A BiCROS hearing aid is a specialized electronic device designed to help individuals with asymmetrical hearing loss, where one ear has significantly poorer hearing than the other. The acronym BiCROS stands for Bilateral Contralateral Routing of Signal, describing the two-part system’s main function. This technology is a solution for people whose hearing loss in one ear is so profound that a standard hearing aid offers no meaningful benefit. It works by capturing sound on the non-functional side and transmitting it to the ear that still has usable hearing.
The Mechanism of Contralateral Routing
The core function of the system is the “Contralateral Routing of Signal,” or CROS, which involves two separate components worn on each ear. A microphone and transmitter unit is placed on the side with the severe or profound hearing loss. This unit captures sounds originating from that deafened side of the head.
The captured sound signal is then converted into a digital format and sent wirelessly across the head to a receiver unit worn on the opposite ear. This process effectively overcomes the “head shadow” effect, a phenomenon where the head physically blocks high-frequency sound waves traveling from the deaf side to the hearing ear. Without this routing, sounds like speech coming from the non-functional side would be muffled or inaudible to the hearing ear.
By routing the signal, the system restores sound awareness from the deaf side, which helps improve the wearer’s situational awareness. This transfer minimizes the need for the person to constantly turn their head to hear a speaker or sound source on their poorer side. The goal is to provide information from both sides of the environment, even though all the auditory processing occurs in a single ear.
The “Bi” Difference: When Amplification is Necessary
The “Bi” in BiCROS distinguishes it from a standard CROS system, which only routes sound to an ear with normal hearing. BiCROS is required when the receiving ear—the “better” ear—also has a measurable hearing loss that requires assistance. This means the device worn on the better ear must perform two distinct functions simultaneously.
The device functions as a standard hearing aid, capturing sounds naturally entering the better ear and amplifying them according to the wearer’s specific hearing loss profile. It must also receive the wirelessly transmitted signal from the transmitter unit on the deaf side. It integrates and processes both the local and the routed signals before delivering the combined, amplified sound into the better ear.
This dual processing capability makes the BiCROS system a comprehensive solution for bilateral hearing issues where one ear is completely unaidable. The device ensures that sounds from both sides are heard and made clear enough for the impaired better ear to process effectively.
Hearing Loss Profiles Suited for BiCROS
The BiCROS system is indicated for individuals with a highly asymmetrical hearing loss profile. This profile is defined by a severe or profound hearing loss in one ear that cannot be helped by traditional amplification, coupled with a mild to moderate hearing loss in the other ear. The unaidable ear typically has thresholds worse than 80 or 90 decibels, while the better ear’s loss falls within the 25 to 70 decibel range.
This condition is often referred to as asymmetric sensorineural hearing loss, characterized by a significant difference between the two ears’ ability to hear. The system offers practical benefits by allowing the individual to perceive environmental sounds and speech originating from their deaf side. This awareness can lead to improved speech understanding, particularly in environments where the source of speech is on the poorer side.
While a BiCROS system does not fully restore the natural ability to precisely locate the source of a sound, it greatly increases the overall audibility and clarity of the surrounding environment. The technology addresses the challenge of hearing loss in both ears by consolidating all auditory input into the ear best able to process it.