Background: Bilateral contralateral routing of signals (BiCROS) hearing aids function to restore
audibility of sounds originating from the side of the unaidable ear. However, when
speech is presented to the side of the aidable ear and noise to the side of the unaidable
ear, a BiCROS arrangement may reduce intelligibility of the speech signal. This negative
effect may be circumvented if an on/off switch is available on the contralateral routing
of signals (CROS) transmitter.
Purpose: This study evaluated if the proper use of the on/off switch on a CROS transmitter
could enhance speech recognition in noise and sound localization abilities. The participants’
subjective reactions to the use of the BiCROS, including the use of the on/off switch
in real-life were also evaluated.
Research Design: A between-subjects, repeated-measures design was used to assess differences in speech
recognition (in quiet and in noise) and localization abilities under four hearing
aid conditions (unaided, unilaterally aided, fixed BiCROS setting, and adjusted BiCROS
setting) with speech and noise stimuli presented from different azimuths. Participants
were trained on the use of the on/off switch on the BiCROS transmitter before testing
in the adjusted BiCROS settings. Subjective ratings were obtained with the Speech,
Spatial, and Sound Quality (SSQ) questionnaire and a custom questionnaire.
Study Sample: Nine adult BiCROS candidates participated in this study.
Data Collection and Analysis: Participants wore the Widex Dream-m-CB hearing aid on the aidable ear for 1 week.
They then wore the BiCROS for the remainder of the study. Speech recognition and localization
testing were completed in four hearing aid conditions (unaided, unilateral aided,
fixed BiCROS, and adjusted BiCROS). Speech recognition was evaluated during the first
three visits, whereas localization was evaluated over the course of the study. Participants
completed the SSQ questionnaire before each visit. The CROS questionnaire was completed
at the final visit. A repeated measures analysis of variance with Bonferroni post
hoc analysis was used to evaluate the significance of the results on speech recognition,
localization, and the SSQ.
Results: The results revealed that the adjusted BiCROS condition improved speech recognition
scores by 20 rau (rationalized arcsine unit) when speech was presented to the aidable
ear and localization by 37% when sounds are presented from the side of the unaidable
ear over the fixed BiCROS condition. Statistically significant benefit on the SSQ
was also noted with the adjusted BiCROS condition compared to the unilateral fitting.
Conclusions: These findings supported the value of an on/off switch on a CROS transmitter because
it allows convenient selective transmission of sounds. It also highlighted the importance
of instructions and practice in using the BiCROS hearing aid successfully.
Key Words
Asymmetrical sensorineural hearing loss - bilateral contralateral routing of signals
- contralateral routing of signals - hearing aid - localization - speech recognition
- unilateral hearing loss - on/off switch
