AUTHOR=Chen Ji , Wright William Geoffrey , Keshner Emily , Darvish Kurosh 

TITLE=Design and usability of a system for the study of head orientation

JOURNAL=Frontiers in Rehabilitation Sciences

VOLUME=Volume 3 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/rehabilitation-sciences/articles/10.3389/fresc.2022.978882

DOI=10.3389/fresc.2022.978882

ISSN=2673-6861

ABSTRACT=The ability to control head orientation relative to the body is a multi-sensory process that 
mainly depends on three sensory pathways namely, proprioceptive, vestibular, and visual. 
A system to study the sensory integration of head orientation was developed and tested. 
A test seat with five-point harness was assembled to provide the passive postural support. 
A light-weight head-mount display (HMD) was designed for mounting multi-axis 
accelerometers and a mini- CCD camera to provide the visual input to virtual reality (VR) 
goggles with 39° horizontal field of view. A digitally generated sinusoidal signal was 
delivered to a motor-driven computer-controlled sled on a 6m linear railing system. A 
data acquisition system was designed to collect acceleration data. A pilot study was 
conducted to test the system. Four young healthy subjects were seated with their trunks 
fixed to the seat. Subjects received a sinusoidal anterior-posterior translation with peak 
acceleration of 0.06g at 0.1Hz and 0.12g at 0.2Hz, 0.5Hz and 1.1Hz. Four sets of visual 
conditions were randomly presented along with the translation. These conditions included
eyes open looking forward, backward, and sideways, and also eyes closed. Linear 
acceleration data were collected from linear accelerometers placed on the head, trunk and
seat and were processed using MATLAB. The head motion was analyzed using Fast Fourier 
Transform (FFT) to derive gain and phase of head pitch acceleration relative to seat linear
acceleration. A randomization test for two independent variables was used to test 
significance of visual and inertial effects on response gain and phase shifts. Results show 
that the gain was close to one with no significant difference among visual conditions 
across frequencies. The phase was shown to be dependent on the head strategy each 
subject use.