Many families of stroke patients notice that the patient stands fairly steadily with the eyes open and holding a handrail, but as soon as the eyes close, or the patient steps on a soft mat or uneven ground, the body sways straight away and the patient may even need someone to hold on. This is often not simply a matter of weak muscles, but a problem with the brain's ability to integrate sensory signals.
From a physiotherapy point of view, this article looks closely at a separate balance impairment mechanism after stroke that is often overlooked, visual dependence and imbalanced sensory integration. It explains the core training principle of "sensory reweighting" and the specific method of progressing along three axes. The article is a single-mechanism deep dive under the overview of balance and fall prevention after stroke. To see the overall picture of balance and falls and the routes for sorting patients first, read that overview page.
The sensory integration problem behind unsteadiness
A person can stand steadily because the central nervous system integrates three sensory signals at onceand flexibly adjusts the "weight" given to each according to how reliable the environment is:
The three sensory signals that keep standing balance
- Vision: the eyes observe the surroundings and tell the person where the body is
- Proprioception: pressure under the feet and receptors in the joints and muscles tell the brain about body position
- Vestibular sense: the inner ear detects changes in head position and speed of movement
How a healthy brain adjusts these three senses (reweighting)
- On firm ground, the brain relies mainly on proprioception
- When the light is dim, the brain automatically relies more on proprioception and the vestibular sense
- When the floor is soft, the brain relies less on proprioception and lets the vestibular sense fill in, adjusting flexibly as the surroundings change
A stroke can disturb this integration. Research has found that stroke patients with hemiplegia often put too much weight on vision (visual dependence or visual field dependence). When the eyes are closed or the patient steps on soft ground, so that the senses conflict, balance is badly affected. Bonan and colleagues (2004, Part I) used dynamic posturography to show that, when vision was removed, or when vision and somatosensory input conflicted and somatosensory input was disturbed, stroke patients had balance scores significantly lower than healthy controls, which reflects impaired ability to organise and integrate the senses (Bonan et al. 2004a). Slaboda and colleagues (2009) went further and found that stroke patients stood about as well as healthy people in the dark, but when facing a moving visual scene their centre of pressure shifted faster and over a wider range, and they made larger errors on the Rod-and-Frame test, which objectively confirms that the mechanism of "visual dependence" really exists (Slaboda et al. 2009).
Summary: After a stroke, if the patient "is unsteady as soon as the eyes close and sways on a soft mat", it is often not only because the legs are weak. The brain relies too much on vision and cannot switch in time to proprioceptive and vestibular signals. This sensory integration problem can be improved by targeted training.
Clinical assessment: testing different standing conditions to find the type of problem
For training to work, it is first necessary to find which sensory channel is causing the block. A physiotherapist usually changes the standing conditions systematically and observes the patient's response, using four quadrants made from eyes open or closed combined with firm floor or foam (based on the concept of the Clinical Test of Sensory Interaction on Balance, CTSIB):
Visual field dependence can be analysed quantitatively in research with the Rod-and-Frame test (judging a vertical line inside a tilted frame). In the clinic, a simplified observation is usually used, such as watching whether the body is "pulled off course" when the patient faces a moving or tilted visual scene. The aim of the whole assessment is to divide the general complaint of "unsteady" into a visual-dependent type, a weak proprioception type or a weak vestibular type, so that training can be tailored, and not given as the same set of exercises for every patient. To see how this four-quadrant manipulation of conditions works with standardised scoring tools to form a complete balance and fall risk assessment after stroke, read that dedicated page.
What is "sensory reweighting"?
Once it is clear which sensory channel the patient relies on too much, the core of training is sensory reweighting. Within safe limits, the weight of the over-relied-on sense (mostly vision) is deliberately turned down, creating a controlled "sensory conflict or sensory deprivation", which forces the central nervous system to recalibrate and call on proprioception and the vestibular system.
This approach has evidence behind it. The single-blind randomised controlled trial by Bonan and colleagues (2004, Part II) showed that, compared with free vision, balance retraining with a visual deprivation element (eyes covered) improved balance after stroke more effectively, which directly supports the strategy of "correcting abnormal visual dependence by manipulating or reducing visual input" (Bonan et al. 2004b). In other words, covering the eyes or standing on a foam pad is a method of "redistributing sensory weight" that has evidence to support it.
Progressing training difficulty along three axes
The key to sensory reintegration training is to progress step by step along three axes. Raise the difficulty of only one axis by one level at a time, and make sure there is a firm handrail and someone supervising, so that the difficulty stays on the line of "challenging but still safe and controllable":
Safety always comes first. Covering the eyes or standing on an unstable surface itself raises the risk of falling, and this is how the nervous system is stimulated to adapt. At every stage of practice, there must be a firm handrail and someone close by watching, and the level must go up slowly, one step at a time. Do not raise the difficulty of several aspects at once, and never stand on a foam pad with the eyes closed without someone watching.
Of the three axes, the third, "adding a dual task (a cognitive or upper-limb task)", is the closest to everyday life, because walking in the street usually means talking, avoiding passers-by or reading signs at the same time. To learn how to carry the ability to stand steadily over to real multitasking situations, see the page on dual-task balance training. This three-axis progression also does not replace lower-limb strength and gait training. The two support each other, and even with good sensory integration, enough gait retraining and trunk control are still needed. For details on trunk and sitting-to-standing balance, see the overview of trunk control after stroke.
The role of head-turning training and safety rules
Of the three axes, "head turning" deserves a separate look. Turning the head can induce vestibular stimulation. When vision is removed and proprioception is unreliable, the vestibular system has to fill in, and adding head movement is a way of making the vestibular system work. Two points need attention when carrying it out, however:
- If the patient has clear dizziness or symptoms of otolith vertigo (BPPV), they must be told apart first, because vestibular rehabilitation and sensory reintegration are handled differently
- Both the range and the speed of head turning go from small to large and from slow to fast, with a handrail and someone watching throughout
- Watch for orthostatic hypotension, and do not turn the head while standing up quickly, to avoid dizziness or a fall
- If the patient already has dizziness, do not push on with head-movement training, to avoid handling a vestibular disorder as an ordinary balance problem
How this page's training differs from other areas of rehabilitation
"Balance" is a very wide topic, and this page covers only one part. Drawing clear lines between areas avoids confusion about the direction of training and helps readers find the relevant page:
- Mechanism: visual dependence and imbalanced three-sense integration
- Task: manipulate sensory input during standing and reweight it
- Feedforward: what is trained is "how senses are distributed when standing steadily"
- Re-education of touch and proprioceptive discrimination in the upper limb and hand → sensory re-education
- Reactive and perturbation balance for "catching oneself at the moment of a fall" (Handelzalts 2019) → another area
- Spatial neglect and application to ADL → occupational therapy
The first thing to separate is upper-limb sensory re-education. It also concerns "sensation", but that area is aimed at the re-education of touch and proprioceptive discrimination in the hand. How proprioception and motor control affect postural adjustment is a deeper mechanism. The body part, the assessment method and the training tasks are all quite different from the standing balance described on this page. Another concept that is easy to confuse with this page is pusher syndrome. These patients actively push their weight towards the hemiplegic side and resist being brought upright, which comes from a distorted sense of the midline. This is a separate mechanism that must be identified separately, and is covered on the page on pusher syndrome. For reactive balance, the RCT of Handelzalts and colleagues (2019) showed that perturbation training mainly improves reactive recovery (raising the threshold for multiple-step responses and balance confidence). It targets the response mechanism "at the moment a fall occurs", and is a different level of training from the feedforward sensory reweighting described on this page (Handelzalts et al. 2019). Spatial neglect and functional application in daily life belong to occupational therapy after stroke.
This page also deals with the mechanism of visual dependence and impaired sensory organisation that is specific to stroke patients. For general fall-prevention strategies for older adults who have not had a stroke, see exercise to prevent falls in older adults. The content of the two does not overlap.
Research evidence and the benefit of sensory integration training after stroke
Sensory reweighting and training on unstable surfaces have positive research support for improving balance after stroke, but the strength of the evidence also needs to be stated truthfully:
The pilot RCT by Lim (2019) showed that movement training combining proprioception and multiple senses improved proprioception and anteroposterior balance control more than treadmill training alone (Lim 2019). The review by Arienti and colleagues (2019) also lists training on unstable support surfaces as one of the interventions with positive evidence for balance after stroke, but notes that the overall quality of evidence varies (Arienti et al. 2019). In summary, this kind of training is worth doing, but it must be tailored to the person and progressed step by step, together with lower-limb strength and gait training, and it should not be exaggerated into "a few sessions and the patient can stand steadily".
What can be done next? If a patient at home is "unsteady with the eyes closed after stroke and sways on a soft mat", the first step should be a detailed assessment by a registered physiotherapist to separate a visual-dependent type, a weak proprioception type or a weak vestibular type, and only then to arrange targeted three-axis progressive training. Do not copy short online videos and practise at home with the eyes covered on a foam pad.