The PTA is observing the PT administering a Sensory Organiza…

The PTA is observing the PT administering a Sensory Organization Test with a patient.  The PTA notes the patient has an excessive sway while standing with eyes open on a foam surface.  This sway was not apparent when standing on a firm surface with eyes open or closed.  This would MOST likely indicate the patient has more reliance on the __________ system(s) to maintain his/her balance.