Hi Yinghua,
Thanks for this question! The common link between all of this patient’s losses of balance are an absence of visual cues (conditions 2 and 4). He does not have any losses of balance when visual cues are available (conditions 1 and 3). Therefore, we can safely conclude that he is visually dependent.
He may also have impaired use of vestibular cues, but we cannot say that with certainty given his loss of balance on condition 2 when he had somatosensory+vestibular cues available and did not lose his balance on condition 1 when somatosensory cues were also available.
Hope this helps!
Chrissy