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Publication Date



UM campus only

Embargo Period


Degree Type


Degree Name

Doctor of Philosophy (PHD)


Biochemistry and Molecular Biology (Medicine)

Date of Defense


First Committee Member

Xue Zhong Liu

Second Committee Member

Suhrud Rajguru

Third Committee Member

Michael E Hoffer

Fourth Committee Member

Ozcan Ozdamar

Fifth Committee Member

Tony Spahr


Studies have estimated that only 5% of individuals with bilateral profound sensorineural hearing loss receive bilateral cochlear implants (CI) and that a maximum of 36% of CI patients are bilateral recipients. At present, more than 60% of CI recipients function as monaural listeners (MLs), thereby subject to the deficits inherent to monaural listening. These deficits include reduced localization ability and speech perception in noise. Monaural listeners lose access to critical timing and level cues provided through binaural hearing. Providing bilateral input, however, for monaural listeners has the potential to overcome some of these limitations. The objective of this research was to assess the rehabilitative benefits in monaural listeners derived from contralateral routing of signal technology (CROS). The present study aimed to 1) compare the benefits of non-invasive CROS technology to the more invasive bone-anchored implant (BAI) system for monaural listeners, and 2) determine if CROS technology results in improved hearing outcomes in unilateral CI patients and provides similar gains in speech perception in noise to traditional monaural listeners. Speech perception in noise and localization ability was assessed in the unaided (normal ear only/CI only) and aided condition (normal ear +BAI, normal ear + CROS, CI + CROS) condition. Speech in noise stimuli were presented in a sound booth utilizing four speech/noise configurations. Subjects were evaluated in the speech front/noise front (0º/0º azimuth), speech deaf ear/noise monaural ear (90º/270º azimuth), speech monaural ear/noise deaf ear (270º/90º azimuth), and speech front/noise back (0º/180º azimuth) configurations. Three custom stimuli consisting of 1/3 octave narrow band noises centered at 500 and 4000 Hz, as well as a broadband speech stimulus were presented at random to the front hemifield by 19 speakers spatially separated by 10 degrees were used to assess localization error. A prospective clinical trial was conducted to compare the performance of three monaural listening groups in the unaided (monaural) and aided (normal ear +BAI, normal ear + CROS, CI + CROS) conditions. Between and within subject studies comparing BAI to CROS performance demonstrated significant aided benefit for listening in noise across most listening conditions for speech perception in noise with the greatest benefit observed in the speech deaf ear/noise monaural ear (90º/270º azimuth) condition (p<0.0005), with no significant difference in aided performance between BAI and CROS. In the unilateral CI group significant benefit was again observed from unaided to aided (CI+CROS) condition for listening in noise across most listening conditions with the greatest benefit observed in the speech deaf ear/noise monaural ear (90º/270º azimuth) condition (p<0.0005). For tasks of localization, there was no observable benefit in the horizontal plane for any of the subject groups (BAI, CROS or CI+CROS) and no significant difference between systems. These findings support that unilateral CI users are capable of achieving similar gains in speech perception to that of traditional MLs with wireless CROS. Like traditional MLs, unilateral CI subjects present with a high degree of variability on tasks of speech-in-noise performance as a function of the speaker/noise configuration. This variability was observed to resolve with wireless CROS input, allowing for equal performance across listening conditions. These results indicate the use of wireless CROS stimulation in unilateral CI recipients provides increased benefit and an additional rehabilitative option for this population when bilateral implantation is not possible.


Monaural Listener; CROS; cochlear implant; bone anchored implant; unilateral hearing