Performance of Directional Microphone Hearing Aids in Everyday Life

13 Pages·2004·0.94 MB·English

J Am Acad Audiol 13: 295-307 (2002)
Performance of Directional Microphone
Hearing Aids in Everyday Life
Mary T. Cord*
Rauna K. Surr*
Brian E. Walden*
Laurel Olson'
Abstract
This study explored the use patterns and benefits of directional microphone technology in real-
world situations experienced by patients who had been fitted with switchable omnidirectional/directional
hearing aids. Telephone interviews and paper-and-pencil questionnaires were used to assess per-
ceived performance with each microphone type in a variety of listening situations. Patients who
used their hearing aids regularly and switched between the two microphone configurations reported
using the directional mode, on average, about one-quarter of the time. From brief descriptions,
patients could identify listening situations in which each microphone mode should provide supe-
rior performance. Further, they reported encountering listening situations in which an omnidirectional
microphone should provide better performance more frequently than listening situations in which
the directional microphones should be superior. Despite using the omnidirectional mode more
often and encountering situations in which an omnidirectional microphone should provide supe-
rior performance more frequently, participants reported the same level of satisfaction with each
microphone type.
Key Words: Directional microphone, hearing aid benefit, hearing aids, satisfaction
Abbreviations: APHAB = Abbreviated Profile of Hearing Aid Benefit; cd = critical difference;
MPQ = Microphone Performance Questionnaire
Sumario
El estudio explora el patron de use y los beneficios de la tecnologia del micr6fono direccional en
situaciones de la vida real experimentadas por pacientes a quienes se les han adaptado audi-
fonos con un modo intercambiable omnidireccional/direccional. Se utilizaron entrevistas telef6nicas
y cuestionarios a papel y lapiz para evaluar el rendimiento percibido con cada tipo de microfono
en una variedad de situaciones de escucha. Los pacientes que utilizaron su auxiliar auditivo regu-
larmente y alternaron entre las dos configuraciones microf6nicas, reportaron el use del modo
direccional, en promedio, un cuarto del tiempo total. De descripciones breves, los pacientes
pudieron identificar situaciones de escucha donde cada modalidad de microfono deberia aportar
un rendimiento superior. Mas aOn, ellos reportaron mas frecuentemente situaciones de escucha
donde un microfono omnidireccional deberia dar mejor rendimiento, que situaciones en las que
un microfono direccional deberia comportarse en forma superior. A pesar de utilizar el modo omni-
direccional mas a menudo y de encontrar situaciones en las que el micr6fono omnidireccional
deberia dar un rendimiento superior mas a menudo, los participantes reportaron el mismo nivel
de satisfacci6n con cada tipo de microfono.
Palabras Clave: microfono direccional, beneficio del auxiliar auditivo, auxiliar auditivo, satisfacci6n
Abreviaturas: APHAB = Perfil Abreviado de Beneficio del Auxiliar Auditivo; cd = diferencia critica;
MPQ = Cuestionario de Rendimiento del Micr6fono
ifficulty understanding speech in the phones are one of the few options available on
presence of background noise is a com- wearable hearing aids that can improve speech
D mon complaint of hearing aid users and understanding in noise. Although many studies
a primary reason for dissatisfaction with hear- have demonstrated this advantage in controlled
ing aids (Kochkin, 1993). Directional micro- laboratory situations (Neilsen, 1973; Chasin,
*Army Audiology and Speech Center, Walter Reed Army Medical Center, Washington, DC; tGN ReSound North America
Research Audiology Group, Chicago, Illinois
Reprint requests Mary T. Cord, Army Audiology and Speech Center, Walter Reed Army Medical Center, Washington,
DC 20307-5001
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Journal of the American Academy of Audiology/Volume 13, Number 6, June 2002
1994; Valente et al, 1995; Agnew and Block, Hawkins and Yacullo, 1984; Leeuw and
1997; Voss,1997; Preves at al, 1999; Ricketts and Dreschler, 1991; Ricketts, 2000). In everyday
Dhar, 1999; Wouters et al, 1999; Boymans and listening situations, such factors are uncon-
Dreschler, 2000; Pumford et al, 2000), the extent trolled and may interact in complex ways to
to which this advantage is realized in the real limit the benefit from directional microphones.
world is less clear. In some studies in which sub- Several procedural aspects of the clinical
jective benefit, preference, or both were assessed trial done by Walden and colleagues (2000) may
in everyday life, directional microphones also account for the minimal reported differences
appeared to provide a substantial performance between the two microphone types in daily life.
advantage over omnidirectional microphones in To minimize bias, participants were not told what
certain listening situations (Mueller et al, 1983; the different memories (omnidirectional and direc-
Kochkin, 1996; Kuk, 1996; Schuchman et al, tional) of the trial hearing aids were for or how
1999; Yueh et al, 2001). Other studies in which to optimize their use. They were simply instructed
both laboratory and field measures were obtained to switch between the different memories in each
suggest that the directional benefit perceived in new listening situation they encountered. Fur-
everyday listening environments typically is less thermore, no control was exercised over the types
than might be expected based on the directional of listening situations participants encountered
advantage observed in the laboratory (Nielsen, in their everyday life over the course of the 6-week
1973; Valente et al, 1995; Preves et al, 1999; trial. Consequently, if participants had encoun-
Boymans and Dreschler, 2000). tered few noisy environments during the trial
A discrepancy between laboratory and field period, they would have had little opportunity to
measures was also noted in a recently completed experience the potential benefits of the direc-
clinical trial of switchable omnidirectionaVdirec- tional microphone configuration.
tional microphone hearing aids (Walden et al, To learn more about the real-world benefits
2000). Participants performed significantly bet- of directional microphone technology, clinic
ter on speech recognition in noise tasks in the lab- patients were queried about their experiences
oratory when using a directional microphone and satisfaction with their switchable omnidi-
mode than they did with an omnidirectional rectional/directional hearing aids. Clinic patients,
microphone mode. However, these dramatic per- in contrast to the clinical trial participants,
formance differences were not seen in the field received instruction from the dispensing audi-
measures of perceived benefit in everyday life. ologist in how to optimize the directional micro-
When participants were asked to compare the two phone effect. Further, the majority of these clinic
microphone configurations in everyday listening patients presented with the complaint of diffi-
situations, they reported only small, nonsignifi- culty hearing in noise with their current hear-
cant differences between the omnidirectional and ing aids, which is why the directional microphone
the directional microphones. hearing aids were recommended to them by
There are a number of possible explana- their audiologist. We can assume that these
tions for the disparity between laboratory and patients encounter noisy situations that are
real-world performances of directional micro- enough of a problem that they were willing to
phones. Prominent among these is that labora- invest in new hearing aids with the expecta-
tory measures of speech recognition in noise tion that their ability to understand speech in
may overestimate the practical benefits of direc- noise would be improved.
tional microphones (Amlani, 2001). Laboratory The following questions were addressed in
test conditions are often configured to take this investigation:
advantage of directional microphone technol- 1. Do patients who are fitted with binaural
ogy (i.e., signal presented from the front and switchable omnidirectional/directional hear-
noise from the back or sides) and may be quite ing aids use the directional option in daily
different from listening situations experienced living and, if so, how much?
by patients in the real world. The effectiveness 2. Do experienced users of these hearing aids
of directional microphones is influenced by spe- recognize the characteristics of everyday
cific aspects of the acoustic environment, such listening situations that provide the great-
as reverberation, the listener's distance from est performance advantages for directional
the signal, and the degree of separation of the microphones?
signal from the competing noise (Nielsen and 3. How frequently are such listening situa-
Ludvigsen, 1978; Mueller and Johnson, 1979; tions encountered in everyday life?
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Performance of Directional Microphone Hearing Aids/Cord et al
You are at a restaurant having lunch with a friend who is seated across the table from
you. You are seated with your back toward a large group of people who are talking
loudly.
a o 0
Omnidirectional Omnidirectional Omnidirectional No difference Directional is Directional is Directional is
is much better is better is a little better a little better better much better
0 Every day
Several times a week
0 Several times a month
How often are you in this type of situation? About once a month
0 Several times a year
Once or twice a year
Fj I am never in this situation
Figure l A sample item from the Microphone Performance Questionnaire (MPQ). Items were scored on a 7-point scale,
with 1 indicating "omnidirectional is much better" and 7 indicating "directional is much better."
METHOD assess both unaided performance ("without
my hearing aid") and aided performance
linic patients who had obtained binaural ("with my hearing aid"). For this study, the
C
switchable omnidirectional/directional APHAB response form was modified so that
microphone hearing aids at least 6 months, but a rating was obtained for each microphone
not more than 2 years, previously were con- type. That is, participants rated each item
tacted for a telephone interview. Those who to indicate their aided performance with
reported regular use of their hearing aids (at the omnidirectional microphone configura-
least 4 hours/day) and indicated at least occa- tion and with the directional microphone
sional use of both microphone configurations configuration.
were mailed two paper-and-pencil question-
naires designed to compare perceived perfor- Microphone Performance Questionnaire
mance between the two microphone types in a
variety of listening environments. Participants were also asked to complete the
Microphone Performance Questionnaire (MPQ).
Questionnaires The MPQ was developed for use in this study
and describes listening situations in which
Abbreviated Profile of Hearing Aid Benefit there should be an advantage for either the
omnidirectional or directional microphone con-
Participants were asked to complete the figuration. The 31 items were created by sys-
Abbreviated Profile of Hearing Aid Benefit tematically varying the listening situations
(APHAB, Cox and Alexander, 1995), a 24-item with respect to presence or absence of noise,
self-assessment inventory designed to assess amount of reverberation, location of the signal,
hearing aid benefit in daily life. The APHAB location of the noise, and distance of the listener
yields subscale scores for perceived speech com- from the signal. The categorization of each MPQ
munication ability in favorable, reverberant, item according to these situational variables
and noisy environments, as well as for reac- is given in the Appendix. Using a 7-point scale,
tions to loud environmental sounds. Partici- participants indicated which of the two micro-
pants are asked to indicate their agreement phone modes they believed would work best for
with each statement (e.g., "It's hard for me to them in each situation described in the ques-
understand what is being said at lectures or tionnaire. Participants also indicated how fre-
church services.") on a 7-point response scale. quently they encounter listening situations like
The standard APHAB response format the one described. Figure 1 displays a sample
asks respondents to rate each item twice, to item.
297
Journal of the American Academy of Audiology/Volume 13, Number 6, June 2002
0,
Right DOMNI
20 ~ -c- Left "DIR
m 40 -
'= 60 -
L
N
N 80
L
H
120
120 -1 . ~ I . ~ . - ~-~ i~-*~~-,-,~
EC RV BN AV
100 1000 10,000
Subscales
Frequency (Hz)
Figure 3 Mean Abbreviated Profile of Hearing Aid Ben-
Figure 2 Mean audiometric data for 48 participants. The efit (APHAB) results comparing aided performance with
error bars in this and subsequent figures indicate 1 SD. omnidirectional (OMNI) and directional (DIR) micro-
phones. Note that data are presented as "frequency of suc-
RESULTS cess" (100 minus the frequency of problems), so that a
higher score indicates better performance. APHAB sub-
scales: EC = ease of communication; RV = reverbera-
Telephone Interview
tion; BN = background noise; AV = aversiveness.
One hundred and twelve patients were con- devices, following the manufacturer-recom-
tacted by telephone. Twenty-two (20%) reported mended procedures.
less than 4 hours/day of hearing aid use. Four As part of the telephone interview, partici-
patients had hearing aids in need of repair. pants were asked to estimate the percentage of
Three patients reported using the directional time they used each microphone type. On average,
mode very rarely and for only one particular they reported using the omnidirectional micro-
situation (in the car, in a restaurant). Twenty- phone 77.7 percent of the time (SD = 24.3, range
six patients (23%) were not switching between = 10-99%) and the directional microphone 22.3
the two microphone configurations for various percent of the time (SD = 24.3, range = 1-90%).
reasons (e.g., did not understand the different
settings of their hearing aids, did not notice any APIIAB
difference between omnidirectional and direc-
tional, just did not bother to switch from the Figure 3 displays the mean APHAB results
default setting). Because these patients were comparing aided performance between the omni-
less likely to make reliable comparisons of the directional and directional microphones. Note
two microphone configurations, they were not that data are presented as "frequency of success"
asked to complete the questionnaires. (100 minus the frequency of problems), so that
The remaining 57 (51%) patients met the a higher score indicates better performance.
inclusion criteria (reported regular use of their Four of the returned questionnaires were incom-
hearing aids and at least occasional use of both plete. Thus, these results are based on 44 par-
microphone configurations) and were mailed ticipants. Analysis of variance on the four
the APHAB and the MPQ. Forty-eight patients subscales revealed both a significant main effect
completed and returned the questionnaires. for microphone type (F = 34.4, p < .00001) and
This group had an average age of 73.6 years a significant interaction of microphone type and
(SD = 8.9, range = 45-91). Their mean audiogram subscales (F = 8.1, p < .0001). T- tests on the
is shown in Figure 2. Average duration of hear- individual subscales revealed significant dif-
ing aid use was 11.6 years (SD = 7.1, range = ferences between the two microphone configu-
0.5-34) and average duration of hearing aid use rations (ease of communication, t = 3.0, p < .05;
per day was 12.3 hours (SD = 4.4, range = 4-18). reverberation, t = 3.4, p <.01; background noise,
Several different hearing aid makes and mod- t = 5.4, p < .00001; and aversiveness subscales,
els were worn by these patients, but all fea- t = 4.3, p < .001). For each subscale, partici-
tured a switchable directional/omnidirectional pants reported fewer communication problems
microphone through remote control or a switch when using the directional microphone.
or button on the hearing aid itself. Detailed In Figure 4, individual difference scores
descriptions of the hearing aid fittings were not (directional minus omnidirectional) for the four
available. However, all instruments were fit by APHAB subscales are displayed. Bars above the
audiologists experienced in the fitting of these zero line indicate better performance with the
298
Performance of Directional Microphone Hearing Aids/Cord et al
EC: 0 exceed 90% cd RV: 13 (30%) exceed 90% cd
55 55
45 45
35 35
25 ------------------- ------------ A- 25 .n
Z 15 15 T E
O 5 "mom 5 19 u LS1
v7 -5 `U -5 K-
U
c -15 -15
-25 --------------------------------- -25
-35 -35
D
BN: 14 (32%) exceed 90% cd AV: 4 (9%) exceed 90% cd
U
55 55
C!)
45 45
0
>, 35 35
25
a 15 -n-~-~--rr- 11 a-fl
15
a) 5 I11 111h1h n R1 4 5 rh-n I I , f
u_ -5 -5
-15 -15
-25 ---------------------tr..----------- -25 r-----------------------------
-35 Individual Subjects -35 Individual Subjects
Figure 4 Differences between omnidirectional and directional microphone ratings for the Abbreviated Profile of Hear-
ing Aid Benefit (APHAB) subscales for each of 44 participants. Each bar represents one participant. Bars above the
zero line indicate better performance with the directional microphone. Bars below the zero line indicate better perfor-
mance with the omnidirectional microphone. The 90 percent critical difference (cd) for each subscale is as indicated by
the dashed line. EC = ease of communication; RV = reverberation; BN = background noise; AV = aversiveness.
directional microphone than with the omnidi- MPQ
rectional microphone. The dashed horizontal
lines indicate the 90 percent critical difference Ratings for each item of the questionnaire
(cd) values for each subscale. Difference scores were averaged across participants and rank
that exceed this value likely reflect true differ- ordered from the item that was rated highest
ences rather than those occurring by chance. for the directional microphone to the item rated
Some of the participants exceeded the cd for the highest for the omnidirectional microphone,
reverberation and background noise subscales, and quartiles were calculated. One question-
and a few exceeded the cd for the aversiveness naire was returned incomplete; therefore, these
subscale. None of the participants exceeded the data are based on the responses of 47 partici-
cd for the ease of communication subscale. pants. The characteristics of items in each
The APHAB revealed relatively small but quartile are displayed in Figure 5. The first
statistically significant differences for the omni- quartile includes the items that most strongly
directional and directional microphones, with favored directional microphone use. The mean
participants reporting fewer communication rating for these items is 5.8, which corresponds
problems on average when using the directional to "directional is better" on the 7-point response
microphone mode, especially for the background scale. Panel A displays the characteristics of
noise subscale. However, individual data revealed these items. Note that in every case the loca-
relatively few significant differences. It should be tion of the signal is in front and that noise is
noted that the APHAB was not designed to com- present. Additionally, directional microphones
pare microphone configurations. Item wording is tend to be favored when the signal source is rel-
quite general; that is, characteristics of the lis- atively near and when the competing noise is
tening environment that may be critical for direc- behind the listener, rather than at some other
tional microphone benefit (e.g., location of signal location. An example of an item from the first
source) are not always apparent. quartile is "You are at a restaurant having
299
Journal of the American Academy of Audiology/Volume 13, Number 6, June 2002
A
1st Quartile (Favor DIR)
Mean Rating = 5.8, "Directional is Better"
N
E
N
O
C
N
U
N
a
Front Other Near Far Low High Present Absent Back Other
Signal Location Signal Distance Reverberation Noise Noise Location
B
2nd Quartile
Mean Rating = 5.1, "Directional is a Little Better"
Front Other Near Far Low High Present Absent Back Other
Signal Location Signal Distance Reverberation Noise Noise Location
C
3rd Quartile
Mean Rating = 3.2, "Omnidirectional is a Little Better"
100
co 80
E
a)
60
0
c 4011
N
U
N 20 ffl f :i I E- 1
0 J
Front Other Near Far Low High Present Absent Back Other
Signal Location Signal Distance Reverberation Noise Noise Location
D
4th Quartile (Favor OMNI)
Mean Rating = 2.2, "Omnidirectional is Better"
Front Other Near Far Low High Present Absent Back Other
Signal Location Signal Distance Reverberation Noise Noise Location
Figure 5 Characteristics of the Microphone Performance Questionnaire (MPQ) items whose mean rating placed them
in the first quartile (panel A), second quartile (panel B), third quartile (panel C), and fourth quartile (panel D). The
first quartile encompasses the items that most strongly favored use of the directional microphone. The fourth quartile
encompasses the items that most strongly favored use of the omnidirectional microphone.
300
Performance of Directional Microphone Hearing Aids/Cord et al
lunch with a friend who is seated across the
table from you. You are seated with your back
toward a large group of people who are talking
loudly."
Panel B displays the characteristics of items
in the second quartile (mean rating 5.1: "direc-
tional is a little better"). These items (i.e., lis-
tening situations) share characteristics in
common with those in the first quartile, except 1 st Quartile 4th Quartile
that more of the items describe situations where (Favor DIR) (Favor OMNI)
reverberation is present or where the competing
Figure 6 Mean ratings of the frequency with which sit-
noise is at a location other than behind the lis- uations described in the first and fourth quartiles of the
tener (i.e., more diffuse). Microphone Performance Questionnaire (MPQ) are
Panel C displays the characteristics of items encountered (n = 47).
in the third quartile (mean rating 3.2: "omnidi-
rectional is a little better"). The most notable
change from the first two quartiles is for signal How Often Are These Situations
location: the omnidirectional microphone tends Encountered?
to be preferred when the signal is from a loca-
tion other than in front of the listener. Addi- Recall that the MPQ asked participants to
tionally, noise is generally absent. In the few rate (on a 7-point scale) how often they experi-
instances where noise is present, it is from a loca- ence the listening situations described by each
tion other than behind the listener. item. Figure 6 displays the frequency with which
The fourth quartile includes the items that the situations in the first quartile (favor direc-
most strongly favor omnidirectional microphone tional) and fourth quartile (favor omnidirec-
use (mean rating 2.2: "omnidirectional is better"). tional) are encountered in participants' everyday
Panel D displays the characteristics of these life. Participants reportedly encounter signifi-
items. In these listening situations, the loca- cantly more situations that favor omnidirec-
tion of the signal is other than front, noise is tional microphone use (p < .0001). This is
almost always absent, and reverberation is low. consistent with the report noted earlier that, on
An example of an item that fell in the fourth average, participants used the omnidirectional
quartile is "You are out taking a walk on a quiet mode 77.7 percent of the time and the directional
neighborhood street and want to be able to hear mode only 22.3 percent of the time.
cars, bicycles, and other pedestrians approach-
ing from behind you." Satisfaction
In summary, the results of the MPQ
revealed that, overall, the most important sit- As part of the initial telephone interview,
uational conditions in determining which micro- patients were asked to rate overall satisfaction
phone configuration is preferred are spatial with their hearing aids, as well as satisfaction
location and separation of the signal and the with the omnidirectional microphone mode and
competing noise. Participants reported that the directional microphone mode. These results
directional microphones are preferred when are displayed in Figure 7. Overall, the 48 par-
the signal is in front and a competing noise is ticipants reported being "satisfied" with their
to the rear. As the location of the noise source hearing aids and with each microphone config-
moves from behind the listener (or becomes uration. Even though most participants used
more diffuse) or as reverberation increases, the the directional microphone much less frequently
directional microphone is somewhat less effec- than the omnidirectional microphone, they were
tive, though still preferred to the omnidirec- equally satisfied with the performance of the
tional microphone. The omnidirectional directional microphone in situations where they
microphone is preferred over the directional did use it.
when the signal is located other than in front
of the listener, reverberation is low, and noise DISCUSSION
is either absent or coming from a location other
than behind the listener. The strength of pref- his study explored the real-world use pat-
erence for either microphone type decreases as T terns and perceived benefits of directional
reverberation increases. microphone technology among experienced users
301
Journal of the American Academy of Audiology/Volume 13, Number 6, June 2002
Very Satisfied 7 Do experienced users of these hearing aids rec-
Satisfied 6 ognize the characteristics of everyday listening sit-
Somewhat Satisfied 5 uations that provide the greatest performance
advantages for directional microphones? Patients
Neutral 4
who reported regularly using both microphone
Somewhat Dissatisfied 3 modes could recognize listening situations in
Dissatisfied 2 which directional microphones should provide a
Very Dissatisfied t performance advantage over an omnidirectional
Overall OMNI DIR microphone. Results of the APHAB showed a
Satisfaction Satisfaction Satisfaction significant preference for the directional micro-
phone in situations where background noise was
Figure 7 Mean ratings for overall hearing aid satis-
faction, satisfaction with the omnidirectional microphone present. This finding is in general agreement
mode, and satisfaction with the directional microphone with APHAB results reported by Valente and
mode (n = 48). colleagues (1995), Preves and colleagues (1999),
and Boymans and Dreschler (2000).
of switchable omnidirectionaldirectional micro- Results of the MPQ revealed that the direc-
phone hearing aids. The following questions tional microphone mode was judged to be most
were addressed: helpful in situations where noise is present, the
Do patients who are fitted with binaural signal is in front of the listener, and the signal
switchable omnidirectional/directional hearing source is relatively near. As the noise becomes
aids use the directional option in daily living and, more diffuse or reverberation increases, the
if so, how much? It appears that a substantial directional microphone mode was judged to be
percentage of patients who are fitted with switch- less helpful. Patients reported the omnidirec-
able omnidirectionaUdirectional hearing aids tional microphone to be most helpful in situations
eventually do not use the directional micro- where the location of the signal was other than
phone option. Of the patients contacted who front (i.e., behind, beside, all around) and noise
reported using their hearing aids for at least was absent.
4 hours/day, over one-third of them were not These patient reports are consistent with
switching between the two microphone config- the signal processing provided by each micro-
urations, generally leaving the hearing aids set phone type and suggest that patients can iden-
to the default (omnidirectional) mode. This find- tify listening situations in their everyday lives
ing is in agreement with that of Kuk (1996), that should favor one microphone type or the
who observed that one-third of patients fitted other. It may be argued that participants were
with switchable omnidirectionaUdirectional hear- simply reporting back what they had been told
ing aids used their instruments almost exclu- by their audiologist or read in hearing aid pam-
sively in one mode, usually omnidirectional. phlets about listening situations that should
Two reasons were commonly reported by the favor each microphone mode. However, it is
participants in the current study for not using unlikely that, after 6 months to 2 years of expe-
the directional microphones. First, many of these rience, users would continue to switch to the
patients could not remember what the different directional microphone if it did not provide ben-
programs of their hearing aids were or how to efit over the omnidirectional mode. That partic-
use them. Second, a number of patients reported ipants were able to discern the influences of
that the directional microphone feature pro- reverberation and signal distance on microphone
vided no advantage over the omnidirectional effectiveness and did not base their responses
when they had tried to use it. strictly on the presence or absence of noise in the
The patients who used both microphone listening environment provides further support
modes reported using the omnidirectional mode, for the notion that participant responses were
on average, more than three-quarters of the based on real-world experience.
time. This use pattern may be influenced by How frequently are such listening situations
the omnidirectional mode being programmed encountered in everyday life? In everyday life,
as the default setting of the hearing aids for all participants reported encountering far fewer sit-
the participants in this study. Patients fitted uations of the type that favored directional micro-
with switchable omnidirectionaUdirectional hear- phone use than of the type that favored
ing aids are generally instructed to use the omnidirectional microphone use. However, the fre-
default setting for most situations and to switch quency with which situations that favor one or the
to the directional mode when in a noisy place. other microphone mode were encountered was not
302
Performance of Directional Microphone Hearing Aids/Cord et al
related to overall hearing aid satisfaction or sat- ipants had difficulty finding situations in their
isfaction with either microphone configuration. daily lives in which there was a clear perfor-
mance advantage for one microphone mode over
CONCLUSIONS the other, and, in situations where performance
differences were noted, they tended to be sub-
number of studies have demonstrated the tle. The findings of the study of Surr and col-
A superiority of directional microphone tech- leagues (2002) highlight the importance of
nology for improved speech understanding in counseling patients regarding realistic expec-
noise in controlled laboratory settings. However, tations of directional microphone technology.
this dramatic directional microphone advantage The results of the current study demonstrate
has not been observed in some field measures of that patients who persist in experimenting with
perceived benefit in everyday life. Results of this the directional microphone option in daily living
study suggest that the disparity between labo- are eventually able to identify the listening sit-
ratory and field results are primarily due to the uations in which they will derive significant
specific characteristics of the listening situa- benefit from its use.
tions encountered in daily living. When the every-
day listening situation closely matches the ideal Acknowledgment. This work received support from GN
conditions in the laboratory (i.e., signal in front ReSound Corporation, Copenhagen, Denmark. Local
of and relatively close to the listener, spatial approval and monitoring of the study was provided by
separation of the signal and the noise), a strong the Department of Clinical Investigation, Walter Reed
Army Medical Center, under Work Unit 01-2501. All par-
preference for the directional microphone is
ticipants in the study volunteered and gave informed
reported. However, it appears that this specific consent. The opinions or assertions contained herein are
set of circumstances occurs less frequently in the private views of the authors and are not to be con-
daily living than conditions that are less favor- strued as official or as reflecting the views of the
able to directional microphones or that actually Department of the Army or the Department of Defense.
Portions of this study were presented at the Annual
favor omnidirectional microphone use.
Convention of the American Academy of Audiology, San
The results of this study reinforce the impor- Diego, California, April 2001.
tance of the prefitting evaluation of patients
who may be candidates for switchable omnidi- REFERENCES
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APPENDIX
Microphone Performance Questionnaire (MPQ) Items
Mean Signal Signal Noise Noise Reverberation
Item Item (Front/ (Near/ (Present/ (Back/ (Low/
Number Item Rating Other) Far) Absent) Other) High)
4 You are at a restaurant having lunch with 6.15 Front Near Present Back High
a friend who is seated across the table
from you. You are seated with your back
toward a large group of people who are
talking loudly.
13 You are seated in the middle of a large, 6.00 Front Near Present Other High
crowded, noisy cafeteria or dining hall
having lunch and are conversing with
the person seated directly across the
table from you. There are the sounds of
many people talking at tables all around
you, trays, dishes, and cutlery clattering,
etc.
16 You are having a face-to-face conversa- 5.98 Front Near Present Back High
tion with someone at a reception in a
hotel ballroom. You are standing with
your back toward the band, which is
playing loud music.
6 You are outdoors at a large, noisy party 5.93 Front Near Present Other Low
or reception and are in face-to-face
conversation with one person. There is
music playing and people are talking
loudly all around you.
18 You are at an outdoor gathering talking 5.70 Front Near Present Back Low
to a friend or family member. Behind you,
adults are trying to comfort a crying child.