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Older published studies comparing CROS and BAHD
(11,12,15,24) (including a systematic review of these
studies [10]) have generally concluded that BAHD were
preferred for SSD, particularly because of subjective
scores rather than objective improvements in speech in
noise performance. Two newer studies (3,13) used a
BAHD on a headband rather than a percutaneously im-
planted device and found better speech-in-noise results
with noise directed to the better ear with the CROS rather
than the BAHD. Because the skin can attenuate the signal
in the high frequencies substantially (32), the headband is
not a fair comparison of device function in actual usage.
All these studies used wired CROS aids. Patients have
expressed dissatisfaction with the older wired CROS
devices, citing poor cosmetics, discomfort with occlusion
of the better ear, poor sound quality and distortion, social
stigma, ineffective reduction of high ambient noise, elec-
tromagnetic interference by other devices, and interference
with sounds heard in the better ear as reasons for being
dissatisfied with the CROS (2,23,24,33).
Since these studies, evolution in both technologies
(CROS and BAHD) has occurred, particularly in the
CROS wearing experience. Modern CROS aids avoid a
physically wired connection passing behind the head, are
smaller, and do not occlude the functioning ear as much
as older devices. However, both devices have changed
in ways that should improve the sound quality, such as
the sophistication of their signal processing of noise and
speech and adaptive directionality of the microphones.
Hence, the relative rankings of these devices may well
differ from previous studies. Contralateral routing of sound,
whether by CROS or BAHD, can be both deleterious and
helpful in the hearing experience. When speech is directed
to the poorer ear, with noise at the better ear (e.g., SpeN0),
then routing speech to the better ear should increase
performance (12,24). However, in the S0Nbe condition,
contralateral routing actually should decrease perfor-
mance (12,24). In everyday life, the overall benefit will
depend on the relative abundance of these conditions,
which may vary from person to person. Across devices,
the ability of the processor to distinguish noise from
speech and to suppress it, as well as the adaptive direc-
tionality of the microphone system, will determine how
deleterious the S0Npe situation will be.
It is important to note that the degree of head shadow
alleviation is programmable in the CROS device, whereas
it is much more limited by the physics of head impedance
for bone conduction in the BAHD, particularly in the high
frequencies (34).
Our results overall show the trends that we would ex-
pect, i.e., an increase in word recognition with SSD aids
compared to the unaided state in the SpeN0 condition and
a decrease in the S0Npe condition (Fig. 2), an effect also
seen with the QuickSin (Fig. 3). With our relatively low
numbers, neither the benefit or decrement is significantly
different from unaided in Figure 2.
Figure 3 again shows the difference between the con-
dition in which the SSD aid is useful (noise to better ear)
and harmful (noise to poor ear). Our results confirmed,
as expected, that performance is better (lower SNR) in
all device conditions with noise to the poorer ear, i.e.,
in the condition in which the noise is attenuated by the
head shadow before it reaches the better ear to mask
speech. The addition of an SSD aid should lower the
SNR with noise to the better ear, as it would route more
of the speech signal to the better ear. We were not able
to show a significant improvement with either SSD aid
in this condition, but importantly, nor was there a sig-
nificant difference between devices, unlike older studies
(11,12,15,24).
Subjective results for both questionnaires, which are
focused on the particular handicaps of SSD, seem to be
similar for both CROS and BAHD (Figs. 4 and 5) as well
as conditions and duration of use. This finding is in con-
trast to older studies, which admittedly used a different
questionnaire, the APHAB, but often favored the BAHD
(10,18). Perhaps the most telling aspect of the results is
that out of the eight participants, four expressed a pref-
erence for the CROS device, despite at least 6 months
of experience with a BAHD. This finding was not de-
pendent on the device as two of four Cochlear BP100
users preferred the BAHD, with one undecided, and with
the Oticon Medical Ponto Pro, three of four users pre-
ferred the CROS. The main reasons for preferring the
CROS was the sound quality, and reasons for preferring
the BAHD were comfort; those participants who pre-
ferred the BAHD also expressed difficulty with retention
of the dome tips with the CROS and the annoyance of
wearing two aids. It should be noted that for the CROS
device, disposable dome tips were used. Custom-fitted ear
tips may have further improved comfort for the CROS.
This study is the first study to compare BAHD on a
percutaneous implant with newer models of CROS de-
vices and to randomize the exposure. Although previous
studies have randomized exposure (e.g., Hol et al. [14]),
the BAHD was on a headband. The main limitation of this
study is the small number of participants. Although the
number of participants is comparable to some previous
studies (3,14,17), clearly this work should be considered
a pilot study to explore if one device provides greater
benefit than the other in objective or subjective testing.
Differences between the devices, if they exist in objective
or subjective measurements, are likely to be relatively
small if this study can be considered a point estimate.
Obviously, future work will need to include a larger
number of participants to determine if differences be-
tween devices emerge. Other factors to explore include
whether the Unitron CROS aid used in this study is rep-
resentative of all modern wireless CROS aids from other
manufacturers, such as Phonak. It is not known whether
there are differences among different CROS hearing aid
models and different BAHD models. We did not have a
large enough sample to compare Oticon Medical and
Cochlear Corporation BAHD products. Moreover, the
CROS device experience may have been enhanced by
giving participants more than a 2-week trial and with
custom tips rather than domes; these issues should be
considered in future research.
J. FINBOW ET AL.
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