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

Abstract

The ability to control head orientation relative to the body is a multisensory process that mainly depends on proprioceptive, vestibular, and visual sensory systems. A system to study the sensory integration of head orientation was developed and tested. A test seat with a five-point harness was assembled to provide passive postural support. A lightweight head-mounted display was designed for mounting multiaxis accelerometers and a mini-CCD camera to provide the visual input to virtual reality goggles with a 39° horizontal field of view. A digitally generated sinusoidal signal was delivered to a motor-driven computer-controlled sled on a 6-m 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. The subjects received a sinusoidal anterior-posterior translation with peak accelerations of 0.06g at 0.1 Hz and 0.12g at 0.2, 0.5, and 1.1 Hz. 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 to derive the gain and phase of head pitch acceleration relative to seat linear acceleration. A randomization test for two independent variables tested the 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 used.

Keywords: acceleration; head mount display; head–neck complex; linear track; motion stimuli; multisensory integration.

Figure 1

Seating system configuration.

Figure 2

Wh120 linear railing system: (A) MH8500 servo motor and (B) linear track.

Figure 3

Generation of sinusoidal motion.

Figure 4

Frontal panel of the LabVIEW program to generate the sinusoidal signal.

Figure 5

(A) Helmet with a gimbaled mini-camera mounted on the top. (B) Virtual reality.

Figure 6

Acceleration data collection. (A) Accelerometers 1 and 4 on the head. (B) Accelerometer 2 on the torso and accelerometer 3 on the sled. Cross lines at 1 and 4 mean that their Y directions point inward.

Figure 7

(A) Raw acceleration of the head, trunk, and sled with SW at 0.5 Hz. (B) Acceleration processed by the fitted-sine model with SW at 0.5 Hz. T and F on Y-axis labels mean the acceleration measured at the frontal part of the head and the acceleration measured at the temporal part of the head, respectively.

Figure 8

Frequency spectrum of acceleration at 0.5 Hz and SW. (A) principal direction and (B) secondary direction. T and F on Y-axis labels mean the acceleration measured at the frontal part of the head and the acceleration measured at the temporal part of the head, respectively.

Figure 9

Gains of the head across frequencies in each visual condition. Visual conditions included here are (A) EO, (B) SW, (C) BW, and (D) EC.

Figure 10

Phase of head acceleration relative to the sled.