Multi-Monitor Mouse
Hrvoje Benko
Steven Feiner
Department of Computer Science, Columbia University
500 West 120th Street, 450 CS Building, New York, NY{benko, feiner}@cs.columbia.edu
ABSTRACTMultiple-monitor computer configurations significantly
increase the distances that users must traverse with themouse when interacting with existing applications, resulting
in increased time and effort. We introduce the MultiMonitor Mouse (M3) technique, which virtually simulates
having one mouse pointer per monitor when using a single
physical mouse device. M3 allows for conventional controlof the mouse within each monitor's screen, while permitting
immediate warping across monitors when desired to increase mouse traversal speed. We report the results of auser study in which we compared three implementations of
M3 and two cursor placement strategies. Our results suggestthat using M3 significantly increases interaction speed in a
multi-monitor environment. All eight study participants
strongly preferred M3 to the regular mouse behavior.

Figure 1: a) Using standard pointer movement to move
between monitors from S to T. b) M3 warps the cursor(dashed line) to the next screen, reducing the distance traversed by conventional mouse movement. “Sonar” circles
are displayed to increase cursor visibility.

among monitors, treating them as separate, but connected,
spaces, and only rarely do they straddle an application window across multiple physical displays.

Multi-monitor, mouse pointer, interaction technique.

This research inspired us to create Multi-Monitor Mouse(M3), a pointer interaction technique that warps the pointerbetween screens in a multi-monitor system configuration.
M3 simulates having one independent mouse pointer per
screen, using a single physical mouse device.

ACM Classification Keywords

RELATED WORK

Author Keywords

H.5.2. [User Interfaces]: Graphical User Interfaces, Input
Devices and Strategies.
INTRODUCTION

Increased display size and resolution and the proliferationof multiple-monitor display configurations have significantly extended the amount of desktop space available tocomputer users. However, increased desktop space forces
users to move their mouse cursor over larger distances. To
compensate, users can increase pointer speed or acceleration, which have drawbacks pointed out by Baudisch et al.
[3]. In addition, tiling several displays in a row often results
in one dimension (typically width) being drastically larger
than the other, causing excessive “clutching” when traversing multiple displays with a mouse.
While the operating system considers the multi-monitor
desktop as one seamless environment, previous research by
Grudin [6] clearly suggests that users treat multi-monitor
systems as means of partitioning their desktop space. Thisis primarily due to the physical gaps between monitors, butdifferences in resolution, size, and apparent mouse speed
can also contribute towards this mental partitioning. As
Grudin points out, users have a tendency to distribute tasks
Copyright is held by the author/owner(s).
CHI 2005, April 2–7, 2005, Portland, Oregon, USA.
ACM 1-59593-002-7/05/0004.

Improving target acquisition across multiple monitors has
been explored in context with eliminating warping effects
caused by mismatched monitor alignment and differing
screen resolutions with mouse ether [1], as well as avoiding
the need to cross the bezels by bringing the targets closer tothe current cursor location with drag-and-pop [2]. Baudischet al. also proposed visual enhancements, such as highdensity cursor [3], that increase visibility of cursors at highspeeds. Interactions that warp the pointer closer to a target
location have previously been explored on a single monitor
in combination with eye gaze (e.g., [8] and MAGIC pointing [9]) or hand gestures (e.g., flick [5]). Zhai, Smith, andSelker compared one- and two-handed techniques for compounding tasks of scrolling and pointing [10].
MULTI-MONITOR MOUSE

We have implemented M3 as a Windows application thatruns in the background, minimized to the system tray.
When M3 is launched, it reads the system’s information
about the size, number and relative location of attachedscreens and forms a corresponding set of virtual frames torepresent the screens. When the user issues a frame switch
command, M3 warps the mouse pointer to the new frame(screen). The new location of the cursor is signaled to theuser by invoking the “mouse sonar” animation around thepointer (Figure 1b), a built-in Windows option that enhances pointer visibility. Otherwise, pointer movement iscompletely unaffected by M3. (For example, the user is still
free to move the pointer across screen boundaries by physically moving the mouse, but now has the option of directly
warping to a different screen.)
M3 segments the pointer space according to screen space
divisions, thus allowing for pointer warping across screens.
While the techniques presented in this paper have been applied to switching between screens in a multi-monitor configuration, the same techniques, without modification, canbe applied to any desktop space by dividing it into a set ofvirtual rectangular frames. These frames can be of arbitrary
number and size, and can even overlap. For example, alarge high-resolution monitor could be divided into several
virtual frames, each containing the windows for one application. M3 would in this case switch the mouse pointer between different applications.

working. At a constant working distance from the user, thelarger the screens, the larger the horizontal angle subtended
by each screen that can be reliably measured with an absolute orientation sensor. We outfitted a pair of headphones
with a 3DOF orientation sensor (InterSense InertiaCube2)
and measure the user’s head orientation to determine thescreen at which they are looking. When the user turns theirhead towards another screen, the head orientation switch
performs a frame switch.

We have experimented with several switch designs. Two of
the final four designs (mouse button and keyboard switches)require only standard computer peripherals, thus making
them easy for most computer users to adopt. The other two(head orientation and mouse location switches) support
more direct switching, but require extra equipment.

While 6DOF tracking combined with eye-gaze tracking
would reduce errors, we wanted to design a minimally invasive switch that would perform well with minimal calibration time. We have noticed that while eye gaze alone issometimes used to glance at another screen, users tend toalign their head with a monitor when performing tasks on
its screen (especially with the larger, 24" diagonal, monitors
we used), which supports our head orientation switch solution. In general, our technique is similar to MAGIC pointing [9], insofar as it warps the pointer to the area “in focus”(in our case, a screen), followed by fine selection by mouse
movement alone. However, while MAGIC pointing warps
the pointer within one screen whenever the eye gazechanges, we warp only across frame boundaries and leave
all mouse manipulation within a single screen unchanged.

Mouse Button Switch

Mouse Location Switch

M3 FRAME SWITCH ALTERNATIVES

The mouse button switch command is issued by pressing
one of the two side buttons (XButtons) on the five-button
Microsoft IntelliMouse Explorer mouse. Since multimonitor configurations are typically side-by-side arrangements, we decided to map the top side button to advance theframes forward (clockwise), and the bottom side button toadvance the frames backward (counterclockwise). This decision is technically arbitrary, but we believe that it has
ecological validity in that it mimics the behavior of themouse itself when those side buttons are pushed: Pushing
the top button would tend to rotate the whole mouse clockwise, while pushing the bottom button would have a counterclockwise effect. The virtual frames form a loop, making
it possible to cycle through all the screens using just one of
the buttons.
Keyboard Switch

The keyboard switch is modeled after a built-in Windows
task-switch command (ALT+TAB). We mapped the forward frame switch to the ALT+“~” key combination, andbackwards to ALT+SHIFT+“~”. As with the mouse button
switch, looping is supported and it is possible to use justone key combination to switch among all screens. Thismode, although implemented, was not evaluated in our tests
because of its similarity to mouse button switch.

The last switching method we implemented is based on theidea that every screen could have a corresponding mousepad. The user still manipulates only one physical mouse,but physically placing the mouse on a different pad warps
the cursor to the screen corresponding to that pad. We implemented mouse location switch using a touch-sensitive
surface (MERL DiamondTouch table) on which the user
can define any axis-aligned rectangle as a pad for a given
screen. To aid the user in remembering the locations of thevirtual mouse pads, we provided paper mouse-pad cutouts
to be placed on the surface (Figure 2). Since the table operates through electrostatic coupling, the mouse is wrapped inaluminum foil to allow it to be tracked by the DiamondTouch surface when held by the user.
M3 POINTER-PLACEMENT STRATEGIESIn addition to deciding on how to trigger the frame switch,
there are several possibilities for where to warp the mouse
cursor in the target frame after the frame switch has oc-

Head Orientation Switch

By observing the work of several individuals in a multidisplay environment, we noticed that a user’s head position
does not change much, but their head orientation changes
continuously, depending upon the screen on which they are

Figure 2: M3 test setup consisting of four monitors and four
corresponding “mouse pads” used by mouse location
switch. The background is set to an inactive spreadsheet
image to simulate a typical noisy working environment.

curred. After some preliminary experimentation, threestrategies emerged as plausible candidates: fixed location,frame-relative, and frame-dependent.
Fixed-Location Placement Strategy

Our initial implementation of M3 used the single fixedlocation placement strategy of always warping the cursor tothe center of the next frame (Figure 3a). While the center
location is somewhat arbitrary, it does ensure that the
maximum mouse traversal distance after the frame switch
will always be at most half of the frame’s diagonal. Thiscan be beneficial if users distribute their tasks equallyaround the center, which is often the case with active working windows. However, it can be a nuisance when the target
is located near an edge, which is the case for some frequent
selection tasks, such as accessing the taskbar. In our current
M3 implementation, it is possible to select any fixed location as the warping target, as long as that location is available on all frames.
Frame-Relative Placement Strategy

Frame-relative placement works by translating the pointerto 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 3b). This strategy essentially collapses the entire available space into one frame of mouse
movement and is the only strategy we implemented inwhich the effect of pointer movement prior to the frame
switch will not be negated by the switch itself.
Frame-Dependent Placement Strategy

If all frames are considered as completely independent
spaces, the system can remember the last location of the
cursor in each frame and warp the incoming cursor to thatlocation. Thus, the last position of the cursor when the user
warps out of the frame, becomes the starting location when
the user eventually warps back to that frame (Figure 3c).
This frame-dependent placement strategy, while preferredby some initial test users in the two-monitor setup, was notformally evaluated for four monitors, due to its increasing
difficulty as the number of frames increases. This is presumably due to the memory load imposed on the user having to remember each frame’s cursor position.
USER STUDY

Eight right-handed participants (6 male, 2 female, ages 23–32), all unfamiliar with the techniques, participated in atarget-selection experiment, with a counterbalanced withinsubject design. We decided to test regular unassisted mouseinteraction (CTRL mode) with three M3 frame-switch
modes: mouse button (MB), head orientation (HEAD), andmouse location (ML). We tested each switch mode using
two pointer-placement strategies: frame-relative (FR) andcenter fixed-location (C). This resulted in a total of sevendifferent conditions. Each user was allowed to familiarize
themselves with all mouse behaviors, and performed ablock of 10 practice trials before completing the block foreach condition. Each block consisted of five trials for each

Figure 3: Traversing between S, T1 and T2 locations using
different M3 pointer placement strategies: a) fixed-location(center), b) frame-relative, c) one of many possible framedependent scenarios. Dashed lines indicate warping; solidlines indicate conventional movement.

of three different start-target distances and two directions(right and left) for a total of 30 movements per block.
Our hypothesis was that participants would acquire targets
faster when using M3 relative to the control mode as thenumber of screen bezels that needed to be crossed increased. In addition, we speculated that the users would befaster using the frame-relative strategy rather than the center fixed-location strategy because of the utility of movement prior to the frame switch in the former strategy.
The experiment was conducted on a Dual Xeon (2.6GHz,
2GB RAM) computer running Windows XP, with fourmonitors tiled in a horizontal arrangement, driven by two
ATI Radeon 9800 and 9000 graphics cards. All four monitors were Samsung SyncMaster 240T (24" diagonal,
1920×1200 resolution, 60Hz refresh), for a total desktop
space of 7680×1200 pixels. The monitors were arranged ina semicircle of 80cm radius, with 12cm horizontal separation (including bezels) between each monitor’s display, andthe user was seated in the center to ensure equal distanceand viewing angle to all monitors (Figure 2). Thus, eachdisplay occupied a 35° horizontal viewing angle with 8°
separation. The mouse speed was set to the medium setting.
The task was based on a Fitts’ Law target acquisition task[7], but without any variation of start and target sizes (fixedat 30 pixels square). To eliminate target discovery overhead, we presented the participant with both start and target
buttons at the same time, asked them to locate both before
starting a trial, and recorded the time it took between clicking on the start button and clicking on the target button. We
selected distances of 2134, 4047, and 5956 pixels, such thateach required crossing one, two, or three bezels, respectively. To eliminate strategy bias, each target was locatedexactly halfway between the center of the screen and theframe-relative location of the start button on that target
screen (Figure 4). The direction varied between left-to-rightand right-to-left.

Figure 4: Start (S) and target (T) button layout in our user
study. To eliminate strategy bias, T is located at the halfway point between the warping locations for frame-relative(fr) and center fixed-location (c) strategies. Control path
(ctrl) is also shown.

a)

Results

Movement times were first cleared by removing outliers(movement times more than two standard deviations larger
than the mean for each condition), which accounted for lessthan 3.5% of all the trials. All data analysis was performed
on a median movement time for each participant, distance,
direction, and condition combination. We performed a 7(Condition) × 2 (Direction) × 3 (Distance) ANOVA, with
our subjects as a random variable. There were significant
main effects for all three factors. The Direction factor contained a significant main effect, F(2,14)=82.72, p<<0.001:
transitioning left-to-right was on average 0.2s faster thangoing right-to-left, which is consistent with previous research showing that right-handed users performed mouse
movements faster from left-to-right than from right-to-leftwhen using their right hand [4].
The mean movement times across Condition, F(6,42)=3.88,
p<0.01, are shown in Figure 5(a). The interaction of Distance and Condition (Figure 5b) also had significant effects,
F(12,84)=9.509, p<<0.001. As predicted, in all cases the
FR strategy outperformed the C strategy by an average of
0.1s, which we believe is due to the C strategy discarding
pointer movement prior to the frame switch. Of the M3
modes using the FR strategy, MB (1584ms) was the fastest
compared with CTRL (1906ms), presenting a 17% improvement in performance. MB was followed by HEAD
(1698ms) and ML (1710ms), which were both significantly
faster than CTRL. It is interesting to notice that for the
shortest distance (2134 pixels) there were no significant
differences between movement times across conditions. Allof the M3 performance gains come from time saved whentraversing two bezels or more, with the biggest gains (up to29%) being present at the largest distance (5965 pixels).
In the post-experiment questionnaire, all subjects strongly
preferred some M3 mode to the CTRL condition, and 6 outof 8 users preferred the FR strategy over the C strategy.
While 7 out of 8 users preferred the MB mode over all theother modes, some mentioned that they would actually prefer a combination of HEAD and MB modes, in which thescreen switch is triggered with the mouse button, but the
cursor warps directly to the screen at which they are looking. This combination would resolve the “Midas touch”
issue of pure HEAD mode, and also eliminate the multiple
clicks necessary to switch across more than one screen.

b)
Figure 5: Aggregated movement times (ms) with 95% confidence intervals: a) Condition factor, b) Interaction ofDistance and Condition.
CONCLUSIONSOur user study confirmed that M3 can improve target acquisition performance in multi-monitor systems; as predicted,
the effect was higher with increased distance and FR strategy. Subjective evaluations show a strong preference forM3 over regular mouse pointing, and we believe that theperformance advantage could significantly increase withexperience. In future work, we would like to evaluate additional M3 modes and strategies, as well as implement a hybrid mouse button + head orientation switch mode.
ACKNOWLEDGMENTS

This work is funded in part by NSF Grant IIS-01-21239,
ONR Contract N00014-04-1-0005, and a gift from Mitsubishi Electric Research Labs.
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