Contralateral routing of signal (CROS) amplification systems are intended to be used when (essentially) one ear is normal or has a mild/moderate hearing loss (i.e., is generally a candidate for amplification) and the other ear is (more-or-less) not “aidable.” CROS hearing aids might be recommended for single-sided deafness (SSD) or for people with very poor unilateral word recognition scores. BiCROS (bilateral microphones with contralateral routing of signal) amplification systems are sometimes recommended when both ears have hearing loss, but one ear hears substantially “better” than the other.
Hayes (2006) notes that CROS and BiCROS systems may be wired, wireless, or transcranial. Hayes notes that “It is not very realistic to expect substantial benefit with a CROS aid in most types of background noise. The resources required for perceiving speech in a diffuse noise background (localization and figure/ground separation) cannot be provided by a device that only aids one ear. Those skills require binaural input….”
With respect to single-sided deafness, other treatments are available that include bone-anchored hearing solutions (BAHS), cochlear implants (CIs), and dental prosthetics. Arndt and colleagues (2011) reported that SSD patients who received CIs experienced improved hearing and had better localization percepts than did people with CROS and BAHS. Of note, their data suggests binaural integration of acoustic/natural and electric/CI auditory signals is possible. Popelka and colleagues (2010) report there are 60,000 new SSD patients annually and they described an intra-oral (i.e., dental) bone-conduction device with a microphone in the ear canal and a sealed thin, flat piezoelectric vibratory transducer (and battery) custom made to fit alongside the teeth. In their preliminary report of 12 patients, they review many successes, among them a possible 37 percent increase in speech recognition in noise.
Oeding and Valente (2013) note that noise reduction (NR) was recently introduced on the receiver and transmitter sides of two BiCROS systems. Their goal was to examine differences in the reception threshold for sentences (RTS) using the Hearing In Noise Test (HINT) across four conditions—(1) unaided, (2) no NR, (3) mild NR, and (4) maximum NR conditions. Twenty one adults with asymmetric sensorineural hearing loss participated and the NAL-NL1 prescriptive targets were used. Participants acclimatized for four weeks.
Oeding and Valente report that “no significant differences were found (with regard to the RTS) across the four conditions. Further, they state that “none of the three aided listening conditions were significantly different from unaided performance…” consistent with “…previous studies examining CROS hearing aids….” However, subjectively, significant benefits were found via the APHAB (Abbreviated Profile of Hearing Aid Benefit) on EC, BN, and RV subscales. The authors suggest that the contradiction between objective and subjective measures may be due to subjective factors not addressed in their protocol.
For More Information, References, and Recommendations
Arndt S, Aschendorff A, Laszig R, Beck R, Schild C, Kroeger S, Ihorst G, Wesarg T. (2011) Comparison of Pseudo-binaural Hearing to Real Binaural Hearing Rehabilitation After Cochlear Implantation in Patients With Unilateral Deafness and Tinnitus. Otology & Neurotology 32(1):39-47
Baguley DM. (2010: Cochlear Implants in Single-Sided Deafness and Tinnitus. Seminars in Hearing 31(4):410-413.
Buechner A, Brendel M, Lesinki-schiedat A, Wenzel G, Frohne-Buechner C, Jaeger B, Lenarz, T. (2010) Cochlear Implantation in Unilateral Deaf Subjects Associated With Ipsilateral Tinnitus. Otology & Neurotology 31(9):1381-1385.
Hayes D. (2006) A Practice Guide to CROS and BiCros. Audiology Online June 24.
Oeding K, Valente M. (2013) Sentence Recognition in Noise and Perceived Benefit of Noise Reduction on the Receiver and Transmitter Sides of a BiCROS Hearing Aid. Journal of the American Academy of Audiology 24:980-991.
Popelka GR, Derebery J, Blevins NH, Murray M, Moore BCJ, Sweetow RW, Wu B, Katsis M. (2010) Preliminary Evaluation of a Novel Bone-Conduction Device for Single-Sided Deafness. Otology & Neurotology 31:492-497.