Interfacing FM Systems with Implantable Hearing Devices

Interfacing FM Systems with ImplantableHearing Devices

Linda Thibodeau, Ph.D.1

ABSTRACT

Cochlear implant recipients can reduce the challenges theyencounter in noisy environments through the use of a remote micro-phone. Although there are numerous options for delivering the signalfrom the frequency modulated (FM) transmitter worn by the speaker tothe FM receiver coupled to the implant, several have now been verifiedthrough research as viable, beneficial arrangements. Recommendationsfor the settings on the implant include mixing ratio and settings on theFM receivers (i.e., FM advantage). Because coupling of the FM systemwith the implant cannot be tested with traditional electroacousticmethods, behavioral verification using speech recognition in noisewith the implant alone and with the implant plus the FM system isnecessary. A variety of resources are available for the audiologist toconsult for the specific components, start sequence of switches, andverification protocols. Resources can be found through manufacturerand professional association Web sites.

KEYWORDS: Cochlear implants, FM systems, verification

Learning Objectives: As a result of this activity, the participant will be able to (1) describe the FM components

and common coupling arrangements with cochlear implants, (2) describe the research to support the benefits

achieved through use of FM systems with implants, and (3) describe the verification techniques to ensure proper

settings for maximum benefit in speech recognition.

Cochlear implants (CIs) have had a tre-mendous impact on the ability of children withsevere to profound hearing loss to developcommunication. However, communication inthe educational setting is compromised by

inherent classroom noise. The benefits ofimplantable devices to restore audibility topersons with hearing loss can be extended tonoisy environments through the use of remotemicrophones. A frequency modulated (FM)

1Professor, Advanced Hearing Research Center, Univer-sity of Texas at Dallas, Dallas, Texas.

Address for correspondence and reprint requests: LindaThibodeau, Ph.D., Professor, Advanced Hearing ResearchCenter, University of Texas at Dallas, 1966 Inwood Rd.,Dallas, TX 75235 (e-mail: [email protected]).

Implantable Hearing Devices; Guest Editor, Jaclyn B.

Spitzer, Ph.D.Semin Hear 2010;31:47–72. Copyright # 2010 by

Thieme Medical Publishers, Inc., 333 Seventh Avenue,New York, NY 10001, USA. Tel: +1(212) 584-4662.DOI: http://dx.doi.org/10.1055/s-0029-1246324.ISSN 0734-0451.

47

system operates on radio frequency waves tobring the signal from a remote microphone toa receiver worn by the listener. The varietyof coupling options makes the selection andfitting of the FM systems quite challenging,so the audiologist needs several resources.Although FM systems can be used with anyimplantable aid, much attention has beenfocused on the issues surrounding the use ofFM systems with CIs. Following a review ofFM system options, the research to support theuse of FM systems with CI users is presented.The article concludes with the fitting and ver-ification protocols that have been recommendedin the literature and in professional guidelines.

FM OPTIONS FOR IMPLANTABLEDEVICESThe two basic components to an FM systemare the transmitter worn by the speaker and areceiver worn by the listener. These compo-nents have many options, which are summar-ized in Tables 1 and 2 and illustrated in Figs. 1and 2. The selection of the FM arrangementis generally related to the purpose for whichit is used. If the primary use is for a groupeducational setting, the commonly used ver-sions are the Phonak Inspiro (Warrenville, IL)or the Oticon Amigo. However, if the purposeis primarily individual use, then one mightconsider the Phonak Smartlink (Somerset,NJ), which has other features such as greatermicrophone directivity and interaction withBluetooth technology in cell phones. A reviewof these and older body-worn connections isprovided by Thibodeau.1

The FM signal may be received by theimplant user by one of two possible methods,either audio or electrical coupling. Audio cou-pling is the simplest and most compatibleacross implants because it requires no physicalconnections and therefore can be used with anydevice. Although verification is still necessary,there are no special switches or settings thatneed to be programmed in the implant tobenefit from this arrangement. Speech recog-nition in noise is improved because the voice ofthe speaker arrives at the implant microphoneat an increased intensity level relative to thebackground noise. One common arrangement

for audio coupling is a desktop FM systemshown in Fig. 2, in which the teacher’s voiceis transmitted to a speaker that is placed nearthe student. Alternatively, the audio signal canbe sent to speakers that are mounted on thewall or ceiling. These options have the advant-age of benefiting more students than just theone with the implant.

With electrical coupling, also known asdirect audio input (DAI) connection, the FMreceiver attaches directly to the implant in oneof two ways, either through attachment to theimplant case or via a cord to the case (Fig. 2).The complexity is increased because there areno standard connections, settings, or startupsequence for the speech processor and FMequipment. Some FM receivers require a dedi-cated battery, whereas others share the powerthat drives the speech processor. Typically, theFM receiver for the implant is determined bythe type of CI speech processor. Althoughchoices may be limited for the FM receiver,there are many general factors to consider whenselecting an FM system to be used with animplant (Table 3).

Some may argue that DAI is not the bestconnection for the FM system with the im-plant because the teacher cannot listen to theoutput to verify the quality of the FM signal.However, it also can be argued that with-holding this technology on the basis that anadult cannot verify the signal quality is contra-dictory with putting on the implant itself. Theimplant itself is a device that cannot be verifiedthrough listening checks. Typically, parentsand teachers have established routines forchildren who receive implants to indicate insome way that they are receiving the implantsignal. These same routines can be used toestablish that the CIþFM connection isworking and that the child is receiving theFM signal.

Because of the numerous cords and adap-tors for interfacing FM systems with implants,it is helpful to have a comprehensive referencefor determining the appropriate connectors andequipment. There are Web sites where the typeof FM transmitter and implant can be enteredand the appropriate connectors will be provided(e.g., http://www.phonakpro.com/us/beb/en/support/compatibility/fm_configurater.html

48 SEMINARS IN HEARING/VOLUME 31, NUMBER 1 2010

Table 1 Available Options for FM Transmitters

Feature Variations Options Pros Cons

Microphone Location External (lapel) & Clips easily onto clothes. & More likely to pick up noise

from clothes.

& Located farther away from

talker’s mouth.

& If talker turns head, intensity of

microphone signal may vary.

External (head boom,

cheek boom)

& Keeps microphone close

to the talker’s mouth at

all times.

& Uncomfortable and distracting

for some talkers.

Internal (Lavalier) & Easy to hang around neck

of talker.

& More likely to pick up noise

from clothes.

& No microphone cord to

snag or break.

& Located farther away from

talker’s mouth.

& If talker turns head, intensity of

microphone signal may vary.

Conference & Used in groups or at a table. & Diminished SNR due to distance

from talker.& Picks up the voices of

multiple talkers.

Type Omni-directional & Sensitivity in all directions. & May transmit more noise,

especially in large crowds.

Directional fixed & Able to focus on selected signal

with less amplification of

surrounding noise.

& If positioned incorrectly, the

talker’s voice may be attenuated.

Directional user

select

& User can change the

directionality when needed

to improve signal reception.

& Additional buttons for selection

may be confusing.

Channel Number Single fixed & Easy for personal use–don’t

have to worry about

changing channels.

& May cause interference with

other FM users in a confined

space (e.g., school).

Multichannel

selectable

& If interference is encountered,

can change channel easily.

& Options for multiple channels

adds complexity and may result

in getting on the wrong channel

inadvertently.

& Adds flexibility for use of

multiple FM systems

in schools.

Frequency 72–76 MHz & Compatible with older

FM equipment.

& Prone to interference from

unwanted sources.

216–217 MHz & Less interference; smaller

receivers.

& Not compatible with older

FM equipment.

Synthesis Direct (user changes

channel)

& User is in control of

switching channels.

& May be tedious if having to

change channels for multiple

users.

Automatic (channel

changes when in

close proximity

to receiver)

& Convenient when changing

channels for more than

one user.

& Can cause confusion when large

group of FM users is in close

proximity —channels may

change inadvertently.

Controls AGC Trimpot & Easy to adjust without

connecting to PC.

& Can inadvertently be changed.

Volume Dial & Easy to adjust without

connecting to PC.

& Can inadvertently be changed.

Programmable Channels Reduce number to

those frequently

used

& Do not have to cycle through

channels that are never used.

& May restrict flexibility to move

equipment to other classrooms.

Batteries Type NiCad only & Rechargeable battery is cost

efficient over long-term use.

& Expensive in the short term.

INTERFACING FM SYSTEMS WITH IMPLANTABLE HEARING DEVICES/THIBODEAU 49

and http://www.medel.com/US/MAESTRO-Cochlear-Implant-System/Speech-Processors/Assistive-Listening-Devices.php).

Setup tips include the specific equipment/adaptors needed, as well as the instructions forconnecting the devices. An example is shown inAppendix A. There is also an option to create apersonalizeduser’s guide as shown inAppendixB.In general, any FM transmitter designed foruse with hearing aids (HAs) also can be usedwith implants. Also, FM receivers that have astandard three-pin Euro connection can be usedwith implants.

BENEFITS OF FM SYSTEMSWITH IMPLANTSCochlear implants have provided significantadvantages to persons who could no longerbenefit from traditional amplification. Thesebenefits have most often been determined inquiet settings. Expectations by implant users tocommunicate in noisy environments are typi-cally guarded. Adults may control their envi-ronment to reduce the deleterious effects ofnoise by moving to a quieter place or alteringthe source of the noise. However, students withimplants are often in classroom settings that

have typical noise levels that exceed theþ15 dBsignal-to-noise ratio (SNR) recommendedby the American Speech-Language-HearingAssociation (ASHA).2 Knecht et al reportedthat only 1 of 32 classrooms they measured metthese criteria, and some had noise levels as highas 66 dBA.3 In addition, children are trying tolisten to fragments of new auditory informationthat they are unable to relate to past experi-ences, which adds to the challenges of listeningin noise. It is unfortunate that the benefitsafforded by the CI, combined with numeroushours of aural habilitation, could be potentiallylost in the noise of the classroom. Even adultswith CI who know the language and canpredict missing information may experienceup to a 60% reduction in speech recognitionin adverse conditions.4,5 Therefore, methods toimprove speech recognition in noise for personswho use amplification should be considered forpersons who use CIs.

The greatest improvement in speech rec-ognition in noise for persons with hearing losshas been accomplished with wireless technol-ogy where a microphone is placed on a speakerand the acoustic signal is sent via FM trans-mission to a receiver worn by the listener.Lewis et al showed that FM technology

Table 1 (Continued )


& Need backup in case of battery

failure; need access to electrical

outlet.

NiCad and alkaline & Increased flexibility

in case of emergency.

& Chance of mistakenly charging

alkaline battery and damaging

system.

Replacement User access & Convenient for user. & Increased chance of user error.

Manufacturer only & Decreases chance of

damage to device.

& Inconvenient for user if battery

needs to be replaced.

Indicator lights On front Low battery & Alerts user to change/

charge battery.

& May be distracting in public

venue with limited lighting,

such as a theater.

FM transmission & Alerts user to function

of device.

& May be distracting in public

venue with limited lighting,

such as a theater.

Accessory

jacks

Audio input jack & Increases flexibility of device

(for use with other devices).

& May be confused with jack for

charging.

Secondary

transmission

Bluetooth & Allows user to use cellular

phone with FM device.

& Decreases battery life of

transmitter.

FM, frequency modulated; AGC, automatic gain control; PC, personal computer; NiCad, nickel-cadmium.Adapted from American Academy of Audiology. AAA clinical practice guidelines: remote microphone hearing assistancetechnologies for children and youth birth–21 years. Available at: http://www.audiology.org/resources/documentlibrary/Documents/HATGuideline.pdf. Retrieved July 24, 2009.


Table 2 Available Options for FM Receivers for Cochlear Implants


Type Dedicated FM receiver works with

a single CI model.

& Typically interfaces easily and

securely within the CI case.

& Can only be used with one

model resulting in costly

upgrades.

Interchangeable Receiver attaches to

CI via adaptor or cable

and can be used with

more than one CI.

& Flexibility to use with other

CIs increases need to have

backup equipment.

& Adaptor adds another part

with the potential to

malfunction.

Connection of

interchangeable

FM receiver

Type Adaptor at CI base. & May be easily removed

when FM not in use.

& Adds length/weight to the CI.

& May fall off.

Earhook. & Doesn’t add length to

the CI.

& May need to be removed

when FM not in use.

Cable. & Doesn’t add length to

the CI.

& FM receiver must be

attached to clothing.

Channel Number Single fixed. & Easy for personal use—don’t

have to worry about

changing channels.

& Less flexibility.

Multichannel

selectable.

& Good for use in close

proximity to other FM users

(e.g., schools).

& Can be automatically

changed to specific channel

by transmitter.

& May be confusing for

some users.

Multichannel

selectable.

& Good for use in close

proximity to other FM

users (e.g., schools).

& Can be automatically

changed to specific channel

by transmitter.

& May be confusing for

some users.

Batteries Type Independent battery. & May increase battery life for

CI use.

& Adds to troubleshooting.

Runs off CI battery. & No extra battery required. & May decrease CI battery life.

Programmable Frequencies Default channel. & Simplifies the startup for the

user so that when turned on,

correct channel is received.

& If transmitting situation

changes, default may no

longer be appropriate.

Channel set. & Reduces chance of

inadvertently getting to

wrong channel.

& Not as flexible if situation

changes or equipment

needed as backup.

FM:HA ratio Adjust level of FM

signal re: mic signal.

& Allows for customization of

system for specific

situations and user needs.

& May require PC to adjust

settings.

Indicator Lights Continuous or

interrupted.

& May indicate reception of

FM signal.

& May not give indication if

battery exhausted.

Indicator Lights Continuous or

interrupted.

& May indicate low battery

function.

& May decrease battery life.

Switches Type Automatic ON/FM. & Less opportunity for

user error.

& Cannot confirm setting

visually.

Manual ON/FM. & May aid in troubleshooting. & Possibility for user error re:

turning on FM switch.

Mechanical FM, FMþHA, HA. & Can check settings visually. & Requires manual dexterity

& Inadvertently changed.

FM, frequency modulated; CI, cochlear implant, HA, hearing aid.Adapted from American Academy of Audiology. AAA clinical practice guidelines: remote microphone hearing assistancetechnologies for children and youth birth–21 years. Available at: http://www.audiology.org/resources/documentlibrary/Documents/HATGuideline.pdf. Retrieved July 24, 2009.


combined with binaural amplification foradults with hearing loss could result in speechrecognition performance in noise that wasactually better than that achieved by listenerswith normal hearing.6 Numerous options areavailable for FM technology, including micro-phone arrangements, receiver features, andconnections with other audio electronics suchas cell phones. In general, the FM systemoptions for persons with CIs have includedsoundfield (wall, ceiling, or desktop speakers)and electrical coupling (direct- or cord-con-nect). There has been some reluctance to in-vestigate the use of FM technology with CIsbecause the output cannot be verified withthe traditional electroacoustic measurementsas is done with HAs and FM technology.

Therefore, the verification relies on the behav-ioral performance of the user with the bodyworn and sound-field FM systems.

One of the first investigations of interfac-ing FM technology with CIs was conductedwith adults who would be reliable reporters ofacoustic quality. Ludena and Thibodeau eval-uated percent correct sentence recognition inquiet and in noise (þ10 SNR) in an auditoriumwith two young adults with CI experiencewhile using body-worn FM systems (Telex,Comtek, and Phonic Ear).7 The improvementsin speech recognition with the use of the FMsystems ranged from 34 to 52%, compared withperformance with the CI alone. Subjective re-ports were favorable with respect to clarity andquality. Davies et al evaluated the effectiveness

Figure 1 Frequency modulated (FM) transmitter options.


with a body-worn FM system (Phonic EarSolaris) with 14 children who used body-wornspeech processors (Nucleus Sprint) in a typicalclassroom.8 Sentence recognition in noise(0 and �3 SNR) significantly improved inboth SNRs while using the FM system.Children with previous FM experience receivedgreater benefit, which suggests that theymight have selected higher FM volume levels.However, there was still reticence to use thebody-worn FM system in the real world be-cause of the addition of the bulky FM receiverto the already cumbersome body-worn CIspeech processor.

Although in the 1990s the body-worn FMsystems were routinely used with students withear-level HAs for improved speech recognitionin the classroom, they were not promoted forstudents with CIs. Often, a desktop FM systemwas used with school-age children with CIs as afirst means to incorporate FM technologywhile avoiding adding devices on the body;this also allowed easy verification of the FM

signal. The negative aspect was the need tocarry the speaker (600 � 400 � 300) wherever in-struction was occurring. To avoid this incon-venience, wall-mounted speakers to deliver theFM signal also were considered. Speech recog-nition in noise (þ6 SNR) was evaluated byHanin and Adams in a simulated classroomwith a wall-mounted soundfield FM system forsix children with CIs (ages 6 to 10 years).9

Average speech recognition performance im-proved by 12% while using the soundfield FMsystem in noise. They recommended soundfieldFM systems for students with CIs because ofreported electrical interference experiencedwhen using an electrically coupled FM system.Shortly thereafter, however, Crandell et alreported no significant improvements whileusing a wall-mounted soundfield FM systemand live-voice speech presentation.10 The lackof improved speech recognition in noise (þ6SNR) for the 8 children and 10 adults with CIsmay have been the result of the limited gainprovided by the soundfield FM system (7 to

Figure 2 Frequency modulated (FM) receiver options.


10 dB). More recent investigations of thebenefit of soundfield FM systems for CI lis-teners resulted in mixed evidence. Andersonet al11 reported no improvement for 6 students,whereas Iglehart12 reported significant benefitfor 14 students with CIs listening to the signalfrom the FM transmitter via wall-mountedspeakers. The lack of improvement found byAnderson and colleagues was most likely re-lated to a ceiling effect caused by the highperformance level when using the CI alonefor some students. Therefore, when testingwith CIþFM, there was no room for improve-ment in the percent correct score.

As the options increased for ‘‘cube-like’’FM receivers that could be interfaced withspeech processors, interest in comparing thesmaller FM receivers to the desktop systemsincreased. Schafer and Thibodeau (2004) com-pared speech recognition in quiet and in noise(þ5 SNR) for eight adults with cochlearNucleus CIs using three FM system arrange-ments: desktop soundfield (Phonic EarToteable), body-worn (Phonic Ear EasyListener), and cube-like (AVR LogicomCI).13 Although use of the desktop soundfieldcondition resulted in an average increase of 6%in speech recognition in noise relative to thequiet condition, this improvement was notsignificant compared with increases of 28%and 22% in speech recognition in noise ob-tained with the body-worn and cube-like sys-tems, respectively. For this group of adults,there were no reports of signal distortionswhen interfacing the FM signal with themicrophone signal from the speech processor.

As more cube-like FM receiver options forCIs became available and instances of interfer-ence were limited to anecdotal reports, the needto verify benefit with the smaller receivers inchildren became paramount. Speech recogni-tion in multitalker babble was evaluated when acube-like FM (Phonak Microlink CI) wasinterfaced with Nucleus body-worn processorsof 12 children by Aaron et al.14 As expected,the noise significantly degraded speech recog-nition, and the FM system significantlyimproved performance for all but one ofthe participants. Significant benefit also wasreported by Schafer and Thibodeau (2003)for 10 children with CIs who completed an

Table 3 Considerations in Selecting an FM

System

1. Audiological:

A. Hearing Status: conductive/sensorineural/mixed,

unilateral/symmetrical, neuropathy

B. Audiogram: thresholds, configuration, stability

C. Speech recognition performance in noise

D. Special considerations: drainage, allergy, atresia

2. Developmental:

A. Age: chronological, developmental

B. Academic performance: better performance¼more flexibility

C. Additional problems: cognition, mobility, attention,

sensory integration, vision, auditory processing, etc.

3. Listening environment at school:

A. Learning environment: lecture, discussion, team

teaching, multiple groups

B. School access: single talker, multiple talkers,

technology, etc.

C. School acoustics: room size, reverberation, noise

sources

D. Current HAT at school: teacher/peer support

E. Other school locations: gym, therapy, cafeteria,

specials

4. Listening environment at home:

A. Activity needs: meals, play

B. Access needs: family, friends, peers, audio from

technology

C. Acoustic needs: room size, reverberation, noise

sources

D. Other locations: recreation, church, community

5. Technology considerations:

A. Convenience, wearability, reliability

B. Maintenance, ease of monitoring

C. Manufacturer support, compatibility with

amplification

D. Compatibility with other devices

E. Signal interference, multiple FM channels

6. Funding considerations:

A. Considered assistive technology under IDEA

IEP–provided by school district; IFSP–State’s part C

funding

504–provided by local district

B. Interface with personal hearing aids

HAT, hearing assistive technology; IDEA, Individuals withDisabilities Education Act; IEP, Individualized EducationPlan; IFSP, Individualized Family Service Plan.Adapted from American Academy of Audiology. AAAclinical practice guidelines: remote microphone hearingassistance technologies for children and youth birth–21 years. Available at: http://www.audiology.org/resources/documentlibrary/Documents/HATGuideline042208.pdf. Retrieved July 24, 2009.


adaptive listening task with sentences in noisevia four FM system arrangements: desktopsoundfield, body-worn, miniature direct-con-nect, and miniature cord-connect.15 The chil-dren were allowed to adjust the volume on theFM receivers to comfortable listening levelswhile listening to running speech. The thresh-olds for speech-weighted noise were obtainedvia the four FM system arrangements to de-termine relative audibility levels. The finding ofequivalent thresholds across systems suggestedthat the children were able to adjust the volumesettings on the FM system receivers to rela-tively equal perceptual levels. There were nosignificant differences across the FM systems—they all resulted in significantly improved per-formance in noise relative to the implant-alonecondition.

Monaural versus Binaural FM Fittings

As the ear-level options for FM receiversbecame more readily available, additional ques-tions were raised regarding the relative benefitof monaural or binaural fittings. Based onfindings of Lewis et al, who reported thatbinaural FM fitting to ear-level HAs providedsignificantly greater benefit over monauralFM fittings for adults, one might predict thesame for implant users.6 However, the listeningexperience for bilateral CI users can be quitedifferent, depending on whether they wereimplanted simultaneously or sequentially.Furthermore, it has been recommended thatmonaural implant users continue to use ampli-fication on the unimplanted ear (i.e., bimodalarrangement). The best arrangement of FMsystems for bilateral or bimodal CI childrenwas evaluated by Schafer and Thibodeau(2006), who compared speech recognition innoise thresholds for phrases in two groups of10 children each.16 The best performance wasobtained when the FM signal was received oneach side regardless of the bilateral or bimodalarrangement. If only one FM receiver was used,the performance was significantly better whenused on the side of the first implant for thebilateral users and on the implant side for thebimodal users.

The research regarding benefit of FM sys-tems with CIs was summarized by Schafer and

Kleineck in a meta-analysis.17 After reviewingnine studies in which benefits of classroom,desktop, and/or direct-connect FM systemswere evaluated, they determined that the largestimprovement in percent correct speech recog-nition in noise with the FM system comparedwith the implant alone was obtained with thedirect-connect option (38.0% average improve-ment) followed by the desktop system (17.1%average improvement). The least improvementwas found when using the wall-mounted speak-ers (3.5%) to deliver the FM signal to theimplant users. Such an analysis is the strongesttype of evidence to support clinical practiceprocedures. Therefore, it can be concludedthat, on average, students will perform thebest with directly connected FM receivers ratherthan audio coupling options.

The one remaining option that has notbeen addressed in controlled studies is induc-tive coupling. Many implants now have a tele-coil, which makes them capable of receiving theFM signal from a neck loop. This may be aviable coupling option in some cases, particu-larly when a student loses the small FM re-ceiver. This larger, sturdier option also may benecessary when teachers need more obviousverification that the student is using the FMsystem; the small receivers are often not asvisible behind long hair covering the ears.

Evaluation of Optimal Settings for

Cochlear Implants with FM Systems

The FM technology has now advanced beyondthe early questions—whether to interface itwith implants and whether to fit it monaurallyor binaurally—to further questions surround-ing settings on the implant (i.e., mixing ratio)and on the FM receiver (i.e., FM advantage).Early body-worn systems allowed the CI userto adjust the volume of the FM signal to acomfortable level. This was determined incombination with the setting in the speechprocessor known as the mixing ratio or therelative energy of the signals from the CIprocessor microphone and the FM transmittermicrophone. The comparable adjustment inthe ear-level receivers is known as the adjust-ment for FM advantage. Schafer and Wolfeevaluated the FM advantage settings in five


children using Advanced Bionics Auria pro-cessors with Phonak MLxS receivers coupledvia an iConnect earhook (Fig. 2).18 Speechrecognition in noise was evaluated in CI aloneand CIþFM conditions when the FM ad-vantage was adjusted toþ10 andþ16 dB.Schafer et al found similar results for17 older children and adults when listeningto FM advantage settings in Phonak MLxSreceivers ofþ6,þ10,þ14, andþ20 dB forAdvanced Bionics Auria and ESPrit 3Gusers.19 Performance increased for the Auriausers as FM advantage was increased, but notfor the 3G users. This lack of increase forthe 3G users was likely because the dynamicrange for processing incoming signals wassmaller for the 3G and did not allow theincreases in the FM signal to be coded forthe listeners. The lack of better performancewith increased FM advantage settings alsowas reported for Cochlear Freedom users.Across the Schafer studies, most listenerspreferred theþ14 dB FM advantage.

The FM advantage also interacts with asetting in the speech processor known as mix-ing ratio. This setting allows the intensity ofthe DAI signal to be adjusted relative to thesignal from the processor microphone. If thesetting is 50/50 (Advanced Bionics processors),the signals are weighted equally. If the settingis 3:1 (Cochlear Corporation), the signal fromthe processor microphone is given greaterweight than the FM signal received via theDAI connection. Wolfe and Schafer20 eval-uated the different mixing ratios in 12 adultswearing Auria units. The results differed de-pending on whether testing for speech recog-nition was done in noise or in quiet. Based ontheir results, they recommended a 50/50 ratiofor children to hear the FM and environmentalsignals optimally. For adults, they suggestedallowing them to switch to the 30/70 settingfor improved hearing in noise. Because theyfound that this setting limits hearing environ-mental signals, they recommended it only beavailable for adults who can judge the relativeimportance of hearing the signals from the FMversus the implant microphones.

Rather than having one fixed FM setting, anew FM receiver (Phonak MLxi) has adaptiveFM advantage. The adaptive FM processing

adjusts the output of the FM receiver based onthe ambient noise. If the transmitter detectsthat the ambient noise exceeds 57 dB soundpressure level (SPL), a signal is sent to the FMreceiver to increase the gain of the FM receiverand therefore increase the FM advantage to amaximum ofþ24 dB. The transmitter and thereceiver must both have the adaptive processingcapability to experience the benefit of increas-ing the SNR. Wolfe et al evaluated 13 subjectswith Advanced Bionics implants and 12 sub-jects with Cochlear Corporation implantswhen using traditional fixed versus adaptiveFM advantage in background noise levels of55, 65, 70, and 75 dBA.21 The listeners withAdvanced Bionics implants showed significantimprovement in speech recognition as noiselevel increased. The listeners with implants byCochlear Corporation did not show the im-proved performance until the autosensitivityfeature was activated. With that feature acti-vated, the likelihood that signals from the FMtransmitter will be compressed is reduced andthe effects of adaptive FM advantage can beobserved. They also found that speech recog-nition in noise when listening only through theimplant microphone (FM microphone muted)was significantly better with the autosensitivityfeature activated. Based on these results, Wolfeand colleagues recommended using the defaultprogram settings for Advanced Bionics CIusers and enabling the autosensitivity featurefor Cochlear Corporation CI recipients tooptimize speech recognition in noise with dy-namic FM and also without FM.

Research has supported the use of FMsystems with CIs through a variety of couplingarrangements. The best arrangement is to usean electrically connected FM receiver on eachside, whether the child wears two implants oran implant and an HA. For those bilateralarrangements that require a cord connection,a y–cord may be used so that only one FMreceiver is needed. However, no data to supportthis arrangement have been reported. Alsothere are no published studies of using FMsystems with bone-anchored HAs; manufac-turers provide instructions for DAI connec-tions of FM receivers. There will continue tobe new arrangements that will require verifica-tion and comparison with previous technology


through research. New connections also shouldbe evaluated, first with adult implant users sothat fine acoustic variations in quality can beadequately described.

CHALLENGES WITH FM SYSTEMSWITH IMPLANTSAlthough studies have shown significant ben-efits for speech recognition when using FMsystems with implants, some challenges inher-ent in these systems can be addressed effi-ciently when known in advance. Some of thechallenges are specific to the equipment ar-rangement and some are related to generaltransmission of FM signals. The issues relatedto specific equipment arrangements are re-viewed in this article, with suggestions toalleviate them. The challenges relating tomore general educational issues are not soeasily remediated and typically are addressedthrough increased communication amongprofessionals.

Following the initial challenges associatedwith body-worn FM receivers adding bulkinessto small bodies already laden with body-wornspeech processors, smaller FM receivers werewelcomed but came with the disadvantage ofless secure connections. When adapters to holdthe FM receiver to the ear-level speech pro-cessors would fall off, various taping effortswere tried. An acceptable, economical tapeoption was the use of ‘‘paper tape,’’ whichdoes not leave a residue on the case. A supplyof this tape in the classroom for daily use mayprevent hours of searching for lost receivers.

With the advent of various ear-level de-signs, new connectors for existing FM receiverswere developed. When the connector providedthe power source for the FM receiver, it wasimportant to verify that adequate power wasreceived. All the FM components could beworking perfectly in an HA arrangement andthen fail to work when used with an arrange-ment where the power was supplied in theconnector. In one case, it was determined thatthe slightly thicker batteries by a specific man-ufacturer made better contacts. Having an FMreceiver that contained light-to-signal FM re-ceptions would be very helpful to confirm thepower supply was adequate.

The miniaturization of the FM receiver sothat it could be attached to the ear-level pro-cessor resulted in it being positioned close tothe magnetic coil where the electrically codedsignals were transmitted across the skull to theinternal components. In some cases, this closeproximity of the FM receiver to the transmittercoil resulted in audible interference described asa high-pitched wavering signal. When the coilwas removed from the speech processor, theinterference detected via a listening earphonedisappeared. The FMmanufacturers reported aset of optimal frequencies to be used with CIarrangements to avoid frequency interference(Table 4).

A final challenge when interfacing FMsystems with CIs relates to the diversity of theprofessionals involved in fitting the systems.Generally, an audiologist who specializes inmapping CIs determines the optimum settingsin the implant. Then the child receives theFM system through the educational system,which has a different audiologist. Unlike HAs,CIs cannot be connected to a computerthrough a standardized interface and internalsettings that are read digitally. The educa-tional audiologist must communicate withthe mapping audiologist to know the mixing

Table 4 Optimal FM Frequencies to Use When

Interfacing FM Systems with Cochlear

Implants

Phonak Number FM Frequency

09 216.2125

12 216.2875

13 216.3125

16 216.3875

17 216.4125

18 216.4375

61 216.5125

62 216.5375

52 216.5750

64 216.5875

65 216.6125

68 216.6875

73 216.8125

57 216.8250

76 216.8875

FM, frequency modulated.From Phonak Inc., Warrenville, IL. Recommended FMchannels for use with cochlear implants (personalcommunication, March 30, 2009).


ratio or the program designated for FM use.The educational system is not responsible forthe actual mapping of the CI according to theASHA.22

The regulations in the Individuals withDisabilities Education Act (IDEA) now spe-cifically state that mapping is not a relatedservice, and also clarify that optimization doesrefer to mapping a CI. Therefore, school dis-tricts are not required to provide optimizationservices to comply with IDEA. Further, thelanguage makes clear that a child with a CI orother surgically implanted medical device isentitled to those related services (e.g., speechand language services, audiology services) thatare required for the child to benefit from specialeducation, as determined by the child’s Indi-vidualized Education Plan (IEP) team.

Therefore, communication between theimplant audiologist and the educational audiol-ogist is critical for documenting the settings toconduct efficient behavioral verification proce-dures. Although these are only a few of thechallenges with interfacing FM systems withCIs, they are examples to illustrate that solu-tions can be found. Often the solutions requireadditional effort to establish ongoing commu-nication or to verify appropriate connections.Regardless of the arrangement, there will needto be close monitoring to ensure the child isresponding as well in quiet and even better innoise situations when using the FM technology.

VERIFICATION OF FM WITHIMPLANTABLE DEVICESThe verification of FM systems with implantsvaries depending on the options available onthe processors. Some speech processors allowconnection of listening earphones for checkingby someone with normal hearing, and otherscan be verified only through informal andformal procedures with the implant user. First,one must ensure the connections and settingsare correct. Next, informal measures are neces-sary to verify functioning of the local andremote microphones. Formal objective meas-urements may be used to compare differentsettings within an arrangement or the speechrecognition benefits across different types ofFM systems.

Preassessment Verification

Before any informal or formal checks, theproper equipment arrangements must be con-firmed by reviewing information provided bythe manufacturers of both the implant and theFM system. Important information is providedon their Web sites regarding the FM-to-CIconnections. Contact information for severalmanufacturers is provided in Table 5. To assistwith documentation, a form was included inthe American Academy of Audiology (AAA)Clinical Practice Guidelines (Fig. 3).23 Becausenumerous options are currently available, theform is needed to record the FM/CI equip-ment, model information with serial numbers,processor and FM settings, and speech recog-nition results. Some information regarding theCI settings may only be available throughconsultation with the implant audiologist whodoes the mapping of the implant system. Forexample, the implant audiologist sets the mix-ing ratio in the mapping software. For theAdvanced Bionics Auria and Harmony speechprocessors, the mixing ratio may be 50/50,which results in equal emphasis for the signalfrom the microphone of the speech processorand FM signals, or 30/70, which results in theprocessor signal being attenuated by 10 dBrelative to the FM signal. Two other possiblesettings are (1) auxiliary input only, where theprocessor microphone is deactivated (i.e., FMonly), and (2) processor microphone only,where the auxiliary input is deactivated. Forthe Cochlear Corporation’s Freedom Speech

Table 5 Contact Information for

Manufacturers of FM Systems and Cochlear

Implants

For Cochlear Implants by:

Cochlear (800–523–5798):

www.cochlearamericas.com

Advanced Bionics (800–678–2575):

www.bionicear.com

MED-EL (888–633–3524): www.medel.com

For FM Systems by:

Phonak (800–679–4871): www.phonak.com

Oticon (800–526–3921): www.oticon.com

Sonovation (800–462–8336): www.avrsono.com

Comtek (800–469–3463): www.comtek.com


Figure 3 FM/CI verification form fromAmerican Academy of Audiology Clinical Practice Guidelines. FM,

frequency modulated; CI, cochlear implant; HA, hearing aid; HL, hearing level; B, behavioral. (Adapted from

American Academy of Audiology. AAA clinical practice guidelines: remote microphone hearing assistance

technologies for children and youth birth–21 years. Available at: http://www.audiology.org/resources/

documentlibrary/Documents/HATGuideline042208.pdf. Accessed July 24, 2009.)


processor, the mixing ratio may be 1:1—wherethere is equal emphasis for the processor andFM microphones—2:1, 3:1, or 10:1, whichcorrespond to the processor mic being attenu-ated by 6 dB, 9 dB, or 20 dB, respectively. The3:1 mixing ratio is the manufacturer’s defaultsetting.

The startup sequence for the implant andFM systems recommended by the manufac-turer also should be recorded on the documen-tation form. All of the components should be inthe off position when the FM receiver is con-nected to the processor. In most cases, theimplant is turned on first followed by the FMreceiver if it has a power switch. The FMtransmitter is then turned on last. There aresome exceptions to this sequence, however, anddeviations from the recommended order couldresult in malfunction.

Informed Assessment

Two steps to the informal assessment firstinvolve just the implant audiologist and secondthe educational audiologist who works with thestudent. Initially, the audiologist will want toverify that the signals are received through boththe local microphone on the CI speech pro-cessor and through the remote microphone onthe FM transmitter. Some speech processorsallow checking these signals through the use ofa listening earphone, as is shown in Fig. 4. ForCochlear’s Sprint and Freedom body-wornprocessors and Cochlear’s ESPrit 3G and Free-dom ear-level processors, the listening ear-phone can be attached at the same time as the

FM receiver. While listening through the lis-tening earphone, the FM and processor micro-phones can be verified by tappingeach microphone separately to determine thatboth signals are received at the speech pro-cessor. It is important to note that activation ofthe listening earphone requires an increasedbattery drain. Therefore, in the Cochlear ES-Prit 3G processor, there is an option to deac-tivate the port for the listening earphone. In thenewer Freedom processor by Cochlear,the listening earphone option remains activefor only 90 seconds to limit battery drain. Thecheck via the listening earphone must be madeas soon as the processor is activated.

Some CI speech processors do not haveseparate ports for the FM receiver and thelistening earphone, so the FM equipment willneed to be verified with an HA. Knowing thatthe FM receiver and transmitter are function-ing before connection to the CI will facilitatetroubleshooting. If the FM system is workingcorrectly with an HA, then any problems thatoccur when used with the CI system could beattributed to the connection of the FM receiverto the processor. The functioning of some FMreceivers, such as the Phonak MLCIþ, can beverified through the use of a small speaker asshow in Fig. 5. When the signal from the FMmicrophone is heard through the connection ofthe MLCIþ to the speaker, several compo-nents are verified including the transmitter andmicrophone, the battery in the MLCIþ re-ceiver, the volume setting on the MLCIþreceiver, the connector cord, and the FMreceiver channel.

Figure 4 Listening earphone attached to Co-

chlear Corporation’s ESPrit 3G Speech Processor.

Figure 5 Verification of Phonak MLCIþMLxS

FM receiver with Radio Shack speaker.


The second step in the informal assess-ment following the initial equipment check isto verify the arrangement on the user. A com-mon listening check arrangement for CI/FMverification with a child is to turn on thecombined CI/FM devices in the recommendedsequence and present simple directions whilestanding behind the child. If the child respondscorrectly, it could be the result of hearing viathe local microphone or through the FM trans-mitter microphone. Furthermore, if a childwears bilateral processors, it is tempting toget all the CI/FM devices in place and presentsimple speech while standing behind the child.However, when the child responds correctly,it is unknown if each speech processor wasfunctioning adequately.

If the child wears bilateral CIs or CI plusHA, each side should be verified separately.Verification of each side requires two steps:(1) confirm the child receives input from thelocal CI microphone, and (2) confirm the childreceives input from the FM microphone. TheCI microphone typically remains active whilethe FM system is connected so that the childhears the speaker as well as his or her own voiceand other voices nearby. One exception is theAdvanced Bionics body-worn Platinum SoundProcessor, which requires a separate micro-phone to be added to the FM receiver. Withthis additional microphone, the child can self-monitor and hear the signals nearby.

To confirm that the CI user receives inputfrom the local CI microphone while the FMsystem is connected, the FM microphoneshould be placed across the room where thereis no direct input while simple directions aregiven to the child by someone who is standingdirectly behind the child. For older children, amore challenging task may be used such asnaming the capital or a sports team associatedwith a given state. For younger children, speechawareness may be verified using play audiome-try techniques.

Following verification of the local micro-phone, the remote microphone on the FMtransmitter should be evaluated by repeatingthe speech recognition task while standing inan adjacent room. It is important to be farenough away that the child does not hearthrough the CI local microphone. In addition,

no visual speech recognition cues should beavailable so that the responses from the childcan be interpreted as verification of the signalsreceived through the CI/FM system. Afterverification of the local and remote micro-phones for one implant, it should be turnedoff and the process repeated for the secondimplant.

Formal Assessment

After the equipment has been verified throughinformal measures, a formal assessment ofbenefit can be performed to ensure the propersettings and relative benefits from the local andremote microphones. The purpose of this for-mal assessment is to determine if there is asignificant increase in speech recognition per-formance when listening through the CIþFMarrangement relative to the CI alone. Appro-priate speech materials for the child’s age thathave multiple lists must be selected. Back-ground noise should be added to degrade theperformance with the CI alone so that thebenefit of using the FM system with the CImay be observed. The noise may be speech-weighted continuous noise or fluctuating class-room noise. One possible test arrangementrecommended by the AAA Clinical PracticeGuidelines is shown in Fig. 6.23 The child isseated in the sound booth with two speakers,one at 0 and another at 180 degrees. Theexaminer is seated at the audiometer outsidethe sound booth with the FM transmitterin proper position but turned off. The speechis presented via monitored live voice at 50 dBhearing level (HL) while competition is pre-sented also at 50 dB HL. Although the live-voice testing adds variability compared withusing recorded materials, it is important toevaluate the speech recognition performancethrough the transmitter microphone ratherthan via a DAI connection that would berequired for recorded materials. Furthermore,the benefit received through the use of an FMtransmitter is typically several times greaterthan the possible variability.

The first step is to evaluate the speechrecognition performance via the CI alone at0 SNR. This behavioral test arrangementwithout the FM transmitter activated can be


referred to as BCI50/50, where the first letterrefers to the type of testing (B for behavioral),the next letters refer to the equipment used (CIfor cochlear implant; FM for frequency modu-lated system), and the numbers to refer to thesignal and competition levels. The first numberalways refers to the signal level, and the secondnumber refers to the competition level. If theinitial performance is better than 80%, then the

noise must be increased to �5 dB SNR andanother list presented.

Following the assessment of the perform-ance for BCI50/50, the FM transmitter isactivated, and the signal and noise levels remainthe same. If a �5 dB SNR was needed toreduce performance in the CI condition, thebenefit of adding the FM system is tested inthat same �5 dB SNR. If time permits, it is

Figure 6 Test arrangement for behavioral verification of speech recognition of CIþ FM arrangement. CI,

cochlear implant; FM, frequency modulated; B, behavioral; HA, hearing aid; SPL, sound pressure level

(Adapted from American Academy of Audiology. AAA clinical practice guidelines: remote microphone

hearing assistance technologies for children and youth birth–21 years. Available at: http://www.audiology.

org/resources/documentlibrary/Documents/HATGuideline.pdf. Accessed July 24, 2009.)


suggested that the measures be repeated inquiet (BCI50 and BCIFM50) to ensure thatadding the FM system does not alter the signalquality in the quiet arrangement.

The results of a similar protocol with eightstudents with CIs, mean age 8 years, conductedby Thibodeau et al24 resulted in an averageimprovement in speech recognition of 30%.Students were tested in an SNR of þ5 dB, asis recommended in the ASHA Desk Referen-ce’s guidelines,25 rather than the 0 dB SNRmentioned in the current AAA Clinical Prac-tice Guidelines.23 A variety of CIs and FMsystems were worn by the eight students, whowere evaluated at their individual user settings.All of the students showed improved perform-ance with the FM system without the benefit ofany fine tuning to the CI or FM settings. The95% confidence interval for improvementranged from 13 to 47%. Although the samplesize was small, one may consider 13%, the lowend of the confidence interval, as an estimate ofthe minimal improvement expected when anFM system is used with a CI at þ5 dB SNR.When tested with the currently recommended0 dB SNR, the improvements may be evengreater. If speech recognition does not improveby more than 13%, then changes to the FMreceiver settings or the FM device arrangementshould be considered.

One limitation of the AAA Clinical Prac-tice Guidelines is the use of a percent correctscoring because it has high variability. Forexample, Thornton and Raffin showed thatfor the typical speech recognition list that has25 words, a 20% difference is the minimumchange needed for significance if the initialscore without the FM system is between 16and 80%.26 Therefore, the use of an adaptivespeech recognition protocol may be considered.Schafer and Thibodeau (2006) used an adap-tive task involving simple phrases such as‘‘brush his teeth’’ and ‘‘comb his hair.’’16 Theyshowed an average 13 dB improvement inspeech recognition threshold in noise whenthe FM system was combined with a singleCI. An additional 3 dB improvement on aver-age was measured when the FM system wasbilateral rather than monaural. In percent cor-rect, this translates to an �30% increase whenadding the FM signal to the second side.

Another limitation of the formal assess-ment recommended by the AAA ClinicalPractice Guidelines is that the child mustbe capable of giving some consistent responseto speech.23 Adaptations to testing routinesmay be necessary and should always be notedin the records. For a very young child, thestimuli may be body parts presented in bothconditions, CI alone and then CIþFM.Although the probability of guessing ishigher than for a longer list of open setmaterials, it can be an indication that thechild is performing better with the CIþFMthan the CI alone.

When limited language developmentprecludes conducting verification with speechrecognition, speech awareness tasks may beused in the same test arrangement suggestedin Fig. 6. Rather than measuring the percent-age of words correctly repeated, the level atwhich the examiner’s voice may be detectedin the presence of 50 dB HL speech noisemay be determined first with the CI alone.Then with the CIþFM arrangement,speech awareness may be measured at thelowest limit of the audiometer because thevoice is sent via the FM transmitter at aconstant intensity level. If the speech aware-ness threshold does not improve within theCIþFM arrangement, further investigationis required to verify adequate functioning ofeach component.

SUMMARYChildren with CIs can receive significant ben-efit in speech recognition through the use of anFM system in noise environments. However,because of the numerous settings and equip-ment arrangements that may be selected for anindividual child, protocols and Web sites forequipment connections and verification of per-formance to determine the optimum settings/arrangement must be consulted. The AAAClinical Practice Guidelines for the Fittingand Monitoring of FM Systems suggest meth-ods for behavioral evaluation of FM systemswith implants. The average improvement inpercent correct score when using the FM sys-tem with the CI was 30%. Although theCIþFM fitting may be verified in the clinical


setting, it is especially critical to follow-upwith classroom observations for school-agechildren to ensure a child is using the FMtransmitter/receiver properly and that the childis responding to signals that are presentedthrough the FM transmitter in the educationalenvironment. As technological advances con-tinue, there will be increasingly novel ways forstudents to benefit from FM technology. Forexample, students may easily hear up to10 speakers in a room who are wearing FMtransmitters that are networked to transmit ona single channel. This may be especially usefulin situations with multiple instructors, such asmarching practice in a large high school bandprogram. In addition to multiple band directorsgiving instructions from around the field, thechallenge of transmission range across a foot-ball field can be addressed through the use of awide-area transmitter. This is just one exampleof how advances in technology will continue toexpand opportunities for persons with impairedhearing.

ABBREVIATIONSAAA American Academy of AudiologyASHA American Speech-Language-

Hearing AssociationBCI behavioral testing with the cochlear

implantCI cochlear implantDAI direct audio inputFM frequency modulatedHAT hearing assistive technologyHL hearing levelIDEA Individuals with Disabilities Educa-

tion ActIEP Individualized Education ProgramIFSP Individualized Family Service PlanSNR signal-to-noise ratioSPL sound pressure level

REFERENCES

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2. American Speech-Language-Hearing Association.Position Statement and Guidelines for AddressingAcoustics in Educational Settings. ASHA DeskReference 2005. Available at: www.asha.org/pdf

3. Knecht H, Nelson P, Whitelaw G, Feth L.Background noise levels and reverberation timesin unoccupied classrooms: predictions and meas-urements. Am J Audiol 2002;11:65–71

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6. Lewis MS, Crandell CC, Valente M, Horn JE.Speech perception in noise: directional micro-phones versus frequency modulation (FM) sys-tems. J Am Acad Audiol 2004;6:426–439

7. Ludena L, Thibodeau L. Evaluation of thebenefits of FM systems with cochlear implants.Presented at: Meeting of the American Speech-Language-Hearing Association; Nov. 18–22, 1993;Anaheim, CA

8. Davies M, Yellon L, Purdy S. Speech-in-noiseperception of children using cochlear implantsand FM systems. Aust N Z J Audiol 2001;23:52–62

9. Hanin L, Adams S. Use of sound-field FMsystems with multi-channel cochlear implants.Paper presented at: American Academy ofAudiology Convention; April 20–22, 1996; SaltLake City, UT

10. Crandell C, Holmes A, Flexer C, Payne M.Effects of soundfield FM amplification on thespeech recognition of listeners with cochlearimplants. Journal of Educational Audiology 1998;6:21–27

11. Anderson K, Goldstein H, Colodzin L, IglehartF. Benefit of S/N enhancing devices to speechperception of children listening in a typicalclassroom with hearing aids or a cochlear implant.Journal of Educational Audiology 2005;12:14–28

12. Iglehart F. Speech perception by students withcochlear implants using sound-field systems inclassrooms. Am J Audiol 2004;13:62–72

13. Schafer E, Thibodeau L. Speech recognitionabilities of adults using cochlear implants inter-faced with FM systems. J Am Acad Audiol 2004;15:678–691

14. Aaron R, Sonneveldt V, Arcaroli J, Holstad B.Optimizing microphone sensitivity settings ofpediatric Nucleus 24 cochlear implant patientsusing Phonak MicroLink CIþFM system.Poster presented at: ACCESS: Achieving Clear


Communication Employing Sound Solutions -Proceedings of the First International Confer-ence; Nov. 4–6, 2003; Chicago, IL

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16. Schafer E, Thibodeau L. Speech recognition innoise in children with bilateral cochlear implantswhile listening in bilateral, bimodal input, andFM-system arrangements. Am J Audiol 2006;15:114–126

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APPENDIX A Example of downloadable setup tips for interfacing frequency modulated

(FM) systems with implants. FM, frequency modulated; CI, cochlear implant.


APPENDIX A (Continued )


APPENDIX A (Continued )


APPENDIX B Example of downloadable user guide for frequency modulated (FM)

system with advanced bionics implant.


APPENDIX B (Continued )




