a signal model The results of the signal process are used in the Predicted Analysis window for analysis and plotting purposes. Hearing aid parameters of a selected hearing aid model are adjusted automatically or manually depending on the hearing aid adjustment Automatic/Manual option and the fitting method selected.
• a hearing aid control parameter set is typically unique to the hearing aid model selected.
• the control parameters are volume control (VC), Low Frequency Cut (LFL), compression Threshold Knee (TK), Microphone type (MIC), Receiver type (REC), and Vent Size selection which reflects vent size of the ICP inserted. If a different vent size is selected, either manually via the vent insert selection, or electronically via the programmable micro-valve vent selection, a new H !C p-spkr (M transfer function is preferably measured to improve the accuracy of the analysis.
• the predicted analysis window is essentially identical to the unaided analysis window, described above, with the exception of the signal processing model that includes the measured face-plate transfer function H fp (Pn, jw ) (292, 293; Fig. 33), hearing aid transfer function Hh a (jw) (294; fig. 33), and the measured ICP receiver to real-ear H tC p-rec (/w) transfer function for the aided ear (295; Fig. 33)
• the hearing aid Hha (jw) transfer function is typically non-linear and vanes depending on the hearing aid selected.
• the total hearing aid transfer function Hha-t (jw) typically includes transfer functions of the microphone H m ic(J w ) ⁇ hearing aid circuit H n -rec (jw), and the receiver Hha-rec 0 W ) Tne transfer function Hha (jw) differs from Hf,a-t ⁇ w ) b Y excluding the hearing aid receiver and, instead, including a receiver correction transfer function HRec-corr(jw), that defines the difference between the predicted hearing aid receiver and the ICP receiver employed.
• This correction transfer function HR e -corr 0 W ) is typically a linear transfer function and is supplied by the VEA system.
• the predicted aided analysis process for an aided right ear and unaided left ear for a child-iistener/teacher-talker scenario is shown in Fig. 33.
• the results of the digital signal process are stored in the system memory 106 for analysis and display.
• the analysis of the predicted data in the system memory includes audibility analysis as described above
• the plotting includes an Audibility Spectrogram that indicates audibility contours of Betow-Threshold, Above- Threshold and Above-UCL with respect to critical audibility regions (CRAs)
• Fig. 26 shows improved audibility in the predicted aided condition versus unaided condition shown in Fig. 25, / e increased Above-threshold contour areas.
• Another prediction measurement unique to the present invention is the measurement of occlusion effect caused by the insertion of the ICP into the ear canal that is characterized by the perceived amplification of the person's own voice
• the present invention provides a method of measuring, subjectively and objectively, the magnitude of the occlusion effect.
• the subjective method is performed by asking the individual wearing the ICP to evaluate his own voice when speaking. If the response is objectionable to the hearing-impaired candidate then an alternative ICP, representing a different hearing aid, may be considered.
• the objective method involves the measured response via the probe system in the occluded ear canal and subtracting the occlusion effect reference measurement, i.e. unoccluded ear-canal measurement, as described above
• the patient microphone 57 external to the ear canal, is typically employed to record the individual's own voice during occlusion effect measurements to ensure constant intensity level during both unoccluded and occluded ear canal measurements (see Mueller, H.G., Hawkins, D.B., Northern, J. L., Probe Microphone Measurements: Hearing Aid Selection and Assessment. 1992, pp. 221-224)
• a unique feature of the present invention is to eliminate not the only requirement of constant voice intensity, but also constant voice spectral characteristics. This is accomplished by adjusting the calculated occlusion effect measurement by the difference in the spectral characteristics of the individual's own voice.
• ICP-ITC The occlusion effect created by two types of ICP, i.e. ICP-ITC and ICP-ITE, is shown in the plot of Fig. 27. This plot indicates a significant occlusion effect due to the ICP-ITE versus the ICP-ICP for an individual. This is expected since the ICP-ITE creates a greater residual volume, to which the occlusion effect is known to be directly proportional.
• the advantage of ICP measurement at the probe reference point is that all measurements taken are independent of the ICP selected or its placement in the ear canal
• the H lC p-rec 0 W ) transfer measurement is required whenever a new ICP is selected and inserted into the ear canal of the individual.
• Another measurement unique to the invention is that of acoustic feedback caused by acoustic leakage from the ICP receiver, when simulating a hearing aid receiver, to the face-plate of the ICP, which simulates the face ⁇ plate of the hearing aid.
• the transfer function H, C p-fb(jw) (338; Fig. 37), e.g amplitude and phase response, is measured at the face-plate as desc ⁇ bed above
• the opening created by the removal of the probe tube from the ICP probe tube canal is preferably plugged during the feedback measurement to exclude acoustic leakage due to the probe canal
• a significant application of the feedback transfer function is in the simulation, and thus prediction, of oscillatory feedback of the simulated hearing aid This undesirable oscillatory feedback manifests itself in the form of whistling, which interferes with the normal operation of the hearing aid
• the prediction and simulation of the oscillatory feedback of a simulated hearing aid having a selected setting is accomplished by incorporating the ICP feedback transfer function H IC p-fb(jw) 337, as shown in Fig. 37.
• Oscillatory feedback can be audible to the individual wearing the ICP via the ICP receiver
• the oscillatory feedback can also be measured via the ICP microphone system in conjunction with the VEA system. This feature allows the operating clinician to adjust the settings of the simulated hearing aid, particularly the gain, frequency response, and vent size, such that oscillatory feedback is minimized or eliminated
• the VEA system can be employed to select automatically an alternate hearing aid or alternate hearing aid parameter set, such that oscillatory feedback is minimized or eliminated
• the predicted aided analysis window also includes other analysis and corresponding plots of Audiogram, Distortion, Time Analysis, Spectrogram, 2-cc Curve These are standardized measurements and plots that are known to persons skilled in the art of hearing sciences and technology
• the 2-cc coupler curves involve conversion of measured in-the-ear-canal response to standard 2-cc coupler curves using real-ear-to-2-cc coupler conversion formulas.
• Standard signal models such as pure tones, are typically involved in the 2-cc coupler measurements (see Specification of Hea ⁇ ng Aid Characteristics, ANSI-S3.22-1987, American Standards National Institute)
• Other evaluation methods conceived and well within the means of the invention include the Articulation Index (AI) measures for unaided, predicted aided, simulated aided, and aided conditions
• An objective of the predicted aided module is to predict objectively the performance of a selected hearing aid according to the selected signal model, selected hearing aid parameter set, and the individual's hearing profile, without the involvement of the hearing-impaired individual
• the fourth phase, simulated aided evaluation, is implemented by the simulated aided evaluation module, as shown in Fig 27
• This module allows the operator to seiect and optimize one or more hearing aids and simulate their audible characteristics
• the module consists of a Hearing Aid Simulation window, shown open, a Simulated Aided Analysis window, shown open, a Signal Model window, shown iconized, a Spatialization window, shown iconized, and the Audiometric Evaluation module, shown iconized
• the Signal Model, Spatialization, and Audiometric Evaluation windows are essentially identical to those described above
• the Simulation Aided window is essentially identical to the Hearing Aid Select/Adjust window of the Predicted Aided Evaluation module
• the Simulated Aided analysis window is essentially identical to the Predicted Analysis window
• a major difference in the simulated aided evaluation moduie is the module's ability to synthesize simulated aided conditions and to present the audible results to the hearing-impaired individual Another significant difference is that analysis is performed by the module
• FIG. 34 An example of a simulated aided signal process, shown in Fig. 34, involves the transfer function of the hearing Hfia (jw) that includes the HR ec . corr (jw), and the face-plate transfer function Hfp (p n , j ) for simulation of the aided ear
• the results of the process are converted to analog signals via the digital-to-analog-converter 1 15 and routed to the right and left ICPs, 119 and 120 respectively, inserted in the ear canals of the individual
• a digital audio file 107 is retrieved from the system memory 106 and processed with face-plate transfer functions Hf (p ⁇ ,jw) (310, Fig. 35) and Hfp (P2, jw ) (312, Fig. 35), where p-f and p ⁇ represent two points in a three-dimensional space
• Signal paths from pj and p2 may represent direct and primary reflective paths, respectively Secondary reflective paths p ⁇ , P4 ., pn (not shown) can be similarly represented in the digital signal process
• each face-plate transfer function step is further processed with the corresponding microphone transfer function 318, 320 for each signal path from points P1 , P2 , --Pn
• the results are summed 326 and are processed by the hearing aid circuit transfer function Hh a -c ⁇ r ( jw ) 322, HR ec . corr (jw ) 324, as shown in Fig. 35
• the resulting digitally processed signal is then converted to analog signal via the digital-to-analog converter 115 and routed to the appropriate ICP within the ear canal via the audiometric transducer interface 117
• the simulated aided analysis window includes measurements and corresponding plots of Audiogram, Distortion, Time Analysis, Spectrogram, Audibility Spectrogram, 2-cc Curve, Occlusion Effects, and Feedback Analysis These measurements are essentially identical to those described above for the predicted analysis window This process is based on the system's ability to compute a hea ⁇ ng aid prescription based on a selected fitting prescription formula/rational. The selected hearing aid can be adjusted and results analyzed and plotted with or without the involvement of the hearing-impaired individual.
• An objective of the simulated aided module is to optimize, objectively and subjectively, the performance of a selected hearing aid according to measured in-the-ear-canal probe response as a function of the selected signal model, hearing aid parameter set, the individual's measured hearing profile, and subjective responses to the presented audible signal.
• One feature unique to the invention is the ability to compute the characteristics of a simulated monaural or binaural hearing aid system that produces natural sound perception and improved sound localization ability to the hearing impaired individual This is accomplished by selecting a simulated hearing aid transfer function that produces, in conjunction with the face-plate transfer function, a combined transfer function that matches that of the unaided transfer function for each ear.
• the matching requirement typically involves frequency and phase responses.
• the magnitude response is expected to vary because most hearing impaired individuals require amplification to compensate for their hearing losses.
• Manufacturing specifications include: hearing aid components simulated by the VEA system, including the microphone and receiver; shape and size of hea ⁇ ng aid according to the ICP selected; hearing aid circuit blocks and circuit components; hearing aid parameter setting; and vent type/size.
• An objective of the VEA system is to provide a detailed specification to the manufacturer/assembler to manufacture/assemble a monaural or bmaurally matched hearing aid system that closely matches the preferred simulated hearing aid. Ordering of the actual hearing aid is performed from the Order menu shown in Fig. 27 which provides a printout of detailed hearing aid specification.
• the final step in the process, aided evaluation is represented by the aided evaluation module as shown in Fig. 28.
• This module consists of an Aided Evaluation window, shown open, an Aided Analysis window, shown open; an Audiometric Evaluation window, shown iconized, a Signal Model window, shown iconized, and a Spatialization window, shown iconized
• the latter three windows are essentially identical to those in the predicted aided evaluation and simulated aided evaluation windows
• the aided evaluation window permits electronic adjustment of manufactured hearing aid parameters as in the case of a programmable hearing aid, shown in Fig 21 , or displaying the suggested parameter setting in the case of a manually adjusted hearing aids, shown in Fig 20
• the aided analysis window is similar to the analysis window for unaided, predicted aided, and simulated aided evaluation process steps, except that the measurements and corresponding plots reflect the response from the actual hearing aid inserted in the ear canal of the individual rather than predicted or synthesized signal, i e simulated aided, response analysis
• Synthesized realistic acoustic signals are presented to the hearing aid by coupling spatialized sounds directly to the microphone of the hearing aid, as shown in Figs 19-21
• the face-plate transfer function, Hfp (p n , jw ), and the supplied ICP receiver-to-micropho ⁇ e transfer function H, C p-m ⁇ c 0 W ) are employed in the digital synthesis process, as shown in Fig.
• a digital audio file 107 representing an audio source at location p n in space is retrieved from the system memory 106 for processing with the free-field to face-plate transfer function Hfp (p n , jw ) 340, 342 for right and left ears, individually Other parallel processes reflecting filtering of additional audio sources or filtering of reflective paths, shown collectively in the dashed rectangles 341 , 343, are summed with the ⁇ ght 112 and left 113 summing nodes The outcome of summing nodes is further processed to equalize the ICP receiver to hearing aid microphone coupling effects by applying the inverse transfer function 1 / H tC p-m ⁇ c (jw) 344, 345
• the acoustic signals supplied to the microphones 350 of the hearing aids 351 represent spatialized signals with characteristics selected and controlled by the VEA system operator via the Spatialization, Signal Module, and Audiometric Evaluation windows
• Electroacoustic testing of the hearing aid, coupled with the ICP as described above may also be performed external to the ear canal, for example 2-cc coupler measurements can be performed by connecting the receiver output of the hearing aid to the 2-cc coupler input
• the ICP in conjunction with the signal generation capability of the VEA, can produce various acoustic stimuli as input to the hearing aid during its 2-cc coupler-based hearing aid evaluation.
• 2-cc coupler measurements can be performed on the ICP, i.e. a simulated hearing aid, by connecting the receiver output of the ICP to the 2-cc coupler input.
• the invention not only deals effectively with today's diagnostic and fitting problems but also provides a basis for new tools that are audiologically significant.
• the system's ability to synthesize realistic acoustic conditions can be used as an auditory rehabilitative tool where a hearing impaired listening ability is improved by interactive training.
• the hearing impaired person is presented with spatialized signals that represent spoken words in noisy background Even though the words might be audible as determined from the audibility measurements and methods described above, these words might not be intelligible for the untrained hearing-impaired individual.
• the VEA system can provide audible or visual feedback to the hearing impaired individual that indicates the appropriateness of the response.
• the object of this new test is to teach the hearing-impaired how to improve speech perception and intelligibility beyond mere audibility.
• Another test made possible by the invention determines the individual's ability to localize a sound in a plane or in three-dimensional space.
• An example is the detection of minimal audible angle (MAA) test whereby the individual s ability to detect, in degrees, the minimal angular separation of pure tones versus frequency (see Mills, A. W., On the Minimum Audible Angle, Journal of Acous. Soc. of Am. 30:237-246, 1956).
• MAA minimal audible angle
• Mills, A. W., On the Minimum Audible Angle, Journal of Acous. Soc. of Am. 30:237-246, 1956 see Mills, A. W., On the Minimum Audible Angle, Journal of Acous. Soc. of Am. 30:237-246, 1956.
• a comparison of the individual's localization ability can be compared across unaided, simulated aided, and aided conditions.
• the invention also makes it possible to determine the individual ' s ability to detect sound movements in a plane or in a three-dimensional space. For example, a sound object can be synthesized to represent movement in a particular geometrical and frequency pattern. The individual's impaired ability to detect the movement can be assessed. Furthermore, a comparison of the individual's ability to detect sound movements can be compared across various listening conditions in the unaided, simulated aided, and aided conditions.

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• 1996
  • 1996-08-14 AU AU67236/96A patent/AU724786B2/en not_active Ceased
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