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9

Fitting Strategies for Patients with Unilateral Loss

MICHAEL VALENTE, MAUREEN VALENTE, JANE ENRIETTO, KAREN M. LAYTON

Introduction Definition of Unilateral Patients with unilateral hearing loss typi- For the purposes of this chapter, unilateral cally have difficulty with (1) locating the hearing loss is defined as unaidable hearing sources of , (2) understanding speech in one and normal hearing [15 dB hear- when the signal arrives on the side of the ing level (HL) or better at 250 to 8000 Hz] in poorer ear, and (3) understanding speech in the opposite ear. Unaidable hearing is de- background noise (especially if the noise is fined as an ear having one or more of the fol- arriving on the side of the better ear). Pa- lowing characteristics: tients with unilateral hearing loss can pres- 1. Profound sensorineural hearing loss so ent a challenge to the dispensing audiolo- that amplified sound cannot be heard gist. The dispenser can choose a traditional with any degree of usefulness. dispensing model, which suggests provid- 2. Very poor word recognition score. ing extensive counseling on the communica- 3. Marked intolerance for amplified tion problems likely to occur as a result of . unilateral hearing loss, or recommend con- tralateral routing of the signal (CROS) am- plification to the good ear. On the other Incidence and Prevalence of Unilateral hand, the dispenser could explore with the Hearing Loss patient several alternate fitting strategies. This chapter focuses on the problems as- Although information is available regarding sociated with unilateral hearing loss and the incidence of unilateral hearing loss in provides information beneficial for dis- children (Bess and Tharpe, 1986; Kielmovitch pensers who want to explore alternative fit- and Friedman, 1988; Oyler et al, 1988; Brook- ting strategies for patients with unilateral houser et al, 1991), there is less information hearing loss. regarding the incidence of unilateral hearing

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loss in adults. Much of the information re- (1991) estimated that nearly seven million garding the incidence of unilateral hearing Americans have some degree of unilateral loss in adults involves sudden hearing loss, hearing loss. They quoted a prevalence rate often as a result of illness (Van Dishoeck and for school-aged children of 3:1000 in which Bichman, 1957; Petheram, 1976; Shanon et al, hearing loss was 45 dB HL or greater, which 1982), otologic surgery (acoustic neuroma), increased to 13:1000 if milder losses (26 to 45 or nonotologic surgery (Arenberg et al, 1972; dB HL) were included. They provided no Wright and Saunders, 1975; Plasse et al, 1980; information for children under age 3 years. Millen et al, 1982). The authors reported that Everberg (1960) re- Rambur (1989) reported that the incidence vealed a greater prevalence of unilateral of sudden unilateral hearing loss in the deafness among males (62.3%) than females United States was approximately 40,000 per (37.7%); he also reported a higher rate of left year, equally distributed between males and ear impairment (52.5%). Of interest is that females. Her report and reports by Bye unilateral impairment is generally detected (1978) and Berg and Pallasch (1981) indicate later in life because speech and language that sudden hearing loss usually occurs in skills appear to develop more normally. Of adolescents or older adults, with the greatest Everberg’s 122 subjects, 52.5% were identi- incidence occurring between 30 and 60 years fied after the first year in school. Bess and of age (Megighian, 1986). Hearing loss was Tharpe (1986) cited Tarkkanen and Aho usually unilateral, although Rambur (1989) (1966) to corroborate these findings, with an and Megighian (1986) found bilateral sud- average identification age of 6 years. The den hearing loss in up to 17% of the cases. hearing loss in 50% of the children was not Bergenius (1985) studied vestibular find- detected until 7 years of age or older, which ings in sensorineural hearing loss. Of 1,635 the authors find unacceptable in view of the patients undergoing audiologic evaluation deleterious effects unilateral hearing loss has from 1979 to 1982, 12.9% fulfilled the criteria on academic performance (see below) (Bess for “pure unilateral sensorineural hearing and Tharpe, 1986). loss or alone.” Noury and Katsarkas Brookhouser et al (1991) investigated uni- (1989) cited various references that stated lateral hearing loss in children, the results that sudden hearing loss has no sexual of which may lend information related to predilection and a mean age of occurrence adult populations. They also reported an in- between 40 and 47 years of age. Sudden cidence in unilateral hearing loss of 3:1000 hearing loss is usually unilateral, with bilat- when including hearing loss greater than 45 eral involvement reported in 7% of the cases. dB HL or 13:1000 when including hearing Although statistics related to children may loss between 26 and 45 dB HL. They re- not easily be generalized to adults, they may ported that Kinney (1953) found 1307 cases provide general trends. Oyler et al (1988) ex- of sensorineural hearing loss in children, of amined the incidence of unilateral hearing which 48% were unilateral. Of 1829 consecu- loss in a large school district of approxi- tive patients studied by Brookhouser et al, mately 54,000 students, with a second part of 690 (37.7%) had asymmetrical hearing loss. the study looking at academic performance. Of those 690 cases, 391 (56.7%) were described The prevalence of unilateral sensorineural as having isolated unilateral sensorineural hearing loss was approximately 2 students hearing loss. When 67 of these 391 cases per 1000. In 106 children, there were slightly were deleted from the study (due to various more males than females and almost twice as factors, such as conductive component), the many children with hearing loss in the right authors reported on the results of 324 chil- ear as the left ear. Almost three fourths of the dren; 62% were males and 38% were fe- hearing losses were sensorineural (N = 78). males. The left ear was affected in 52% and Bess and Tharpe (1986) and Tharpe and Bess the right ear was affected in 48%. This find- 12843.C09.PGS 3/8/02 11:11 AM Page 255

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ing was not statistically significant. The in- (acquired). Congenital unilateral hearing vestigators felt their statistics were consis- loss can be genetic (dominant, recessive, or tent with previous investigators’ prepon- sex-linked) or nongenetic [cytomegalovirus derance of males over females. However, (CMV), low birth weight, syphilis, , previous findings of greater right-sided ver- or anoxia]. In addition, unilateral hearing sus left-sided hearing losses were not sup- loss can be acquired at any age, and the re- ported by this study. sulting hearing loss may be progressive, Tieri et al (1988) observed 280 cases of uni- fluctuating, or sudden. lateral sensorineural hearing loss from 1979 to Several investigators have examined the 1986. The age range was 8 months to 12 years, etiology of unilateral hearing loss in chil- with a mean age at diagnosis of 7.6 years; 62% dren. In each investigation, the cause of the were males and 38% females. They felt these unilateral hearing loss was unknown (idio- findings were in agreement with those of pathic) in the majority of cases. Kinney Tarkkanen and Aho (1966) and Hallmo et al (1953) reported that of known causes in a se- (1986). The right ear was affected in 49.6% of ries of 310 children, , measles, and cases and the left ear in 50.3% cases. Degree of mumps were the most common etiologies. hearing loss ranged from mild to profound, Tieri et al (1988) examined 280 children be- with 79.3% falling in the latter range. In addi- tween 1979 and 1986 and found that the etio- tion, 250 audiograms revealed a flat configu- logic factor was known in only 23% of the ration. Tieri et al, noting that incidence is diffi- cases, and that of the known factors mumps cult to evaluate, cited the following statistics: was predominant. Everberg (1960) evalu- Everberg (1960), an incidence rate of 0.06%; ated 122 children with unilateral hearing Tarkkanen and Aho (1966), 0.09%; and Kinney loss and noted that congenital factors are (1953), 8.5%. Tieri et al noted that 24.7% of responsible for approximately 75% of the their children were diagnosed before the age cases, with heredity being the major causal of 6 years, as compared with the 47.5% under factor. 7 years noted by Everberg and the 7% before With the recent technologic advances in school age noted by Hallmo et al. They con- the treatment of neonates, additional risk cluded that school age diagnosis may be a factors for unilateral hearing loss have result of critical teacher observation, older emerged. These include persistent pulmo- children’s awareness of sensory skills, and nary hypertension of the newborn (PPHN) exposure to a greater number of infectious (Hendricks-Munoz and Walton, 1988), hy- diseases. perbilirubinemia (Bergman et al, 1985), Although no clear-cut statistic is available intraventricular hemorrhage (Slack et al, regarding the incidence of unilateral sensori- 1986), and low birth weight (Clark and neural hearing loss in adults, perhaps the Conry (1979). Although these factors are findings summarized earlier in this chapter most typically associated with bilateral hear- may provide some insight. The incidence of ing loss, unilateral hearing loss has also been unilateral hearing loss is of such significance reported. that audiologists and otologists should be Other less common causal agents have prepared to see these patients on a regular also been reported and include chicken pox basis and plan rehabilitation programs to (Hendricks-Munoz and Walton, 1988), CMV help maximize the residual hearing in both (Pass et al, 1980), Meniere’s disease (Hen- the affected and better ear. dricks-Munoz and Walton, 1988), trauma (Hendricks-Munoz and Walton, 1988), and perilymphatic fistula (Goodhill et al, 1973). Etiologies Middle ear disease, such as congenital Unilateral hearing loss can be present at and , has been birth (congenital) or at any time after birth known to cause unilateral hearing loss. 12843.C09.PGS 3/8/02 11:11 AM Page 256

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Many external ear deformities such as con- to cause unilateral hearing loss in approxi- genital atresia of the external auditory canal mately 50% of all cases (Schuknecht, 1991). are typically unilateral. Head trauma, leading to a transverse (sen- Many of the causes of childhood unilat- sorineural hearing loss) or longitudinal eral hearing loss can also cause adult-onset (conductive hearing loss) fracture of the or acquired unilateral hearing loss. Mumps temporal bone can precipitate a unilateral and other viral etiologies (Wilson et al, 1983) hearing loss. In addition, syphilis, Cogan’s such as viral are well-known syndrome, postotologic surgical loss, multi- causes of unilateral hearing loss in adults. ple sclerosis, perilymphatic fistula, herpes Other well-documented etiologies include zoster oticus, hemorrhage, thrombosis, em- vascular pathologies (occlusion, emboli, bolism, spasms, aneurysm, and sludging of hemorrhage) (Arenberg et al, 1972; Wright blood have been reported to cause unilateral and Saunders, 1975), neoplasms (acoustic hearing loss (Jerger and Jerger, 1981). Table neuroma), and labyrinth membrane rup- 9–1 summarizes many etiologies that have tures (perilymphatic fistula) (Goodhill et al, been reported to cause unilateral hearing 1973). Meniere’s disease has been reported loss in children and adults.

Table 9–1. Summary of Etiologies Resulting in Unilateral Hearing Loss

Study N Pathology Percentage

Kinney (1953) 310 Meningitis Measles Mumps Tieri et al (1988) 280 Mumps 23 Everberg (1960) 122 Congenital: heredity 75 Other etiologies: Chicken pox Cogan’s syndrome Congenital cholesteatoma Cytomegalovirus Embolism External ear deformities Herpes zoster oticus Hyperbilirubinemia Hypertension Intraventricular hemorrhage Labyrinth membrane rupture Low birth weight Meniere’s disease Multiple sclerosis Neoplasms Otitis media Perilymph fistula Persistent pulmonary Postotologic surgical Sludging of blood Syphilis Thrombosis Trauma Vascular pathologies Viral labyrinthitis 12843.C09.PGS 3/8/02 11:11 AM Page 257

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Problems Associated with Unilateral ing situation for a normal hearing patient. Hearing Loss Clearly, if this listening situation is reversed, then the unilaterally impaired patient is not at The individual with unilateral hearing loss a disadvantage relative to the normal listener. can no longer enjoy the advantages of binau- Valente (1982) summarizes a series of studies ral hearing. For the interested reader, the ad- concerning speech recognition for monaural vantages of binaural listening are covered in direct versus monaural indirect listening. The greater detail in Chapters 7 and 8 and in Va- advantage of monaural direct to monaural in- lente (1982). These advantages include direct word recognition can be as high as 20% 1. elimination of the head shadow effect, to 50% depending on the type of signal, noise, 2. presence of the squelch effect, azimuth, and SNR. 3. improved localization, and 4. presence of binaural summation. Squelch Effect Giolas and Wark (1967), Koenig (1950), and Head Shadow Effect others (Keys, 1947; Markides, 1977; Gulick The head shadow effect for spondee words et al, 1989) have described the advantages was initially described by Tillman et al (1963), of binaural hearing to “squelch” or reduce who reported that, as a spondee word arrives the deleterious effects of background noise from one side of the head (near ear or monau- and/or reverberation on speech recognition. ral direct), the intensity of the signal is attenu- Gulick et al (1989) reported improved binau- ated across the head by an average overall ral “release from masking,” particularly when level of 6.4 dB before the signal reaches the time, intensity, or phase differences of the sig- opposite ear (far ear or monaural indirect). nal are present (i.e., signal presented at any Furthermore, the head shadow effect in- azimuth in a sound field other than 0 degrees, creases as a function of frequency. For exam- and these differences are not present for the ple, at frequencies above 2000 Hz, the inten- masker (i.e., masker presented at 0-degree az- sity level of the signal to the far ear can be as imuth). That is, the presence of differences in much as 15 to 20 dB less intense than the level time, intensity, and/or phase of the speech of the signal at the near ear (Markides, 1977; signal between the two will result in im- Hodgson, 1986). proved performance compared with the situa- The reduction in signal level in the higher tion in which these differences are not present frequencies at the far ear can have a signifi- between the two ears. cant impact on speech recognition. For exam- ple, if speech is delivered to the impaired ear Localization side and noise directed to the good side (monaural indirect) at the same intensity Gulick et al (1989) devoted a section of their level, the patient can experience great dif- text to , describing various ficulties in communicating. In this situation, studies that have contributed to our knowl- the speech signal is reduced overall by 6.4 dB edge. Explanations of directional hearing to the good ear due to the head shadow effect, have centered on differences in stimulation but the noise is unattenuated to the good ear. between the two ears in time and intensity As a result, a –6.4 dB signal-to-noise ratio (i.e., duplex theory of localization) and the in- (SNR) is present at the good ear. Furthermore, tegration of this information for improved a +6.4 dB SNR is present at the impaired ear sound localization. In particular, the normal (monaural direct) because the noise is attenu- listener uses interaural time (low-frequency ated by 6.4 dB but the signal is unattenuated. cue) and intensity differences (high-frequency In essence, the unilaterally impaired patient cue) for improved localization in the horizon- has a 13-dB deficit relative to the same listen- tal plane. If there were a large difference in 12843.C09.PGS 3/8/02 11:11 AM Page 258

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hearing between the ears, localization skills ties. Oyler et al (1988) reported a failure would be reduced. rate of 2% for grades kindergarten through eight, which is approximately 10 times Binaural Summation greater than in the normal-hearing popula- tion. Some children were even reported to Brookhouser et al (1991) report that individ- have dropped out of school. Brookhouser et uals with binaural hearing demonstrate im- al (1991) reiterated that children with unilat- proved thresholds for pure-tone and speech eral loss may be disadvantaged in the class- stimuli that are presented binaurally (Keys, room, particularly if noise occurs close to the 1947; Shaw et al, 1947; Pollack, 1948; Breaky better ear. These children do not have the and Davis, 1949; Reynolds, 1960). Gulick et advantages of normal-hearing children in al (1989) described this binaural summation selecting meaningful signals mixed with phenomenon as an advantage in processing background noise. Localizing a sound source information (specifically, detecting thresh- in horizontal plane may also present diffi- old) with two ears over listening with one culty. Brookhouser et al appear to corrobo- ear. They stated that if the ears are equally rate reports of academic and behavioral dif- sensitive, the binaural threshold is about 3 ficulties. Suggestions for teachers and parents dB better than the monaural threshold and were listed, including careful audiologic/ the binaural advantage expands to 6 dB dur- otologic monitoring and strategies to allevi- ing suprathreshold listening (i.e., most com- ate localization and auditory figure-ground fortable loudness) and 10-dB sensation level difficulties. (SL). This additional advantage may have Bess and Tharpel (1986) provide a profile significant effects on improved word recog- of the unilaterally hearing-impaired child nition scores when listening binaurally in who experiences academic difficulty: comparison to monaural listening. That is, if speech recognition increases at a rate of 5% 1. Severe to profound sensorineural hear- per each additional decibel (i.e., articulation ing loss function), then the binaural advantage at 2. Early age of onset suprathreshold levels could be 30% better 3. Impairment in the right ear. (6 dB 5% dB) than the monaural score. Culbertson and Gilbert (1986) reported de- creased performance in word recognition, language, and spelling. The investigators Performance in the Classroom provided some useful suggestions for man- Several studies have described the deleteri- agement strategies, especially within the ous effects of unilateral hearing loss on chil- classroom. dren. Bess and Tharpe (1988) studied a Bovo et al (1988) submitted a question- group of 60 children with unilateral sensori- naire to 115 unilaterally hearing-impaired neural hearing loss (greater than 45 dB HL individuals who had become impaired dur- in the speech frequencies). They felt that ing the first 12 years of life; 55 males and 60 children would experience similar listening females were included in their study, with 62 difficulties as adults, especially in the class- having hearing loss in the left ear and 53 in room and with language development. In the right ear. Seventy percent were over 6 their study, they found that 35% failed at years of age when diagnosed. Difficulties in least one grade (rate for general school pop- speech recognition and localization were de- ulation was 3.5%), and an additional 13.3% scribed, as well as feelings of embarrass- required resource assistance at school. A ment, passivity, and avoidance. Twenty-two greater incidence of behavior problems was percent failed at least one grade, 12% re- reported also. There seemed to be a correla- ceived special services in the area of learning tion between early onset/severity of loss disability, and 27% described embarrass- and risk for experiencing academic difficul- ment and a sense of inferiority. Fifty percent 12843.C09.PGS 3/8/02 11:11 AM Page 259

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had not been provided preferential seating. batteries that patients undergo to diagnose The investigators recommended counseling etiology are time-consuming and may be classroom teachers in the areas of reducing somewhat stressful. He acknowledged that environmental noise levels and reverbera- some reports describe unilaterally impaired tion in the classroom. children as having only minor communica- tive difficulties, if any. Adults were felt to have even fewer difficulties, especially if the Patient’s Perspective of Unilateral loss developed later in life; these viewpoints Hearing Loss were opposed by Bardon. Giolas and Wark (1967) stated that, although Bardon went on to state that tinnitus was a communication difficulties for patients with “masker” that interfered with speech percep- unilateral hearing loss have been minimized tion. Furthermore, it was harder to attend to by some professionals in the past, the diffi- tasks, and he found himself shifting his head culties can be quite significant. A report by to perform tasks better. Large rooms such as Harford and Barry (1965) described some hallways, hotel lobbies, and airports created of the significant difficulties encountered difficult listening environments where sounds by these patients. The investigators inter- appeared blended. Several talkers at the same viewed 20 patients with unilateral hearing time presented difficulty, as did competing loss. An increased difficulty in recognizing conversation or music during dining conver- speech in noise (i.e., reduction or elimina- sation. There were difficulties outdoors, and tion of the binaural squelch effect) was re- in some situations (such as in traffic) there ported as the most adverse listening situa- was a safety issue involved with reduced lo- tion. The greatest difficulty appeared when calization abilities. Additional listening diffi- the noise was directed to the better ear and culties were encountered when the sound speech was directed to the impaired ear came from behind, when visual cues were (i.e., head shadow effect). However, speech limited, and with children’s voices. The qual- recognition was reported to be “affected” re- ity of listening to music was affected with gardless of location of the speech or noise to monaural listening, as was the ability to moni- the “good” ear. Interviewees further re- tor the patient’s own speaking voice. Feelings ported difficulty with localization of the of fatigue and irritability seemed to accom- sound source, especially in noisy situations. pany continual attempts to perceive conversa- In addition, there was difficulty receiving tions and other meaningful stimuli. Profes- and understanding speech, even in quiet, sionals were urged to take note of these when the sound source was some distance deleterious effects in counseling their patients away. They expressed feelings of confusion, and helping them to recognize the need to embarrassment, helplessness, and annoy- change their listening situations and lifestyles. ance. On a final note, interviewees were interested in responding to the questions, because they felt professionals had not ex- Hearing Aid Fitting Process for pressed concern regarding their communi- Unilateral Hearing Loss cation difficulties. Case History and Referral From another patient’s perspective, Bar- don (1986) described some of the detrimen- As mentioned earlier, the problems associ- tal physiologic effects accompanying uni- ated with unilateral hearing loss appear to lateral hearing loss. Both dizziness and have been largely ignored by hearing health tinnitus, which can accompany unilateral care professionals. In addition, patients with hearing loss, are frightening and bother- unilateral hearing loss generally perform some; in addition, if a hearing loss is sud- well in quiet or have the ability to rotate den, it can be especially confusing and dis- their head so that the good ear is directed to- tressing. Bardon felt that the extensive test ward the speech signal and therefore may 12843.C09.PGS 3/8/02 11:11 AM Page 260

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not consider amplification to be required or ment of sudden unilateral hearing loss may beneficial. However, rotation of the head so include vasodilating drugs, anticoagulants, that the good ear is directed toward the histamine, cervical ganglion blocks, steroids, speech signal is not always possible. For ex- inhalation therapy of 95% oxygen and 5% ample, if a patient has an anacusic right ear carbon dioxide, and calcium antagonists and is driving a car with a passenger on the (Rambur, 1989). right side, it would be very difficult, if not impossible, for the patient to rotate his head Fitting Options so his good left ear is facing the passenger! cros When attempting to provide audiologic care for patients with unilateral hearing loss, One of the most successful attempts in help- the audiologist should seek answers to some ing patients with unilateral hearing loss important questions prior to considering overcome the head shadow effect was the in- amplification. Information should include troduction of CROS in 1964 (Harford and the age of the patient, occupation, demands Musket, 1964; Harford and Barry, 1965; Har- on listening, and indications of motivation ford and Dodds, 1966; Harford, 1969; Punch, toward amplification. Many authors (Har- 1988). In the earliest version, CROS amplifi- ford and Dodds, 1966; Harford, 1969; Matkin cation consisted of a microphone placed and Thomas, 1972; Hodgson, 1986; Courtois over or near the unaidable ear to pick up sig- et al, 1988; Pollack, 1988; Kenworthy et al, nals arriving at the side of the impaired ear. 1990) have stated that there is a greater like- The output from the microphone was wired lihood of success with amplification in this to an amplifier, receiver, and volume control, group if (1) a high degree of motivation is via a headband, and the amplified signal present toward amplification, (2) the de- was delivered via tubing gently placed in mands on listening are high because of life- the open ear canal of the good ear. Due to style or occupation, and (3) the patient is an the presence of the open earmold, no gain adult. These authors report a higher rate of was provided below 800 Hz and only mar- failure with CROS amplification when at- ginal gain was provided between 800 and tempted to be fitted for children. Kenworthy 1500 Hz. The greatest amount of gain was et al (1990) reported significantly greater provided in the frequency region above 1500 success during monaural direct listening Hz. Therefore, patients likely to receive the with an FM auditory trainer coupled to the greatest benefit from CROS amplification better ear than with either CROS amplifica- were patients with normal hearing in the tion or recommending preferential seating good ear through 1500 Hz and a slight to in children with unilateral hearing loss. mild hearing loss above 1500 Hz. The patient history should include as An eyeglass version of the CROS aid soon much detail as possible regarding the dura- became available, with the wire running tion and etiology of the hearing loss and any through the frames of eyeglasses. For those related symptoms such as tinnitus or dizzi- who did not wear glasses, the CROS was de- ness. Like any other hearing aid fitting, the veloped into behind-the-ear (BTE) hearing audiologist should require a medical clear- aids connected by a wire worn under the ance prior to dispensing hearing aids. This is hairline. One of the major drawbacks of especially true in cases of unilateral hearing CROS amplification was the need for a wire loss, because the hearing loss may be the re- to connect the output from the microphone sult of a space-occupying lesion. on the impaired ear to the receiver on the If the hearing loss is sudden, waiting sev- good ear. To solve this problem, Telex intro- eral weeks before pursuing amplification is duced a wireless BTE to BTE CROS (Fig. suggested because approximately 65% of 9–1), BTE to in-the-ear (ITE) bilateral CROS cases of sudden hearing loss report complete (BICROS) (Fig. 9–2), and BTE to BTE Multi- or partial recovery (Rambur, 1989). Manage- CROS (Fig. 9–3) hearing aids in 1973. The 12843.C09.PGS 3/8/02 11:11 AM Page 261

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Figure 9–2. Example of a wireless BTE to in-the- Figure 9–1. Example of a wireless behind-the- ear (ITE) bilateral CROS (BICROS) hearing aid. ear (BTE) to BTE contralateral routing of signal Note the absence of a volume control on the hear- (CROS) hearing aid. Note the absence of a vol- ing aid on the left. The hearing aid on the left is ume control on the hearing aid on the right. The the transmitter side (placed over the poorer ear) hearing aid on the right is the transmitter side and the hearing aid on the right is the receiver (placed over the poorer ear) and the hearing aid side (placed in the good ear). (From Telex Com- on the left is the receiver side (placed over the munications, Inc., with permission.) good ear). (From Telex Communications, Inc., with permission.)

wireless CROS uses an amplitude modu- lated carrier frequency to transmit signals from the microphone on the side of the im- paired ear to the receiver placed in the good ear. The distance between the transmitter and receiver is critical (approximately 6.5 inches). For every half-inch increase in dis- tance between the transmitter and receiver, there is a 3- to 4-dB decrease in gain (Punch, 1988). Currently, three CROS models and BI- CROS models are available from Telex. In each of these cases, the receiver portion is placed in the near normal ear (CROS fitting) or better ear (BICROS) and all the models in- clude adaptive compression. Clinically, one of the major drawbacks of the wireless CROS/BICROS systems is the limited ability to shape the frequency-gain Figure 9–3. Example of a wireless BTE to BTE response to provide the prescribed gain to MultiCROS hearing aid. Note the presence of vol- ume controls on both sides. The hearing aid on the aided ear. Most of the wireless hearing the right is the receiver side (placed over the bet- aids are delivered with only a low-frequency ter ear; C, CROS; BC, BICROS; T, telephone) and tone control or a low- and high-frequency the hearing aid on the left is the transmitter side tone control as a means to shape the fre- (placed over the poorer ear; M, microphone on; quency response. Due to this limitation, the O, microphone off). (From Telex Communica- authors over the past several years have tions, Inc., with permission.) 12843.C09.PGS 3/8/02 11:11 AM Page 262

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been proactive in counseling patients on the sponse of the hearing aid to either match a advantage of being fit with wired program- prescribed target or to present an aided sig- mable CROS/BICROS hearing aids (Fig. nal that the patient feels has better sound 9–4) that have several advantages over the quality. Second, and more importantly, this wireless systems. First, this aid is program- aid contains a dual-microphone that pro- mable, which allows the audiologist greater vides the user with greater intelligibility of flexibility in shaping the frequency-gain re- speech in noise than the omnidirectional mi- crophone (Valente et al, 1995) available on the wireless models. Using a counseling session favoring the advantages of dual-microphone technology in more effectively addressing the issue of improved intelligibility of speech in noise, our clinic has had such success with these wired CROS/BICROS hearing aids that we have not dispensed any wireless CROS hearing aids over the past 5 years. Clinically, the authors have experienced some confusion within the professional com- munity with the nomenclature used for CROS/BICROS fittings. When the aided sig- nal is being routed to the left ear, it is impor- tant to remember that this is a left CROS or BICROS fitting, whereas on the other hand, a right CROS or BICROS fitting means that the aided signal is routed to the right ear. Although CROS amplification effectively eliminates the head shadow effect by ampli- fying signals from the hearing-impaired side, localization and speech intelligibility in noise still remain a problem. Some CROS users report some improved localization based on differences of the quality of sounds from the two ears. If the signal appears “nat- Figure 9–4. Example of a wired CROS hearing ural,” it may be judged to be arriving from aid with remote control. The hearing aid on the left is an off-microphone placed over the poorer the good side. If the sound appears “tinny” ear. The hearing aid (with dual microphones) on or “metallic,” it may be judged to be arriving the right is placed over the better ear. The hearing from the impaired side (Harford, 1969). aid on the right can be programmed so that when Also, if the level of ambient noise is high, the switch is placed in the “M” position the aid few users of CROS amplification report any provides omnidirectional performance and when significant benefit regardless of which side placed in the “T” position the aid provides dual- the signal or noise may be arising from. In microphone performance. When used with the these environments, it is best to counsel the remote control, the “T” position is used for tele- patient to reduce the volume control setting coil and the patient can be provided omnidirec- or remove the hearing aids (Hodgson, 1986; tional performance by pressing “I” and dual- Harford, 1969; Pollack, 1988; Punch, 1988). microphone performance by pressing “II” and/or “III” (depending on how the hearing aid is pro- One final point must be emphasized re- grammed by the audiologist). This remote control garding CROS amplification. In the original also allows the user to turn the hearing aid “on” report by Harford and Barry (1965) and sub- and “off” and increase (“+”) or decrease (“”) the sequent reports by Harford (1969), Harford volume. and Dodds (1966), Courtois et al (1988), and 12843.C09.PGS 3/8/02 11:12 AM Page 263

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Punch (1988), there is a clear recommenda- the authors referred to this type of fitting as a tion that success with CROS amplification is transcranial CROS. significantly related to the magnitude of The concept in developing the transcra- hearing loss in the good ear. If hearing in the nial CROS is apparent to any audiologist good ear is within normal limits, then the proba- who has experience in testing a patient via bility of success with CROS amplification will be air conduction (earphone or insert receiver) minimal. On the other hand, if a mild hearing who has normal hearing in one ear and a loss is present above 1500 Hz, then a greater moderately severe to severe hearing loss in probability of patient acceptance will be the opposite ear. That is, the initial un- achieved. Our experience with CROS ampli- masked air conduction threshold for the im- fication over the past several years supports paired ear represents the magnitude of inter- this recommendation. Very few (less than aural attenuation (i.e., “shadow curve”). For 10%) of our patients with normal hearing in this patient, this represents the lowest inten- the good ear reported that the benefits from sity at which stimuli (nonspeech or speech) CROS outweighed their perceptions of the will pass through the temporal bone and is presence of “harshness” or “tinniness” of the heard by the cochlea of the normal ear. In amplified sound heard in the good ear. much the same way, the output (input signal Based on these findings, we have adopted a plus the gain of the hearing aid) from a policy that CROS amplification is not our strong BTE or ITE hearing aid placed on the primary choice for unilaterally hearing- impaired ear can deliver sound to the impaired listeners if the patient has normal cochlea of the normal ear via bone conduc- hearing in the good ear. On the other hand, tion. Signals picked up by the microphone of CROS becomes our primary recommenda- a hearing aid placed over or in the impaired tion if a mild to moderate high-frequency ear can be amplified and eventually cross sensorineural hearing loss is present in the through the head and be heard by the good ear above 1500 Hz. cochlea of the normal ear via bone conduc- tion (Miller, 1989). In one study (Miller, 1989) comparing con- transcranial cros ventional CROS with transcranial CROS am- Another approach to providing benefits of plification, the subjects reported improved amplification to the unilaterally hearing im- recognition of speech in “quiet” when the paired has been advocated by several authors speech signal was presented to the impaired (Sullivan, 1988; McSpaden and McSpaden, side, improved speech recognition in noise, 1989; Miller, 1989; McSpaden, 1990; Char- and some improvement in the ability to lo- trand, 1991), who suggest placing a high- calize. In addition, some subjects reported gain, high-output ITE or BTE hearing aid into that the amplified sound presented through the impaired ear to take advantage of the fact their transcranial CROS was more “natural” that the cochleas for each ear, which are con- than the sound processed through their con- tained within the temporal bone, are not ventional CROS hearing aid. Other reports acoustically isolated. That is, if a signal of in- by McSpaden (1990), McSpaden and Mc- creasing intensity is presented to the cochlea Spaden (1989), and Sullivan (1988) indicated of an impaired ear, the signal will eventually that listeners found transcranial CROS fit- be heard in the cochlea of the better ear be- tings were “more natural,” provided im- cause it will be intense enough to overcome proved localization via cues from a metallic the acoustic isolation [interaural attenuation sound from the aided side and a natural (IA)] between the cochleas of the two ears. sound from the normal side, and improved Because the signal picked up by a micro- listening in noise when the signal was from phone placed in the impaired ear is trans- the impaired-ear side. Patients did not re- ferred to the cochlea of the good ear through port the harshness that some experience the cranial structures of the temporal bone, with CROS fittings. 12843.C09.PGS 3/8/02 11:12 AM Page 264

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In an effort to determine if transcranial fit- placed in the unaidable ear. A recent modifi- tings had merit, Valente et al (1995) evalu- cation of the eyeglass CROS version pro- ated 12 patients with an anacusic ear or pro- vides for the offside frame on the poorer ear found sensorineural hearing loss in one ear to contain two microphones. One micro- and normal hearing in the opposite ear. For phone is for the CROS or BiCROS arrange- each patient, a strong ITE hearing aid (maxi- ment to forward the signal to the better ear. mum saturation sound pressure level of 120 The second microphone is part of a separate dB; full-on gain of 55 to 65 dB) with a long hearing instrument (i.e., microphone, ampli- canal and pressure vent was fitted to the im- fier, and receiver with a closed mold) to for- paired ear. Four patients were experienced ward the signal to the poorer ear. This effec- users of CROS amplification to the better tively eliminated the need for a separate ITE ear. Two patients had experience with an to be placed in the unaidable ear. In addi- eyeglass bone conduction hearing aid tion, this arrangement can be modified for placed on the mastoid process of the im- BTE fittings to both ears. According to the paired ear. Five patients had no experience authors, the CROS-plus has been fitted to with amplification, and one patient had ex- over 150 patients for whom many report im- perience with a mild ITE hearing aid cou- proved clarity of speech, improved localiza- pled to the better ear. At the end of 4 weeks, tion, and improved recognition of speech in half of the patients felt that the ITE transcra- noise. nial CROS provided significant benefit, whereas the other half noted little additional Bone Conduction benefit and decided to continue to utilize their current hearing aids or not pursue Whereas 30 to 50 dB or more of gain is neces- amplification. sary for the output from an air-conducted It is important to remember that the ac- transcranial CROS fitting to reach the cochlea ceptance rate at this facility for conventional of the good ear, minimal gain is required for a CROS fittings for this population is 10%, signal delivered via bone conduction to reach whereas the acceptance rate for the transcra- the cochlea of the good ear. This is because in- nial CROS was 50%. It is interesting to note teraural attenuation for a bone conducted sig- that the reasons for rejection of the transcra- nal is virtually 0 dB. That is, as soon as a sig- nial CROS by many of the patients were re- nal is transmitted by bone conduction to the lated to feedback or to a sensation of vibra- cochlea embedded in the mastoid process of tion generated from the hearing aid. The the temporal bone of one ear, it is instanta- results of this evaluation were encouraging, neously heard in the cochlea embedded in the and we are currently in the process of di- temporal bone of the opposite ear. Therefore, rectly comparing transcranial CROS BTE fit- the signal detected by the microphone placed tings (to eliminate, we hope, the problems over the anacusic ear and amplified by a bone related to feedback and at the same time conduction hearing aid is immediately heard provide greater output) to traditional CROS in the cochlea of the good ear. fittings in a large sample of unilaterally Fowler (1960) appears to be the first to hearing-impaired adults. have advocated placement of a bone-conduc- tion hearing aid over the mastoid process of the impaired ear for patients with unilateral cros-plus hearing loss. Usually, bone-conduction aids A modification of transcranial CROS was in- are advocated for ears with chronic middle troduced by Hable et al (1990). This fitting ear drainage or an ear canal with atresia. Be- system was coined “CROS-plus” by the au- cause interaural attenuation for a bone- thors because a traditional CROS is fitted conducted signal is negligible, only one ear is to the better ear in the usual manner and is required to have normal hearing via bone combined with a power ITE hearing aid conduction. 12843.C09.PGS 3/8/02 11:12 AM Page 265

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Bone-conduction aids are currently avail- amplification. Second, not all unilaterally able in eyeglasses (Fidelity F228 or F229). hearing-impaired patients have visual im- In addition, bone-conduction aids are avail- pairments and therefore may not be inter- able in body aid or BTE configurations, with ested in pursuing an eyeglass fitting. This the bone vibrator tightly held in place on the problem was solved for two patients by hav- mastoid process via a headband. Just like the ing the optician fit ordinary glass into the transcranial CROS, a bone-conduction eye- eyeglass frame. Third, it is very important glass hearing aid has a microphone, ampli- for the bone vibrator to fit directly on the fier, volume control, and bone-conduction mastoid with sufficient static pressure to de- receiver mounted in the eyeglass temple be- liver the amplified signal effectively to the hind the ear with a vibrating pad projecting mastoid process. slightly toward the mastoid process on the Each eyeglass bone-conduction aid is side of the impaired ear. It delivers sound available with a series of 10 extension tips to from that ear, routing it transcranially via place the bone vibrator directly on the mas- bone conduction to the cochlea of the nor- toid. It is often necessary to make several mal ear. For a patient with an anacusic ear trips to an experienced optician before the and normal hearing in the opposite ear, the ideal placement and pressure are achieved. bone-conduction aid can provide improved For some patients, the required pressure awareness and recognition of speech arriv- necessary for maximum benefit from this ing on the side of the poor ear. However, like type of hearing instrument may cause irri- CROS and transcranial CROS amplification, tability of the skin under the bone vibrator, bone conduction aids do not appear to im- discomfort, and headaches. In fact, these prove localization significantly or the recog- problems led to rejection by one of our pa- nition of speech dramatically in high levels tients, although he found the hearing aid fit- of background noise for most patients. ting to be beneficial. In addition, audiolo- In an attempt to determine if fitting a gists tend to stay away from eyeglass fittings bone-conduction hearing aid had any merit, because they themselves assume the patient the authors evaluated seven patients with would not be interested in pursuing such a anacusic hearing on one side following sur- fitting. The findings of Hable et al (1990), gical removal of an acoustic neuroma. Of the clearly point to the fact that the need to place seven patients, six decided to purchase the hearing instruments in an eyeglass is not the hearing instrument (rejection rate of 14.3%) obstacle many audiologists believe it to be. after a 30- to 60-day trial period. Interest- ingly, one patient who decided to purchase the bone-conduction hearing aid had a long Verification Strategies history of experience with CROS amplifica- Sound-Field Evaluation tion. These seven patients reported similar improvements in communication that were Figures 9–5 illustrates a suggested proce- described earlier for our patients using a dure for evaluating sound-field unaided and transcranial CROS. Again, it is important to aided speech recognition in noise for CROS, remember that the acceptance rate at this fa- CROS-plus, and bone conduction hearing cility for conventional CROS fittings for this aids. Similar procedures have been sug- population is 10%, whereas the acceptance gested by Harford (1969), Skinner (1988), rate was 86% for an eyeglass bone-conduc- Pollack (1988), and Hodgson (1986). In Fig- tion hearing aid. ure 9–5a, the signal [NU-6 word lists at Although this fitting was very successful 70-dB sound pressure level (SPL) on the C with this small group of patients, a bone- scale] is presented from a loudspeaker 90- conduction eyeglass fitting is not without degree azimuth on the side of the good ear, numerous obstacles. First, when the eye- and multitalker babble is presented at 64 dB glass is removed the patient will be without SPL (C scale) from a loudspeaker 90-degree 12843.C09.PGS 3/8/02 11:12 AM Page 266

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(a) (b)

Figure 9–5. a: Loudspeaker arrangements for measuring word recognition scores in +6 dB signal-to-noise ratio (SNR). NU-6 word lists presented to the side of the normal ear, and mul- titalker babble presented to the side of the unaidable ear. b: Multitalker babble presented to the side of the normal ear, and NU-6 word lists presented to the side of the unaidable ear.

azimuth on the side of the unaidable ear. In In Figure 9–5b, the position of the subject this configuration, unaided and aided word remains the same, but the loudspeaker out- recognition scores are determined with a cal- put has been reversed so that the signal ar- ibrated +6 dB SNR without the head present. rives at the side of the unaidable ear, while It should be anticipated that the results the multitalker babble arrives at the side of using the loudspeaker arrangement illus- the good ear. In the loudspeaker arrange- trated in Figure 9–5a will reveal the best un- ment illustrated in Figure 9–5b, the audiolo- aided and the poorest aided scores and thus gist should anticipate the poorest unaided the smallest difference between unaided and and the best aided scores and thus the larg- aided performance. That is, in the unaided est difference in aided versus unaided per- condition the good ear is directly receiving formance. In fact, it is not uncommon for the the NU-6 words (70-dB SPL). The intensity differences between unaided and aided per- level of the multitalker babble (64-dB SPL) formance to exceed 20 to 30%. In the un- presented from the side of the poor ear is re- aided condition, the speech signal is on the duced to the good ear by approximately 6.4 side of the poor ear and is attenuated by ap- dB due to the head shadow effect (Tillman et proximately 6.4 dB to the good ear, whereas al, 1963). This effectively reduces the noise the noise is unattenuated to the good ear. level of the multitalker babble to 57.6 dB at In this situation, the effective SNR at the the side of the good ear. Therefore, the effec- good ear is 12.4 dB for the same reasons tive SNR at the good ear has been improved described above, and unaided performance to +12.4 dB (70–57.6 dB SPL), whereas with- should be rather poor. In the aided condi- out the presence of the head the SNR was tion, a microphone is on the side of the poor calibrated at +6 dB (70–64 dB SPL). For the ear to deliver the amplified signal (either by aided condition, the multitalker babble from air or bone conduction) to the good ear. This the poor side is now amplified because a mi- effectively eliminates the head shadow effect crophone is placed over or near the poor ear. and significantly improves speech recogni- In this situation, the reduction of noise to the tion scores in comparison to the unaided good ear has been eliminated and the noise condition in which the head shadow effect is amplified and mixed at fairly high levels was present. with the unamplified signal entering the Although the results of the four unaided good ear directly. and aided comparisons are fairly predictable, 12843.C09.PGS 3/8/02 11:12 AM Page 267

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it is important for the audiologist to com- cess in the impaired ear. As can be seen for plete these comparisons. These procedures the transcranial CROS patient, the aided im- clearly demonstrate to the listener the impor- provement was 2% for the condition de- tance of placing the microphone on the im- scribed in Figure 9–5a where the NU-6 word paired ear in a favorable position depending lists were presented on the side of the good on the origin of the signal or noise to the im- ear and the noise was presented on the side paired ear. In essence, this verification pro- of the impaired ear. However, for the eye- cess allows the patient to experience the full glass bone-conduction patient, the aided im- spectrum of listening situations in which un- provement was 16%, which is significant at aided and aided performance will be the 0.01 confidence level (Raffin and Thorn- markedly different. That is, the listening situ- ton, 1980). When the listening situation was ation in which the patient had the greatest reversed as described in Figure 9–5b, the difficulty without amplification (i.e., speech aided performance was 18% better than the on the poor side and noise on the good side) unaided score for the ITE transcranial CROS will now result in the best listening environ- and a 26% improvement for the eyeglass ment with the use of amplification. On the bone-conduction fitting, both of which were other hand, the listening situation that cre- significant at the 0.01 confidence interval ated the least difficulty without amplifica- (Raffin and Thornton, 1980). tion (i.e., speech on the good side and noise on the poor side) will now result in the poor- Probe Measures for Traditional est listening environment with the use of am- CROS Fittings plification. The patient needs to experience and realize that situations will arise in which The method of choice today for verification amplification will provide a poorer listening of hearing aid fittings is real-ear probe tube environment in comparison to when amplifi- measures. For an in-depth description of cation is not used. real-ear probe tube measures, see Chapter 3 Table 9–2 provides the speech recognition and Tecca (1990) or Valente (1991). results for two patients using the loud- Probe tube measures can be a very useful speaker arrangements discussed in the pre- tool for measuring the performance of CROS, vious section. The results are for one patient transcranial CROS, and CROS-plus fittings. fitted with a transcranial ITE CROS on the Punch (1988) suggested measuring the real- impaired ear and for a second patient fitted ear unaided gain (REUG) and the real-ear in- with an eyeglass bone-conduction aid with sertion gain (REIG) at 250 to 6000 Hz for a the bone vibrator placed on the mastoid pro- CROS fitting with the probe tube placed 6

Table 9–2. Speech Recognition Scores Measured in Sound Field (as Illustrated in Fig. 9–1)

Aid Unaided (%) Aided (%)

Transcranial CROS NU-6 to good ear/multi-talker babble to 92 94 the impaired ear (Figure 9–5a) NU-6 to impaired ear/multi-talker babble 74 92 to the good ear (Figure 9–5b) Eyeglass bone conduction NU-6 to good ear/multi-talker babble to the 84 100 impaired ear (Figure 9–5a) NU-6 to impaired ear/multi-talker babble to the 56 82 good ear (Figure 9–5b)

CROS, contralateral routing of signal. 12843.C09.PGS 3/8/02 11:12 AM Page 268

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mm from the tympanic membrane of the phone remaining in the poor ear. The differ- good ear with the loudspeaker at 45- to 90- ence in the REUG between these two mea- degree azimuth to the impaired ear where sures represents the magnitude of the head the microphone for the various CROS fit- shadow effect, and it can be on the order of tings will reside. He suggested that the mea- approximately 6 to 7 dB. In addition, these sured REIG will demonstrate if the CROS measurements illustrate the effectiveness of fitting eliminated the head shadow effect be- the microphone placed on the poor ear when cause the measured REIG should not exceed desired signals originate from the side of the the magnitude of the head shadow (6 to 7 poor ear. dB) plus an amount of gain appropriate for Finally, the REAG is measured once with the magnitude of hearing loss in the good the loudspeaker located 45 to 90 degrees on ear between 1500 and 6000 Hz. Punch did the side of the better ear. This REAG mea- not suggest a prescriptive procedure, but sure can be compared with either REUG the National Acoustic Laboratories’ revised mentioned in the previous paragraph. Com- (NAL-R) prescriptive procedure (Byrne and parison of the REAG to the REUG measured Dillon, 1986) appears to be an appropriate from the side of the poor ear determines the choice for the magnitude of loss in the good magnitude of the elimination of the head ear, which is appropriate for a CROS fitting. shadow effect. Comparison of the REAG to For fitting an ear with normal hearing in the the REUG measured from the side of the good ear, less than 10-dB gain would be de- good ear determines the “real” real-ear gain sired in the frequency region above 1500 Hz. (REIG), and this should be compared with For many CROS fittings measured at our fa- the prescribed REIG to verify if the patient is cility, the measured REIG exceeds this goal, receiving adequate amplification. and this may be the major reason why many patients with normal hearing in the good ear Probe Measures for Transcranial reject CROS amplification. CROS Fittings Tecca (1990) indicates that several real-ear probe tube measures should be made for The authors developed a procedure using CROS fittings. First, Tecca suggests measur- the real-ear aided response (REAR) that may ing the REUG, real-ear aided gain (REAG), be useful for the verification of transcranial and REIG with the loudspeaker at ±45-degree CROS fittings. Using this procedure, the azimuth with the probe microphone in the probe tube from the Frye 6500 real-ear ana- better ear and the reference microphone lyzer is initially placed in the ear canal of the placed over the poor ear. In this manner the impaired ear at a distance of approximately audiologist first measures the REUG. Then 4 to 6 mm from the tympanic membrane, the BTE or ITE CROS hearing aid is placed and the reference microphone is disabled. over or in the poorer ear, and the REAG is An earphone (or ER-3A insert receiver) is measured in the better ear. The REIG is cal- placed over the ear canal of the poor ear and culated as the difference between the REAG unmasked air conduction thresholds are de- and the REUG. termined at 250 to 4000 Hz. Because these To determine the magnitude of the head patients have known profound sensorineu- shadow effect, the REUG can initially be ral hearing loss in the poor ear and hearing measured with the loudspeaker at 45- to 90- is within normal limits in the good ear, the degree azimuth to the good ear with the ref- unmasked thresholds represent the IA for erence microphone over the good ear, but the air-conducted signal. These thresholds the probe microphone in the poor ear. The can range between 40 and 90 dB HL depend- REUG is repeated with the loudspeaker relo- ing on test frequency and intersubject vari- cated at 45- 90-degree azimuth to the side of ability. The SPL measurements from the the poor ear with the reference microphone probe microphone placed in the ear canal of moved to the poor ear, but the probe micro- the poor ear correspond to the individual IA 12843.C09.PGS 3/8/02 11:12 AM Page 269

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at each test frequency. Next, the good ear is canal ranged from 66.5-dB SPL at 1500 Hz to plugged and muffed while an ITE or BTE 89.3-dB SPL at 4000 Hz. With the transcranial transcranial CROS hearing aid is placed in ITE CROS placed in the poor ear, the REAR the poor ear. The volume control is adjusted for 70-dB SPL of speech-weighted composite to where amplification is comfortably loud noise ranged from 63-dB SPL at 4000 Hz SPL while the patient listens to 70-dB SPL of to 96-dB SPL at 1000 Hz. More importantly, speech-weighted composite noise presented the aided REAR was below the measured ear- by the loudspeaker from the Frye 6500. Fi- phone SPL response at 250 and 3000 to 4000 nally, 70-dB SPL of speech-weighted com- Hz (6.6, 10.3, and 26.3 dB, respectively) posite noise is presented to the listener, and and above the measured ear canal SPL re- the REAR is measured to determine if it ex- sponse at 500 to 2000 Hz (+5.8, 16.5, 26.9, 19.5, ceeds the IA previously measured in SPL in and 2.7 dB, respectively). The goal for such a the ear canal of the aided ear. This process fitting would be that the aided REAR mea- verifies if the amplified signal is sufficiently sures would provide approximately 15-dB loud to be heard in the cochlea of the good sensation level or greater at 1000 to 4000 Hz. ear via bone conduction. If this goal could be achieved without feed- Thus, when using this procedure, the back or a sensation of vibration, then the au- “prescriptive target” for a transcranial CROS diologist could be assured that the amplified fitting is the measured SPL in the canal of signal reached the cochlea of the good ear. Of the impaired ear corresponding to the IA. course, these measures would be supple- The goal is for the REAR to exceed that tar- mented by the sound-field measures de- get by approximately 15 to 20 dB so that scribed above. It would be anticipated that the amplified speech signal would be at a the SPL of the REAR for this patient may sensation level (re: IA threshold) sufficient to have been greater if a BTE transcranial CROS make the amplified signal audible in the had been fitted, because the appropriate vol- cochlea of the good ear. ume control setting [i.e., adjusted to the most Table 9–3 provides an example of this pro- comfortable loudness (MCL) level] could not cedure in a patient in whom a transcranial be achieved due to feedback. ITE hearing aid was fitted. In this case, the In yet another approach for using real-ear unmasked air conduction thresholds repre- probe tube measures to verify transcranial senting the interaural attenuation ranged CROS fittings, Sullivan (1988) measured the from 55- to 75-dB HL (column 2, Table 9–3). occluded transcranial REIG in the good ear. With the probe microphone in the ear canal of To do this, he placed the probe tube near the the poor ear, the measured SPL in the ear tympanic membrane of the good ear, placed

Table 9–3. Measures of Interaural Attenuation (IA), IA Threshold, Measured REAR for Speech-Weighted Composite Noise, and Sensation Level

IA Measured Frequency Threshold IA Threshold REAR (dB Sensation (Hz) (dB HL) (dB SPL) SPL) Level (dB)

250 60 80.6 74.0 6.6 500 65 78.2 84.0 +5.8 750 60 69.5 86.0 +16.5 1000 60 69.1 96.0 +26.9 1500 55 66.5 86.0 +19.5 2000 60 77.3 80.0 +2.7 3000 70 87.3 77.0 10.3 4000 75 89.3 63.0 26.3

HL, hearing level; IA, interaural attenuation; REAR, real-ear aided response; SPL, sound pressure level. 12843.C09.PGS 3/8/02 11:12 AM Page 270

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a cotton block lateral to the end of the probe Bess F, Tharpe A. An introduction to unilateral sensori- neural hearing loss in children. Ear Hear 1986;7:3–13. tip, and filled the ear canal with impression Bess F, Tharpe A. Performance and management of chil- material. Warble tones were presented at dren with unilateral sensorineural hearing loss. 0-degree azimuth at 0.5 m using an input Scand Audiol Suppl 1988;30:75–79. Bocca M. Binaural hearing: another approach. Laryngo- level of 60-dB SPL. Measurements were scope 1955;45:1164–1171 made in the occluded good ear with the Bovo R, Agnoletto M, Beghi A. Auditory and academic transcranial CROS off (REUG) and at full-on performance of children with unilateral hearing loss. Scand Audiol Suppl 1988;30:71–74. (REAG) in the impaired ear. He reported a Breaky M, Davis H. Comparison of thresholds for median occluded REIG of 9.5 dB at 1500 to speech. Laryngoscope 1949;59:236–250. 3000 Hz. One patient revealed an REIG peak Brookhouser P, Worthington D, Kelly W. Unilateral hearing loss in children. Laryngoscope 1991;101:1264– gain in the occluded good ear of almost 25 1272. dB in the 3000-Hz region. Bye F. Sudden hearing loss research clinic. Otolaryngol Clin North Am 1978;11:71–79. Byrne D, Dillon H. The National Acoustic Laboratories Conclusion (NAL) new procedure for selecting the gain and frequency response of a hearing aid. Ear Hear 1986; Several fitting options are available for the 7:257–265. Chartrand M. Transcranial or internal CROS fittings: sensorineural unilaterally hearing-impaired Evaluation and validation protocol. Hear J 1991;44: patient. The ideas contained in this chapter 24–28. explored the concept that unilaterally hearing- Clark B, Conry R. Hearing impairment in children of low birth weight. J Audiol Res 1979;19:277–291. impaired patients experience significant com- Courtois J, Johansen P, Larsen BV. Hearing aid fitting munication problems, and suggesting “turn- in asymmetrical hearing loss. In: Jensen JH, ed. Hear- ing your head to the desired signal” or ing Aid Fitting: Theoretical and Practical Views. 13th Danavox Symposium. Copenhagen: Stougaard Jen- recommending CROS amplification to the son, 1988, pp. 243–255. good ear should not be the exclusive rehabili- Culbertson J, Gilbert J. Children with unilateral sensori- tative options for these patients. neural hearing loss: cognitive, academic and social development. Ear Hear 1986;7:38–42. We have gained considerable experience Everberg G. Etiology of unilateral total deafness. Ann with the fitting strategies outlined in this Otol Rhinol Laryngol 1960;69:711–713. chapter and urge clinicians to consider Fowler E. Bilateral hearing aids for monaural total deaf- ness. Arch Otolaryngol 1960;72:57–58. transcranial CROS, CROS-plus, or bone- Giolas T, Wark D. 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