By Anat V. Lubetzky, PT, Ph.D.
Recent studies have demonstrated a relationship between hearing loss and an increased risk of falls and reduced balance performance, but it is unclear whether this applies to people with hearing loss in one ear (unilateral) and typical hearing on the other ear. While unilateral hearing loss was once considered to have no functional limitations, data now suggests that it may lead to participation restrictions in social, family, and work settings.
We are investigating three theories regarding balance in individuals with hearing loss:
When healthy individuals perform balance tasks in complex sensory environments, they tend to respond to sensory perturbations (e.g., moving visual environments) by increasing their body sway. If a sense is impaired (e.g., such as loss of balance or vision) people tend to over-rely on the other senses for balance. Accordingly, people with vestibular loss (an inner ear disease) tend to be visually dependent and sway more than healthy controls when the visual environment is moving. Do people with hearing loss rely more on visual and somatosensory input because of the loss of auditory input?
The auditory and vestibular system are anatomically very close. Do people with hearing loss rely more on visual and somatosensory input because they also have undiagnosed vestibular loss?
Individuals with hearing loss compensate for the loss of auditory cues by utilizing a “feed-forward” mechanism for balance, i.e., relying on prior expectation and motor planning rather than responding to dynamic sensory cues. If this is the case, people with hearing loss would not increase their sway with changing visual load as normally expected in healthy controls.
To begin investigating these theories, our study, published in PLOS ONE in October 2022, recruited people with unilateral vestibular loss or with unilateral hearing loss, along with healthy controls. The mean ages for the three groups ranged from 48 to 62 with the youngest 28 and the oldest 82.
We analyzed postural sway (from a force platform) and head sway (from a virtual reality headset) in response to two levels of auditory cues (none or rhythmic sounds via headphones), visual cues (static or dynamic), and somatosensory cues (floor or foam) within a simulated, virtual three-wall display of stars. We found no differences with the rhythmic auditory cues. The effect of foam was magnified in the unilateral balance loss group compared with controls for front to back and side to side postural sway, and all head directions except for side to side.
A diagram of postural sway front to back when people are standing on the floor (red) or foam (green). Healthy controls increase sway with dynamic vs. static visuals, especially when standing on foam (left panel). People with vestibular loss (middle panel) have even higher sway than controls on the easy scene (static on the floor) and the difference gets larger as the task gets more challenging (foam with dynamic visuals). People with hearing loss in one ear (right panel) do not increase their sway with dynamic visuals as much as healthy controls. Credit: Lubetzky et al./PLOS ONE
The vestibular loss group had significantly larger front to back and side-to-side postural and head sway on the static scene compared with controls. Differences in pitch, yaw, and roll emerged between the balance loss group and controls only with sensory perturbations.
The unilateral hearing loss group did not increase their postural sway and head movement with the increased visual load as much as controls did, particularly when standing on the foam. They also did not increase their side-to-side sway with the foam as much as controls did.
These findings support theory #3: They suggest that individuals with hearing loss in one ear employ a compensatory strategy of conscious control of balance. Overall, in this study, patients with vestibular loss disorders had exaggerated responses to sensory stimuli, as expected, while the unilateral hearing loss patients’ response to stimuli was less reactive, demonstrating a stiffer posture.
Patients with hearing loss in one ear appear to have more conscious control over their response to sensory cues in their environment, resulting in a more deliberate control of balance with less degrees of freedom to respond to changes in the environment, almost like a guarding behavior. The functional implications of these preliminary findings need to be tested in future research.
A 2019 Emerging Research Grants scientist, Anat V. Lubetzky, PT, Ph.D., is an associate professor at New York University’s department of physical therapy.
Applications are now open for the 2023-2024 Emerging Research Grants cycle. See hhf.org/how-to-apply for more information.
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