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26 FM Systems and Communication Access for Children Dawna Lewis and Leisha Eiten Introduction With the expansion of newborn hearing screening programs, infants with hearing loss are being identified at very early ages. Once hearing loss has been identified, an essential goal for pediatric audiologists is to provide children with communication access across a wide variety of listening environments. Although there are many factors that may impact communication access, audibility of the signal of interest is of primary importance. In addition to degree and configuration of hearing loss and amplification issues, audibility will be affected by distance between the sound source and listener, background noise, and reverberation. Communication Access As the distance between listeners and talkers varies throughout the day, the audibility of speech also will vary. This affects both the level of the primary signal reaching the listener’s ears and the level of that signal relative to background noise. For example, the overall level of a classroom teacher’s voice one meter from the listener is approximately 71 dB SPL and at four meters is approximately 61 dB SPL (Pearsons, Bennett, & Fidell, 1977). The level of average conversational speech at one meter is approximately 60 dB SPL (Cox & Moore, 1988). Instances of “conversational speech at one meter” may not be as common for children as for adults. Any parent of a young child will be quick to report that the distance between a talker and a young listener can vary considerably in a very short period of time. In addition, there will be many times when the talker and listener will not be face-to-face. For infants and young children, there will be times when the level of speech reaching their ears will be higher than that of speech at one meter. The level of speech at the near ear of an infant held in the cradle position is approximately 68 dB SPL and at the near ear of a young child held on the hip is approximately 76 dB SPL (Stelmachowicz, Mace, Kopun, & Carney, 1993). At other times the level of speech reaching an infant or young child’s ears may be lower, such as when the talker is farther away or the orientation of talkers is not face-to-face. For example, in the United States infants up to 20 pounds or one year of age are placed in rear-facing infant seats in the back seat of cars. Even when they move to front-facing car seats, it is recommended that they remain in the back seat until they are 12 years of age (American Red Cross, 2007). In this environment, the combined effects of distance, orientation, and car noise may significantly impact the audibility of speech. For school-age children, the ability to hear and understand verbal information is critical to learning in the classroom. However, in many schools poor classroom acoustics may impact this ability. Background noise can be defined as unwanted sounds that interfere with the primary signal. Noise can come from sources outside the school building (e.g., traffic, playground noise), inside the building but outside the classroom (e.g., sounds from the hallway, a nearby music class), or in the classroom (e.g., heating and air conditioning systems, the students themselves). Reverberation is the repeated reflection of sound and typically is reported in terms of the time it takes for a sound to decrease 60 dB from its original intensity once the sound stops (reverberation time). Long reverberation times may negatively impact perception of the primary speech signal. 554 Comprehensive Handbook of Pediatric Audiology In 2002, the American National Standards Institute (ANSI) published guidelines for classroom acoustics. These guidelines recommended maximum background noise levels of 35 dB(A) and maximum reverberations times of 0.6 to 0.7 seconds (ANSI, 2002) for typical classrooms. However, many classrooms fail to meet these criteria (Crandell, 1991; Crandell & Smaldino, 1994; Finitzo-Heiber, 1981). For example, Knecht, Nelson, Whitelaw, and Feth (2002) evaluated background noise levels and reverberation times in 32 elementary classrooms in three different school districts. Noise levels ranged from 34 to 66 dB(A), with only four classrooms having noise levels below the ANSI recommended levels. Reverberation times ranged from 0.2 to 1.27 seconds, with 13 classrooms exceeding the ANSI recommendations. The deleterious effects of noise, distance and reverberation on the speech perception of listeners with hearing loss are well known (e.g., Johnson, Stein, Broadway, & Markwalter, 1997; Ross & Giolas, 1971). Finitzo-Heiber and Tillman (1978) examined word recognition for 12 children with hearing loss and 12 children with normal hearing under various conditions of noise and reverberation. In all conditions, children with hearing loss performed more poorly than their peers with normal hearing. In adverse listening conditions, children with minimal hearing loss perform more poorly than their peers with normal hearing on tasks of speech perception in noise, especially when speech is directed to the poor ear and noise to the good ear for those with unilateral hearing loss (Bess, Klee, & Culbertson, 1986; Crandell, 1993; Kenworthy, Klee, & Tharpe, 1990; Ruscetta, Arjmand, & Pratt, 2005). The effects of distance, noise, and reverberation also may negatively impact some groups of children with normal hearing (e.g., Bradley & Sato, 2004; Crandell & Smaldino, 1996; Jamieson, Kranjc, Yu, & Hodgetts, 2004; Nelson, Kohnert, Sabur, & Shaw, 2005). Over 25 years ago, Zentall and Shaw (1980) compared the performance of children who had been identified as hyperactive with children who were not hyperactive on classroom tasks in the presence of background noise with a high linguistic content. When the task was familiar, the hyperactive children performed more poorly in high noise levels than the other children. When the task was unfamiliar, both groups performed poorly in high noise levels. More recently, Bradlow, Kraus, and Hayes (2003) showed that children with normal hearing who have learning disabilities (LD) also may experience difficulties understanding speech in adverse environments. They compared sentence perception in noise (−4 and −8 dB signal-to-noise ratio) for children with and without LD. Children with LD performed more poorly than their peers and were more adversely affected by decreasing signal-to-noise ratio. Children with normal hearing sensitivity who may be negatively impacted in adverse listening environments include young children and children who are English language learners, as well as those with the following: ■ ■ ■ ■ ■ ■ ■ ■ Attention deficit disorders, Auditory processing disorders, Developmental delays, Dyslexia, Recurrent middle-ear dysfunction, Speech and language disorders, History of conductive hearing loss, Hyperactivity. Challenges experienced by children with hearing loss in adverse listening environments may negatively impact development/performance in a number of areas. For example, difficulties perceiving speech in noise may impede a listener’s ability to follow conversations with multiple talkers. In addition, because most communication takes place in environments where noise is present, children with hearing loss may experience difficulties following conversations from a distance or acquiring information via overhearing. These difficulties may, in turn, affect speech and language development as well as social-emotional functioning. Subtle difficulties in language abilities might be expected to have an impact on advanced language skills, such as social reasoning (e.g., emotion understanding, theory of mind), discourse participation, complex narratives (justifying opinion, explanations), complex syntax (cohesive ties, complementation), and complex vocabulary. Difficulties in advanced language skills may, in turn, negatively affect psychosocial development. Numerous studies have suggested that children with hearing loss experience difficulties in areas such as self-esteem, stress, energy, peer relations, and social confidence (e.g., Bess, Dodd-Murphy, & Parker, 1998; Cappelli, Daniels, Durieux-Smith, McGrath, & Neuss, 1995; Loeb & Sarigiani, 1986; Oyler, Oyler, & Matkin, 1988). Educational performance also may be affected since the acoustic conditions in typical classroom environments are less than ideal (Blair, Peterson, & Viehweg, 1985; Brookhouser, Worthington, & Kelly, 1991; Culbertson & Gilbert, 1986; English & Church; 1999). Oyler et al. (1988) reported results of teacher questionnaires completed for children with unilateral hearing loss in a large school district. Twenty-four percent of these students had repeated at least one grade (compared to a district average of 2%) and 41% were receiving special services (compared to a district average of 8.6%). FM Systems and Communication Access for Children Listeners with hearing loss also may need to exert more effort than their peers with normal hearing in the same listening environment (Bess et al., 1998). Hicks and Tharpe (2002) found that children (5–11 yrs.) with mildto-moderate or high-frequency hearing loss expended more listening effort than children with normal hearing in both easy and difficult classroom listening situations. In 2006, the National Institute on Deafness and Other Communication Disorders at the National Institutes of Health sponsored a workshop on outcomes in research in children with mild-severe hearing loss. Among the outcomes from that workshop was a series of papers on the current state of knowledge regarding this population of children. Topics included psychosocial development (Moeller, 2007), language and literacy (Moeller, Tomblin, Yoshinaga-Itano, Connor, & Jerger, 2007), perceptual processing (Jerger, 2007), speech recognition and production (Eisenberg, 2007), as well as research considerations (Tomblin & Hebbeler, 2007) and implications for future research (Eisenberg et al., 2007). These papers provide an overview of many of the challenges experienced by children with hearing loss as well as directions for future research. Communication Solutions When hearing loss is first identified, hearing instruments typically are the most common technology option for achieving auditory access. Cochlear implants also are an option available for children with severe to profound hearing loss. Although these devices provide communication access in many situations, access will continue to be negatively impacted by noise, distance and reverberation (Anderson & Goldstein, 2004; Anderson, Goldstein, Colodzin, & Iglehart, 2005; Schafer & Thibodeau, 2006). Leavitt and Flexer (1991) used the Rapid Speech Transmission Index (RASTI) to examine the integrity of a speechlike signal at multiple seating positions in a classroom in relationship to a sound source at the front of the room. Perfect reproduction of the signal was only obtained 6 inches from the sound source. The integrity of the signal reaching typical seating positions in the classroom was far from ideal. Although direct correlations between RASTI scores and speech perception were not examined, these results reveal that the signal reaching a hearing instrument or cochlear implant microphone will be significantly degraded at all but the closest listening distances. One way to ensure a high quality speech input to the hearing instrument or cochlear implant is to maintain a close distance between the talker and listener; a solu- tion that is neither practical nor desirable. A more feasible solution is to place a microphone on the talker, transmitting the signal directly to a receiver worn by the listener. Remote microphone technologies can provide reproduction of close, un-degraded input signals with no reverberation effects and reduced impact of noise. A variety of remote-microphone hearing assistance technology (HAT) choices are available for classroom and home use. Large area systems are often used for educational and public venue applications. They may utilize induction loops/mats, sound-field FM (frequency modulation) or IR (infrared) transmission. Personal systems can be adapted to both in-school and out-of-school use. Personal remote-microphone systems include portable desktop FM or IR systems and individual FM systems. Expansion of the use of wireless connections has resulted in many questions about the use of Bluetooth technology as a remote-microphone HAT. Wikipedia defines Bluetooth as: A wireless protocol utilizing short-range communications technology facilitating data transmission over short distances from fixed and/or mobile devices, creating wireless personal area networks. The intent behind the development of Bluetooth was the creation of a single digital wireless protocol, capable of connecting multiple devices and overcoming problems arising from synchronization of these devices. (Wikipedia, 2008) A number of factors impact the application of Bluetooth technology as a remote microphone HAT option (Fabry, 2008). These include: ■ High power consumption, ■ Limited transmission range, ■ Latency (delay) in signal transmission. Though not a direct remote-microphone HAT, Bluetooth technology is being used as a means of connecting the listener to other electronic accessories such as cell phones, MP3 players, and computers. FM Solutions to Enhance Communication Access Frequency-modulated (FM) systems are an effective solution to the problems of noise, distance and reverberation because they use a microphone near a talker’s mouth to maintain a close listening distance between 555 556 Comprehensive Handbook of Pediatric Audiology the talker and the listener. FM systems use a low-power radio transmitter to send FM radio signals from this remote microphone to a miniature receiver worn by the listener. The FM transmitter/microphone is worn by the primary talker who is often a parent or teacher. The use of a remote microphone provides an advantage because the transmitted signal preserves a consistent input level even if the distance between the talker and the listener changes. Because the speech signal is picked up inches from the talker’s mouth, the transmitted signal maintains a positive signal-to-noise ratio advantage above the level of background noise without reverberation effects. FM Developments The changes in FM technology in the last 20 years have been significant. Prior to the mid 1990’s most FM systems transmitted in the 72- to 76-mHz frequency range. Transmission in this range was prone to interference and required strong antennae. Many FM systems used one dedicated transmission channel that could not be changed. FM receivers were body-worn units that originally required the hearing instruments to be removed entirely, and later could be connected to a child’s personal hearing instrument(s) via direct audio input cords. Environmental (local) microphones on these bodyworn receivers used linear amplification circuits with limited frequency-response adjustability. Prior to 1982, the local microphone was always on the body-worn receiver, which resulted in its placement at chest level (P. Henry, personal communication, May 30, 2008). One of the most significant changes in wireless technology has been the introduction of smaller and more flexible FM receiver options (Figure 26–1). Unlike the previous body-worn FM systems that had fixed receiver channels, today’s FM receivers have a large number of channels that can be easily changed or synchronized with different transmitters. Federal Communications Commission approval of additional FM channels in the 216- to 217-MHz bands (Federal Communications Commission, 1996) reduced the need for large antennae on the receiver. This, along with increased miniaturization of integrated circuitry, has allowed smaller FM receivers to be built. FM receivers are now designed to be ear-level devices that can be worn with a child’s personal hearing instruments or cochlear implants. Because of the change to ear-level FM receivers, the hearing instrument or cochlear implant microphone acts as the local microphone for the system. One advantage of ear-level FM systems is that the advanced circuitry and signal processing of digital hearing instruments or cochlear implants can be available to the child at the same time as the benefits of a remote (FM) microphone system. With the availability of ear-level receivers, the FM system has moved away from serving only as a classroom “auditory trainer” and now is utilized as hearing assistance technology (HAT) in many areas of the child’s home and family life. In any listening situation where background noise and reverberation or distance from the FIGURE 26–1. Examples of ear-level FM receivers coupled to behindthe-ear hearing instruments. FM Systems and Communication Access for Children talker makes understanding difficult, an FM system can be used. Conversations in the car, family trips to the zoo and recreational activities can all be enhanced. Current state-of-the-art FM receivers allow the audiologist to adjust or program the output level of the FM signal in relation to the local microphone signal to accommodate an individual child’s needs. In addition, a teacher or parent can quickly change or synchronize FM receiver channels as the child moves from classroom to classroom or from classroom to home. A range of integration options are available, including FM receivers fully integrated into the hearing instrument, modular or dedicated receivers for specific hearing instruments or cochlear implant models, and universal receivers that can be switched between hearing instrument and cochlear implant models and manufacturers. Ear-level FM-only devices also are now available for children with normal hearing who have special listening needs and may benefit from an improved signalto-noise ratio, such as those populations previously listed in this chapter. Changes in FM transmitters also have improved their flexibility. Current FM transmitters incorporate features such as directional microphones, cheek or boom microphone placement options, digital noise reduction circuitry and Bluetooth wireless compatibility for integration with cell phones, computers, and MP3 (e.g., iPod™) players. The choice of directional microphone settings allows flexibility in using the FM system in a variety of settings outside traditional classrooms. Some examples include using the transmitter as a conference microphone to hear a number of talkers in a group activity, or choosing a narrow directional setting to use the transmitter as a hand-held “pointer” microphone in a family gathering or party setting, where the main talker frequently changes. Recent advances in FM system technology include transmitters that incorporate adaptive FM levels to maintain ideal signal-tonoise ratios, as well as technology to adjust for varying voice levels and microphone placements. Talker networks can be activated to improve team-teaching with multiple FM transmitters active in a classroom. More functions are becoming available to assist teachers and families with troubleshooting and daily monitoring of FM system use. Audiologists who evaluate FM systems should be knowledgeable about current transmitter features and how those features impact daily use. Developmental Aspects of FM System Use Although FM systems have been utilized outside the classroom for a number of years (Benoit, 1989; Madell, 1992; Moeller, Donaghy, Beauchaine, Lewis, & Stelma- chowicz, 1996), body-worn FM systems were considered bulky and cumbersome, limiting their use beyond classroom environments. The introduction of the first integrated FM/hearing instrument combination in 1992 (Sonovation, 2008) and, more significantly, the miniaturization of FM receivers coupled directly to hearing instruments (Phonak, 2008) had a tremendous impact on the extension of FM system use beyond classroom environments and on their use with infants and young children. With the miniaturization of FM receivers, it has become more common for audiologists to recommend FM systems for infants and young children with hearing loss. Gabbard (2005) reported preliminary findings from a loaner FM project in the state of Colorado. Parents of nine children between the ages of 15 and 30 months completed a questionnaire designed to provide information regarding use and benefit from hearing instruments and FM systems. On average, hearing instruments were used 10 hours per day and FM systems were used four hours per day. Both were rated as easy to operate and comfortable for the children. Comments from parents suggested that the FM system benefits were seen in the expected areas of distance and noise and that they helped the children attend to speech in those environments. As stated earlier in this chapter, while very young infants spend much of their time in close proximity to talkers, there will be many situations where noise, distance, and reverberation become factors in their ability to hear and understand speech. Once the child is mobile, these situations become even more common. Also, unlike adults, children (especially young children) are in the process of learning speech and language. As such, they require good audibility to develop adequate speech and language skills. Thus, a primary reason for using FM systems with infants and young children is to provide them with a consistently audible signal during this crucial period of speech and language development. Anecdotally, concerns occasionally are expressed regarding a possible negative impact of FM system use on the development of localization abilities in infants and young children as well as on their ability to learn to understand speech in noise. Currently, no research exists to support either of these concerns. There also are practical reasons to question such concerns. It is important to remember that FM systems typically are not worn 100% of the time. There will be many situations in which infants and young children will be using only their hearing instruments. During those times, they will be receiving inputs from many directions, providing information about the location of the sound source. In addition, the signal of interest will arrive at the ears embedded within any background noises 557 558 Comprehensive Handbook of Pediatric Audiology within the environment. Even when the infant uses the FM system, it is most common that both the FM system and hearing instrument microphones are active simultaneously. Thus, the only input signal that would not be providing information about sound-source location would be that of the person wearing the FM microphone. Although the signal from the FM microphone will be received at a better SNR than it would through the hearing instruments alone, background noise is not eliminated completely. It also is important to remember that there are many adverse listening environments where practice will not be able to improve speech understanding for an individual with hearing loss. Recall the Leavitt and Flexer (1991) data presented previously in this chapter. If the signal reaching the ear has been severely degraded by noise, distance, and reverberation, even a hearing instrument that perfectly reproduces the signal will be presenting that severely degraded signal to the listener. As children grow, and before they reach school age, the potential benefit of FM system use enlarges as their listening experiences expand. Adverse listening environments where FM systems may improve audibility include car trips, family outings and group activities (e.g., dance lessons, children’s sports teams). As parents of children seen in our clinics have reported, the FM system increases the language learning opportunities the child experiences in daily life. When children reach school age, listening environments continue to expand. Although the ability to hear and understand verbal information is critical to learning in most classrooms, acoustics may impede audibility for many children with hearing loss and some groups of children with normal hearing. FM systems can improve audibility of the teacher’s voice, the voices of other students if they use the FM microphone, and audibility of the audio signal from televisions, videos, and computers. FM systems also may be used in extracurricular activities such as sports, dance, or drama. As they reach adolescence, students may be involved in after-school jobs or in volunteer organizations where utilizing FM systems can improve communication access in a variety of adverse listening environments. Especially in adolescence, the ability to couple a small FM receiver to a personal hearing instrument or to have the FM receiver incorporated into a BTE hearing instrument case makes utilization in a variety of listening environments much more feasible and attractive to users. As high school students transition to college or full-time employment, FM systems can continue to play a role in communication access. Those individuals who have benefited from FM system use for many years may be more likely to continue using the devices into adulthood, viewing them as an integral part of their hearing assistance technology. Audiologists can remain a vital resource in helping to examine technology options and funding sources for changing needs. FM Verification The development of ear-level FM receivers has meant that the hearing instrument microphone acts as the local microphone of the FM system. This allows the FM system user to hear other talkers and sounds in the environment and monitor one’s own voice, while still receiving a consistent input from the main talker using the FM microphone/transmitter. With most current hearing instrument circuits incorporating some type of nonlinear compression processing, verification of FM systems has been significantly impacted. Any verification of the function of the FM system is dependent on accurate evaluation of the hearing instrument processing. Hearing instrument processing options may include multiple channels, frequency compression/transposition and active noise-reduction. Previous FM system verification guidelines (ASHA, 1994, 2002) assumed local microphones functioned with single-channel linear circuitry. It has become clear in recent years that the rapid advances in hearing instrument and FM technology require a re-examination of FM system fitting and verification procedures. Another technological advance that has impacted FM system verification is the availability of hearing instrument test systems that offer speech-mapping using real speech inputs, rather than broadband noise or pure-tone inputs. As an input signal, real speech allows more accurate evaluation of how hearing instruments and FM systems respond to typical inputs. Speech is one of the primary signals that both FM systems and hearing instruments are designed to transmit and amplify. Advanced compression and noise reduction processing react differently to rapidly changing speech than they do to constant-level signals. Current guidelines recommend the use of calibrated real-speech inputs for the evaluation of hearing instrument and FM microphone responses. Electroacoustic FM System Verification There are three assumptions that guide current verification processes and assist in prioritizing testing (American Academy of Audiology [AAA], 2008a, 2008b). FM Systems and Communication Access for Children 1. Ear-level FM systems use the microphone of the hearing instrument as the local microphone, and the input from the FM microphone is processed by the hearing instrument circuitry. All verification measures of the relationship between the FM and hearing instrument microphones are based on the assumption that the hearing instrument processing has been adjusted to provide appropriate audibility and output for the individual user (AAA, 2004). Before verifying FM system performance, the audiologist must first verify that the hearing instrument is set appropriately and is meeting chosen prescriptive targets for a variety of speech input levels. True estimates of maximum output are obtained from input to the hearing instrument microphone, not the FM microphone. High compression ratios in the FM microphone/transmitter likely will prevent the hearing instrument from reaching its maximum output in response to FM input. The audiologist must also confirm that the hearing instrument is able to accept an FM input. 2. Most FM systems are worn with both the FM microphone and hearing instrument microphone(s) active at the same time. Therefore, all verification should be completed with the FM system and hearing instrument microphones active simultaneously. The FM system output level can then be adjusted in relationship to the hearing instrument response so as to preserve as much of a speech-to-noise benefit as possible. Traditionally, it has been recommended that the signal from the FM system maintain a 10 dB advantage over other signals coming to the local microphone. 3. Because of the nonlinear characteristics of current hearing instrument and FM system circuitry, different input levels to the two microphones will result in changing compression and gain results. This will create problems during electroacoustic verification measures as testing only can be completed sequentially, meaning that the hearing instrument microphone response is evaluated, followed by the FM microphone response. Current test systems do not allow for simultaneous inputs to both the hearing instrument and FM system microphones with separate outputs for the two inputs. Therefore, if the FM microphone response is evaluated using input levels that are typical for close microphone placements (80–95 dB SPL) and the hearing instrument microphone response is evaluated separately for conversational input levels (60–65 dB SPL), the compression parameters in response to these input signals will be significantly different than they will be when those signals reach both microphones simultaneously. Consequently, no valid comparisons could then be made between the FM system and hearing instrument responses if different input levels were tested sequen- tially. A thorough discussion of the impact of nonlinear compression characteristics and the use of sequential versus simultaneous measurements can be found in Platz (2004, 2006). Because current test systems do not allow simultaneous measures of hearing instrument and FM system microphones, electroacoustic verification protocols require that input levels to the FM microphone be less than actual use inputs. This is required to ensure that the hearing instrument response to an FM system input has the same compression characteristics as its response to input from the hearing instrument microphone. Verification of the relationship between FM system and hearing instrument responses can be completed with equal inputs to the FM system and hearing instrument microphones. The input level to both systems must be sufficiently low so that input compression in the FM transmitter is not activated, and compression in the hearing instrument will act equally on both the FM and hearing instrument test signals. The goal is to achieve equal outputs for equal inputs to the two microphones. This new approach to FM system verification is defined as transparency. With the FM receiver set at its default FM system gain position of +10 dB, the AAA Guidelines (AAA, 2008b) recommend a 65 dB SPL input to the hearing instrument microphone and a 65 dB SPL input to the FM microphone (in the HA+FM position) to evaluate for transparency (Figure 26–2). If the FM system output at this +10 dB setting is more than ±2 dB different from the hearing instrument output, adjustments (offsets) are made to the FM system level to achieve equal outputs, or transparency. When verified in this manner, the FM system has been shown to maintain a 10 dB signal-to-noise advantage in relationship to the hearing instrument when typical use inputs are presented simultaneously to both microphones (Platz, 2006). This 10 dB recommendation is offered as a general starting point for selecting the FM system level. It is based on the relationship between typical use inputs to the FM and hearing instrument microphones and the kneepoint for compression in the FM microphone/transmitter. For step-by-step verification procedures, see AAA (2008b). Because of the nonlinear nature of current hearing instrument and FM system technology, functional gain or amplified sound field threshold (ASFT) testing should never be used to verify FM system function. With the changing compression characteristics of both FM and hearing instrument microphones, no predictable relationship exists between amplified threshold information and FM system performance at typical use input levels. 559 560 Comprehensive Handbook of Pediatric Audiology FIGURE 26–2. SPLogram graph illustrating transparency measures with 65 dB SPL input to the hearing instrument (test 1) and 65 dB SPL input to the FM microphone (test 2). Circles are hearing thresholds, crosses are long-term average speech spectrum targets, and asterisks are maximum output targets. Real-Ear FM Verification Real-ear verification of FM systems can be completed for any hearing instrument + FM or FM-only combination. Due to the number of measures and possible adjustments needed when verifying FM receivers coupled to hearing instruments, electroacoustic verification in a test box is typically the more efficient approach. However, verification of ear-level FM-only systems requires special considerations. Ear-level FM-only fittings are primarily used with children/students who have normal or near-normal hearing. The child’s ability to hear oneself and others needs to be preserved; therefore, ear-level FM-only fittings are designed to be nonoccluding. Electroacoustic verification in a test box with the FM receiver coupled to a 2 cc coupler does not provide accurate information about how the system functions on the child’s ear when open-ear acoustics are preserved. In addition to open-ear acoustic considerations, the FM-only receiver is not coupled to personal hearing instruments and has no local microphone that amplifies other talkers. Using the same transparency approach previously described for FM receivers coupled to hearing instruments is not appropriate when verifying ear-level FM-only receivers. When verifying any nonoccluding fitting, two sound pathways must be considered (Figure 26–3): (1) the amplified sound pathway, which is the transmitted signal from the FM system. This is the primary signal of interest for verification; and (2) the direct or unamplified sound pathway, which includes unamplified portions of the main talker’s voice, other talkers, the FM user’s own voice and background noise. In a nonoccluding fitting, unamplified signals can move freely into and out of the ear canal. At the same time, much of the low-frequency regions of the amplified input signal leak out of the open ear canal (Hoover, Stelmachowicz, & Lewis, 2000). This will affect the expectations and targets for the FM system response in the child’s nonoccluded ear (Figure 26–4). FM Systems and Communication Access for Children FIGURE 26–3. Two sound paths into the ear when wearing a nonoccluding FM system. FIGURE 26–4. Graphic representation of amplified (gray arrows) and direct (black arrows) sound as it enters (left) and leaves (right) the nonoccluded ear canal. Verification priorities for ear-level FM-only fittings are two-fold. First, maximum output should be confirmed in the child’s ear. Because most FM-only devices are fitted on normal-hearing ears, it is critical to verify the maximum output of the system using a high-level pure-tone input. Output or volume control adjustments may be needed to prevent exposure to excessive sound pressure levels. Second, the FM system should maintain consistent audibility and comfort for the main talker’s voice. Recommended use settings are determined based on the response of the FM-only system to close speech inputs (1-6” from talker’s mouth). Specific procedures for real-ear verification of FMonly receivers will vary depending on the real-ear test system that is utilized. These procedures will be influenced by how the real-ear reference microphone is used during testing and whether FM specific inputs and targets are available in the test system (AAA, 2008b; Eiten, 2008; Eiten & Lewis, 2008). For step-by-step real-ear verification procedures, see AAA (2008b). Behavioral FM System Verification Behavioral verification of FM systems using speech perception measures is a recommended option when an appropriate sound-field test environment is available (AAA, 2008b). Although behavioral verification 561 562 Comprehensive Handbook of Pediatric Audiology is not a substitute for electroacoustic verification for HA+FM and FM-only systems, it remains the primary method of verification for FM systems coupled to cochlear implants. When using speech perception tasks to verify FM system performance, testing should be completed under listening conditions that are representative of the child’s typical listening environments. Priority is given to testing in noise. The child’s performance when the FM microphone is not active (unaided, hearing instrument only, cochlear implant only) is compared to performance with the FM microphone active under the same noise conditions. The vocabulary and language level of the child must be considered when choosing this verification option. Testing with adaptive or variable noise and/or speech levels is not recommended as part of the behavioral verification of FM systems. When testing is conducted with varying speech levels and a fixed noise level, the input to the FM microphone will most likely be significantly lower than that found in normal use (Boothroyd & Iglehart, 1998). Similarly, when testing is conducted with varying noise levels and a fixed speech level at the FM microphone, the resulting noise levels may exceed typical classroom noise levels. For these reasons, the use of such testing to determine a threshold signal-to-noise ratio is not recommended for behavioral FM system verification. These types of procedures are appropriate when evaluating performance with personal hearing instruments or cochlear implants alone for determining HAT candidacy. Some currently available speech-in-noise tests that use adaptive or variable speech and/or noise levels include the BKBSIN (Bamford-Kowal-Bench Speech-In-Noise test; Etymotic Research, 2005) and HINT-C (Hearing-In-Noise Test-Child; Nilsson, Soli, & Gelnett, 1996). Conclusions Research continues to support the need for hearing assistance technology in poor acoustic environments for children with hearing loss and for children with normal hearing who have special listening needs. Developments in FM system technology have expanded their use and now provide audiologists with many options for addressing communication access needs. Miniature, ear-level FM receivers are appropriate for children of all ages both in and out of school. Fitting and verification techniques have evolved to keep pace with technological developments in both hearing instruments and FM systems. It is important for audiologists who work with children to understand current methods for selecting and fitting FM systems in order to address the specific communication needs of each child. Audiologists must also incorporate appropriate verification guidelines into their clinical practice and be aware of future advances as they become available. References American Academy of Audiology. (2004). Pediatric amplification guideline. Audiology Today, 16(2), 46–53. American Academy of Audiology. (2008a). 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