LM105 - Overcoming the Head Shadow: Demystifying CROS BiCROS Verification

As a profession, we have come a long way recognizing the importance of hearing amplification verification. However, the necessity of performing on ear measurements seems to be overlooked when it comes to CROS BiCROS systems. These systems can provide tremendous benefit; however, we know that many clinicians are not comfortable and confident performing verification. This interactive learning module will demonstrate how to verify these systems, leading to an improved fitting and experience for both the patient and clinician.

Summary:

Fitting individuals with unilateral hearing loss (UHL) or asymmetrical hearing loss can pose unique challenges in the clinic. For example, the attenuation of some sounds as a result of head shadow effects can reduce the detection of sounds arriving to the ear opposite from the sound source (Fletcher, 1953; Shaw, Newman, & Hirsh, 1947; Taylor, 2010; Tillman, Kasten, & Horner, 1963). The subsequent reduction in audibility can make speech understanding challenging for individuals with UHL, particularly when the speech signal is presented from the side of the poorer-hearing ear. Contralateral routing of signal (CROS) and bilateral CROS (BiCROS) systems help to overcome these limitations and are commonly used in the treatment of UHL.

CROS systems are best suited for individuals with one normal-hearing ear and one unaidable ear. An ear can be deemed unaidable if traditional amplification can no longer provide sufficient benefit due to severity of the audiometric thresholds, or if there is unacceptable distortion of the sound (Kuk, Korhonen, Crose, & Lau, 2014). A CROS system is composed of a transmitting device, or transmitter, and a receiving device, or receiver. The transmitter is fit on the side of the unaidable ear and acts only as a microphone to pick up sounds originating from that side of the head. The signal is then streamed to the receiving device, which is worn on the side of the normal hearing ear. In a CROS fitting, the patient will hear the streamed signal from the unaidable side in addition to hearing all other natural incoming sound in their normal hearing ear.

BiCROS systems are designed for individuals with bilateral asymmetric hearing loss, in which one ear is aidable and the other ear is unaidable. Like a CROS system, the transmitter is worn on the unaidable ear and has a microphone that picks up sound and transmits it to the receiving device on the better-hearing ear. In contrast to the CROS system, the receiving device in a BiCROS System also acts as a fully functioning hearing aid. The signals from the transmitter and receiving device are summed and amplified through the receiving device in the aidable ear. In other words, sounds from both sides of the patient’s head are combined and then amplified to ensure audibility of both signals in the patient’s better-hearing ear.

The value and importance of real ear measurements is frequently overlooked when it comes to CROS / BiCROS systems. These systems can provide tremendous benefits but if they are not properly verified, can lead to reduced patient satisfaction and increased returns. This learning module will review the functionality of CROS/BiCROS systems along with step-by-step instructions for proper verification. Instructors will be prepared with CROS and BiCROS systems and fitting equipment on hand to demonstrate in real time. Attendees will leave the session comfortable and confident performing on-ear verification of CROS and BiCROS systems.