You will be walking approximately 15 feet in a straight line within a 3-foot path width until they reach an approximate 3 square-foot section of thick cloth during each trial. During the entire period, you will be wearing an Oculus Rift S virtual reality (VR) headset and will thus not see where they are along the path. The VR headset will be connected to a Dell Precision 3630 Tower Workstation with a 32.8-foot active USB 3.0 extension cable and 30 feet of daisy-chained StarTech 6-foot DisplayPort video extension cable.
Figure 1. Schematic with dimensioning of the SDSU HealthLINK Clinical Research Center where we propose to conduct human subjects fall experiments.
These two cable lines will be routed up and across the room ceiling and held in place using an Impact LSA-WMB7HD 7 ft wall-mounted boom arm, to keep the cable off the floor and away from you (Figure 2). The Precision 3630 Tower Workstation is configured with an NVIDIA GTX 1060 graphics card. You will be presented with a virtual scenario of a straight path. When you reach the cloth, unbeknownst to you, the Research Assistant will pull on the carpet, with one of three randomly assigned levels of vigor (fall, stumble and walk). These levels will be designed to induce you to either (1) fall, (2) stumble, regain balance and continue walking, or (3) continue to walk normally with no interference. The randomization of conditions (fall, stumble or walk) will be done using a custom scenario scheduling computer program developed by Dr. Paolini. He will show the RA which condition to assign you just before you being asked to start walking. In cases (2) and (3), the RA will yell “Stop!” to tell you to stop advancing forward once she/he reaches the end of the walking area in the lab.
Figure 2. The Clinical Research Center is in Room 233-11 (yellow highlighted area). A VR station will be used to present different walking scenarios to each participant.
If you fall, two Dollamur 5′ x 8′ x 6″ landing pads made from high-density poly foam with a heavy-duty vinyl enclosure will cushion impact. These pads have 6 inches of thick foam and are specifically designed and engineered for throws, takedowns, and falls that occur in martial arts, jiu-jitsu, wrestling, cheerleading, and gymnastics. You will wear a Riddell SpeedFlex Adult Football Helmet with a protective face mask that covers your mouth, jaw, and chin, as well as knee and elbow pads designed for skateboarding.
We will affix a Lattice iCE40 UltraPlus Mobile Development Platform (MDP) device on your left or right lower legs, in front of the shinbone, using a Velcro harness. The MDP has an STMicroelectronics LSM330 iNEMO inertial module configured in the ±2g range, and a LIS2DH MEMS digital output motion sensor configured in the ±4g range. We will capture and record x-, y-, and z-axis acceleration measurements (g) from both sensors, and yaw, pitch, and roll measurements (degrees) from the LSM330.
Fall experiments are conducted in room 11, the HealthLINK Multipurpose Room. Each participant will wear a Riddell SpeedFlex Adult Football Helmet with a protective face mask that covers the participant’s mouth, jaw, and chin, as well as knee and elbow pads designed for skateboarding.
During each fall trial, a research assistant will sit in the rear corner of the room at a movable laptop table to control the VR app presented to the participant.
We use both the Oculus Rift and Vive Cosmos Elite VR Headsets.