J Am Acad Audiol 25:529-540 (2014)

Fitting and Verification of Frequency Modulation Systems on Children with Normal Hearing DOI: 10.3766/jaaa.25.6.3 Erin C. Schafer Danielle Bryant Katie Sanders Nicole Baldus Katherine Algier Audrey Lewis Jordan Traber Paige Layden Aneeqa Amin

Abstract Background: Several recent investigations support the use of frequency modulation (FM) systems in children with normal hearing and auditory processing or listening disorders such as those diagnosed with auditory processing disorders, autism spectrum disorders, attention-deficit hyperactivity disorder, Friedreich ataxia, and dyslexia. The American Academy of Audiology (AAA) published suggested procedures, but these guidelines do not cite research evidence to support the validity of the recommended procedures for fitting and verifying nonoccluding open-ear FM systems on children with normal hearing. Documenting the validity of these fitting procedures is critical to maximize the potential FM-system benefit in the abovementioned populations of children with normal hearing and those with auditory-listening problems. Purpose: The primary goal of this investigation was to determine the validity of the AAA real-ear approach to fitting FM systems on children with normal hearing. The secondary goal of this study was to examine speech-recognition performance in noise and loudness ratings without and with FM systems in children with normal hearing sensitivity. Research Design: A two-group, cross-sectional design was used in the present study. Study Sample: Twenty-six typically functioning children, ages 5-12 yr, with normal hearing sensitivity participated in the study. Intervention: Participants used a nonoccluding open-ear FM receiver during laboratory-based testing. Data Collection and Analysis: Participants completed three laboratory tests: (1) real-ear measures, (2) speech recognition performance in noise, and (3) loudness ratings. Four real-ear measures were con­ ducted to (1) verify that measured output met prescribed-gain targets across the 1000-4000 Hz frequency range for speech stimuli, (2) confirm that the FM-receiver volume did not exceed predicted uncomfortable loudness levels, and (3 and 4) measure changes to the real-ear unaided response when placing the FM receiver in the child’s ear. After completion of the fitting, speech recognition in noise at a -5 signal-to-noise ratio and loudness ratings at a +5 signal-to-noise ratio were measured in four conditions: (1) no FM system, (2) FM receiver on the right ear, (3) FM receiver on the left ear, and (4) bilateral FM system. Results: The results of this study suggested that the slightly modified AAA real-ear measurement pro­ cedures resulted in a valid fitting of one FM system on children with normal hearing. On average, pre­ scriptive targets were met for 1000, 2000,3000, and 4000 Hz within 3 dB, and maximum output of the FM

Department of Speech and Hearing Sciences, University of North Texas, Denton, TX Erin C. Schafer, Department of Speech and Hearing Sciences, University of North Texas, 1155 Union Circle #305010, Denton, TX 76203-5017' E-mail: [email protected] Funding for this study was provided by Phonak AG. The funds were used to compensate participants for their time, efforts, and mileage to the test center. The authors of this manuscript received no monetary compensation related to the study. The equipment for the study was loaned to the investigators by Phonak AG and returned after the study was completed.

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Jo u rn a l of the A m erican Academy of Audiology/Volume 25, Number 6, 2014

system never exceeded and was significantly lower than predicted uncomfortable loudness levels for the children. There was a minimal change in the real-ear unaided response when the open-ear FM receiver was placed into the ear. Use of the FM system on one or both ears resulted in significantly better speech recognition in noise relative to a no-FM condition, and the unilateral and bilateral FM receivers resulted in a comfortably loud signal when listening in background noise. Conclusions: Real-ear measures are critical for obtaining an appropriate fit of an FM system on children with normal hearing. Key Words: Fitting, FM systems, normal hearing Abbreviations: AAA = American Academy of Audiology; ADHD = attention-deficit/hyperactivity disorder; APD = auditory processing disorder; ASD = autism spectrum disorder; BKB-SIN = Bamford-Kowal-Bench Speech-in-Noise test; DSL = Desired Sensation Level; FM = frequency modulation; HAT = hearingassistance technology; MPO = maximum power output; REOR = real-ear occluded response; REUR = real-ear unaided response; RM ANOVA = repeated-measures analysis of variance; SNR = signal-tonoise radio; UCL = uncomfortable loudness level

INTRODUCTION ecent investigations have supported the efficacy and effectiveness of personal, ear-level frequency modulation (FM) systems for improving speechrecognition performance in noise and auditory behaviors of children who have normal hearing but exhibit signifi­ cantly poorer auditory performance relative to typically functioning peers (Johnston et al, 2009; Purdy et al, 2009; Ranee et al, 2010, 2012; Hornickel et al, 2012; Schafer et al, 2013; Sharma et al, 2012). For example, in two studies on children diagnosed with auditory processing disorder (APD), laboratory testing and trial periods with personal FM systems revealed signif­ icant improvements in speech-recognition performance in noise, academic performance, psychosocial behavior, phonological awareness, and sentence recall (Johnston et al, 2009; Sharma et al, 2012). Two other studies inves­ tigated the potential benefits of personal FM systems for children and adults diagnosed with Friedreich ataxia, a neurodegenerative disease resulting in multisensory decline (Ranee et al, 2010,2012). In these studies, Ranee et al (2010, 2012) reported that personal FM systems improve speech-recognition performance in noise to the level of typically functioning peers. In another study, Schafer et al (2013) evaluated chil­ dren with autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) to examine speech recognition and classroom behavior without and with a personal FM system. Relative to the no-FM trial period, use of the FM system in the classroom resulted in significantly improved teacher-rated and investiga­ tor-observed behavior, and the FM system improved the children’s speech-recognition performance to the level of typically functioning peers. In another investi­ gation, Alcantara et al (2004) reported poorer speech recognition in noise of children with ASD compared with typically functioning peers. Additionally, several studies on children with ASD showed abnormal physio­ logical encoding of auditory stimuli in quiet and noisy

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listening conditions from the level of the brainstem to the cortex (Barry et al, 2002; Russo et al, 2009a, b). Two studies investigated the potential benefit of FM systems for children with reading delay or dyslexia (Purdy et al, 2009; Hornickel et al, 2012). In the first study, Purdy et al (2009) evaluated the potential benefit of FM systems for children with reading delay via stu­ dent and teacher questionnaires. The 46 children who used the FM system for a 6-wk trial period reported less difficulty hearing in challenging listening situations compared with a control group m atched for age and reading abilities, and teachers rated children as having significantly better listening when the FM system was used. In the second study, Hornickel et al (2012) eval­ uated the potential benefits of bilateral personal FM systems for children who were diagnosed with dyslexia by comparing groups who did versus those who did not use an FM system for a trial period. Results of the study showed that children who used the FM system for a 1-yr period exhibited significantly improved phonological awareness, reading ability, and neural-response consis­ tency to speech stimuli on auditory brainstem response testing. The findings in the Hornickel study were well supported by recent anim al research th a t revealed alterations in phoneme processing in the auditory cor­ tex of rats when they had a reduced expression of the gene associated with dyslexia (Centanni et al, 2014). Given the highly positive benefits of personal FM sys­ tems reported in the aforementioned studies on children with APD, ASD, ADHD, Friedreich ataxia, and dyslexia, evidence-based procedures for fitting and verification of these devices will be required to optimize device settings and maximize benefit for children with normal hearing sensitivity. In 2008, the American Academy of Audiology (AAA) published clinical practice guidelines for fitting remotemicrophone, hearing-assistance technology (HAT) on children with normal hearing sensitivity, hearing aids, and cochlear implants. This guideline recommends th a t children w ith norm al hearing sensitivity use a

FM System s on Children w ith Normal Hearing/Schafer et al

(1) targeted-area, desktop audio distribution system; (2) whole-classroom audio distribution system; or (3) non­ occluding, ear-level, FM-only receiver. When the FMonly receiver is fitted on children with normal hearing, real-ear measures with speech-weighted inputs are rec­ ommended over electroacoustic testing because the 2 cc coupler used in the electroacoustic measures does not simulate the acoustics of a nonoccluding, open-ear fitting of an FM system. As described in the guideline, the realear measures are conducted with placement of the FM transm itter microphone in a test box sound chamber or in a calibrated location in the soundfield. Once the location of the FM transm itter microphone has been selected, the audiologist should determine (1) the realear-saturation response at full volume using a pure-tone sweep signal at 85 or 90 dB SPL, (2) volume-adjusted response to meet prescribed targets using speech or speech-weighted stim uli at typical FM microphone intensities (80-85 dB SPL for a chest-level microphone, 90-95 dB SPL for a boom microphone), and (3) the realear-saturation response at the volum e-adjusted level using the same stimuli described in step 1. After comple­ tion of the fitting, behavioral verification in the form of speech-recognition testing in quiet and in noise at a 0 dB signal-to-noise ratio (SNR) is recommended to determine th a t the device improves performance relative to a noFM condition. It is important to note th at neither AAA test approach provides an exact representation of the amplified sound through the FM receiver as well as the direct, unamplified sound entering the ear canal. As described, this AAA guideline provides specific recommendations for the fitting and verification of FM systems for children with normal hearing sensitivity. However, the guidelines do not cite research evidence to support the validity of the recommended procedures for fitting and verifying nonoccluding open-ear FM sys­ tem fittings on children with normal hearing sensitivity. Documenting the validity of this objective, real-ear ap­ proach to fitting open-ear FM systems is critical to maximize the potential FM-system benefit in several populations of children with normal hearing and those with auditory-listening problems. The objective nature of this approach is even more critical in specific popula­ tions of children with normal hearing who may be nonver­ bal (i.e., ASD) or have intellectual disabilities, significant expressive and receptive language delays, or motor dis­ orders th at preclude behavioral testing with the FM system. Given the increasing use of open-ear FM systems on the previously mentioned populations of children with norm al hearing sensitivity, the prim ary goal of this investigation was to determ ine the validity of the AAA (2008) real-ear approach to fitting and verifying FM systems on children with normal hearing. The AAArecommended real-ear procedures were modified slightly in this study to improve the efficiency of the measures

and to explore potential changes to the natural ear canal resonance as a function of the FM receiver placement in the ear. The secondary goal of this study was to examine speech-recognition performance in noise and loudness ratings without and with FM systems in children with normal hearing sensitivity.

METHODS Participants Study participants included a total of 26 children with typical speech and language development per parent report and normal hearing thresholds of less than 25 dB HL from 250 to 6000 Hz. Case history forms completed by the parents of the children revealed typ­ ical development with no reports of speech/language disorders, chronic otitis media, special education ser­ vices, or diagnosed disability. The children were sepa­ rated into two age groups to examine the potential effect of age on the ability to meet prescriptive fitting targets with the FM receiver and to determine the potential for greater change to ear canal resonance with placement of the FM receiver in the ears of younger children. The first group consisted of 12 children who were 5 to 8 yr old (M = 6.6 yr; SD = 1.3), and the second group included 14 children who were 9 to 12 yr old (M = 10 yr; SD = 0.94).

Equipment Participants were fit with bilateral Phonak iSense Micro FM receivers with Standard xReceivers and small domes. The receiver in the canal (i.e., Standard xReceiver) used in this study represents a new and smaller option for coupling to the iSense Micro th at was not originally released on the market. The FM receivers were synched to a Phonak inspiro transm itter. Real-ear m easures were conducted using an Audioscan Verifit. Speech rec­ ognition and loudness ratings were conducted in a doublewalled soundbooth, and stimuli for these measures were presented from a clinical audiometer (GS1 61), two CD players (Sony 5-CD Changer; Sony CD-Radio-CassetteCorder CFD-ZW755), and four loudspeakers (two GrasonStadler Standard; two Sony CFD-ZW755). The signal loudspeaker was located at 0° relative to the participant’s head at a distance of 5 feet from the listener. When the FM transm itter was in use, the microphone of the trans­ mitter was placed on a stand that was located at 6 inches in front of the single-coned loudspeaker. The three noise loudspeakers were located at 90°, 180°, and 270° azi­ muth, all at a distance of 4 feet from the listener’s head. Stimuli intensities were determined with a sound level meter (Larson Davis Model 824). The noise loudspeakers were a distance of approximately 5 feet (speakers at 90° and 270°) or 8 feet (speaker at 180°) from the location of

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the transm itter microphone. All noise speakers were calibrated separately to provide equal output as well as together to provide the appropriate combined output. Stim uli Stimuli for the real-ear measures will be described in detail in the Procedures section below. The speech recogni­ tion sentence stimuli were from the Bamford-Kowal-Bench Speech-in-Noise (BKB-SIN; Etymotic Research, 2005) test, which is recorded on a CD. The sentences, presented at 0° azimuth, were fixed at 60 dBA at the location of the participant’s head. Fixed-level, uncorrelated, multitalker babble, also on the BKB-SIN CD, was presented from the three noise loudspeakers at a combined noise level of 65 dBA at the participant’s head. At the location of the transm itter microphone, speech was presented at 75.8 dBA, and noise from the three loudspeakers was at 61.4 dBA. The -5 dB SNR for the BKB-SIN stimuli was deter­ mined with pilot data from three children with normal hearing sensitivity. The use of the 0 SNR recommended by the AAA (2008) guideline with spatial separation of the speech and noise stimuli on the BKB-SIN resulted in ceiling effects (100%) in one or more conditions in these three children. The -5 SNR as well as the use of three noise speakers helped to avoid ceiling effects and resulted in a sufficiently difficult task for these normal­ hearing children. The signal levels used in the present study (i.e., 60/65 dBA) are not unreasonable given the fact that noise levels in occupied classrooms are reported to range from 56-76 dBA during different types of classroom activities such as silent reading, one person speaking, individual work, group work, and group work with move­ ment (Shield and Dockrell, 2004). If the teacher’s voice was 60 dBA at the listener’s ear, as simulated in the present study, the SNR at the child’s ear in a typical classroom would range from +4 to -16 dB when using the noise levels from the Shield and Dockrell study. Loudness-scale ratings were conducted using a scale created by the examiners (Fig. 1), which was posted on the wall in the soundbooth. Before testing, the exam­ iners explained to the children each loudness level on the scale. Children were asked to point to the loudness level of the m an’s speech after listening to four BKBSIN sentences at a +5 SNR with speech presented at 60 dBA from a loudspeaker at 0° azimuth and noise pre­ sented at 55 dBA from one loudspeaker at 180° azimuth in four conditions: (1) no FM system, (2) FM receiver on the right ear, (3) FM receiver on the left ear, and (4) bilateral FM receivers. A more favorable SNR was used for the loudness-scaling procedure to ensure audibility of the speech signal, and thus the ability to rate the speech signal, in every condition. The number corre­ sponding to the child-indicated loudness level in each condition was recorded by the examiners.

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Figure 1. Loudness scaling chart used by the participants to rate levels of loudness in no-FM and FM-system conditions.

Procedures Three separate laboratory tests were included in the investigation: real-ear measures, speech-recognition per­ formance in noise, and loudness ratings. An overview of all test procedures is provided in Table 1. Before testing, an informed consent form was signed by the parent, and children older than age 7 yr completed an assent form. Once consent/assent to participate was obtained, parents completed a case history form, and pure-tone hearing thresholds were determined for the children in each ear at frequencies ranging from 250 to 6000 Hz. Real-Ear M easures All 26 participants (52 ears) completed fitting and real-ear verification portions of the investigation, which involved four separate measurements. The goals of the fitting with the Audioscan Verifit were (1) to ensure that the output from the child’s ear met the Desired Sensation Level (DSL) v5 (Scollie et al, 2005) prescriptive targets, (2) to ensure that output from the FM receiver did not exceed the maximum power output (MPO) recommenda­ tions generated by the DSL software, and (3) to examine changes to the unaided ear canal resonance resulting from the placement of the Standard xReceiver and small dome in the participant’s ear. As mentioned in the Intro­ duction section, the following procedures reflect slightly modified AAA (2008) recommendations to improve the efficiency of the measures (MPO only conducted after targets met) and to measure changes to the real-ear unaided response (REUR) when the Standard xReceiver was placed in the ear. The real-ear saturation response

FM Systems on Children with Normal Hearing/Schafer et al Table 1. Outline of Test Measures and Conditions in the Study Test Measure Real-ear

Test Conditions

Description

M easurem ent 1

Attem pt to meet DSL targets at 1000, 2000, and 4000 kHz

M easurem ent 2

Ensure MPO from FM receiver did not exceed recom m ended

M easurem ent 3

Real-ear aided response with FM receiver off

M easurem ent 4

REUR

No FM

No system used during this test condition

m aximum output

Speech recognition in noise: - 5 SNR

Loudness ratings: + 5 SNR

FM right

FM receiver used on right ear

FM left

FM receiver used on left ear

FM bilateral

FM receiver used on both ears

No FM

No system used during this test condition

FM right

FM receiver used on right ear

FM left

FM receiver used on left ear

FM bilateral

FM receiver used on both ears

(MPO) was not conducted at full volume, as suggested by the AAA (2008) procedures, because the volume level in this device is preprogrammed by the audiologist and can­ not be adjusted by the child. Therefore, the MPO at full volume is likely not relevant to the fitting or actual lis­ tening levels that will be used by the child. Before the fitting with the Audioscan Verifit was begun, “DSL child” was selected as the target for all children, and the “child’s age” was selected in the Verifit Speechmap function under Audiometry. The participant’s hearing thresholds for both ears were then entered into the Ver­ ifit software. Measurement 1 on each separate ear was focused on meeting the DSL targets provided by the software at 1000, 2000, and 4000 Hz, as recommended by AAA (2008) for open-ear fittings. During this measurement, the FM transm itter microphone was placed in the test box and the real-ear microphone was placed in the par­ ticipant’s ear. The reference microphone in the sound chamber of the Verifit was active, and as a result, the reference microphone on the child’s ear was deactivated during these measurements. On the Verifit, “FM” was selected as the instrum ent, and “On-ear” was selected as the mode. Testing was initiated with a standard speech passage (Speech-std[l]) presented in the test chamber at intensities appropriate for a chest-level transm itter microphone (i.e., 84 dB SPL). If the DSL targets at 1000, 2000, and 4000 Hz were not met, the volume of the FM receiver was adjusted with the Phonak inspiro trans­ m itter by entering the “receiver options menu,” select­ ing “set FM volume,” and selecting a volume level. After completion of the volume adjustment, the test measure­ m ent was repeated. This process was repeated until ta r­ gets were met as closely as possible for 1000-4000 Hz. The measurement was saved, and the final receivervolume setting was recorded. Measurement 2 on each ear was conducted to ensure th at the MPO from the FM receiver would not exceed the recommended maximum output (i.e., estimated

uncomfortable loudness level [UCL]) from the DSL soft­ ware. The same settings were used on the Verfit as those used for the first measurement; however, MPO was selected as the stimulus instead of the standard speech signal. The examiner compared visually the MPO with the estimated UCL provided on the Verifit screen. Measurements 3 and 4 on each ear were conducted to examine potential changes in unaided ear canal reso­ nance when placing the Standard xReceiver and small dome into the ear. For the third measurement, the Pho­ nak inspiro transm itter microphone was turned off, and the settings on the Verifit were changed to an “Open” instrument. This measurement was conducted with standard speech input at 65 dB SPL. The fourth mea­ surem ent was identical to the third measurement, but the iSense Micro was removed from the ear (i.e., realear unaided response; REUR). M easurements for all participants were stored for data analysis. S p eech -R eco g n itio n P erform an ce in N oise

After the fitting was applied, all participants were tested at a —5 dB SNR with four randomly selected BKB-SIN list pairs (16 sentences), one in each of the randomly ordered test conditions: no FM system, FM receiver on the right ear, FM receiver on the left ear, and bilateral FM receivers. The three FM-system condi­ tions were included to examine a potential ear effect or bilateral-listening effect for this sample of children with normal hearing. Sentences in each list pair were scored for the percentage of key words repeated correctly. RESULTS L ou d n ess R atin gs

After the completion of the speech-recognition testing in a particular condition, all participants were asked to listen to four BKB-SIN sentences from a fifth randomly

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selected list pair at a +5 SNR using the rating scale shown in Figure 1. A separate rating was determined and recorded for each of the four listening conditions: (1) no FM system, (2) FM receiver on the right ear, (3) FM receiver on the left ear, and (4) bilateral FM receivers. R eal-E ar M easures

During Measurement 1, the FM-receiver volume was adjusted from the default FM volume level of 0 to approximate the child DSL targets for each ear. The vol­ ume level of 0 represents a standard default output level of the iSense receiver, and volume adjustments with the Phonak inspiro transm itter allow for an increase or decrease in output relative to this default. With FM vol­ ume settings that most closely met the DSL targets, the average receiver volume level for the 5- to 8-yr-old chil­ dren was 5.6 (SD = 3.5), which suggests the need for sub­ stantially increased output relative to the default output provided at the volume level of 0. Four children had the same volume between ears, whereas the remainder had volume levels that differed by two (n = 7) to four (n = 1) units. The average volume for the 9-to-12-yr-old children was 4.7(SD = 3.3). Eleven of these children had the same volume between ears, whereas the remainder had vol­ ume levels that differed by two (n = 2) or four (n = 1) units. For both age groups combined, the volume level necessary to approximate DSL targets correlated weakly (r = 0.12) with the age of the child. Average DSL targets and average output from Meas­ urement 1 are shown in Figure 2 for 1000-4000 Hz for both age groups combined. A three-way, repeated-measures analysis of variance (RM ANOVA) was conducted to

5

determine if the output in Measurement 1 differed sig­ nificantly from the DSL targets (i.e., output type: mea­ sured; target) and to examine potential effects of age group (5-8 yr; 9-12 yr) and frequency (1000-4000 Hz). The analysis revealed no significant main effect of output type (F[l,416] = 0.98; p = 0.33), no significant main effect of age group (F[l,416] = 2.0; p = 0.17), and a significant main effect of frequency (F[3,416] = 30.3;p < 0.00001). There was also a significant interaction effect between frequency and output type (F| 3,4161= 9.0; p = 0.00004). The significant difference across the fre­ quencies was irrelevant for the main effect analysis because differences in targets and outputs would be expected across the frequencies. However, the two-way interaction effect between frequency and output type suggested that, at some frequencies, targets were signifi­ cantly different from the measured outputs. Specifically, according to the post hoc Tukey-Kram er multiplecomparison test, targets were not significantly different from measured outputs at 1000 and 2000 Hz. Conversely, targets and measured outputs at 3000 and 4000 Hz were significantly different; however, the 2-3 dB average dif­ ferences may not be clinically relevant. In most cases, the target could not be met at 3000 and 4000 Hz because the maximum volume setting was in use. In the remaining cases, a volume level that allowed for targets to be met in the high frequencies resulted in an output that was too high in the low frequencies. According to Measurement 2 with the MPO stimuli, the receiver-volume settings determined in Measure­ ment 1 resulted in output that never exceeded and was often substantially lower than the estimated UCL curve from the DSL software for frequencies ranging from

110

100

90 80 Sh

so 70 -

Target - a - Output

pa X)

60 50 40 30 ------------1000

2000 3000 Frequency (Hz)

4000

Figure 2. Average DSL v5 targets and average real-ear output measured with a 65 dB SPL speech input. Vertical lines represent 1 SD.

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FM S y stem s o n C h ild ren w ith N orm al H earing/Schafer et al

250-6000 Hz bilaterally in all children (Fig. 3). A threeway ANOVA w ith th e independent variables of output type (estim ated UCL; m easured MPO), age group, and frequency (250-6000 Hz) was conducted to exam ine any significant differences. The analysis suggested a sig­ nificant m ain effect of output type (F[l,728] = 1302.3; p < 0.00001), no significant m ain effect of age group (F[ 1,728] = 1.5; p = 0.23), and a significant m ain effect of frequency CF[ 6,728] = 7703.6; p < 0.00001). Also, a sig­ nificant interaction effect was detected between output type and frequency CF[6,728] = 612.8;p < 0.00001). Post hoc analyses for the significant effect of output type showed th a t the m easured average output across the fre­ quencies of 250-6000 Hz was significantly lower (p < 0.05) th an the predicted UCLs. As with Measurement 1, th e significant m ain effect of frequency was expected because differences in estim ated UCL and m easured outputs would be expected across the frequencies. Finally, the post hoc analysis on the significant interaction effect between output type and frequency revealed that, at each frequency examined, the m easured output was signifi­ cantly lower than the estim ated UCL. M easurements 3 and 4 were conducted to determ ine th e presence the REUR and real-ear occluded response (REOR) w ith th e S tandard xReceiver placed in the child’s ear. Average output for M easurements 3 and 4 are shown in Figure 4 for 1000-4000 Hz for both age groups combined. A RM ANOVA was conducted to determ ine if th e responses from M easurements 3 and 4 differed significantly and also to examine the potential effects of age group and frequency. The analysis revealed a significant m ain effect of m easu rem en t (F[l,416] = 8.9; p = 0.006), no significant m ain effect of age group

CF[1,416] = 0.02; p = 0.90), and a significant m ain effect of frequency (F[3,416] = 14.8; p < 0.00001). There was also a significant interaction effect betw een the m ea­ surem ent and the frequency CF[3,416] = 29.7; p < 0.00001). Post hoc analyses on the m easurem ent sug­ gested a significantly higher (p < 0.05) REUR by an average of 1 dB, which is not clinically relevant and could be the resu lt of test-retest variability. W hen we examined the interaction effect between the m easure­ m ent and the frequency, the output was significantly lower for the REOR compared w ith the REUR at 3000 and 4000 Hz by an average 3 dB at both frequen­ cies. On the other hand, there was no significant differ­ ence between Measurements 3 and 4 at 1000 and 2000 Hz (0-1 dB average differences). Speech Recognition in Noise After the fitting was applied, all participants (n = 26) completed the four speech-recognition conditions all at a -5 SNR to validate the fitting procedure and to exam ­ ine the presence of a bilateral-listening effect for this sample. Average percent-correct perform ance across the four conditions is shown in Figure 5. According to a two-way RM ANOVA w ith the independent variables of condition and age, there was a significant m ain effect of condition CF[3,104] = 86.2; p < 0.00001) and a signifi­ cant m ain effect of age group (F[l,104] = 5.9; p = 0.02). Post hoc analysis suggested th a t the no-FM condition resulted in significantly poorer perform ance (p < 0.05) compared w ith all other FM conditions, w ith no signifi­ cant differences (p > 0.05) among comparisons of the rem aining FM conditions. On average, the children

—0—UCL -□ -O u tp u t

250

500

1000 2000 3000 Frequency (Hz)

4000

6000

F ig u re 3. Estimated average UCL using DSL v5 and average real-ear output measured with a sequence of 85 dB SPL tone bursts. Vertical lines represent 1 SD.

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Journal of the American Academy of Audiology/Volume 25, Number 6, 2014

Figure 4. Real-ear output measured in an unaided and in an aided, FM-inactive condition using a 65 dB SPL speech input.

who were 5-8 yr old had significantly better speech rec­ ognition in noise than the children who were 9—12 yr old. The cause of this age-group discrepancy will be addressed under Discussion. L o u d n e s s R a tin g s

The purpose of the loudness ratings was to ensure a comfortable FM-receiver volume when listening to audible speech in the presence of background noise and to examine the presence of binaural summation in the bilateral FM condition relative to the unilateral

FM conditions. The average ratings across the four lis­ tening conditions are shown in Figure 6. Average ratings in all four conditions are associated with a “comfortable, but slightly soft” or “comfortable” listening level for all conditions (see Figure 1 for rating scale). An RM ANOVA was conducted, and the results suggested a significant main effect of condition (F[3,104] = 3.7; p = 0.02) and no significant main effect of age group (F[l,104] = 3.2; p = 0.09). The post hoc analysis suggested th a t p ar­ ticipants rated the FM -right and bilateral-FM con­ ditions as significantly louder (p < 0.05) th an the no-FM condition. There was no significant difference

JS

a. in

■ 5-8 yrs • 9-12yrs

o

U

Listening Condition

Figure 5. Average speech-recognition performance in noise at a -5 SNR in four listening conditions. Vertical lines represent 1 SD.

536

FM System s on Children w ith Normal Hearing/Schafer et al

6.0

5.0

Left FM

Right FM

Bilateral FM

No FM

Listening Condition

F igure 6. Average loudness ratings at a +5 SNR in four listening conditions. Vertical lines represent 1 SD.

(p > 0.05) in loudness ratings between the FM-left and no-FM condition.

DISCUSSION he results suggested th at the AAA (2008) real-ear measurement procedures, which were slightly modified in the present study, resulted in a valid fitting of the FM system used in this study on children with normal hearing. The results of Measurement 1 suggested that, on average, DSL prescriptive targets were met for 1000, 2000, 3000, and 4000 Hz within 3 dB. Measure­ ment 2 showed that the maximum output never exceeded and was significantly lower than predicted UCL for the children. Measurements 3 and 4 revealed a minimal dif­ ference between the REUR and REOR with the Standard xReceiver in the ear. After application of the real-ear fitting procedure, the validity of the real-ear measures was assessed through behavioral testing of speech rec­ ognition in noise and perceived loudness. Use of the sys­ tem on one or both ears resulted in significantly better speech recognition in noise relative to a no-FM condition, and the unilateral and bilateral FM receivers resulted in a comfortably loud signal when listening in background noise. The following paragraphs will expand on the data and clinical relevance of each real-ear measurement and behavioral test as well as the limitations of the proposed real-ear measures and results of this study.

T

Real-ear M ea su rem en t 1 On average, the adjustment of the volume of the iSense Micro to meet DSL targets was successful in achieving the desired real-ear output from 1000 to 4000 Hz in 5- to

12-yr-old children. These data support the use of the AAA (2008) real-ear measurements for fitting FM sys­ tems, at least for the system tested in the present study. This real-ear measurement, in particular, is critical when fitting an FM system on a child with normal hearing given the large range of normal hearing thresholds (i.e., -10 to 24 dB HL) and the variability in children’s REUR, which was 10-15 dB in the present study (Fig. 4). Rather than selecting an arbitrary or manufacturerrecommended FM-volume setting, this procedure uses a prescriptive strategy to determine the appropriate FMreceiver volume for a particular child’s hearing thresh­ olds and ear canal acoustics. According to the statistical analysis, significant dif­ ferences were detected between the target and mea­ sured output at 3000 and 4000 Hz but not at 1000 and 2000 Hz, although the average differences between ta r­ get and output at 3000 and 4000 Hz were only 2-3 dB, which is an acceptable variation from target. When the individual data were examined across the 52 ears, it was difficult to meet the target (within 3 dB) at every frequency on a particular ear, and in several children, the target was not met at most frequencies when the highest FM-receiver volume was used. To address this issue, manufacturers of FM systems for this population may consider additional flexibility of programming to allow the audiologist to increase overall and frequencyspecific FM-receiver volume. Of course, what cannot be simulated with these real-ear measurements is the potential for increased output at certain frequencies from natural sound entering the ear canal via the open fit of the FM receiver (i.e., direct, unamplified sound path). The inability to measure natural gain is related to the placement of the FM transm itter microphone

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Journal of the American Academy o f Audiology/Volume 25, Number 6, 2014

into the sound chamber, which is then closed during Measurement 1. As a result, the speech stimulus is not presented simultaneously to the FM transm itter microphone and the ear canal during testing, and thus, only amplified sound from the FM system is measured in the ear canal. The inability to measure the unampli­ fied and amplified sound in the ear canal is one major disadvantage of this real-ear procedure. The other realear procedure recommended in the AAA guidelines, with the FM transm itter microphone placed in a cali­ brated location in the soundfield, was attempted by the examiners but was unsuccessful. When attempting this procedure, we could not determine how to achieve the appropriate test location and distance for the child, FM transm itter, and soundfield loudspeaker. In our lab­ oratory, we did not have the physical space to adequately separate the FM transm itter and FM receiver worn by the participant. Future research will need to be con­ ducted to develop a better, simultaneous (i.e., measures amplified and unamplified sound) real-ear approach to testing FM systems.

differences in output occurred at 3000 and 4000 Hz where there was a slightly lower REOR (M = 3 dB). In our opinion, this difference in REUR and REOR is negligible; however, this difference could be detrimen­ tal for sounds not directed to the FM microphone such as speech from a student in the same classroom. This receiver in the canal represents a new and slightly smaller receiver option for the ear canal. Similar to Measure­ ments 1 and 2, the primary disadvantage of this real-ear procedure is the inability to simulate a more realistic listening experience where unamplified and amplified sound would enter the ear canal. Measurements 3 and 4 were not recommended by the AAA (2008) guideline and may not be necessary unless the audiologist has some concern about the FM receiver and dome causing substantial occlusion. However, the results of this study only address the fitting of this par­ ticular Phonak FM receiver, Standard xReceiver, and small dome. As a result, audiologists may wish to com­ pare REUR and REOR with other coupling methods and products.

R eal-E ar M ea su rem en t 2

S p eech R e co g n itio n an d L ou d n ess R atin gs

The FM-receiver volume settings that were necessary to meet DSL targets did not result in real-ear outputs (i.e., MPO) that exceeded the estimated UCL, based on the child’s age, on any of the 52 ears (Fig. 3). In fact, the measured output was significantly lower than the esti­ mate at each frequency measured (250-6000 Hz). How­ ever, as with Measurement 1, only the amplified signal was measured, which did not include any natural, unam­ plified sound entering the ear canal through the open-fit FM receiver. As a result, higher output would be expected during typical use. Given the large average differences between estimated UCL and MPO with this device, it is not likely that the combined amplified and unamplified signals would exceed the child’s UCL during use of the device, with the exception of extremely noisy environ­ ments such as the gymnasiums and cafeterias at school. The MPO closest to the estimated UCL occurred at 2000, 3000, and 4000 Hz with average differences ranging from 6.6-10.6 dB. To avoid any potential issues with the UCL, some children may need to use the device on a trial basis in these particularly noisy environments to ensure a com­ fortable listening experience. Children with severe lan­ guage disorders or ASD, who are not able to articulate levels of listening comfort, will need to be observed closely when using the device in extremely noisy environments or should only use the device during academic courses or at home.

To validate th at the above-described real-ear mea­ sures resulted in a beneficial and comfortable fitting, we determined speech recognition in noise and loudness ratings after the fitting of the FM system. It is impor­ tant to note th at the fitting was conducted in a quiet environment. However, when the Phonak iSense Micro and Phonak inspiro transm itter is used in everyday environments, the Dynamic FM feature is activated when the background noise exceeds 57 dB SPL. The goal of Dynamic FM is to provide the listener with a con­ sistent SNR by systematically increasing the volume of the FM receiver as the noise level increases. The speech recognition test condition in the present study repre­ sented a particularly challenging listening environ­ ment with speech presented at 60 dBA and noise at 65 dBA (-5 SNR). As a result, the Dynamic FM feature was active during all speech-recognition test conditions. The speech-recognition testing showed a large and significant benefit of the FM receiver(s) in both age groups in the FM right, FM left, and bilateral FM con­ ditions relative to the no-FM condition. When the differ­ ence between bilateral FM and no FM was calculated, there was an average 49% and 69% improvement in speech recognition of the 5- to 8-yr old and 9- to 12-yr old children, respectively. Across all of the speech rec­ ognition conditions, the younger age group showed sig­ nificantly better performance than the older age group. This appears to be the result of poorer performance of three children in the 9- to 12 -50- old sample. The exact cause of their poorer performance in noise could not be explained by hearing thresholds or any information pro­ vided on the case history form completed by the parents.

R eal-E ar M ea su rem en ts 3 an d 4

Overall, there was a minimal difference between REUR and REOR at the frequencies tested. The largest

53S

PM System s on Children w ith Normal Hearing/Schafer et al

It is possible th at the fitting algorithm was slightly dif­ ferent for the older children, but at the same time, the Dynamic FM feature (i.e., adaptive FM gain) would have been activated for all children during the speech recognition conditions in noise resulting in FM volume increases for all children. The results of the speech-recognition testing provide strong support for the fitting. However, it is important to recognize th at these results do not directly predict average speech-recognition benefit or comprehension in the classroom. The stimuli and poor SNR used in the present study were specifically designed to chal­ lenge the participants. In real classroom environments, the speech and noise are dynamic and, throughout the day, consist of good and poor SNRs. Therefore, the actual speech-recognition benefit achieved by a child in a classroom will also be dynamic and will be highly dependent on numerous factors including the presence of disabilities; cognition; behavior; attention; sensory processing; visual distractions; comprehension abil­ ities; and SNR in the environment, which would be par­ tially addressed with the Dynamic FM feature used in this study’s device. Given these influential variables, the audiologist will need to include multiple test mea­ sures into a school-based evaluation for HAT including speech recognition in noise, classroom observations, acoustic measurements of the classroom, teacher ques­ tionnaires, and a trial period with the FM system (AAA, 2008; Schafer, 2010; Schafer et al, 2013). For use of HAT at home, the audiologist may include test measures in the evaluation such as speech recognition in noise, parent questionnaires, child questionnaires, assessment of the home environment (AAA, 2008), and a trial period with the device. If the SNR (-5 dB) used for speech recognition in noise testing in the present study is too difficult for a particular child, the SNR may be adjusted to meet the needs of the student. When loudness ratings were examined, there was no significant effect of age group despite noticeable differ­ ences in the average group ratings in the no-FM condi­ tion (Fig. 6). These findings may be related to the variability in the ratings provided by the participants. The examiners believe that concept of loudness ratings was a difficult task for many of the younger children in the study, which may have influenced the reliability of some ratings. However, it is evident from Figure 6 that both age groups provided similar loudness ratings across all FM listening conditions. As a result, the uni­ lateral and bilateral FM fittings were comfortable and did not result in any perceivable binaural-summation effects that would necessitate changes to the fit of one versus two FM receivers. Although the speech recogni­ tion and loudness ratings in the present study did not reveal any significant differences in performance or com­ fort with one versus two receivers, the authors always recommend the use of two receivers for populations of

children with normal hearing sensitivity. Rothpletz et al. (2004) showed th at children with normal hearing who were listening to degraded signals gained substan­ tial improvements in speech recognition in noise when listening in a binaural listening condition versus an asymmetrical listening condition. The children with normal hearing in the present study were not receiving a degraded signal; therefore, the lack of bilateral benefit from the bilateral FM system may have been less than what would be expected for children with auditory pro­ cessing issues in noise.

CONCLUSIONS n summary, the results of this investigation support the use of the slightly modified AAA (2008) real-ear measures for fitting nonoccluding, ear-level, FM-only receivers on children with normal hearing sensitivity. Although typically functioning children were used in this study, all methods and most results should be appli­ cable to populations with disorders. In fact, a follow-up study is underway in our laboratory with 12 children diagnosed with one or more disability (ASD, ADHD, APD, language disorder), and initial analyses suggest th at these children perform favorably and tolerate the same real-ear fitting approach and DSL algorithms used in the present study. Given the results of the study and the variability in necessary FM-volume settings across the 5- to 12-yr-old children, we recommend con­ ducting real-ear measures to verify that prescriptive gain targets are met and estimated UCLs are not exceeded. If occlusion of the ear canal is a concern, par­ ticularly in a child with a small ear canal, the audiolo­ gist may consider measuring changes in output without and with the inactive receiver in the ear canal. Behav­ ioral speech-recognition performance and loudness ra t­ ings indicated significant benefit and comfort from the FM system and validated the fitting procedures used in this study.

I

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