## 3 The Details of the Proposed Human Study
### Study Methods  
#### 3.3.1 Outcome Measures and Assessment Procedure  
Vestibulocular Reflex  
The video head impulse test (vHIT) device (GN Otometrics, Taastrup, Denmark) will be used to assess horizontal and vertical VOR gain. Participants will be seated 1.3 m away from a wall target, be fitted with vHIT device, and the device will be calibrated. The researcher will grip the participant's head and quickly rotate it either to the left or right about 10-15 degrees for horizontal VOR assessment or up or down along the right anterior left posterior (RALP) or left anterior right posterior (LARP) orientations. During this, the participant will be instructed to keep their eyes fixated on the wall mounted target. Twenty unpredictable head impulses (ten in each direction) will be performed to assess the left/right horizontal and up/down vertical semicircular canals (SCCs) (Figure 1) [24]. Figure 1: VOR gain testing using the ICS impulse system. Electromyography and Acceleration  
The Delsys Trigno inertial measurement unit (IMU) wireless system (Delsys Inc., Boston, MA, USA) will be used to record EMG and acceleration data only during toes-up and toes-down rotations (i.e., perturbation trial assessments) on the force plate perturbation device. The 16-channel Delsys system will be used to assess muscle activity of eight postural muscles, namely: sternocleidomastoid, cervical erector spinae, rectus abdominis, lumbar erector spinae (L1/L2), rectus femoris, biceps femoris, medial gastrocnemius, and tibialis anterior (sampling rate = 1100 Hz). Electrode placement will follow the standard guidelines [25]. After skin preparations using razor blades and isopropyl alcohol wipes, participants will be instructed to lay down on a mat so the researcher can locate and mark the correct placements for the sensors, and then fix the IMU sensors to each participant's forehead, neck, trunk, abdomen, and legs using Delsys adhesive patches. The forehead and first thoracic spinous process (T1) sensors will serve as the accelerometers. Eye Movement Variables  
The BlueGain electrooculography (EOG) device (Cambridge Research Systems) [26; 27] will be used to assess horizontal and vertical eye movements (sampling rate = 1 kHz) only during perturbation trials. After skin preparation using isopropyl alcohol wipes, two sets of two \"duck foot\" surface gel electrodes (20 \(\times\) 15 mm, Ag/AgCl sensor; Ambu Neuroline 700, Denmark) will be placed horizontally and vertically around the eye, with a reference electrode on the forehead. The wireless device will be connected to the EOG software on a desktop computer via Bluetooth connectivity, and the device will be affixed to the participant's arm via its arm band case. The horizontal and vertical calibrations of the EOG device will be performed using two respective targets which are 42 cm apart, with the participant seated 1.3 m away from the wall targets. Quiet Postural Balance  
The mCTSIB is a clinical version of the Sensory Organization Test (SOT) and it is used to assess the sensory contributions necessary for balance during quiet standing. The mCTSIB has four different testing conditions, namely: Condition 1, eyes open (EO) on stable support (SS); Condition 2, eyes closed (EC) on SS; Condition 3, EO on a foam surface (FS); and Condition 4, EC on FS [28]. In this current study, the mCTSIB will be performed using the NeuroCom(r) extended force platform and an Airex foam pad (19.69 \(\times\) 16.14 \(\times\) 2.36 inches). Participants will be asked to stand upright, as stable as possible, for 10 s on the force platform with feet shoulder-width apart and hands by their sides for each of the four conditions. During the foam conditions, the participant will stand on the foam which will be placed on the force platform. Three trials will be performed for each condition. The trial will be terminated when the participant opens their eyes in an EC condition or loses balance and requires manual assistance to prevent a fall.