- Email: [email protected]
Localization by unilateral BAHA users
Localization by unilateral BAHA users JACK J. WAZEN,
MD,
SOHA N. GHOSSAINI,
MD,
JACLYN B. SPITZER,
OBJECTIVES: Patients with unilateral hearing loss report difficulty hearing conversation on their impaired side, localizing sound, and understanding of speech in background noise. The bone-anchored cochlear stimulator (BAHA) (Entific, Gothenburg, Sweden) has been shown to improve performance in persons with unilateral severe-profound sensorineural loss (USNHL). The purpose of this study is to evaluate the effectiveness of BAHA in sound localization for USNHL listeners. STUDY DESIGN: Prospective study of 12 USNHL subjects, 9 of whom received implants on the poorer hearing side. A control group of 10 normal hearing subjects were assessed for comparison. Localization with and without BAHA was assessed using an array of 8 speakers at head level separated by 45 degrees. Error analysis matrix was generated to evaluate the confusions, accuracy in response, and laterality judgment. RESULTS: The average accuracy of speaker localization was 16% in the unaided condition, with no improvement with BAHA use. Laterality judgment was poorer than 43% in both aided and nonaided conditions. CONCLUSIONS: Patients with UNSNHL had poor sound localization and laterality judgment abilities that did not improve with BAHA use. (Otolaryngol Head Neck Surg 2005;132:928-32.)
T
he advantages of binaural over monaural hearing are very well recognized in the literature; these include binaural summation, elimination of the head shadow effect, improvement of speech understanding in background noise, in addition to localization of sound in the environment.1,2 Sound localization in the horizontal plane depends on the ability to detect the differences From the Department of Otolaryngology–Head and Neck Surgery, Columbia University College of Physicians and Surgeons (Drs Wazen, Ghossaini, and Spitzer), and Columbia University Medical Center (Drs Wazen, Ghossaini, Spitzer, and Kuller), New York, New York. Presented at the Annual Meeting of the American Academy of Otolaryngology– Head and Neck Surgery, New York, September 20, 2004. Reprint requests: Soha N. Ghossaini, MD, Department of Otolaryngology– Head and Neck Surgery, Columbia University Medical Center, 630 West 168th St, New York, NY 10032; E-mail, [email protected]. 0194-5998/$30.00 Copyright © 2005 by the American Academy of Otolaryngology–Head and Neck Surgery Foundation, Inc. doi:10.1016/j.otohns.2005.03.014
928
PHD,
and MARY KULLER,
MS,
New York, New York
between interaural time and intensity,3 which then are integrated by the central nervous system.4 There is evidence that interaural time difference is important for localizing low-frequency signals and interaural intensity difference is important for localizing high-frequency signals.5 These benefits are part of the rationale for rehabilitative choices that restore binaural stimulation. Patients with unilateral severe to profound sensorineural hearing loss (USNHL), due to the loss of binaural cues, have difficulty with speech understanding in noisy backgrounds and loss of the ability to localize sound sources. In a recent study6 of patients with USNHL, the use of the bone-anchored cochlear stimulator (BAHA) has been shown to alleviate the degree of hearing handicap resulting from the head shadow effect, to improve speech intelligibility in noise, and to improve quality of life. In the same study, the authors noted that 36% of patients reported subjectively that the BAHA has helped them to localize sound to some extent, despite the fact that the sound was channeled through 1 functioning cochlea. The purpose of this study was to quantify the deficit in localization encountered by persons with severe to profound sensorineural hearing loss on 1 side and normal hearing in the better ear and to evaluate the impact of using a BAHA on localization performance. Specifically, the research questions tested were: (1) Is the localization ability of USNHL subjects different than that of normal hearing controls? (2) Does use of a BAHA improve localization ability for USNHL patients? (3) Is gross accuracy, ie, the ability to localize the sound source to one side or the other, improved by use of a BAHA? MATERIALS AND METHODS This was a prospective study of 12 patients with unilateral severe to profound sensorineural hearing loss, 9 of whom subsequently received a BAHA on the worst hearing ear. One patient declined to return for testing in the aided condition and therefore was excluded from the analysis. Institutional Board Review approval was granted for this study. Ten normal hearing controls were also included. The description of the subject sample appears in Table 1. The mean age was 60.38 years (range, 53 to 74). The group was composed of 3 males and 5 females. In 4 (50%) of the cases, the subjects experienced profound hearing loss as a consequence of removal of
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WAZEN et al 929
Table 1. Subject description (N ⫽ 8)
1
Subject
Affected side
Cause
Age (years)
Gender
S1 S2 S3 S8 S9 S10 S11 S12
L L R L L R L L
Acoustic neuroma Acoustic neuroma Acoustic neuroma Meningitis Acoustic neuroma SSNHL1 SSNHL SSNHL
59 53 74 53 59 54 67 64
M F M F F M F F
Sudden sensorineural hearing loss.
an acoustic neuroma. Causes in the remaining 4 subjects included: 3 (38%) sudden hearing loss, 1 (8.5%) complication of meningitis, and 1 (12%) complication of chronic otitis media. A few of the subjects were included in a clinical trial of single-sided deafness.6 Audiologic Criteria All subjects had preoperative audiological testing under headphones including pure-tone air- and boneconduction thresholds, spondee threshold, and speech recognition using Northwestern University list 6 words. Patients with profound sensorineural hearing loss on 1 side with pure tone thresholds ⬍25 dB at 250 through 4 kHz on the better hearing ear were included in the study. The 3-frequency pure-tone average (PTA3) for the frequencies 0.5k, 1k, 2 kHz) was 101.46 dB HL (SD ⫽ 23.47) with word recognition scores ranging from 0% to 12 % in the affected ear. All equipment was calibrated to the ANSI S.3-1996 standard.7 Localization Testing Localization testing was performed in a soundtreated room; dimensions were 9’10” ⫻ 9’2⬙ with the patient seated in the center, approximately 4 feet from the speakers in any direction. Eight speakers were mounted at head level, separated by 45 degrees (Fig 1). Narrow band noise centered at 500 Hz or 3000 Hz presented at 60 dB HL for a 2 second duration. Localization was tested in 2 different conditions: unaided and BAHA-aided hearing conditions. Randomized trials of 5 presentations per speaker were presented in each hearing condition. This resulted in 40 stimuli per frequency per hearing condition. Subject identified sound source by the number of the speaker. All implanted subjects used the BAHA for at least 1 month before the evaluation of their aided responses. Control group of 10 participants with normal hearing in both ears was used. Data Analysis Subjects’ responses were recorded for subsequent analysis. Hits were calculated as a percentage of the
Fig 1. Layout of localization field; speakers are mounted at head level separated by 45 degrees.
total presentations in that condition, for example, 4 hits/40 presentations ⫻ 100 ⫽ 10% accuracy. Descriptive statistics were calculated. Unaided versus aided performance was examined using t tests for repeated measures. Analysis of variance (ANOVA) was used to evaluate the performance differences of the controls versus the USNHL at each frequency. Laterality judgments were evaluated by collapsing the responses for speakers on the subject’s right (speakers 2, 3, and 4) and those on his or her left (6, 7, and 8). Front/back discrimination was not included in the analysis. The percent correct identification was then calculated as the number of correct identifications of side of origin/the number of total number of presentations to speakers 2, 3, 4, 6, 7, and 8 ⫻ 100. RESULTS Control Subjects Performance of control subjects is summarized in Table 2. Accuracy was 74% for 500 Hz NB and 81% for 3000 Hz NB. The ranges of accuracy were from 65% to 98% at 500 Hz NB and 58% to 100% at 3000 Hz NB. There was no difference in accuracy as a function of frequency (P ⫽ 0.21, NS).
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930 WAZEN et al
Table 2. Summary of percent accuracy* of localization judgments by normal hearing control subjects (N ⫽ 10)
Table 3. Percent accuracy* of unaided localization judgments by subjects with unilateral sensorineural hearing loss (N ⫽ 8)
% Correct Frequency (Hz)
Mean
Minimum
500 3000
74 81
65 58
% Correct Maximum
Frequency (Hz)
Mean
Minimum
Maximum
98 100
500 3000
13 19
8 10
20 35
*Number correct/40 presentations ⫻ 100.
USNHL Performance Table 3 summarizes the accuracy of performance in the unaided condition. The accuracy was 13% correct at 500 Hz NB and 19% at 3000 Hz NB. Table 4 illustrates the accuracy in the BAHA-aided condition. At 500 Hz NB, correct identification was 16% of the time, and 15% at 3000 Hz NB. Accuracy of USNHL subjects was compared for 4 repeated measures with ANOVA. There were no significant differences in performance when comparing results for the 2 stimulus frequency NBs or for unaided versus aided accuracy (F ⫽ 1.42, df ⫽ 7, 24; P ⫽ 0.26, NS). Comparison of Control with USNHL ANOVA for repeated measures was used to test differences in localization accuracy for the controls versus the unaided hearing-impaired sample. At 500 Hz NB, the difference was highly significant (t ⫽ ⫺16.22, df ⫽ 16; P ⬍ 0.001, 2-tailed). At 3000 Hz NB, a similar significant result was obtained (t ⫽ ⫺10.75, df ⫽ 16; P ⬍ 0.001, 2-tailed). Laterality judgments The ability to determine which side the source originated from was evaluated (Table 5). For 500 Hz NB stimuli, the laterality accuracy was 40% unaided, and 43% BAHA-aided. For 3000 Hz NB, the accuracy of laterality judgments was 40% unaided and 40% BAHA-aided. These findings were tested with an ANOVA for repeated measures, with no significant outcome (F ⫽ 0.27, df ⫽ 7, 24, P ⫽ 0.82, NS). All combinations (500 Hz vs 3000 Hz unaided, 500 Hz vs 3000 Hz aided, 500 Hz aided vs 500 Hz unaided, 3000 Hz unaided vs 3000 Hz aided) were not significant (P ⬎ 0.05), as determined using a Dunnett’s control mean comparison test. In summary, the analysis indicated: (1) the USNHL group’s ability to localize was significantly poorer than the control subjects; (2) the performance of the USNHL subjects was equivalent in unaided and aided conditions, irrespective of stimulus NB frequency; and (3) the gross localization ability for laterality of sound
*Number correct/40 presentations ⫻ 100.
Table 4. Percent accuracy* of BAHA-aided localization judgments by subjects with unilateral sensorineural hearing loss (N ⫽ 8) % Correct Frequency (Hz)
Mean
Minimum
Maximum
500 3000
16 15
8 8
23 23
*Number correct/40 presentations ⫻ 100.
Table 5. Percent accuracy* of laterality judgments of subjects with unilateral sensorineural hearing loss % Correct Frequency (Hz)
Unaided
Aided
500 3000
40 40
43 40
*Number of correct identification of side of sound origin/number of presentations ⫻ 100)
source was poor in unaided and aided conditions, regardless of stimulus NB frequency. In this sample, there was no detectable improvement in accuracy as a result of BAHA use. DISCUSSION Sound localization is an important and necessary characteristic of normal binaural hearing that allows human beings the conversational and safety features of recognizing the origin of the sound stimulus. Numerous studies have focused on the mechanisms of sound localization. The ability to detect the stimulus origin depends on both interaural latency and intensity differences. Specifically, localizing sound depends on 3 main acoustic cues: interaural time disparities at low frequencies and interaural intensity disparities and spectral cues at high frequencies.5,8 Binaural hearing is an essential requirement for spatial hearing and sound localization.9 The recognition
Otolaryngology– Head and Neck Surgery Volume 132 Number 6
that binaural hearing is important has driven otolaryngologists and audiologists to seek safe and effective methods to restore binaural cues in patients with partial bilateral hearing loss. Thus, an emphasis on binaural hearing aid fitting pervades the literature.1,10,11 Surgical redress has extended to such techniques as reconstructive surgery including bilateral stapedectomies or other ossicular reconstruction. The restoration of binaural cues has been documented in persons with bilateral conductive loss with bilateral implantation using BAHA.12 The work of Nopp et al13 highlights the necessity to incorporate sound processing parameters that permit interaural intensity and latency information to be captured. The latter work demonstrates that bilateral cochlear implantation alone may be insufficient to support localization as processing parameters may obliterate fine acoustic distinctions. The patient population exemplified in this study, however, is different due to their complete or nearcomplete unilateral sensorineural hearing loss, also referred to as single sided deafness. These patients have 1 functioning cochlea and therefore have lost their localization potential. In a study evaluating the efficacy of the BAHA as a transcranial contralateral routing signal, we were surprised that 36% of patients reported a capability of sound localization while using their BAHA.14 With only 1 functioning cochlea, no localization was expected. Such subjective patient reports led to our present study design, to assess objectively any localization potential. Our data document poor performance in sound localization by this patient sample in the unaided condition, corroborating psychoacoustic evidence. Our patients correctly pointed to the right source 13% of the time at 500 Hz NB and 19% at 3000 Hz NB (Table 3). Subsequent use of the BAHA did not improve their scores. The difference in performance between the unaided and the BAHA-aided conditions was not statistically significant. In order to simplify the analysis of error, we merged the responses into a laterality judgment, right source vs left source (3 speakers each). The front and back speakers were eliminated. The laterality accuracy was 40% unaided, and 43% BAHA-aided for the 500 Hz NB and 40% unaided, and 40% BAHA-aided for the 3000 Hz NB (Table 5). There was, however, no statistically significant difference between the aided and unaided conditions at either 500 Hz NB or 3000 Hz NB stimulations. The results of this study conform with others.14,15 For example, in 9 USNHL subjects, sound localization and speech perception measurements were obtained in 3 different conditions: before intervention, with a con-
WAZEN et al
931
ventional contralateral routing of sound (CROS) hearing aid, and later with a BAHA implanted in the deaf ear. The results showed no sound localization ability in any of the 3 conditions.14 Although the results of this study show no statistically significant improvement in localization with the use of the BAHA, the testing paradigm is artificial and does not replicate real life experiences. Our patients were limited with narrow band noises in a fixed testing booth. Further studies evaluating different stimuli and the use of the directional microphone may shed more light on the localization potential in this patient population. Despite the lack of documented changes in localization, our patients were still very satisfied with the device. It is possible that some patients’ reports of localization ability were attributable to overcoming the head shadow effect. The lack of localization was counterbalanced against the positive impact of better communication at meetings, the dinner table, in a car, or walking down the street, factors that underlie the significant improvement in their quality of life. In a questionnaire assessing patient satisfaction, 7 (88%) of 8 patients reported great satisfaction with the device, would have the surgery again, and would recommend it to a friend despite the limitation in localization. CONCLUSION Patients with UNSNHL have poorer sound localization abilities compared with the control group at 500 and 3000 Hz NB. Their performance with the BAHA (when implanted on the deaf side) was equivalent to the unaided condition, regardless of stimulus NB frequency. The patients’ gross localization ability for laterality of sound source was poor in unaided and BAHA-aided conditions, regardless of stimulus NB frequency. The patients with single sided deafness were still very satisfied with the BAHA results. References 1. Palmer CV, Mueller GH. Hearing aid selection and assessment. In: Alpiner JG, McCarthy PA, eds. Rehabilitative audiology: children and adults, 3rd ed. Baltimore, Maryland: Lippincott Williams & Wilkins; 2001. p. 332-76 2. Feuerstein JF. Monaural versus binaural hearing: ease of listening, word recognition, and attentional effort. Ear Hear 1992; 13(2):80-6. (Grade B) 3. Middlebrooks JC, Green DM. Sound localization by human listeners. Annu Rev Psychol 1991;42:135-59. (Grade C) 4. Polyakov A, Pratt H. Electrophysiological correlates of azimuth and elevation cues for sound localization in human middle latency auditory evoked potentials. Ear Hear 2003;24(2):143-55. 5. Wightman FL, Kistler DJ. The dominant role of low-frequency interaural time differences in sound localization. J Acoust Soc Am 1992;91(3):1648-61. (Grade C) 6. Wazen JJ, Spitzer JB, Ghossaini SN, et al. Transcranial contralateral cochlear stimulation in unilateral deafness. Otolaryngol Head Neck Surg 2003;129(3):248-54. (Grade C)
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7. American National Standards Institute. Specifications for Audiometers. ANSI S3.6-1996. New York: American National Standards Institute, 1996. 8. Searle CL, Braida LD, Davis MF, et al. Model for auditory localization. J Acoust Soc Am 1976;60:1164-75. 9. Durlach NI, Thompson CL, Colburn HS. Binaural interaction of impaired listeners. a review of past research. Audiology 1981; 20(3):181-211. (Grade C) 10. Kobler S, Rosenhall U, Hansson H. Bilateral hearing aids– effects and consequences from a user perspective. Scandinavian Audiology 2001; 30(4):223-35. (Grade B) 11. Kobler S, Rosenhall U. Horizontal localization and speech intelligibility with bilateral and unilateral hearing aid amplification. Int J Audiol 2002; 41(7):395-400.(Grade C)
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12. Priwin C, Stenfelt S, Granstrom G, et al. Bilateral bone-anchored hearing aids (BAHAs): an audiometric evaluation. Laryngoscope 2004;114(1):77-84. (Grade C) 13. Nopp P, Schleich P, D’Haese P. Sound localization in bilateral users of MED-EL COMBI 40/40⫹ cochlear implants. Ear Hear 2004;25(3):205-14. (Grade C) 14. Bosman AJ, Hol MK, Snik AF, et al. Bone-anchored hearing aids in unilateral inner ear deafness. Acta Otolaryngol 2003;123(2): 258-60. (Grade C) 15. Niparko JK, Cox KM, Lustig LR. Comparison of the bone anchored hearing aid implantable hearing device with contralateral routing of offside signal amplification in the rehabilitation of unilateral deafness. Otol Neurotol 2003;24(1): 73-8. (Grade C)
MD,
SOHA N. GHOSSAINI,
MD,
JACLYN B. SPITZER,
OBJECTIVES: Patients with unilateral hearing loss report difficulty hearing conversation on their impaired side, localizing sound, and understanding of speech in background noise. The bone-anchored cochlear stimulator (BAHA) (Entific, Gothenburg, Sweden) has been shown to improve performance in persons with unilateral severe-profound sensorineural loss (USNHL). The purpose of this study is to evaluate the effectiveness of BAHA in sound localization for USNHL listeners. STUDY DESIGN: Prospective study of 12 USNHL subjects, 9 of whom received implants on the poorer hearing side. A control group of 10 normal hearing subjects were assessed for comparison. Localization with and without BAHA was assessed using an array of 8 speakers at head level separated by 45 degrees. Error analysis matrix was generated to evaluate the confusions, accuracy in response, and laterality judgment. RESULTS: The average accuracy of speaker localization was 16% in the unaided condition, with no improvement with BAHA use. Laterality judgment was poorer than 43% in both aided and nonaided conditions. CONCLUSIONS: Patients with UNSNHL had poor sound localization and laterality judgment abilities that did not improve with BAHA use. (Otolaryngol Head Neck Surg 2005;132:928-32.)
T
he advantages of binaural over monaural hearing are very well recognized in the literature; these include binaural summation, elimination of the head shadow effect, improvement of speech understanding in background noise, in addition to localization of sound in the environment.1,2 Sound localization in the horizontal plane depends on the ability to detect the differences From the Department of Otolaryngology–Head and Neck Surgery, Columbia University College of Physicians and Surgeons (Drs Wazen, Ghossaini, and Spitzer), and Columbia University Medical Center (Drs Wazen, Ghossaini, Spitzer, and Kuller), New York, New York. Presented at the Annual Meeting of the American Academy of Otolaryngology– Head and Neck Surgery, New York, September 20, 2004. Reprint requests: Soha N. Ghossaini, MD, Department of Otolaryngology– Head and Neck Surgery, Columbia University Medical Center, 630 West 168th St, New York, NY 10032; E-mail, [email protected]. 0194-5998/$30.00 Copyright © 2005 by the American Academy of Otolaryngology–Head and Neck Surgery Foundation, Inc. doi:10.1016/j.otohns.2005.03.014
928
PHD,
and MARY KULLER,
MS,
New York, New York
between interaural time and intensity,3 which then are integrated by the central nervous system.4 There is evidence that interaural time difference is important for localizing low-frequency signals and interaural intensity difference is important for localizing high-frequency signals.5 These benefits are part of the rationale for rehabilitative choices that restore binaural stimulation. Patients with unilateral severe to profound sensorineural hearing loss (USNHL), due to the loss of binaural cues, have difficulty with speech understanding in noisy backgrounds and loss of the ability to localize sound sources. In a recent study6 of patients with USNHL, the use of the bone-anchored cochlear stimulator (BAHA) has been shown to alleviate the degree of hearing handicap resulting from the head shadow effect, to improve speech intelligibility in noise, and to improve quality of life. In the same study, the authors noted that 36% of patients reported subjectively that the BAHA has helped them to localize sound to some extent, despite the fact that the sound was channeled through 1 functioning cochlea. The purpose of this study was to quantify the deficit in localization encountered by persons with severe to profound sensorineural hearing loss on 1 side and normal hearing in the better ear and to evaluate the impact of using a BAHA on localization performance. Specifically, the research questions tested were: (1) Is the localization ability of USNHL subjects different than that of normal hearing controls? (2) Does use of a BAHA improve localization ability for USNHL patients? (3) Is gross accuracy, ie, the ability to localize the sound source to one side or the other, improved by use of a BAHA? MATERIALS AND METHODS This was a prospective study of 12 patients with unilateral severe to profound sensorineural hearing loss, 9 of whom subsequently received a BAHA on the worst hearing ear. One patient declined to return for testing in the aided condition and therefore was excluded from the analysis. Institutional Board Review approval was granted for this study. Ten normal hearing controls were also included. The description of the subject sample appears in Table 1. The mean age was 60.38 years (range, 53 to 74). The group was composed of 3 males and 5 females. In 4 (50%) of the cases, the subjects experienced profound hearing loss as a consequence of removal of
Otolaryngology– Head and Neck Surgery Volume 132 Number 6
WAZEN et al 929
Table 1. Subject description (N ⫽ 8)
1
Subject
Affected side
Cause
Age (years)
Gender
S1 S2 S3 S8 S9 S10 S11 S12
L L R L L R L L
Acoustic neuroma Acoustic neuroma Acoustic neuroma Meningitis Acoustic neuroma SSNHL1 SSNHL SSNHL
59 53 74 53 59 54 67 64
M F M F F M F F
Sudden sensorineural hearing loss.
an acoustic neuroma. Causes in the remaining 4 subjects included: 3 (38%) sudden hearing loss, 1 (8.5%) complication of meningitis, and 1 (12%) complication of chronic otitis media. A few of the subjects were included in a clinical trial of single-sided deafness.6 Audiologic Criteria All subjects had preoperative audiological testing under headphones including pure-tone air- and boneconduction thresholds, spondee threshold, and speech recognition using Northwestern University list 6 words. Patients with profound sensorineural hearing loss on 1 side with pure tone thresholds ⬍25 dB at 250 through 4 kHz on the better hearing ear were included in the study. The 3-frequency pure-tone average (PTA3) for the frequencies 0.5k, 1k, 2 kHz) was 101.46 dB HL (SD ⫽ 23.47) with word recognition scores ranging from 0% to 12 % in the affected ear. All equipment was calibrated to the ANSI S.3-1996 standard.7 Localization Testing Localization testing was performed in a soundtreated room; dimensions were 9’10” ⫻ 9’2⬙ with the patient seated in the center, approximately 4 feet from the speakers in any direction. Eight speakers were mounted at head level, separated by 45 degrees (Fig 1). Narrow band noise centered at 500 Hz or 3000 Hz presented at 60 dB HL for a 2 second duration. Localization was tested in 2 different conditions: unaided and BAHA-aided hearing conditions. Randomized trials of 5 presentations per speaker were presented in each hearing condition. This resulted in 40 stimuli per frequency per hearing condition. Subject identified sound source by the number of the speaker. All implanted subjects used the BAHA for at least 1 month before the evaluation of their aided responses. Control group of 10 participants with normal hearing in both ears was used. Data Analysis Subjects’ responses were recorded for subsequent analysis. Hits were calculated as a percentage of the
Fig 1. Layout of localization field; speakers are mounted at head level separated by 45 degrees.
total presentations in that condition, for example, 4 hits/40 presentations ⫻ 100 ⫽ 10% accuracy. Descriptive statistics were calculated. Unaided versus aided performance was examined using t tests for repeated measures. Analysis of variance (ANOVA) was used to evaluate the performance differences of the controls versus the USNHL at each frequency. Laterality judgments were evaluated by collapsing the responses for speakers on the subject’s right (speakers 2, 3, and 4) and those on his or her left (6, 7, and 8). Front/back discrimination was not included in the analysis. The percent correct identification was then calculated as the number of correct identifications of side of origin/the number of total number of presentations to speakers 2, 3, 4, 6, 7, and 8 ⫻ 100. RESULTS Control Subjects Performance of control subjects is summarized in Table 2. Accuracy was 74% for 500 Hz NB and 81% for 3000 Hz NB. The ranges of accuracy were from 65% to 98% at 500 Hz NB and 58% to 100% at 3000 Hz NB. There was no difference in accuracy as a function of frequency (P ⫽ 0.21, NS).
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930 WAZEN et al
Table 2. Summary of percent accuracy* of localization judgments by normal hearing control subjects (N ⫽ 10)
Table 3. Percent accuracy* of unaided localization judgments by subjects with unilateral sensorineural hearing loss (N ⫽ 8)
% Correct Frequency (Hz)
Mean
Minimum
500 3000
74 81
65 58
% Correct Maximum
Frequency (Hz)
Mean
Minimum
Maximum
98 100
500 3000
13 19
8 10
20 35
*Number correct/40 presentations ⫻ 100.
USNHL Performance Table 3 summarizes the accuracy of performance in the unaided condition. The accuracy was 13% correct at 500 Hz NB and 19% at 3000 Hz NB. Table 4 illustrates the accuracy in the BAHA-aided condition. At 500 Hz NB, correct identification was 16% of the time, and 15% at 3000 Hz NB. Accuracy of USNHL subjects was compared for 4 repeated measures with ANOVA. There were no significant differences in performance when comparing results for the 2 stimulus frequency NBs or for unaided versus aided accuracy (F ⫽ 1.42, df ⫽ 7, 24; P ⫽ 0.26, NS). Comparison of Control with USNHL ANOVA for repeated measures was used to test differences in localization accuracy for the controls versus the unaided hearing-impaired sample. At 500 Hz NB, the difference was highly significant (t ⫽ ⫺16.22, df ⫽ 16; P ⬍ 0.001, 2-tailed). At 3000 Hz NB, a similar significant result was obtained (t ⫽ ⫺10.75, df ⫽ 16; P ⬍ 0.001, 2-tailed). Laterality judgments The ability to determine which side the source originated from was evaluated (Table 5). For 500 Hz NB stimuli, the laterality accuracy was 40% unaided, and 43% BAHA-aided. For 3000 Hz NB, the accuracy of laterality judgments was 40% unaided and 40% BAHA-aided. These findings were tested with an ANOVA for repeated measures, with no significant outcome (F ⫽ 0.27, df ⫽ 7, 24, P ⫽ 0.82, NS). All combinations (500 Hz vs 3000 Hz unaided, 500 Hz vs 3000 Hz aided, 500 Hz aided vs 500 Hz unaided, 3000 Hz unaided vs 3000 Hz aided) were not significant (P ⬎ 0.05), as determined using a Dunnett’s control mean comparison test. In summary, the analysis indicated: (1) the USNHL group’s ability to localize was significantly poorer than the control subjects; (2) the performance of the USNHL subjects was equivalent in unaided and aided conditions, irrespective of stimulus NB frequency; and (3) the gross localization ability for laterality of sound
*Number correct/40 presentations ⫻ 100.
Table 4. Percent accuracy* of BAHA-aided localization judgments by subjects with unilateral sensorineural hearing loss (N ⫽ 8) % Correct Frequency (Hz)
Mean
Minimum
Maximum
500 3000
16 15
8 8
23 23
*Number correct/40 presentations ⫻ 100.
Table 5. Percent accuracy* of laterality judgments of subjects with unilateral sensorineural hearing loss % Correct Frequency (Hz)
Unaided
Aided
500 3000
40 40
43 40
*Number of correct identification of side of sound origin/number of presentations ⫻ 100)
source was poor in unaided and aided conditions, regardless of stimulus NB frequency. In this sample, there was no detectable improvement in accuracy as a result of BAHA use. DISCUSSION Sound localization is an important and necessary characteristic of normal binaural hearing that allows human beings the conversational and safety features of recognizing the origin of the sound stimulus. Numerous studies have focused on the mechanisms of sound localization. The ability to detect the stimulus origin depends on both interaural latency and intensity differences. Specifically, localizing sound depends on 3 main acoustic cues: interaural time disparities at low frequencies and interaural intensity disparities and spectral cues at high frequencies.5,8 Binaural hearing is an essential requirement for spatial hearing and sound localization.9 The recognition
Otolaryngology– Head and Neck Surgery Volume 132 Number 6
that binaural hearing is important has driven otolaryngologists and audiologists to seek safe and effective methods to restore binaural cues in patients with partial bilateral hearing loss. Thus, an emphasis on binaural hearing aid fitting pervades the literature.1,10,11 Surgical redress has extended to such techniques as reconstructive surgery including bilateral stapedectomies or other ossicular reconstruction. The restoration of binaural cues has been documented in persons with bilateral conductive loss with bilateral implantation using BAHA.12 The work of Nopp et al13 highlights the necessity to incorporate sound processing parameters that permit interaural intensity and latency information to be captured. The latter work demonstrates that bilateral cochlear implantation alone may be insufficient to support localization as processing parameters may obliterate fine acoustic distinctions. The patient population exemplified in this study, however, is different due to their complete or nearcomplete unilateral sensorineural hearing loss, also referred to as single sided deafness. These patients have 1 functioning cochlea and therefore have lost their localization potential. In a study evaluating the efficacy of the BAHA as a transcranial contralateral routing signal, we were surprised that 36% of patients reported a capability of sound localization while using their BAHA.14 With only 1 functioning cochlea, no localization was expected. Such subjective patient reports led to our present study design, to assess objectively any localization potential. Our data document poor performance in sound localization by this patient sample in the unaided condition, corroborating psychoacoustic evidence. Our patients correctly pointed to the right source 13% of the time at 500 Hz NB and 19% at 3000 Hz NB (Table 3). Subsequent use of the BAHA did not improve their scores. The difference in performance between the unaided and the BAHA-aided conditions was not statistically significant. In order to simplify the analysis of error, we merged the responses into a laterality judgment, right source vs left source (3 speakers each). The front and back speakers were eliminated. The laterality accuracy was 40% unaided, and 43% BAHA-aided for the 500 Hz NB and 40% unaided, and 40% BAHA-aided for the 3000 Hz NB (Table 5). There was, however, no statistically significant difference between the aided and unaided conditions at either 500 Hz NB or 3000 Hz NB stimulations. The results of this study conform with others.14,15 For example, in 9 USNHL subjects, sound localization and speech perception measurements were obtained in 3 different conditions: before intervention, with a con-
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ventional contralateral routing of sound (CROS) hearing aid, and later with a BAHA implanted in the deaf ear. The results showed no sound localization ability in any of the 3 conditions.14 Although the results of this study show no statistically significant improvement in localization with the use of the BAHA, the testing paradigm is artificial and does not replicate real life experiences. Our patients were limited with narrow band noises in a fixed testing booth. Further studies evaluating different stimuli and the use of the directional microphone may shed more light on the localization potential in this patient population. Despite the lack of documented changes in localization, our patients were still very satisfied with the device. It is possible that some patients’ reports of localization ability were attributable to overcoming the head shadow effect. The lack of localization was counterbalanced against the positive impact of better communication at meetings, the dinner table, in a car, or walking down the street, factors that underlie the significant improvement in their quality of life. In a questionnaire assessing patient satisfaction, 7 (88%) of 8 patients reported great satisfaction with the device, would have the surgery again, and would recommend it to a friend despite the limitation in localization. CONCLUSION Patients with UNSNHL have poorer sound localization abilities compared with the control group at 500 and 3000 Hz NB. Their performance with the BAHA (when implanted on the deaf side) was equivalent to the unaided condition, regardless of stimulus NB frequency. The patients’ gross localization ability for laterality of sound source was poor in unaided and BAHA-aided conditions, regardless of stimulus NB frequency. The patients with single sided deafness were still very satisfied with the BAHA results. References 1. Palmer CV, Mueller GH. Hearing aid selection and assessment. In: Alpiner JG, McCarthy PA, eds. Rehabilitative audiology: children and adults, 3rd ed. Baltimore, Maryland: Lippincott Williams & Wilkins; 2001. p. 332-76 2. Feuerstein JF. Monaural versus binaural hearing: ease of listening, word recognition, and attentional effort. Ear Hear 1992; 13(2):80-6. (Grade B) 3. Middlebrooks JC, Green DM. Sound localization by human listeners. Annu Rev Psychol 1991;42:135-59. (Grade C) 4. Polyakov A, Pratt H. Electrophysiological correlates of azimuth and elevation cues for sound localization in human middle latency auditory evoked potentials. Ear Hear 2003;24(2):143-55. 5. Wightman FL, Kistler DJ. The dominant role of low-frequency interaural time differences in sound localization. J Acoust Soc Am 1992;91(3):1648-61. (Grade C) 6. Wazen JJ, Spitzer JB, Ghossaini SN, et al. Transcranial contralateral cochlear stimulation in unilateral deafness. Otolaryngol Head Neck Surg 2003;129(3):248-54. (Grade C)
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7. American National Standards Institute. Specifications for Audiometers. ANSI S3.6-1996. New York: American National Standards Institute, 1996. 8. Searle CL, Braida LD, Davis MF, et al. Model for auditory localization. J Acoust Soc Am 1976;60:1164-75. 9. Durlach NI, Thompson CL, Colburn HS. Binaural interaction of impaired listeners. a review of past research. Audiology 1981; 20(3):181-211. (Grade C) 10. Kobler S, Rosenhall U, Hansson H. Bilateral hearing aids– effects and consequences from a user perspective. Scandinavian Audiology 2001; 30(4):223-35. (Grade B) 11. Kobler S, Rosenhall U. Horizontal localization and speech intelligibility with bilateral and unilateral hearing aid amplification. Int J Audiol 2002; 41(7):395-400.(Grade C)
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12. Priwin C, Stenfelt S, Granstrom G, et al. Bilateral bone-anchored hearing aids (BAHAs): an audiometric evaluation. Laryngoscope 2004;114(1):77-84. (Grade C) 13. Nopp P, Schleich P, D’Haese P. Sound localization in bilateral users of MED-EL COMBI 40/40⫹ cochlear implants. Ear Hear 2004;25(3):205-14. (Grade C) 14. Bosman AJ, Hol MK, Snik AF, et al. Bone-anchored hearing aids in unilateral inner ear deafness. Acta Otolaryngol 2003;123(2): 258-60. (Grade C) 15. Niparko JK, Cox KM, Lustig LR. Comparison of the bone anchored hearing aid implantable hearing device with contralateral routing of offside signal amplification in the rehabilitation of unilateral deafness. Otol Neurotol 2003;24(1): 73-8. (Grade C)