||Visual scene movement in a virtual reality simulation can cause symptoms of motion sickness (cybersickness). The purposes of this research were to develop a measuring metric to quantify the visual scene movement in a virtual reality simulation and to verify that the proposed measures do significantly influence the levels of cybersickness. A review of literature indicates that cybersickness is a form of vection-induced motion sickness. The term 'vection' is used to describe the self-motion illusion generated by visual scene movement. This self-motion illusion is in opposite direction to the scene movement and can be nauseogenic. A preliminary experiment has been conducted to investigate the effects of scene oscillations on the rated level of cybersickness. The results showed that the presence of scene movement could significantly increase levels of cybersickness. This experiment confirmed that visual stimulus is an important factor that would influence the rated level of cybersickness. Further reviews of literature indicates that there is yet no quantitative unit to measure visual stimuli in a virtual environment (a computer generated 3D environment). Based on previous studies with vection-induced motion sickness using rotating drums, a new unit called 'Spatial Velocity (SV)' is proposed to quantify visual stimuli. The proposed 'spatial velocity' metric is a measure of the rate of movement of contrasted information perceived by a subject during a virtual reality simulation. Movements of spatially contrasted pattern (e.g. black and white strip) have previously been shown to induce sense of self-motion illusion (vection) and symptoms of motion sickness. This forms the theoretical for the 'spatial velocity' metric. The 'spatial velocity' has two components: (i) 'spatial frequency', and (ii) 'scene velocity'. 'Spatial frequency. is used to quantify scene complexity and 'scene velocity' is used to quantify speed and direction of visual scene movement. Both 'spatial frequency' and 'scene velocity' can be measured, therefore, 'spatial velocity' can be a metric to quantify the movements of visual scene of different complexity. This metric is the first of its kind in the field of cybersickness research. The algorithms and procedures to measure 'spatial velocity' are presented in the thesis. Two experiments have been conducted to study the effect of scene velocity and scene complexity on the rated level of cybersickness. The results of these experiments suggested that increase in either scene velocity or spatial frequency would significantly increase the rated level of cybersickness. Besides, the sickness ratings increase linearly with 'spatial velocity' in the fore-and-aft and yaw axes. This verifies that 'spatial velocity' is an appropriate measuring metric to quantify visual stimuli in a virtual environment. The application of the 'spatial velocity' metric to the formulation of a Cybersickness Dose Value (CSDV) is also discussed in the thesis. This CSDV is proposed to be a time integral of a frequency weighted time history of 'spatial velocity' over the total duration of simulation exposure.