As pointed out by Kotulak, vergence/accommodation mismatch in Night Vision Systems, usually due to
misadjustments of eyepiece focus, is sometimes a source of visual performance decrement. The increased separation
between sensors existing in some modern binocular Helmet Mounted Display systems, creating "hyperstereopsis",
was also identified to be potentially responsible for decreased performance at distances less than 5 meters.
Based upon basic knowledge pertaining to vergence and accommodation mechanisms, a study was performed using
a sensory approach, with the goal of better understanding the problem of dissociation between accommodation and
convergence. In this study, different conditions of interocular separation (nominal IPD, X3, X4) and viewing
distances (6m, 4m, 2m) were used. Six subjects participated in the experiment and were asked to view Landolt C
charts using NVGs and specially developed optical tools allowing changes to sensor separation.
The results show that, with a fixed eyepiece focus at 10m, the decrease in resolution performance is roughly
proportional to the interocular separation when looking at short distances. A fixed focus at a distance of 4m
considerably reduces the conflict and results in improved resolution for increased separation conditions.
An additional experiment was conducted to investigate the setting of objectives lenses focus at infinity (nominal
landing condition). With this setting, for visual acuity test, the decrease in resolution at short distance was such that
effects of the mismatch between accommodation and convergence are no longer apparent regardless of interocular
separation.
TopOwl® is an original concept of binocular Helmet Mounted Sight and Display system (HMSD) for helicopters, where
two Image Intensifier Tubes (IIT) are integrated on the headgear and optically coupled to the clear visor placed in front
of the pilot's eyes.
Thales recently developed a new version of its TopOwl®'s Display Module with the objective to have an HMSD capable
to achieve all kind of missions up to the darkest night levels. The main enhancements are the redesign of the optical
combination, the use of new optical materials and of latest generation of optical design tools.
Two flyable prototypes of this new design were manufactured. A performance assessment has been conducted, showing
a significant improvement of the night vision performances, reaching performances equivalent to those of last issued
NVGs. These evaluations are being completed by different flight test evaluations.
Distance judgments in virtual environments and Head-mounted Displays (HMD) systems are generally underestimated
compared with judgments in the real world. Some visual depth cues may be absent or modified, according to the
technology used.
After a brief review of the literature pertaining to the representation of depth in Helmet-Mounted Displays, we explore
two possible causes for the reduced distance perception in virtual environments: the increased interocular separation (or
hyperstereopsis) and the reduction of the field of view.
Some laboratory and training ground data are reported. The effective influence of each factor on space perception is
discussed.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.