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The Impact of Age-Related Hearing and Vision Decline on Postural Stability and Movement

The human body has three mechanisms for determining its position in space: sight, hearing and proprioception. Individuals lose proprioceptive ability as they age, related to decrease in the dynamic response of muscle spindles and atrophy of nerve axons that result in defects in the processing of sensory input (Ferlinc et. al., 2019). Equally significant are declines in hearing and vision acuity.

How prevalent is this? According to a 2019 study by researchers from Johns Hopkins University based on NHANES data, one in nine adults ages 80 and above has dual sensory impairment (DSI), and only 19% of adults in that age group are free of either hearing or sight impairment (Swenor et al., 2013). In other words, most if not all older adults experience declines in sensory processing significant enough to affect their postural stability and movement.

Compounding this problem are age-related changes in cognition, and the fact that individuals with sensory deficits tend to depend more on cognition to complete motor tasks (Li et al., 2018). The purpose of this report is to explain how visual and auditory input is processed in the brain (including common pathways), how aging changes the way we see and hear things in the environment, and what providers can do to help patients maintain physical function in the wake of age-related decline.

How We See

Human beings are evolutionary creatures. As such, we have maintained the eyes of predators. Our eyes are constantly moving to scan the environment, at a speed that may surprise you. Eye movements are a combination of rapid, jerky movements called saccades, fixations and slow pursuit (which is not very slow, but slower than saccades). The typical saccade takes about 150 milliseconds to initiate and another 50 to complete (Pierce et al., 2019). The purpose of a saccade is to move the fovea- the area in the central part of the eye with the greatest visual clarity- in line with the visual target. Smooth pursuit movements enable the eyes to track moving targets in the environment. In addition, vestibulo-ocular movements enable the eyes to compensate for head movement. Input for these movements comes from the semicircular canals in the inner ear.

If we actually saw everything that our eyes perceive, the world would appear as a blur. Therefore, what we think of as vision is in fact the result of complex cognitive processing in areas such as the parietal cortex, superior colliculus and frontal eye fields. More on this later.

How We Hear

Hearing is a similarly complex process. The human ear has three compartments: the external ear that functions as a sort of funnel for gathering sound (pressure waves), the middle ear that contains the anvil, hammer and stirrup bones, all of which vibrate in response to pressure, and the inner ear that converts this sound energy into electrical signals for the brain to process (Kandel et al., 2013). Because sound arrives earlier and is more intense at the ear closest to the source, the brain can use interaural time delays to locate the source of the sound and also determine the relative position of the head.

The brain uses other sound characteristics to screen and prioritize what we hear. For example, we can hear human speech in the midst of noise because of redundant cues, that enable the brain to recognize these sounds and prioritize their importance (Kandel et al., 2013).

How Sight and Hearing Work Together To Orient the Body in Space

You may recall earlier that we mentioned the superior colliculus: a structure in the rostral midbrain that is responsible for processing stimuli in the environment and coordinating eye movements (Zubricky & Das, 2020). The superior colliculus contains maps of visual space and the body surface that enable it to perform this task. It also contains an auditory map congruent with the other two that is computed from a variety of cues that position a sound source in space.

“Auditory, visual and somatosensory neurons in the superior colliculus all converge on output pathways in the same structure that controls orienting movements of the eyes, head and external ears. The motor circuits of the superior colliculus are mapped with respect to motor targets in space, and are aligned with the sensory maps. Such sensory-motor correspondence facilitates the sensory guiding of movements.” (Oertel & Doupe, 2013, page 697).

The Role of the Parietal Lobe

The parietal lobe is the principal target of the dorsal visual stream, also known as the “where” pathway (Kandel, 2013). It controls our perception of the spatial structure of the world and related to that, our attention to objects in the environment. Different areas of the parietal cortex also process visual inputs and prepare the body for appropriate motor movements. For example, the posterior parietal cortex is involved in the planning and coordination of visually guided movement. This explains why certain types of dementia that affect the parietal lobe impact a person’s motor movement as well as cognitive function.

Cognitive Changes with Aging

Some of the ways in which vision and hearing decline affect postural control and movement are very obvious. For example, when persons lose the ability to hear in one or both ears, he/she will have significant difficulties with spatial orientation. Similarly, a person with less-than-perfect vision may tend to look down more when he/she walks, and have reduced depth perception.

But the more significant age-related changes are those that occur as a result of losses in white matter function that inhibit normal communications channels between different areas of the brain, and gray matter atrophy, particularly in those regions of the brain associated with semantic memory consolidation and short-term working memory (Li et al., 2018). Furthermore, as sensory function declines, individuals are forced to rely more on cognitive function to compensate. This is most evident when comparing the ability of young versus older adults to perform dual-task activities that require concurrent cognitive and motor processing.

The evolving field of cognitive neuroscience has enabled researchers to image the brain in real-time while subjects perform activities such as walking and stationary bicycling. Because of this, we know more about what can be done to help individuals stay more alert and active as they age, to improve gait and postural stability.

Following research studies on the subject, Li and colleagues concluded that “Training studies have abundantly demonstrated that moderate aerobic exercise such as walking, swimming and cycling improves attentional control and executive function in older adults,” (Li et al, 2018). Functional MRI studies comparing an aerobic exercise intervention against sedentary controls revealed that “the aerobic group showed improved attentional control, and increased task-related activity in the right middle frontal gyrus and superior parietal regions. The aerobic group also showed greeted volumetric increases in anterior white matter, gray matter in the left inferior frontal gyrus, anterior cingulate and superior temporal gyrus, (Li et al., 2018).

Researchers concluded that “aerobic training appears to trigger global neuroplastic effects by increasing the production of neurotrophic factors (e.g. BDNF, IGF-1, VEGF) that are able to cross the blood-brain barrier and support neurogenesis, vascularization, axonal repair and synaptogenesis,” (Li et al., 2018).

A Training Program for the Mind and the Body

What then is the ideal training protocol for older adults experiencing vision and hearing decline? The answer appears to be a three-pronged strategy:

This is a fairly rigorous program that requires patients to exercise outside of the clinic. What methods can providers employ to increase motivation and compliance?

Dynamic Balance Training Exercises

Stage 1: Balance Assessment

The basic balance assessment consists of the following progression. Time your patient for each position with eyes open and for higher functioning individuals, eyes closed.

Following are normative values obtained by Springer and colleagues for the single leg stance test, by gender and age:

Stage 2: “Basement-level” Balance Exercises

We recommend having all patients complete these basic exercises, even if they performed well on the unipedal stance test. They include:

The clock: The patient stands with feet shoulder width apart. Direct the patient to move his/her foot to various positions to the front side and back, as if that foot was a hand on a giant clock. For example, straight ahead would be 12 o’clock, to his/her right would be 3 o’clock, to the left 9 o’clock, and directly in back, 6 o’clock. Make the challenge greater by calling out the times more quickly, so the patient has to think and immediately shift position.

Square dance: This exercise also begins with feet shoulder width apart. Beginning with the right foot, have the patient move the “swing” foot to the front and then tap the floor as he/she circles around to the back of the body. A patient with good function will be able to cross the swing foot in back of the stance foot. Repeat this sequence with the left foot.

Door frame touch: Have the patient start in a semi-tandem stance, situated just slightly in back of a door frame. The person will twist to the left and touch the left side of the door frame with the right hand, then twist to the right and touch the right side of the door frame with the left hand. Touching each side of the door frame ten times is a set. Make this exercise more challenging by asking the patient to move his/her feet into a full tandem stance. High functioning patient should be able to perform this exercise in a single leg stance position.

Sit-to-stand: For the exercise, use a sturdy chair with a relatively high seat height and preferably no armrests. The exercise begins by sitting in the chair with arms crossed over the chest. The person leans forward and rises out of the chair, then reverses the motion and sits back down. The purpose of this exercise is to help individuals with spatial recognition, as well as using gravity to direct the standing and sitting motions.

Step up and step down: The height of the step used for this exercise depends on your patient’s functional level. For low level patients, we recommend starting with a 2-inch aerobic platform. As patients progress, add 2-inch risers to raise the platform up to 6-inches. The patient stands on one side of the riser and steps up onto the platform, then steps down on the other side. Stepping up and down ten times for each leg is a set. Ideally this should be done as a walking motion, with the patient stepping onto and over the platform as if climbing a set of stairs.

Stage 3: Dynamic Asynchronous Movement

These “mid-level” exercises increase cognitive load by having patients move their arms and legs in unrelated types of movement. Here is an example of a progression:

Exercise Ball Twist with FlexBar Shake: The patient begins seated on an exercise ball, and practices twisting to the right and left at the waist. Ask the patient to hold a FlexBar in one hand and shake it while he/she continues to twist to the right and left.

Progress to a standing position, continuing with the transverse body motion and FlexBar shake. To make this more challenging, have the patient alternate hands shaking the FlexBar.

Second progression: The patient performs walking lunges while shaking the FlexBar. Begin by holding the FlexBar in one hand and progress to alternating hands.

Each of these progressions involves a greater cognitive load, to help patients learn coordination skills in addition to improving basic movement function. This is important for ADLs, where persons need to move their arms and hands separately from the feet. For example, picking up items while walking down the aisles of a grocery store (or picking up items that may have fallen on the floor while walking through the house), and driving, where a person needs to move the head, arms hands and feet asynchronously to scan the surroundings, operate the steering wheel and turn signals, and engage the accelerator and brake pedals.

Stage 4: Dual-task Strategic Movement

This is the final and most complex set of exercises, since patients are asked to think and plan the movements they need to execute, which are in many instances, asynchronous. One way of doing this is to construct an obstacle course: similar to circuit training but with different types of challenges. Whereas the challenge in circuit training is usually aerobic stamina and strength, the obstacle course focuses more on balancing cognitive load with physical movement. The more the obstacle course is able to replicate activities of daily living, the better.

Following is an example of what we mean:

Obstacle #1: Balance and fine motor movement: Set up a “high-top” table or counter that the patient can easily reach while standing. Put a deck of playing cards on the table, and ask the patient to sort the cards (by type or more challenging, ordinal sorting) while progressing through the basic balance sequence listed earlier in this article (feet shoulder width apart, feet together, semi-tandem stance, tandem stance and single leg stance). Set a timer to signal the patient to change positions every 15 seconds.

Obstacle #2: Dynamic motion and fine motor movement: The patient begins by standing with feet shoulder width apart. Ask the patient to bring the hands together behind the back. Keeping the hands behind the back, the person walks while touching thumb to thumb, then index finger to index finger, third finger to third finger, fourth finger to fourth finger and pinky to pinky, then reversing back one set of fingers at a time to the thumbs.

Obstacle #3: Strategic dynamic motion: One-legged ball toss: Patients do this exercise in pairs. Each person tosses a ball back and forth with his/her partner while maintaining a single leg stance. Encourage patients to make this more challenging by varying the heights of their tosses, and tossing the ball to the partner’s right or left sides.

Obstacle #4: Progression of asynchronous movements: Have the person begin with a simple dynamic motion (simple squat, standing lunge, etc.). At each timed interval, add an asynchronous movement such as a transverse twist, arm abduction, or fine motor hand movements. Have the patient progress through at least four timed 30 second intervals.

Obstacle #5: Timed scavenger hunt: Place five small objects around the room. Make the objects easy to see, but hard to access. For example, a green golf ball in a bucket of white balls, a nickel in a pile of pennies, or a yellow crayon in a carton with crayons of other colors. Hand the patient a container with dividers. Label each divided area as to which object should be placed in it. Make this a contest to see which patient can complete the obstacle course in the shortest amount of time. You may want to consider a small reward (Starbucks card, etc.) for the winner.

References

Ferlinc, A., Fabiani, E., Velnar, T. & Gradisnik, L. (2019). The Importance and Role of Proprioception in the Elderly: A Short Review. Mater Sociomed. Vol. 31. No. 3. pp. 219-221. Open access: ncbi.nlm.nih.gov/pmc/articles.

Kandel, E., Schwartz, J., Jessell, T., Siegelbaum, S. & Hudspeth, A. (2013). Principles of Neural Science. Fifth Edition. McGraw Hill Medical. pp. 556-710.

Klein, C. & Ettinger, U., Eds. (2019). Eye Movement Research: An Introduction to its Scientific Foundations and Applications. Springer Nature. pp. 11-73.

Li, K., Bherer, L. Mirelman, A., Maidan, I. & Hausdorff, J. (2018). Cognitive Involvement in Balance, Gait and Dual-Tasking in Aging: A Focused Review From a Neuroscience of Aging Perspective. Frontiers in Neurology. Vol. 9. Article 913. pp. 1-13. Frontiersin.org.

Oertel, D. & Doupe A. (2013). The Auditory Central Nervous System. In Kandel et al., Eds. Principles of Neural Science. Fifth Edition. McGraw Hill Medical. p. 697.

Springer, B., Marin, R., Cyhan, T., Roberts, H. & Gill, N. (2007). Normative Values for the Unipedal Stance Test with Eyes Open and Closed. Journal of Geriatric Physical Therapy. Vol. 30. No. 1. pp. 8-14.

Swenor, B., Ramulu, P., Willis, J., Friedman, D. & Lin, F. (2013). The prevalence of concurrent hearing and vision impairment in the United States. JAMA Internal Medicine. Vol. 173. No. 4. NIH Public Access. pp. 1-5.

Zubricky, R. & Das, J. (2020). Neuroanatomy, Superior Colliculus. NCBI Resources: Stat Pearls. ncbi, nlm, nih.gov/books.