Augmenting the Field-of-View of Head-Mounted Displayswith Sparse Peripheral Displays
Robert Xiao1,2
Microsoft Research
One Microsoft Way, Redmond, WA 98052
benko@microsoft.com
1

Hrvoje Benko1
2
Carnegie Mellon University, HCI Institute5000 Forbes Avenue, Pittsburgh, PA 15213
brx@cs.cmu.edu

Figure 1. Our sparse peripheral display prototypes: (a) Virtual reality prototype SparseLightVR, with a 170º field of view,
showing LED arrangement. (b) SparseLightVR imaged from the inside showing a forest scene. (c) Augmented reality prototype
SparseLightAR, with a field of view exceeding 190º. (d) SparseLightAR showing a scene with butterflies and beach balls.

ABSTRACTACM Classification Keywords

In this paper, we explore the concept of a sparse peripheral
display, which augments the field-of-view of a headmounted display with a lightweight, low-resolution,
inexpensively produced array of LEDs surrounding thecentral high-resolution display. We show that sparse
peripheral displays expand the available field-of-view up to
190º horizontal, nearly filling the human field-of-view. We
prototyped two proof-of-concept implementations of sparse
peripheral displays: a virtual reality headset, dubbed
SparseLightVR, and an augmented reality headset, called
SparseLightAR. Using SparseLightVR, we conducted a user
study to evaluate the utility of our implementation, and asecond user study to assess different visualization schemesin the periphery and their effect on simulator sickness. Ourfindings show that sparse peripheral displays are useful inconveying peripheral information and improving situationalawareness, are generally preferred, and can help reduce
motion sickness in nausea-susceptible people.

H.5.1. Information interfaces and presentation (e.g. HCI):
Multimedia information systems: Artificial, augmented, andvirtual realities.

Author Keywords

Augmented reality; virtual reality; wide field-of-view;
sparse peripheral display; peripheral vision

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DOI: http://dx.doi.org/10.1145/2858036.2858212

INTRODUCTION

Head-mounted Augmented and Virtual Reality (AR andVR) devices are increasingly popular due to a recent
resurgence in interest, driven by technologicalimprovements such as better displays, processing power
and mobility. Such mixed-reality systems offer the promiseof immersing a person in a virtual environment or digitallyaugmenting a person’s vision, enabling diverse applications
in areas including gaming, information visualization,
medical assistants, and more immersive communication.
However, one common limitation of such devices is theirlimited field-of-view (FOV). The human visual system hasa binocular FOV exceeding 180º horizontally, yet current
head-mounted virtual reality devices, such as the Oculus
Rift, are limited to around 90º horizontally (Figure 3).
Augmented reality devices such as Lumus DK-40 glasses
and the upcoming Microsoft Hololens are even narrower, ataround 40º horizontal (Figure 6). Notably, this means thatthe users of such displays either see pitch black (in VR) oran absence of virtual content (in AR) in their peripheral
vision. This restricted FOV limits the immersive potentialof mixed-reality systems, reduces the situational awarenessof the person, and leaves the vast information-processing
capabilities of the human visual system underutilized.
We propose the concept of sparse peripheral displays,
which fill the periphery of a head-mounted display using a
low-resolution, high-contrast array of diffused, colored
LED lights, rendering of which is tightly coupled to thecontent presented on the device (Figure 1). Because sparseperipheral displays can be lightweight and inexpensive toconstruct, they can easily be retrofitted to existing headmounted displays, enhancing existing devices. To
demonstrate our concept’s applicability to a range of form
factors,
we
implemented
two
proof-of-concept
implementations: a virtual reality display, called
SparseLightVR, and an augmented reality display, called
SparseLightAR.
We evaluated the effectiveness of our concept using ourSparseLightVR prototype in a pair of user studies. In
addition to confirming the benefits of increased situationalawareness, our experiments showed that participantspreferred SparseLightVR, reporting less effects fromsimulator sickness or nausea compared to the plain VR
display. In particular, our participants found our novel
peripheral countervection visualization to be particularly
beneficial in reducing nausea. Our results confirm thatsparse peripheral displays can be used to expand the fieldof-view in mixed-reality environments while alsocountering the common nauseating effects of enlarged
field-of-view [8, 16].
In summary, this paper makes the following threecontributions:•••

The concept of sparse peripheral displays and two
proof-of-concept implementations: a virtual reality
display (SparseLightVR) and an augmented reality
display (SparseLightAR), along with a detailed
description of their hardware and software designs.
A peripheral countervection visualization, designed toreduce the effects of simulator sickness by presenting
motion stimulation on the retina that counters any
additional motions not generated by the user’s head
movement itself (e.g., motion derived from controller
input).
A 17-person evaluation of SparseLightVR testing its
ability to provide additional context to mixed-reality
interactions, and a follow up study examining theeffects of various rendering strategies on simulator
sickness.

BACKGROUND AND RELATED WORKIn contrast to foveal vision, which senses detail, color, andtextures [27], peripheral vision is much lower resolution
and attuned to sensing contrast [1] and motion [20]. Thus,
displays targeting the periphery have different requirements
than displays for the fovea, leading us to design our sparse
peripheral displays to to complement the high-resolution
foveal display.
FOV and Simulator Sickness

Simulator sickness is a type of motion sickness induced byvisual information that conflicts with vestibular andproprioceptive sensory cues [23]. The principal source of
simulator sickness is induced perception of self-motion, or
vection, caused by motion cues in the visual field that are
not corroborated by vestibular sensory data [14]. In turn,

vection is primarily derived from peripheral visual cues [5,6], with the central visual field playing only a small role.
Consequently, research has confirmed that wide FOV
displays can often induce simulator sickness more easily
than narrow FOV displays [8, 16]. However, because wide
FOV displays also result in higher presence and immersion[16], system designers face a difficult decision whenchoosing an appropriate FOV. In addition, technicaldifficulties in producing commercial devices with wide
FOV (e.g., complicated optics, increased weight etc.) often
limit the available FOV, limiting the depth of virtual
experiences available to users.
Explorations of Wide FOV

Outside of AR/VR, many systems have explored displaying
information or visualizations in the visual periphery. Most
commonly, these peripheral displays provide additional
context to a foveal display, an arrangement referred to as afocus plus context display [3]. Such displays often feature
low-resolution context displays paired with a highresolution focus display, similar in concept to the present
sparse peripheral displays.
Other systems have explored using the periphery to present
information and notifications [15], enhance user
experiences through immersive peripheral projections [10],or expand the effective size of a display through lowresolution ambient light [26]. Recently, FoveAR [4]combined optically see-through glasses with wide FOV
background projection as another example of such focus +periphery hybrid displays.
In the HMD space, Jones et al. [11] found that strategicallyplaced static, bright areas in the peripheral visual field
resulted in more accurate distance perception by HMD
users, suggesting that even static illumination in the
periphery can improve HMD experiences. In contrast,
Knapp and Loomis found that reducing the FOV did not
directly cause distance underestimation [13]. Watson et. al.
[28] found that degradation of peripheral resolution did not
significantly affect user performance on a complex visual
search task.
Wide FOV HMDs

A few recent AR research prototypes [2, 18, 19]demonstrate higher FOVs (up to 92º horizontal, comparedwith 40º for commercial devices) albeit with significantly
reduced image quality across the entire display. For
example, Pinlight Displays [19] use a special light field
display consisting of an LCD backed with an array of point
light sources. These displays require significant
computational power to render a full light field.
Furthermore, the ultimate resolution of the display isdiffraction-limited.
In VR, a number of systems have attempted to widen thefield of view with complex optical configurations. For
example, StarVR [9] (210º horizontal) and Wearality Sky[29] (150º diagonal) both use complex Fresnel lenses which

Figure 2. SparseLightVR device. (a) Unmodified Oculus Rift DK2 device. (b) Rift with LED arrays installed. (c) Rift after
Delrin diffuser installed. (d) SparseLightVR in operation. Note that the LEDs above the nose are disabled to avoid crosstalk,since those can be seen by both eyes.

are challenging to manufacture and design, and introduce
optical distortions which are hard to mitigate. Nagahara etal. [21] (180º horizontal) use a novel optical arrangement(catadioptrical optics), significantly increasing the weightof their device (3.75 kg headset).
Other approaches are possible. For instance, Yang and Kim[30] compress the virtual environment to provide higher
virtual FOV. Similarly, Orlosky et. al. [24] warp the display
using fisheye lenses. Although these warping approaches
result in higher virtual FOV, they trade off physicalaccuracy to do so.
Most related to our approach are systems that explicitly
place low-resolution displays in the periphery. Nojima et al.
[22] demonstrate a prototype peripheral display consistingof four 16x32 LED arrays worn on the user’s head. These
display a moving random dot pattern as the user operates anormal computer monitor, increasing the user’s sense of
self-motion. Baek et al. [2] place a pair of low-resolution
LCDs on the either side of an HMD, but do not evaluate
their prototype or describe its implementation in detail.

IMPLEMENTATION DETAILSBoth our VR and AR prototype displays share some of thesame core components. The displays consist of a number ofindividually-addressable RGB LEDs (WS2812S 5050),
connected in series to an Arduino microprocessor. These
LEDs provide 24-bit color (8 bits per channel), and are allcontrolled from a single Arduino pin using a cascading
serial protocol. Due to the high brightness of these LEDs
coupled with their proximity to the eyes, we covered theLEDs with laser-cut diffuser material to absorb some of thelight and smooth out the LED hotspots (Figures 2c, 5d).
To further reduce the brightness of these LEDs (which aredesigned for outdoor lighting applications), we undervolted
the LEDs, driving them at 3.0 V instead of therecommended 5.0 V. We also performed a quick manual
calibration of the LEDs to the central display, adjusting oursoftware’s per-channel scale values so that the LEDs match
both the brightness and color gamut of the display.
The rendering device continuously streams color data to theArduino over a serial connection running at 500 kilobits per
second. The rendering device is responsible for computing
the color value output by each LED.
SparseLightVR

Our VR prototype, called SparseLightVR, is built on acommercial Oculus Rift DK2 head-mounted virtual reality
device (Figure 2a). This device has a central high-resolution
display of 960x1080 per eye, updating at 75 Hz. The
binocular high-resolution field-of-view is approximately

Figure 3. LED placements in SparseLightVR relative to thevisual FOV of human vision. Purple box: Oculus Rift DK2
binocular FOV. Purple circles: SparseLightVR LEDs. Figure
adapted from Jones, et al. [11].

Figure 4. Close-up image from the inside of SparseLightVR.
The sparse peripheral display shows the sky (top), ground(bottom), and a nearby off-screen red helicopter (left).

Figure 5. SparseLightAR construction. (a) Our custom AR head-worn display prototype. A Samsung Galaxy S6 is mounted on
top, connected to the external IMU and the SparseLightAR controller (left assembly). (b) SparseLightAR LED arrays installed.
(c) SparseLightAR with paper diffusers added, in operation showing a scene with flying butterflies (blue).

84º horizontal. The SparseLightVR peripheral display
consists of 70 LEDs broken up into four groups, arranged
as shown in Figures 3b and 4. Two groups of LEDs areplaced in the far periphery inside the left and right edges ofthe display, and the other two groups are configured asrings in the near periphery surrounding the Oculus’ two eye
displays. Laser-cut pieces of Delrin plastic cover the LEDs
to diffuse the light (Figure 2c). The total sparse FOV isapproximately 170º horizontal (Figure 3). The sparse
peripheral display is driven at 100 Hz using an Arduino
Duemilanove microprocessor, slightly faster than the
Oculus’ native display refresh rate of 75 Hz.
SparseLightVR is driven by a desktop computer running
Windows 8.1, a Core i7-3770 CPU and an NVIDIA Quadro
K5000 graphics card. Applications were developed in Unity
5 using the Oculus VR 0.6 SDK.
SparseLightAR

Our AR prototype, called SparseLightAR, is built on acustom-built head-mounted see-through augmented reality
device. This AR device is a modification of the commercial
Samsung Galaxy Gear VR device. It consists of asmartphone (Samsung Galaxy S6) mounted flat across thetop, connected to an external inertial measurement unit
(Figure 5a). Collimating lenses opposite the display split
the display output into two halves, one per eye, with each
image individually projected at infinity. A half-silvered
mirror mounted at a 45º angle between the display andlenses redirects the collimated images onto the eyes. The
effect is that the display’s contents are overlaid onto theenvironment, creating a see-through augmented reality
experience. The Samsung S6 display provides a resolutionof 1280x1440 per eye at a refresh rate of 60 fps. The
horizontal FOV of our AR display is 62º, comparable withsimilar wide FOV AR systems [7].
The SparseLightAR peripheral display for this prototype
consists of 112 LEDs (Figure 5b) updated 75 times per
second and arranged as two 4x14 rectangular matrices, one
along each edge of our unit. In total, the field of viewexceeds 190º horizontally (Figure 6). A DFRobot Beetle
microcontroller drives the sparse peripheral display and isconnected to the smartphone via USB On-The-Go. All
rendering, microcontroller communication and motion
tracking is performed on the phone itself without anexternal computer, and all LEDs are powered from thephone’s USB port. SparseLightAR applications are written
in Unity 5 using Unity’s Android SDK and a modified
version of the Samsung Gear VR SDK. As the Gear VR
SDK is itself based on the Oculus VR SDK, most of ourUnity code is common to both SparseLightVR andSparseLightAR.
As the LED arrays are opaque, we chose to leave the top
and bottom areas of the field of view clear to preserve
environmental peripheral cues (Figure 5c). We later discuss
future designs employing smaller LEDs that could keep theenvironment visible in the spaces between LEDs.

Figure 6. LED placements in SparseLightAR relative to thevisual FOV. Gray box: Lumus AR [17] FOV for comparison.
Purple box: Our custom AR display’s binocular FOV. Purple
circles: SparseLightAR LEDs. Figure adapted from Jones, etal. [11].

Scene and LED Rendering

We used the Unity 5 game engine to implement the 3D
virtual scenes and scenarios for our sparse peripheral
displays. We implemented a reusable rendering component,
which we called a light probe, responsible for updating a

Figure 9. Countervection rendering. (a) Sphere withmotion bars in Unity. (b) Countervection rendering as it
appears in SparseLightVR.
Figure 7. Light probes used to render SparseLightVR. In
the center, light probes for both eyes overlap.

single LED. The designer can place many such light probes
in the scene, matching the arrangement of the LEDs of thesparse peripheral display they are representing (Figure 7).
This configuration is easily attached to the user’s view andis updated as the user moves around the scene.
For each eye, a virtual camera renders the scene into a color
buffer (Figure 8a). The color buffer is partitioned using a
Voronoi diagram (Figure 8b), assigning each pixel in thebuffer to the nearest light probe. The output color from eachprobe is the average color (using the CIELAB colorspace)of all pixels assigned to it. In this way, we guarantee thatevery object in the field of view contributes to at least one
light probe, allowing even small details to be seen.
Our rendering implementation and light probe
configurations are packaged into a prefabricated Unity
object, enabling existing projects to be augmented simply
by dropping this object in the scene. Furthermore, theselight probes can be added to the Oculus VR SDK’s
prefabricated headset object, allowing applications using
the SDK to automatically support our sparse peripheral
displays.
The actual color values sent to the LEDs are adjusted tomatch the colorspace of the central display (convertingfrom the standardized sRGB colorspace to linear RGB), andthen multiplied by predetermined per-channel scale factors,
which correct for color gamut mismatches and brightness
discrepancies. We took special care to match the gamut andbrightness of our sparse peripheral display to the central
display, as that makes the experience seamless andcomfortable for longer use.
Peripheral Visualizations

As has been shown in several focus + periphery hybrid
displays (e.g., Focus+Context [3], IllumiRoom [10]),
designers have many options when creating content to be
displayed in the periphery. They can choose to purely
extend the FOV as faithfully as possible, or use theperiphery for highlighting of a particular feature or style.
We developed a number of proof of concept visualization
schemes to explore how to effectively use the sparse
peripheral displays in head-mounted displays.
In particular, we implemented the following threevisualizations: full environment, objects only, and a novel
rendering mode called countervection visualization.
Full Environment

This is the most naïve visualization, in which the peripheryextends the FOV of the main display as faithfully as
possible. All objects and scenery are rendered into thesparse display.
Objects of Interest Only

As an alternative to rendering the full environment, thedesigners can choose to render only select objects in the
periphery. This can be helpful to draw the person’s
attention to a particular object in their periphery that iscurrently not visible on the main foveal display.
Countervection Visualization

Figure 8. LED rendering using light probes. (a) Original
rendered color buffer. (b) Colors averaged using a Voronoi
diagram with a distance cutoff. Each solid region
corresponds to a single light probe.

We contribute a novel visualization particularly suited toperipheral displays, which attempts to counteract motions
not generated by physical head movement. We designed
this visualization to reduce the negative effects of vectioninduced simulator sickness caused by motion cues in thevisual field [14].
Our countervection visualization consists of a series ofvertical bars, placed in a spherical arrangement around theperson’s avatar and only visible in the sparse peripheral

Figure 10. The forest scene used to introduce users to SparseLightVR. Left: the virtual scene as rendered for the Oculus Rift
DK2. Right: scene as it appears inside the unit with SparseLightVR enabled.

information) while also benefiting from the reduced vection(and thus reduced visual-vestibular conflict) of thecountervection visualization. Our second study specificallyexamines the effects of countervection visualization andfull environment visualizations on simulator sickness.

display (Figure 9). The sphere does not respond to physicalhead motions. However, when the user’s avatar moves orrotates (e.g., due to user input), the bars are shifted (via
texture manipulation) so that they move in the same
direction as the motion, i.e., opposite to what normally
would occur. We call these contrary motions countervection
cues, as they oppose the motion cues of the central display
and thus reduce the feeling of vection (self-motion). For
example, if the user walks forward, the bars will also move
forward. The bars are configured to move slightly slower
than the actual motion, as we found that a 1:1 mapping
produced an overwhelming motion effect in the opposite
direction during pilot testing.

We conducted two evaluations with 17 participants (6female, mean age 28). Participants completed the twostudies in a single session lasting 60 minutes: a search task
where participants moved their head to locate an object, anda simulator sickness evaluation in which participants wereasked to evaluate their subjective nausea over a range ofrendering conditions.

The countervection visualization is designed to partiallycancel the vection experienced in the peripheral regions of
the VR display. As such, we aimed to balance the strengthof the effect (in terms of brightness) and the speed of the
motion with the VR periphery.

Participants were given the option to stop the experiment at
any time. Each participant was compensated $10 forparticipating, regardless of how much they completed. All
17 participants completed the search task, while 14participants completed the sickness evaluation.

Additionally, we implemented a dynamic switchingstrategy in which the full environment is rendered while theuser is not moving or when the movement comes only fromtheir physical movement of their head, but countervection
cues fade in when the user begins to move via external
input (e.g., joystick input). This means that we fade in thecontervection cues only when the person is experiencing
visual-vestibular mismatch. This allows the user to attainthe benefit of a wider field of view (better immersion, more

Figure 11. Search task. The user uses a cursor in the
middle of the screen to select a white target from a grid ofcircles. (a) Narrow FOV condition. (b) Regular FOV
condition. (c) SparseLightVR condition: the white dot (topright) is rendered to SparseLightVR as an activated LED.

USER EVALUATIONS

Procedure

Participants were first asked about their experiences with
virtual reality. Only one person mentioned using virtual

Figure 12. Virtual scene of the first study search task.
Target shown at left. The LEDs are configured to only
show the target.

reality devices regularly; the remainder had either usedthem on a small number of occasions just as a trial, or had
never used them. The experimenter then had the participant
wear the SparseLightVR device and had them move arounda simulated forest environment (Figure 10) using a
gamepad controller, without the sparse peripheral display
enabled. After a minute of familiarizing the participant withthe device and the virtual reality experience, theexperimenter switched on the sparse peripheral display,which rendered an expanded view of the forest. The
participant was asked to describe their reaction and first
impressions of the system. After this initial induction phase,the participant began the first study.
Study 1 – Search Task

The goal of the first study was to examine the effect of fieldof view on performance in an object search task. Threefields of view were tested, as shown in Figure 11: asimulated “augmented reality” field of view measuring 25
degrees vertical and 50 degrees horizontal (slightly larger
than the field of view of the Lumus AR glasses), a full“virtual reality” field of view employing the Oculus Rift’s
full foveal resolution (84 degrees horizontal); and a wide
“peripheral” field of view which used the Oculus Rift’s fullfoveal field-of-view alongside SparseLightVR for a total of
170 degrees horizontal. In this task, SparseLightVR was
configured to render in “object-of-interest only”
visualization mode. For consistency, we term these tasks,
Narrow, Regular, and SparseLightVR, respectively.
Participants were presented with a virtual 10x10 grid ofcircles, arranged in a hemispherical arc 1 meter from theparticipant and occupying a field of view of 160 degrees
horizontal and 80 degrees vertical (shown in Figure 12).
Upon beginning the task, a white target would appear in arandom hole. The participant was to move their head until acursor in the center of their gaze aligned with the target, andclick a button on the gamepad to select it. This constituted asingle trial. The target would then disappear and reappear ata different grid point. The participant performed threeblocks of 75 trials each, with each block having a different
field of view condition. Condition (block) order was

Figure 13. Chase task. Participants follow the red orb toeach waypoint. The orb leaves a long translucent trail forusers to follow.

randomized per participant to control for order effects, andthe first 25 trials for each block were discarded to reduce
learning effects.
Following this first study, participants were asked to give
their impressions of the system, and then took a short break
before the next study.
Study 2 – Simulator Sickness

Wide FOV displays are commonly cited in the literature asincreasing the sickness and nausea experienced by users ofvirtual reality devices [8, 16]. Consequently, we sought toevaluate whether sparse peripheral displays suffered fromthe same limitation and whether our countervection cues
helped people reduce the effects of simulator sickness. We
compared three conditions: full Oculus Rift FOV without
the sparse periphery, extended FOV using the fullenvironment visualization in the sparse periphery to renderan extension of the scene, and countervection extended
FOV in which the sparse periphery displayedcountervection cues while the user was in motion.
Our second study proceeded in two parts. In the first part,
participants acquainted themselves with our rendering
conditions through a simple chase task, following a
glowing orb as it moved around a forest clearing (Figure13). The orb moved along a predetermined path, stopping at
20 waypoints (Figure 14). At each waypoint, the orb
stopped to orbit a nearby tree and waited for the participant
to approach it; once they moved close enough, the orb
moved to the next waypoint. Participants controlled their
movement in the game environment using a gamepad andtheir head movements. The participants repeated this task
under each of our three rendering conditions, with the orb
moving along the same path each time.
Of the 17 participants in this experiment, three participants
did not complete this chase task; all three tried the task onceor twice and felt too sick to continue to a another repetition.
Following each task repetition, participants filled out the
Simulator Sickness Questionnaire [12] and were given a
five-minute rest to alleviate any lingering nausea.

Figure 14. Orb path for the chase task. The orb’s pathconsists of a mix of sharp and shallow turns, so thatparticipants try out different turning radii.

Figure 15. Results of the search task in Study 1.

Following the chase task, participants were asked if they
were willing to continue with a final, possibly difficult task
in which they were involuntarily moved around a space(i.e., moved on “rails”). In this task, participants were able
to switch between the three conditions from study 2 using
buttons on the gamepad, and try different conditions out asthey moved through the space. Participants were asked
specifically to rank the conditions in order of comfort basedon which conditions they felt minimized their nausea.
Participants were given as long as they wanted to make thisdetermination, and were asked to stay until they had fully
determined their ranking.
Participants who declined the involuntary “rails” task wereasked to complete it with voluntary movement instead, i.e.,
where they both moved themselves around and changed therendering mode using the gamepad. Of the 14 participants
who completed the chase task, three participants chose thisoption.
In the involuntary movement-on-rails task, participants
moved along a looping path which repeated until they
stopped the experiment. Along both straightaways, theparticipant’s avatar accelerated gradually to the midpoint
then decelerated to a stop. At the end of each straightaway,
the avatar jumped about 1.2m into the air to provide somevertical motion, then proceeded to execute the turn and thenext straightaway.
RESULTS

Although we did not explicitly ask participants to rate oursystem overall, many participants reacted positively to thesystem, noting that they “liked this much more” (P2),“[SparseLightVR] felt the most natural” (P12), or that tasks
were “a lot easier with [SparseLightVR]” (P4). Twoparticipants (P3, P12) found the LEDs to be too bright,
while others found it hard to see cues (P8), suggesting thatthe brightness of SparseLightVR could be madecustomizable per-person to improve the experience.

Study 1 – Search Task

Completion time of a trial in this task depended strongly on
two factors: whether the next target was visible in the fieldof-view at the start of the trial (i.e., whether the participant
had to actively move his head to find the next target), andthe angular distance to the next target. We also recorded thetotal angular distance traveled – due to the Oculus Rift’sorientation smoothing, this total distance incorporates very
little noise.
We discarded trials in which participants missed the target
on their first click attempt (162 trials in all), and trials inwhich the target appeared in the same location as theprevious trial (21 trials in all). Of the remaining 2367 trials,
988 had initially-visible targets.
To measure task performance, we use two measurements:
the average targeting velocity measure – the ratio between
the angular distance to the next target and the completiontime – and the movement ratio – the ratio between the total
angular distance travelled and the angular distance to thenext target. The former measures in effect how quickly the
person targets the object, and the latter measurement
measures how efficiently they locate the target.
Results are summarized in Figure 15. All significant
differences were determined through repeated measures
Tukey HSD at a p<0.05 significance level.
For trials with initially visible targets, all three conditions
were significantly different for average targeting velocity(SparseLightVR 49.2º/s, Regular 41.4º/s, Narrow 21.2º/s),
and Narrow was significantly different from the otherconditions for movement ratio (Narrow 2.35, Regular 1.29,
SparseLightVR 1.28).
For trials without initially visible targets, all three
conditions were significantly different for average targetingvelocity (SparseLightVR 70.7º/s, Regular 53.1º/s, Narrow
24.2º/s), and AR was again significantly different from theother conditions for movement ratio (Narrow 4.79, Regular
1.70, SparseLightVR 1.28).
The poor performance of the Narrow condition (very low
average targeting velocity and very high movement ratio)
can be explained due to the very small field of view of the“augmented reality” condition: when the object was not
immediately visible in the view, participants had to executea time-consuming grid sweep to locate it, and each motion
only revealed a small amount of the grid. By comparison,with SparseLightVR, the grid was revealed rapidly as theparticipant moved their head.
In the post-study survey, participants were asked to choose
the condition that was most helpful, most comfortable, andmostpreferable.
Participants
uniformly
chose
SparseLightVR as being the most helpful, with several
noting that the expanded field of view helped find the target
faster (“amazing how much those little [peripheral] cueshelp” (P12)). 15 participants chose SparseLightVR as being
the most comfortable, with two participants choosing theRegular experience instead due to the brightness of theLEDs. Finally, all participants indicated they would prefer
SparseLightVR in a VR experience (e.g. “I hate the blackrim” (P1), “this would be useful in [a first person shooter]”(P2)).
Study 2 – Simulator Sickness

Although we attempted to use the Simulator Sickness
Questionnaire [12] to gauge participant nausea after eachchase task repetition, we found that the SSQ results were
extremely subject to order effects. In some participants,
their sickness scores consistently rose through theexperiment, indicating mounting nausea (despite being
given breaks to get up, walk around, drink water, etc.). In
other participants, their sickness scores consistently
dropped through the experiment due to increased familiarity
with the scene. Three participants noted almost no nausea
across all three conditions. Consequently, we did could not
use the collected SSQ scores to establish the effect onnausea. However, the participants also had a chance todirectly compare the three conditions and come up with aranking when specifically asked to rank them in terms of
how nauseating the experience was.
10 of our participants felt comfortable enough after thechase task to do the high-intensity movement-on-rails task,
while the remaining 3 participants moved themselves
through the scene. Remarkably, all participant rankings fall
into only 3 particular orderings: 9 of the 14 participants
ranked countervection first (followed by wide, then noperiphery); 2 participants ranked wide field of view first,
followed by countervection in second place; and threeparticipants ranked the no-periphery condition first,
followed by wide field of view, followed by countervection.
Thus, in total, 11 of the 14 participants preferred thecountervection rendering to the no-periphery condition.

Several participants expressed a clear difference between
countervection and wide FOV rendering (e.g., P8 felt
“immediate relief” when switching to countervection
rendering, P10 noted it was less jarring during rotations,while P15 noted that “[countervection] stabilized me during
turns”). However, a few participants also found thecountervection rendering to be distracting, noting that theordinary wide field of view “looks better” (P15) or simply
expressing a general preference for the ordinary rendering.
These results indicate that participants strongly preferred
SparseLightVR in motion-heavy tasks, and the high rankingof the countervection rendering condition suggests thatappropriate peripheral cues can help mitigate user sickness.
DISCUSSION AND LIMITATIONS

Although the SSQ questionnaire results were inconclusive,the direct comparison ranking in our study showed that theSparseLightVR display was preferred over no periphery forbeing less sickness-inducing, even without the stabilizing
effects of the countervection cues. As this conflicts withprior research results on wide FOV mixed-reality systems(e.g. [16]), we believe this merits further investigation.
We note that the low resolution of the display may
contribute to decreased nausea. Duh, et al. [8] found thathigh-resolution content in the foveal area tended to makeusers lose their balance more often than low-resolution
content. This finding that may extend to the peripheral
display, and should certainly be explored in future work.
Sparse peripheral displays do suffer from a number oflimitations compared with other means of expanding thefield of view. Because they are low resolution, it isinherently difficult to display small objects or fine detail.
We partially mitigate this in our implementation using
Voronoi rendering to ensure that all objects contribute to
the nearest LED, but ultimately system designers will haveto carefully design environments and objects to produce
optimal sparse periphery renderings. This could involve, forexample, rendering only targets or relevant objectives (aswe did in the search task), or rendering simplified lowdetail geometry to make relevant objects stand out more.
Because the sparse peripheral display requires a separate
virtual camera for each eye, in addition to the two eye
cameras already required for the VR/AR headset, rendering
sparse peripheral display content can cause a significant
performance impact. Furthermore, because the sparse
peripheral displays cover a large field of view, the graphics
pipeline must render many more objects, incurring
performance penalties. In our implementations, we use very
low resolution render textures for the sparse periphery(128x128 or lower) and disable most shader effects which
are imperceptible in the low-resolution sparse periphery.
However, the additional rendering load is still significant,limiting the complexity of scenes we can render. The
problem is especially acute in SparseLightAR, with its
smartphone GPU. Designers will have to carefully considerwhat is rendered to the sparse periphery to minimize
rendering cost, and learn optimization techniques specific tothe sparse periphery.
While sparse periphery displays can usefully expand thefield of view for a user who is attending to the central highresolution display, the displays are much less useful if theuser looks directly at them. Thus, users will have to avoid
glancing around too much, which can be limiting andartificial. With a reasonably wide-FOV central display(such as the Oculus Rift display), users may not have tolook directly at the periphery as often, partially mitigating
this issue.
Although super-wide FOV displays are not yet practicallyavailable, some designs on the market (such as theWeareality Sky [29]) are moving in that direction. Should
wide FOV displays become widespread, we argue thatsparse peripheral displays may still be useful. As our
results, and past work (e.g., [8]) suggest, lower resolution
peripheral displays can help to reduce motion sickness.
Thus, even wide FOV displays could have a resolution
toggle to display lower resolution imagery to motionsusceptible individuals, emulating a sparse peripheral
display in software.

Because our countervection visualization helped mitigate
user sensations of motion sickness, we suggest further
research should be done on its applications to various VR
devices and approaches. For instance, studying thecountervection visualization in a high-resolution wide-FOV
display would determine whether its properties depend on
the resolution used.
Repeating our Study 2, but with longer trial exposure andsignificantly longer time delay between trials, might reveal
statistically significant differences in the simulator sickness
questionnaire data, which would be a welcome validation of
our direct comparison results.
Further investigations on the relationship between
peripheral resolution, field-of-view and simulator sickness
in general would also be very valuable to the researchcommunity. In particular, we believe that our sparse
peripheral display concept could offer a practical solution to
the simulator sickness problem, but further investigations
are needed to potentially allow a substantial number ofmotion-sickness-sensitive users to enjoy VR experiences
previously unavailable to them.
CONCLUSIONS

Finally, our current implementations use fairly large LEDs
(5x5 mm). However, extremely tiny SMD LEDs areavailable (as small as 0.65x0.35 mm), making it possible to
make the LED itself nearly imperceptible when placed near
the eye. This in turn would make it possible to develop a
see-through AR display where the environment is fully
visible, with a sparse peripheral display of miniature LEDsin similar arrangement as SparseLightAR. In this way, thefull benefits of see-through AR could be realized inconjunction with a wide FOV sparse peripheral display.

In this paper, we presented the concept of the sparse
peripheral display, which adds a matrix of colored LEDs to
the periphery of an existing high-resolution head-mounted
display. We contribute two prototype implementations,
SparseLightVR and SparseLightAR, which demonstrate thefeasibility of retrofitting such lightweight, inexpensive
display enhancements on top of existing VR/AR hardware.
We also evaluated our SparseLightVR implementation in
two studies that found that people have increased situationalawareness, preference for the experience, and presence inthe 3D scene when using our prototype. Lastly, we foundthat our novel countervection visualization holds promise in
reducing the effects of simulator sickness experienced by
VR users. We believe that sparse peripheral displays offer
an inexpensive, light and highly customizable way tosignificantly improve existing AR and VR head-mounted
displays. We are particularly encouraged by our results
demonstrating that they can also help make mixed-reality
experiences more comfortable and less nauseating.

FUTURE WORKACKNOWLEDGEMENTS

While we did not explicitly evaluate our AR prototype, we
believe that our results for improved situational awarenessin VR (study 1) should apply to AR systems as well. Our“narrow” condition simulated the same field of view as a
typical AR system, and we showed that SparseLightproduced a significant improvement over a narrow field ofview.

The literature contains many examples of uses for wide
field of view displays, as covered in the related work
section. Exploring which of these uses are practicallyfeasible with sparse peripheral displays would produce
further insights into the capabilities of this concept. For
instance, exploring the various peripheral rendering modes
used by IllumiRoom [10] would dramatically increase therichness of peripheral rendering options available todesigners. Another promising area of research would be to
integrate peripheral flicker [25] notifications, like thosedeveloped by Kooi et al. [15], into a sparse peripheral
display, providing unobtrusive but immediately visible
notifications.

We thank Jaron Lanier, Victor A. Mateevitsi, Patrick
Therien, Josh Hudman, Javier Porras Lurashi, Wayne
Chang and all the members of the Microsoft Research
COMRADRE and Hardware Labs for developing thecustom AR display and helping us adapt it for theSparsePeriphery project.
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