The question of whether one or two hearing aids are needed for hearing loss is common, and the answer is rooted in how the human brain processes sound. For the vast majority of people who have measurable hearing loss in both ears, a binaural fitting—meaning two hearing aids—is the standard recommendation. The brain is naturally wired to use input from both ears to create a complete and balanced acoustic picture of the environment, a process that a single device cannot replicate. While cost or personal preference might lead someone to consider only one device, clinical evidence strongly supports the use of two aids to achieve the best hearing outcomes. The decision ultimately depends on a detailed audiological evaluation that determines the degree and pattern of hearing loss in each ear.
The Auditory Basis for Using Two Hearing Aids
The auditory system relies on two ears to perform complex calculations. When sound waves reach the head, they arrive at each ear at slightly different times (interaural time difference, or ITD) and with different intensities (interaural level difference, or ILD). These differences are the primary cues the brain uses to determine sound location and pinpoint its origin with remarkable accuracy. This ability to localize sound is significantly impaired when only one ear is providing amplified information. Furthermore, hearing with two ears enables spatial filtering, allowing the brain to separate a desired signal, like speech, from competing background noise.
Clinical Benefits of Binaural Hearing Aids
The use of two hearing aids provides tangible improvements in daily communication. One of the most significant clinical advantages is improved speech understanding, particularly in environments with high levels of background noise. This is partly due to the “better-ear effect,” where the brain prioritizes the ear receiving the clearer signal with the better signal-to-noise ratio.
The physical presence of the head creates a “head shadow” effect, where high-frequency sounds originating from one side are blocked by the head, causing them to be quieter at the opposite ear. Two hearing aids can overcome this shadow, ensuring that speech, which contains crucial high-frequency consonant sounds, is audible regardless of the speaker’s position. Wearing two devices also leads to a reduction in listening effort, which translates to less mental fatigue. This balanced auditory input allows the brain to process sound more efficiently, requiring less cognitive energy to follow conversations.
Risks of Treating Only One Ear
Choosing to treat only one ear when hearing loss exists in both carries a significant risk known as auditory deprivation, which occurs when the auditory pathways associated with the untreated ear are deprived of necessary sound stimulation. The brain relies on a continuous, balanced flow of acoustic information to maintain its ability to process speech. When one ear is consistently amplified and the other is not, the brain begins to favor the aided side, and the untreated side’s ability to interpret complex speech signals can decline. If a hearing aid is later introduced to the deprived ear, the brain may struggle to adapt to the new input, making the rehabilitation process more challenging and potentially less successful. The lack of stimulation can cause the parts of the brain responsible for hearing to weaken or even reorganize to focus on other senses, like vision.
When Is One Hearing Aid Sufficient
While binaural fitting is generally recommended for hearing loss in both ears, there are specific audiological circumstances where a single hearing aid is appropriate. This is primarily the case with unilateral hearing loss, where the condition is limited to only one ear. If the hearing loss is mild, a single device may be sufficient to make conversations audible in that ear.
A different scenario involves Single-Sided Deafness (SSD), where one ear has no functional hearing and cannot benefit from traditional amplification. Alternatives like Contralateral Routing of Signal (CROS) systems are often used. CROS devices capture sound from the deaf side and wirelessly send it to a receiver on the functional ear, rerouting the sound so the better ear can hear sounds coming from the non-hearing side. These specialized solutions serve to overcome the head shadow effect without attempting to amplify a non-functional ear.