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The Impact of Non-Immersive Head-Mounted Displays



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The Impact of Non Immersive Head Mounted Displays HMD on the Visual Field Russell L Woods 1 Ivonne Fetchenheuer 1 2 Fernando Vargas Mart n 1 3 and Eli Peli 1 1 The Schepens Eye Research Institute Harvard Medical School Boston MA USA 2 University of Applied Sciences Berlin Germany 3 Laboratorio de ptica Dept F sica Univ Murcia Spain Submitted on 20 September 2002 for consideration for the Special Issue on the SID 02 International Symposium of the Journal of the Society for Information Display Figures 7 Tables 1 Communicating author Dr Russell Woods Schepens Eye Research Institute 20 Staniford Street Boston MA 02114 Telephone Facsimile Electronic mail 1 617 912 2589 1 617 912 0169 rwoods vision eri harvard edu Woods et al Non Immersive HMDs and the Visual Field Abstract Binocular head mounted displays HMDs that could be used non immersively produced substantial interruption of the visual field Monocular HMDs designed to be used nonimmersively created minimal interruption of the visual fields making them safe to wear but may be not to use in mobile situations A small opaque display can be positioned to provide a see through functionality Keywords Head mounted displays visual field ergonomics 2 Woods et al Non Immersive HMDs and the Visual Field 1 Objective and Background Non immersive head mounted displays HMDs those that allow the wearer to interact with their environment while using the HMD have considerable potential for use in offices industry and medicine For example a worker could walk warehouse aisles collecting goods listed on a HMD that were transmitted from a central computer In such circumstances the vision through and around the display are important for safety and orientation While central vision is used to view an object of regard peripheral side vision is critical for safe and efficient mobility 1 The extent of peripheral vision is known as the visual field 2 While manufacturers provide the field of view of HMDs the impact of HMDs on the visual field have been addressed only minimally in the literature Most considerations given were to the trade off between the field size and resolution and the effects of these trade offs on target search 3 5 The limitations of these trade offs are important considerations in immersive HMDs but may be less important in non immersive HMDs In fact as noted by Peli 6 and Davis 5 a wide field of view in a HMD may be difficult to use as large eye movements are needed and no head movements can be used to reduce an eccentric eye position Here we consider in addition to the field of view of the display itself the impact of the whole appliance on the visual fields of the user Vision through the HMD display may be reduced or obstructed by the veiling luminance of 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 as shown in Figure 1 A HMD may obstruct the view of an object in a particular direction a scotoma as defined in the methods section Non immersive HMDs may be binocular or monocular so we examined two examples of each We show that the impact of the HMD on the visual 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 the display These impacts on the visual field influence the relative safety of use of non immersive HMDs when planned use requires interaction with the environment and should be considered in HMD design INSERT FIGURE 1 ABOUT HERE 3 Woods et al Non Immersive HMDs and the Visual Field 2 Methods Visual 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 wore their own spectacles or contact lenses to correct any refractive error Visual fields were measured without an HMD and with two binocular HMDs and with two monocular HMDs All evaluated HMDs were non immersive designs Care was taken to ensure that the HMDs did not move relative to the head during a measurement session Visual fields were measured monocularly 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 that allowed examination of the central 50 diameter of the visual field As shown schematically in Figure 1 small circular spots of light targets were projected by the perimeter onto a screen 1 m from the subject Target sizes used were 0 5 1 2 3 6 and 12 mm Measurements were conducted in a dimly lit room 0 26 lux Minolta Illuminance meter TL 1 with a screen luminance 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 or disappeared The Auto Plot projects a bright white target on the screen Targets vary in size and are specified as to their diameter in millimeters on the screen From the observation distance of 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 in slowly 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 the points that define the scotoma edge and are commonly hatched or shaded e g Figure 3 A region in which no target can be seen is known as an absolute scotoma and a region in which one target can be seen but a smaller target cannot be seen is known as a relative scotoma Note that due to the observer s finite size pupil vingetting causes relative scotomata at the edges of opaque obstructions in front of the eye 4 Woods et al Non Immersive HMDs and the Visual Field The Goldmann perimeter Haag Streit Berne Switzerland is a spherical projection kinetic perimeter that allowed wider examination of the visual field 180 diameter Targets varying in size from I about 0 3mm to V about 9mm and in intensity from 1e 20 cd m2 to 4e 328 cd m2 are projected onto the


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