The Impact of Non-Immersive Head-Mounted Displays (HMD)on the Visual FieldRussell L Woods,1 ◊ Ivonne Fetchenheuer,1, 2Fernando Vargas-Martín 1, 3 and Eli Peli 11. The Schepens Eye Research Institute & Harvard Medical School, Boston, MA, USA2. University of Applied Sciences, Berlin, Germany3. Laboratorio de Óptica, Dept. Física, Univ. Murcia, SpainSubmitted on 20 September, 2002 for consideration for the Special Issue on the SID '02International Symposium of the Journal of the Society for Information Display.Figures: 7.Tables: 1.◊ Communicating authorDr Russell WoodsSchepens Eye Research Institute20 Staniford StreetBoston, MA 02114Telephone: 1 617 912 2589Facsimile: 1 617 912 0169Electronic mail: [email protected] et al. Non-Immersive HMDs and the Visual Field2AbstractBinocular head-mounted displays (HMDs) that could be used non-immersively producedsubstantial interruption of the visual field. Monocular HMDs designed to be used non-immersively created minimal interruption of the visual fields making them safe to wear (but maybe not to use) in mobile situations. A small opaque display can be positioned to provide a seethrough functionality.KeywordsHead-mounted displays, visual field, ergonomicsWoods et al. Non-Immersive HMDs and the Visual Field31. Objective and BackgroundNon-immersive head mounted displays (HMDs), those that allow the wearer to interact with theirenvironment while using the HMD, have considerable potential for use in offices, industry andmedicine. For example, a worker could walk warehouse aisles collecting goods listed on a HMDthat were transmitted from a central computer. In such circumstances the vision through andaround the display are important for safety and orientation. While central vision is used to viewan object of regard, peripheral (side) vision is critical for safe and efficient mobility [1]. Theextent of peripheral vision is known as the visual field [2].While manufacturers provide the field of view of HMDs, the impact of HMDs on thevisual field have been addressed only minimally in the literature. Most considerations givenwere to the trade-off between the field size and resolution and the effects of these trade-offs ontarget search [3-5]. The limitations of these trade-offs are important considerations in immersiveHMDs but may be less important in non-immersive HMDs. In fact as noted by Peli [6] andDavis [5], a wide field of view in a HMD may be difficult to use as large eye movements areneeded and no head movements can be used to reduce an eccentric eye position. Here weconsider in addition to the field of view of the display itself the impact of the whole appliance onthe visual fields of the user.Vision through the HMD display may be reduced or obstructed by the veiling luminanceof the display. Vision around the display may be limited by the supporting structure (the body)of the HMD. Between the display and the body is a region that we call the clearance [7], asshown in Figure 1. A HMD may obstruct the view of an object in a particular direction (ascotoma, as defined in the methods section). Non-immersive HMDs may be binocular ormonocular, so we examined two examples of each. We show that the impact of the HMD on thevisual field depends on a range of factors including HMD design and HMD placement.Interestingly, the scotoma caused by the display may be displaced from the direction of thedisplay. These impacts on the visual field influence the relative safety of use of non-immersiveHMDs when planned use requires interaction with the environment and should be considered inHMD design.INSERT FIGURE 1 ABOUT HEREWoods et al. Non-Immersive HMDs and the Visual Field42. MethodsVisual fields (extent of vision) were measured on a small group of young (aged 20 to 30 years)normally-sighted subjects using standard clinical procedures and instruments [2]. Subjects woretheir own spectacles or contact lenses to correct any refractive error. Visual fields weremeasured without an HMD and with two binocular HMDs and with two monocular HMDs. Allevaluated HMDs were non-immersive designs. Care was taken to ensure that the HMDs did notmove relative to the head during a measurement session. Visual fields were measuredmonocularly and binocularly.Two perimeters were used to measure the visual fields. The Auto-Plot perimeter (Bausch& Lomb, Rochester, NY) used for most measurements is a mechanical kinetic perimeter thatallowed examination of the central 50° (diameter) of the visual field. As shown schematically inFigure 1, small circular spots of light (targets) were projected by the perimeter onto a screen 1 mfrom the subject. Target sizes used were 0.5, 1, 2, 3, 6 and 12 mm. Measurements wereconducted in a dimly lit room (0.26 lux: Minolta Illuminance meter TL-1), with a screenluminance of 0.021 cd/m2 and a target luminance of 7.0 cd/m2 (Minolta LS 110 spot photometer).While the subject maintained a steady gaze at a bright red spot (laser pointer directed at screen)white targets were moved on the screen and the subject reported when the target appeared (ordisappeared). The Auto-Plot projects a bright (white) target on the screen. Targets vary in sizeand are specified as to their diameter in millimeters on the screen. From the observation distanceof 1 m a 1 mm target spans 0.057° or 3.44 arcmin of visual angle. As smaller targets (e.g.0.5 mm the smallest target available) are more difficult to see than larger targets (e.g. 6 mm)measured scotomata may vary with target size. In dynamic perimetry the target is moved inslowly (about 2 deg/sec) from the area where it is not seen towards the area where it is seen.When the subjects indicate spotting the target the position is marked. On a visual field plot,scotomata (regions in which a target are not seen) are outlined by isopters (lines joining thepoints that define the scotoma edge) and are commonly hatched or shaded (e.g. Figure 3). Aregion in which no target can be seen is known as an absolute scotoma and a region in which onetarget can be seen, but a smaller target cannot be seen is known as a relative scotoma. Note thatdue to the observer’s finite size pupil vingetting causes relative scotomata at the edges of opaqueobstructions in front of the eye.Woods et al. Non-Immersive HMDs and the Visual Field5The Goldmann perimeter (Haag-Streit, Berne, Switzerland) is a spherical projectionkinetic perimeter that allowed wider examination of the visual field