Hello, I will explain my rationale for this one.
In conditions 1-3 somatosensory is pereserved and in result we have no falls. In conditions 4-6, we impair the somatosensory and start to cause falls. despite the other inputs. For proper balance we need 2/3 of the balance inputs. This patient only preserves his balance with accurate input form the somatosensory system (not on compliant surface)
Condition 1: all 3 are used (somat, visual, vestib) balance is preserveed
Condition 2: somat and vestib are used and balance is preserved
condition 3: somat and visual are used and balance is preserved
condition 4: visual and vestib are used and balance is LOST
condition 5: vestib only and balance is LOST
condition 6: visual only and balance is LOST.
so what we are seeing here is presentation of patient that is somatosensory dependent (must have accurate somatosensory cues) for balance and has some degree of impairment with the visual and vestibular systems for balance.
hope this helps