"Previous research indicates that Helmet Mounted Displays (HMDs) using stereoscopic presentation techniques induce greater Simulator Sickness symptomology than a biocular presentation. However, neither of these presentation methods takes into account the different perspective each eye normally receives as a result of each eye turning to fixate on objects in different depth planes, referred to as vergence movements. The present study examined the effects of a vergence algorithm moderating the stereoscopic display in an HMD in a within subjects comparison to standard stereoscopic and biocular presentations. The experiment used a distance estimation task and the other major variable was incidence of simulator sickness. The experiment task required moving through rooms in a virtual environment and providing distance estimates to different objects. The findings suggest that most participants would recover more easily from simulator sickness symptoms with a vergence viewing condition. However, because this study shows a wide range of individual differences, a vergence adjustment to stereoscopic presentation should not be expected to eliminate the number of participants withdrawing, but only to reduce their number when repeated exposures are involved. Also, the range of individual differences indicates a need for multiple measures of symptomology not only to help identify individuals who are under duress, but to better assess when they have adapted. One candidate measure of duress is dark vergence, based on its objective scaling, its relevance to adaptation, and its correlation with 55 sub-scale scores."--DTIC.