Including night vision capabilities in Helmet Mounted Displays has been a serious challenge for many years. The use of
"see through" head mounted image intensifiers systems is particularly challenging as it introduces some peculiar visual
characteristics usually referred as "hyperstereopsis".
Flight testing of such systems has started in the early nineties, both in US and Europe. While the trials conducted in US
yielded quite controversial results, convergent positive ones were obtained from European testing, mainly in UK,
Germany and France. Subsequently, work on integrating optically coupled I2 tubes on HMD was discontinued in the US,
while European manufacturers developed such HMDs for various rotary wings platforms like the TIGER.
Coping with hyperstereopsis raises physiological and cognitive human factors issues. Starting in the sixties, effects of
increased interocular separation and adaptation to such unusual vision conditions has been quite extensively studied by a
number of authors as Wallach, Schor, Judge and Miles, Fisher and Ciuffreda. A synthetic review of literature on this
subject will be presented.
According to users' reports, three successive phases will be described for habituation to such devices: initial exposure,
building compensation phase and behavioral adjustments phase.
An habituation model will be suggested to account for HMSD users' reports and literature data bearing on
hyperstereopsis, cue weighting for depth perception, adaptation and learning processes, task cognitive control.
Finally, some preliminary results on hyperstereopsis spatial and temporal adaptation coming from the survey of training
of TIGER pilots, currently conducted at the French-German Army Aviation Training Center, will be unveiled.