Comparing CROS Hearing Aids and Bone-Anchored Hearing Devices
Finbow et al (2015) evaluated 8 adults with single-sided deafness (SSD) with regard to contralateral routing of signal (CROS) and bone-anchored hearing devices (BHADs). The authors report CROS and BAHDs are the two main interventions used to treat SSD, although they also report cochlear implants (CIs) have also been used to treat SSD. Indeed, CIs have been used to successfully treat SSD (a CI in the SSD ear facilitates binaural, side-specific information to the brain, see references Arndt et al, 2011; Baguley, 2010; Buechner et al, 2010; Tavora-Vieria, 2015; Van Zon, 2015; and Van De Heyning, 2008) allowing the brain to (generally) compare and contrast information from the two sides.
Finbow and colleagues report that “it is well established that the CROS and BAHD do not improve sound localization abilities for people with SSD….” They report that “with our relatively low numbers, neither the benefit or decrement is significantly different from unaided….”
Further they state that “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 authors conclude CROS and BHAD “seem to perform roughly equivalently…” and they state that given the “risks and costs of surgery, we now recommend a trial of CROS hearing aids as first-line SSD treatment option.”
Editor’s Note: It is well known in the psychoacoustics and audiology literature that to understand sound in very difficult listening situations (i.e., noise), the human brain must compare and contrast sound from the left and right sides. The variation in interaural timing differences (ITDs) and interaural loudness differences (ILDs) from both sides (as well as other factors in binaural summation and binaural squelch) provides enormous information and allows the brain to know where to attend/focus and what to focus on. When reliably and clearly transmitted and perceived, these same factors (ITDs, ILDs) allow the brain to assign meaning to sounds. That is, understanding speech-in-noise is not specifically about loudness, per se, but involves many factors to include:
- Signal-to-noise ratio (how loud the signal of interest is above the noise floor),
- Audibility (are all speech sounds present),
- Preservation of acoustic speech cues, and
- Most importantly, the brain’s ability to compare and contrast information from the left and right side to first identify left and right differences (with respect to ILD and ITD) and to assign meaning to sound.
That is, for the brain to maximally understand speech in noise, the brain requires input from the left and right side. Due to the Weber effect, in cases of SSD, BHAD delivers sound to the better cochlea. Thus, although potentially beneficial (see Finbow et al) neither system (CROS or BHAD) provides true binaural hearing in cases of SSD, as only one cochlea is stimulated.
For More Information, References, and Recommendations
Arndt S, Aschendorff. Laszig R, Beck R, Schild C, Kroeger S, Ihorst G, Wesarg T. (2011) Comparison of Pseudobinaural 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.
Finbow J, Bance M, Aiken S, Gulliver M, Verge J, Caissie R. (2015) A Comparison Between Wireless CROS and Bone-Anchored Hearing Devices for Single-Sided Deafness – A Pilot Study. Otology & Neurotology 36:819-825.
Tavora-Vieira D, Marino R, Acharya A, Rajan GP. (2015): The Impact of Cochlear Implantation on Speech Understanding, Subjective Hearing Performance, and Tinnitus Perception in Patients with Unilateral Severe to Profound Hearing Loss. Otology & Neurotology 36:430-436.
Van De Heyning P, Vermeire K, Diebl M. (2008) Incapacitating Unilateral Tinnitus in Single-Sided Deafness Treated by Cochlear Implantation. Ann Otol Rhinol 117:645-652.
Van Zon A, Peters JPM, Stegeman I, Smit AL, Grolman W. (2015) Cochlear Implantation for Patients with Single-Sided Deafness or Asymmetrical Hearing Loss—A Systematic Review of the Evidence. Otology & Neurotology 36:209-219.