Pointer Warping in Heterogeneous Multi-Monitor Environments
Hrvoje Benko

Steven Feiner

Department of Computer Science
Columbia University
New York, NY{benko, feiner}@cs.columbia.edu

ABSTRACT
Warping the pointer across monitor bezels has previously been
demonstrated to be both significantly faster and preferred to thestandard mouse behavior when interacting across displays in homogeneous multi-monitor configurations. Complementing thiswork, we present a user study that compares the performance offour pointer-warping strategies, including a previously untested
frame-memory placement strategy, in heterogeneous multimonitor environments, where displays vary in size, resolution, andorientation. Our results show that a new frame-memory pointerwarping strategy significantly improved targeting performance(up to 30% in some cases). In addition, our study showed that,when transitioning across screens, the mismatch between the visual and the device space has a significantly bigger impact on performance than the mismatch in orientation and visual size alone.
For mouse operation in a highly heterogeneous multi-monitor
environment, all our participants strongly preferred using pointerwarping over the regular mouse behavior.
Keywords: Multi-monitor, mouse pointer, interaction technique,distributed display environments.
CR Categories: H.5.2. [User Interfaces]: Graphical User Interfaces, Input Devices and Strategies.
1

INTRODUCTION

Multi-monitor display configurations can be characterized as either homogeneous or heterogeneous. The most frequently encountered examples are homogeneous, where two or more displays ofthe same size, resolution, and relative orientation to the user, aretiled next to one another. When displays of different size, resolution, or orientation are used together, they form a heterogeneous
multi-monitor configuration, such as that shown in Figure 1.
Both homogeneous and heterogeneous configurations extend
the available desktop space. However, enlarged distances, coupledwith the need to cross individual monitor edges (bezels), present
difficulties to regular pointer interaction. Several researchers [1-5,12, 16, 17] have noted serious drawbacks with standard mouseinteractions across displays in multi-monitor configurations. In
homogeneous configurations, most of the problems arise from theexaggerated distances that the mouse has to traverse and the path
discontinuities that are caused by monitor bezels. In heterogeneous configurations, these problems are further exacerbated by thediscrepancies between the device space and visual space behavior

Graphics Interface Conference 2007
28-30 May, Montréal, Canada
Copyright held by authors. Permission granted to
CHCCS/SCDHM to publish in print form, and ACM
to publish electronically.

B

CA
Figure 1: Experimental heterogeneous multi-monitor environment consisting of a small low-resolution near-horizontal display(A), a medium-size high-resolution vertical display (B), and alarge low-resolution vertical display (C).

of the mouse (Figure 2, left). We use the term device space todescribe the system’s perspective of the desktop space, where thenumber of pixels determines the area. This is what the computer
graphics community calls device coordinates. In contrast, visual
space is the user’s view of the desktop space, which is determinedby the physical display size. Furthermore, it is possible to consider a perspective space where the distance and orientation between the user and the displays affect how the user perceives thepresented information.
Pointer warping was introduced simultaneously and independently by us [5] and Ashdown and colleagues [1] as an alternative to standard monitor bezel traversal. Pointer warping isdefined as instantaneous relocation of the cursor to the desired
virtual frame (e.g., monitor screen), and such techniques attempt
to reduce the need to traverse monitor bezels through mouse motion, while allowing conventional mouse interactions within eachscreen. We presented a set of Multi-Monitor Mouse (M3) techniques [5], which evaluated pointer warping in a homogeneous
multi-monitor environment and showed significant improvements
when traversing two or more monitor bezels.1 Performance improvements of up to 29% were achieved when traversing threemonitor bezels.
In this paper, we extend our previous M3 research on pointerwarping by implementing the improvements suggested in theearlier study [5] and evaluating the performance of several warping techniques (including a previously untested strategy) in a heterogeneous multi-monitor environment.

1

Virtual frames in M3 were not restricted to entire screens, but could bearbitrary user-defined upright rectangular areas; however, our evaluation
tested only full-screen frames.

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Figure 2: The differences in device space (top) and visual space (bottom) representations of our experimental setup. Traversing a continuous device space path (top left) with a standard pointer can be a cognitively demanding task in visual space (bottom left). Pointerwarping aids the user by removing the need to traverse the bezel (right). Concentric “sonar” circles help increase the visibility of the cursor
after the warp by highlighting the destination.

2

RELATED WORKA substantial amount of work has been done to alleviate the effects of bezel traversal and enhance pointer interaction acrossmultiple displays. Baudisch and colleagues accelerated the mouse
cursor to ease access to distant locations in high-density cursor[4]. A complementary effect has been achieved by bringing distant targets closer to the current cursor location in drag-and-pop[3]. Forlines and colleagues developed HybridPointing [8], whichlets the user switch easily between absolute and relative pointing
to enable access to distant and close targets on a large display.
Reduction of discontinuities caused by mismatched monitor alignment, bezels, and resolutions has been explored in mouse ether [2]and wideband displays [12]. Mouse ether solved the problem ofmismatched visual and device space, by adjusting the pointerspeed on all monitors so that the pointer moves at a consistentvisual speed irrespective of the monitor resolution. Nacenta andcolleagues [13] took a more general approach to display positionand orientation differences by displaying a perspectively corrected
pointer based on the position of the user’s head; however, theirapproach relied on 3D position tracking of all displays in the environment as well as the user’s head.
M3 [5] introduced several pointer warping strategies for placing the pointer on the target display after a user-initiated warp in a
homogeneous multi-monitor configuration. In addition, M3 explored using mouse buttons, mouse location, and head orientation
to trigger the warp. Independent of M3, Ashdown and colleagues[1] presented another implementation of homogeneous multimonitor pointer warping using head orientation.

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Interactions that warp the pointer closer to a target location
have been explored on a single monitor in combination with eye
gaze (e.g., eye gaze interaction [15] and MAGIC pointing [18]) or
hand gestures (e.g., flick [7]). Tan and colleagues [17] exploredthe effects of visual separation between displays that varied insize and depth, while Su and Bailey [16] examined various horizontal distance and angle arrangements between the displays andtheir effect on users’ performance in a multi-monitor environment. In work on Semantic Pointing, Blanch and colleagues [6]provided valuable insight into decoupling the visual and device
space and showed how that can be used to provide assistance inmouse selection.
3

FRAME SWITCHING TECHNIQUESTo test the effectiveness of pointer warping in heterogeneous
multi-monitor configurations, we chose the mouse button frame
switching technique that showed the biggest performance gains(up to 29%) and received overwhelming user preference (7 out of
8 participants) in the previous M3 study [5] and compared it to a
new technique, head-orientation–mouse switch. This new technique extends the original M3 head-orientation switch by incorporating the improvements suggested by the study participants.
The mouse button (MB) switch trigger is issued by pressing
one of the two side buttons (XButtons) on a five-button mouse.
The top side button cycles through the monitors forward (clockwise) and the bottom side button cycles backwards (counterclockwise). The virtual frames form a loop, making it possible tocycle through all the screens using just one of the buttons.

7

(a)

(b)

frame, and warps the incoming cursor to that location (Figure 3b).
Thus, the last position of the cursor when the user warps out of
the frame, becomes the starting location when the user eventuallywarps back to that frame. We had not tested FM in our previous
homogeneous multi-monitor experiments, due to the presumed
high short-term memory load imposed by having to remember
each frame’s cursor position [5]. However, we hypothesized that
this strategy would work well in a heterogeneous setup, where thephysical differences between monitors might make it easier for
the user to remember each frame’s cursor position.
USER STUDY

5

Figure 3: A comparison of two pointer placement strategies
tested in the experiment (shown here in a homogeneous environment). Traversing between locations S, T1, and T2 using:(a) frame-relative (FR) and (b) one of many possible framememory (FM) scenarios. Dashed lines indicate warping; solidlines indicate conventional movement. Note that the position of
the pointer after the warp in the FM strategy is the last positionof the cursor on that frame (i.e., the position that the pointeroccupied before it warped out of that frame).

The head-orientation–mouse (HEAD) switch is a hybrid technique that combines head orientation measurement (for determining the screen at which the user is currently looking) with a sidemouse button trigger (to trigger a warp to that screen). We measure the user’s head orientation with a 3DOF orientation sensor
mounted on a pair of headphones. The original M3 headorientation switch was the close second-best switching alternative[5], but suffered from the “Midas touch” problem [10], causing
the cursor to warp across monitors even when the user just wanted
to glance over without switching monitor focus. Identical problems were present in the head-orientation-based implementationof pointer warping by Ashdown and colleagues [1]. To eliminate
such spurious switching, we have introduced a mouse button trigger, which adds an additional click overhead while switching, but
still reduces the number of clicks compared with the mouse button
switch technique.
4

POINTER PLACEMENT STRATEGIES

We were interested in comparing two strategies for locating the
cursor on the target screen after the frame switch. Therefore, we
decided to compare the winning strategy in the homogeneous
multi-monitor case (frame-relative) [5] with a previously untested
strategy (frame-memory).
Frame-relative (FR) placement works by translating thepointer to the next frame at the same location relative to the newframe’s upper left corner as it was relative to its old frame’s upper
left corner (Figure 3a). This strategy essentially collapses theentire desktop space into one frame of mouse movement and is
the only M3 strategy in which the effect of pointer movement
prior to the frame switch will not be negated by the switch itself.
Frame-memory (FM) placement (called frame-dependent in
the previous M3 work [5]) considers all frames as completely
independent spaces. It stores the last location of the cursor in eachTo evaluate the performance of these display switching andpointer placement methods in a heterogeneous multi-monitor
environment, we conducted a user study with ten right-handed
participants (seven male, three female, ages 21–27), all unfamiliar
with our pointer warping techniques and with no connection to
our lab. The participants were recruited by mass email to students
in our department, and received a small monetary compensation
for their participation.
5.1

Setup

The experiment was performed on a PC running Windows XP
Pro, with two ATI Radeon 9800 and 9000 graphics cards. The
virtual desktop was extended over three displays of different orientation, resolution, and size (Figure 1). From the system’s perspective, the displays were aligned at the bottom (Figure 2). The
displays were arranged in a semicircle (approximate radius 80cm)
Position

Left
A

Middle
B

Right
C

Type

Wacom
Cintiq 15X
LCD

Samsung
SyncMaster
240T LCD

NECWT600
Projector

Size

12"×9"(15” diag.)

20.5"×12.75"(24” diag.)38"×29"(48” diag.)

Resolution

1024×768

1920×1200

1024×768

VisualPixel Size

0.28mm0.24mm1mm

Orientation

Nearhorizontal

VerticalVerticalTable 1: Displays used in the study.

ScreenTransition

A–B

A–C

B–C

Visual Area
Mismatch

2.4

10.2

4.2

Visual–Device
Space Mismatch

0.85

3.57

4.2

Orientation
Mismatch

73°

73°

0°

Bezel
Crossings

1

2

1

Table 2: Display transition characteristics in our experiment.

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2 directions ×
4 identical trials= 360 trials per participant

around the participant’s seat and ordered by increasing diagonal
size from the left: A (15"), B (24"), and C (48"). Table 1 summarizes the relevant characteristics of the displays.
Head orientation was tracked by a set of headphones on which
was mounted an InterSense InertiaCube2 head orientation tracker.
These were worn by participants throughout the entire experiment
to eliminate the potential confound of wearing them only during
head-tracking conditions. Mouse pointer speed and acceleration
were kept at the default Windows XP setting.
In Table 2, we summarize the various types of mismatch present when traversing between monitors in our experiment. Visualarea mismatch represents the ratio between the physical areas of
the two screens and provides us with a simple metric of the visualsize difference between displays. (Note that a more complete
metric would take into account the distances between the displays
and the user and the solid angle subtended by these displays in theuser’s visual field.)
Visual–device space mismatch is the ratio of visual pixel sizes
between displays. It is important to note that all screens were usedat their native resolution, which caused the largest adjacent monitor mismatch between the visual and the device space to occur
between B and C (i.e., pixels on C are 4.2 times larger than on B).
Orientation mismatch is the tilt (pitch) angle difference between screens. The left display (A) was oriented at a nearhorizontal angle of 17o with respect to the desk surface, as perergonomic guidelines suggested by the manufacturer (Wacom).
Thus, A was offset by 73o about the horizontal, relative to theother two displays. Note that arranging all displays in a semicircle
around the participant ensured equal distance to each display.
Therefore, we do not consider differences in yaw as orientation
mismatch. Su and Bailey [16] found that for the optimal performance for a stationary user, the vertical displays should not be positioned in the same plane, but positioned at an angle of up to 45°
with respect to each other to ensure equal visual angles and minimal amount of distortion. Our setup follows their guidelines;
however, note that Nacenta and colleagues [13] take a more general approach to display position and orientation differences.
5.2

Procedure

After greeting the participant, the experimenter gave a brief tutorial demonstrating each of the 5 conditions. Before completing
each block of trials, the participant was familiarized with the current test condition and given a short practice session (32 trials)
which was similar to the actual experiment. The participant completed the entire session with the experimenter watching. Total
running time per session was approximately one hour. At the endof the experiment, the participant completed a satisfaction questionnaire.
5.4

Task

The task was based on a Fitts’ Law target acquisition task [11],but without the variation of start and target sizes in device space(fixed at 25×25 pixels). To eliminate the overhead of the visual
search time, we presented the participant with both start and target
buttons simultaneously, asked them to locate both before commencing a trial, and recorded the elapsed time between clicking
on the start and target buttons. While this reduced the visual
search time, it also allowed the user to plan their action before thetrial. However, we specifically instructed the participants not to
pre-position their pointer on each screen before each trial to avoid
skewing the results.
We selected three target locations on each screen that werealigned, but separated by 100 vertical pixels. Connecting the corresponding targets resulted in nine conceptual paths (Figure 4),
none of which are straight paths in visual space. In device space,paths 1, 2, and 3 are the symmetric equivalents of paths 7, 8, and9, but in visual space these paths cross different size and resolution boundaries. Furthermore, paths 1, 2, 7, and 8 are not straight(a)

MethodWe decided to test standard unassisted mouse movement(CTRL) and compare it to four pointer warping combinations:mouse button with frame relative (MB-FR), mouse button withframe memory (MB-FM), head-orientation–mouse with frame
relative (HEAD-FR), and head-orientation–mouse with frame
memory (HEAD-FM). This resulted in a total of five different
conditions.
The study design was a 5 condition x 2 direction (left-to-rightand right-to-left) x 9 paths (specific paths across displays) x 4
trials within subjects design. In our within-subject experiment,each participant performed five blocks of 72 trials for a total of
360 trials per participant. Each block tested one condition (CTRL,
MB-FR, MB-FM, HEAD-FR, or HEAD-FM) and the order ofpresentation of blocks was counterbalanced across participants.
Each block consisted of four identical trials for each combinationof nine paths and two directions (R and L). All trials within a
block were randomized to reduce ordering and learning effects. In
summary, the experiment consisted of:
5 blocks (one per condition) ×
9 paths ×

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5.3

(b)

Figure 4: (a) Our experimental task setup consists of ninepaths, shown here as dashed lines, each connecting two ofnine targets, distributed over three screens. Notice that portions of paths 1, 2, 7, and 8 are blocked by the edges of thescreens. (b) The actual paths in device space that a pointercould follow in CTRL condition on path 1 (from A to B), 4(from A to C), and 7 (from B to C).

7

5.5

Hypotheses

Prior to our experiment, we postulated the following four hypotheses:
H1: Pointer warping conditions should outperform CTRL,
due to the overall reduction of necessary mouse movement.
H2: Pointer warping conditions using the FM strategy shouldbe the fastest for this task, since they will require the least amountof mouse movement.
H3: Pointer warping conditions should not be as affected by
the distance or visual-device space mismatch between screens as
CTRL.
H4: Paths 1, 2, 7 and 8 should require longer targeting times
than paths 3 and 9 in the CTRL condition, due to screen edges
blocking the direct path between targets; however, this should not
be the case for pointer warping.
5.6

Results

Movement Time (ms) ± SEM

Movement times were first cleared by removing outliers (movement times more than two standard deviations further from themean for each condition), which accounted for less than 1% of alltrials. We performed a 5 (Condition) × 9 (Path) × 2 (Direction)
repeated measures ANOVA on median movement time, with ourparticipants as a random variable. As expected, there were significant effects for the Condition factor, F(4,36)=11.46, p<0.001 (Figure 5). Additionally, the paired samples t-tests comparing CTRL
and HEAD-FM (t(17)=4.758, p<0.001) and CTRL and MB-FM(t(17)=5.101, p<0.001) showed that FM conditions significantly
outperformed CTRL. Since both FR conditions were not found to
be statistically different from CTRL in our experiment, we conclude that our H2 hypothesis was confirmed and that FM wasoverall the fastest strategy. Our participants demonstrated an
overall performance gain of 19% for pointer warping with the FM
strategy compared to CTRL.
2500

2000

1500

We made an interesting observation about the behavior of ourparticipants in CTRL condition. During the experiment, we noticed that they appeared to adopt the following strategy for reaching the target on the next display. First, they appeared to use afast, deliberate, but often imprecise, hand movement to move themouse pointer to the target screen. Second, once the pointer was
found on the next screen, the participants appeared to perform aprecise targeting task. This, in effect, is very similar behavior topointer warping strategies, where the first action warps the pointerto the target screen, followed by precise targeting afterwards. This
Movement Times (ms) ± SEM

To increase the visual grouping of the targets, the display
background showed an inactive Notepad window (of identical
pixel size) on each screen at the target location. This was intended
to reinforce the idea pointed out by Grudin [9] that users tend toswitch among tasks (windows) when switching displays.

H1 was not completely confirmed, since the performance ofboth FR conditions was not statistically different than CTRL.
Although the graph in Figure 5 shows CTRL slightly outperforming HEAD-FR and MB-FR, our analysis shows no statisticallysignificant difference in performance among these three conditions (when compared via t-tests). We believe that there are two
reasons why the FR conditions (HEAD-FR and MB-FR) did notoutperform CTRL. First, the previous study of pointer warpingthat explored homogeneous displays [5] confirmed that the FR
strategy significantly improves targeting performance only whencrossing two or more monitor bezels. However, 2/3 of our current
trials required only one bezel crossing. Second, given our particular experimental task design, the FR conditions were always required to traverse a significant distance on the target display after
the warp. This, in effect, penalized them in comparison with the
FM conditions, which in our test cases always warped the cursor
to a location near the target.

2200
2100
2000
1900
1800
1700
1600
1500
1

(a)

2

3

4

5

6

7

8

9

Path
2100

Movement Time (ms) ± SEM

paths in device space, since the edges of the screen block standard
cursor movement in off-screen space and instead require the participant to move along screen edges, as noted by Baudisch andcolleagues [2]. All paths were evaluated in both left-to-right andright-to-left directions.

1000

2000
1900
1800
1700
1600
1500
A–B

500

(b)

0
CTRL

HEAD-FMMB-FM

HEAD-FR

MB-FR

Condition

Figure 5: Aggregated movement mean times (ms) for theCondition factor.

A–C

B–C

Screen Transition

Figure 6: (a) Movement mean times (ms) for the Path factor.
(b) Mean screen transition times (ms), computed as aggregated path times (e.g., A–B screen transition is the aggregated times of paths 1, 2, and 3).

7115

Direction contained a significant effect (F(1,9) = 17.447,
p<0.005), with overall movement left to right (visually smaller tovisually larger screens) found to be about 5% slower than right toleft. We speculate that visually larger screens required a longer
visual search time to locate the pointer after the pointer transition,
resulting in increased overall time when moving from left to right.
However, our study gives us relatively limited data to make any
definitive conclusions, and we believe that this phenomenon
should be further explored in a separate study.
The Path factor, F(8,72)=7.625, p<0.001, showed significant effects, with the longest overall paths (4–6) taking the longest time
(Figure 6a). The middle paths (2, 5, 8) were the fastest paths overall for their respective screen transitions (A–B, A–C, B–C). Thiswas probably due to the middle target’s placement at the mid
point between the other two targets, which required the least
amount of mouse movement on average. The aggregated screentransition times (Figure 6b) show that two-bezel screen transition(A–C) required on average 10% more time than one-bezel screentransition (A–B or B–C). While this was expected, due to theadditional bezel transition, it is interesting to note that the A–B
screen transition was slightly faster than B–C, even though bothconsisted of transitioning identical device space distances andonly a single bezel.
An explanation for this discrepancy comes from the analysisof the interaction of Path and Condition (Figure 7), F(32,288)=4.351,
p<0.001. Performance of CTRL in the A–B screen transition(paths 1–3) was significantly faster than in the A–C or B–C monitor transition. In fact, performance of CTRL seems to be inversely
proportional to the degree of mismatch between visual and device
space: higher visual–device space mismatch (A–C and B–C) resulted in lower targeting performance, while lower mismatch (A–B) showed improved performance. Interestingly, the mismatch
between the visual and the device space (B–C) had a significantly
bigger impact on CTRL performance than the mismatch in orientation and visual size alone (A–B).
In contrast, we did not observe this drastic difference between
A–B and B–C in any of the pointer warping conditions, which
performed almost uniformly across both the high and low mismatch transitions and across one and two bezel transitions (confirming H3). In particular, pointer warping conditions combinedwith the FM strategy seemed to be the least affected when transitioning visual–device space mismatched screens, requiring on
average 1.6s to reach the target in our experiment. When traversing the paths of high visual–device space mismatch, pointer warping (with FM strategy) provided a performance speedup of up to
30% compared to CTRL (e.g., path 8 in Figure 7).
Our last hypothesis (H4) was not confirmed, since we did notobserve significant effects of screen edges affecting some cursor
paths (1, 2, 7, and 8) more than others (3 and 9) in CTRL condition. We speculate that the difficulties from visual–device spacemismatch may have overshadowed the influence of screen edges
in this particular task. Overall, visually locating the pointer on thetargeting screen seemed to be a fairly challenging task with orwithout the screen edge interruption. However, a more carefulfurther investigation should be performed to systematically evaluate these influences.

116

CTRL

2400

Movement Time (ms)observation is consistent with Sears and Shneiderman’s analysisof touch screen pointing [14], which separated the targeting task
into a gross arm movement, followed by finer finger movements.

HEAD-FMMB-FM

HEAD-FR

MB-FR

2200
2000
1800
1600
1400
1200
1

2

3

4

5

Path

6

7

8

9

Figure 7: Aggregated movement mean times (ms) for theinteraction of Path and Condition.

5.6.1

Subjective Evaluations

The participants filled out a post-experiment questionnaire rating
their experience with five techniques on a 10 point Likert scale (1being most negative and 10 being most positive). They wereasked to comment on the ease of use of each condition and performance of each condition, as well as provide their overall preference for condition and strategy. The participants rated HEADFM the easiest to use (7.9) and the fastest (8.5), followed by MBFM (ease of use of 6.8 and performance of 7.8). In contrast,
CTRL was rated the hardest to use (5.2) and slowest (4.3) overall.
All participants agreed that they would strongly prefer to use
one of the pointer warping techniques over CTRL, with HEADFM being the top choice for five participants, MB-FM for threeparticipants) and HEAD-FR for two participants. Overall, sevenout of ten participants preferred some form of HEAD switching.
Several participants commented on their frustration with
CTRL. One stated that “just using mouse is painful” and anotherthat “it gets very difficult to move between monitors without
warping if their resolution varies significantly.” Additionally,
several participants commented about their lack of familiarity
with the side mouse buttons on a five-button mouse, saying thatthey would definitely improve their performance with extended
use of such mice. This is encouraging, because even though theparticipants were all very familiar with regular mouse use andcompletely unfamiliar with pointer warping and the side mousebuttons, pointer warping conditions performed at least as fast as
CTRL, and outperformed CTRL with the FM strategy. Therefore,
we hypothesize that further extended use would further improve
the overall pointer warping benefits.
6

DISCUSSION AND CONCLUSIONS

Our study confirmed that pointer warping offers a significant
improvement over standard mouse behavior for heterogeneous
multi-monitor environments, even when crossing only a single
bezel. Our previous experiment with homogeneous multi-monitor
configuration showed that performance improvements frompointer warping were mostly due to gains achieved when crossing
two or more bezels [5].
In heterogeneous environments, we found two major advantages to pointer warping compared with standard mouse behavior.
First, the benefits grew in proportion to both the distance and theamount of visual–device space mismatch between monitors.
Therefore, performance improvements were present even whencrossing a single bezel (visible in paths 7–9 in Figure 7). Second,7

pointer warping conditions performed almost uniformly acrossboth the high and low visual–device space mismatch transitions,providing a targeting speedup of up to 30% over standard mouse
behavior.
In addition, the performance of pointer warping was largely
dependent on placement strategy, and not on switching implementation. Remembering cursor locations for each screen was notconsidered too difficult by our study participants, which makes
FM a particularly suitable strategy for pointer warping in heterogeneous environments. However, we believe that this conclusion
depends largely on the task the user is performing. For our task,
where the targets are clustered on each display, FM strategy appears to be preferable. For tasks in which targets are scatteredacross or span multiple displays, FR might be preferable.
While seven out of ten of our study participants preferred
HEAD switching, MB performed similarly. Because of its simplicity, robustness, and reliance solely on standard desktop technology, we would recommend MB as the best technique for multimonitor arrangements with relatively few displays (up to three).
However, for a larger number of displays or display arrangementsthat do not easily lend themselves to a sequential access (e.g., a
3×3 display grid) we believe that HEAD switching is superior
because it allows immediate access to a desired display.
One of the important benefits of pointer warping is that it is acompletely optional enhancement. Pointer warping is only invoked if the user wants to warp across screen bezels, and the behavior of the mouse pointer within any particular screen is left
completely unchanged. In informal observations of our own extended use, we have noticed that we often employ a hybrid approach: we use pointer warping to traverse a larger distance acrossscreens and we resort to traditional bezel crossing when trying toaccess nearby targets on the next screen.
Additionally, we hypothesize that it would be possible tocombine pointer warping with some of the existing multi-monitor
pointer techniques, such as mouse ether [2], to achieve further
benefits. Since mouse ether essentially attempts to reduce thedisplay space to that of a homogeneous configuration, in which
pointer warping has already proven to be of value [5], one would
expect that a combination of mouse ether and pointer warping in aheterogeneous configuration would outperform either alone.
Overall, pointer warping is an easy-to-implement and completely optional enhancement that does not hinder existing mouse
behavior in any way. It provides significant improvements inperformance in multi-monitor configurations, as confirmed formally in the study reported here, and informally in regular use in
our lab. Furthermore, our informal experience shows that extended regular use of pointer warping results in further improvements in performance. We are making the pointer warping widget
available for download for use with Windows XP fromhttp://www.cs.columbia.edu/~benko/projects/m3/.
7

ACKNOWLEDGMENTS

We would like to thank our study participants and the anonymous
reviewers for many helpful comments. This work is funded in partby NSF Grant IIS-01-21239, and a gift from Microsoft Research.

8

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