When performing on a stable surface and well-lit environment, your visual, vestibular, and somatosensory systems are all sending information to your central nervous system (CNS) that is similar.
But you aren’t always performing in perfect conditions.
When you ruck through mud or sand, the information regarding the position of your ankles (somatosensory information) is going to be deceptive regarding your postural orientation. Meaning where your center of mass is relative to gravity.
If your ankle is sinking 30 degrees to the side, your body isn’t necessarily 30 degrees to the side as well.
To address this issue, our CNS will down-weight dependence on unreliable sensory information.
This means that in conditions of mud, sand, or rocky surfaces you will increase your dependence on your visual and vestibular systems, and your CNS will decrease dependence on information from your somatosensory system.
A similar down-weighting situation will happen in low vision environments.
Your CNS will decrease dependence on the information from the visual system and instead increase dependence on the vestibular and somatosensory systems.
Essentially, your visual, vestibular, and somatosensory systems are all important for your orientation and body control.
And because you perform in a variety of conditions, each sensory system should be optimized.
This will allow you to maintain your performance no matter which system gets down-weighted.