`
`WRL
`Research Report 2000/3
`
`Rock ’n’ Scroll is
`Here to Stay
`
`Joel F. Bartlett
`
`Western Research Laboratory 250 University Avenue Palo Alto, California 94301 USA
`
`Lenovo EX-1026,
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`Lenovo EX-1026,
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`
`
`Rock ’n’ Scroll is Here to Stay
`
`Joel F. Bartlett*
`
`Abstract
`Using the example of an electronic photo album, a
`novel user input method for digital appliances is intro-
`duced. Based on tilting and gesturing with the device, the
`Rock ’n’ Scroll input method is shown to be sufficient for
`scrolling, selection, and commanding an application with-
`out resorting to buttons, touch screens, spoken commands
`or other input methods. User experiments with a prototype
`system showed that users could quickly learn how to oper-
`ate such devices and offered some insight into their expec-
`tations. These positive results, combined with improve-
`ments
`in
`the sensor
`technology, encouraged us
`to
`incorporate this input method into an experimental hand-
`held system.
`
`1. Introduction
`Not missing a chance to show off the latest pictures of
`your children, you reach for your new photo album. As
`you remove it from your pocket, it activates and you see a
`display of photograph thumbnails in the album. Tilting the
`album on either axis scrolls through the thumbnails until
`you find the pictures you want to show. A gentle fanning
`gesture zooms in on the first picture, then you hand the
`album to your friend. After admiring the picture, she ges-
`tures to step through the rest of the album. The pictures are
`in both landscape and portrait mode, so a simple gesture is
`all that’s required to reorient the album to best display
`them.
`Before putting it back in your pocket (where it will
`automatically shut down), you stop to admire the album
`itself. The album’s dimensions are that of the display with
`the addition of a thin, black border. In keeping with its
`spare, elegant design, it has no buttons or other visible
`controls: all functions can be accessed by direct manipula-
`tion.
`
`While such an appliance has yet to reach the market,
`my colleagues and I have constructed a prototype that
`demonstrates the user interface we call Rock ’n’ Scroll.
`The photo album is an example of a device with an
`Embodied User Interface[1], where the control mechanism
`is directly integrated into the album’s display. The design
`
`* Compaq Computer Corporation Western Research Labo-
`ratory, 250 University Avenue, Palo Alto, CA 94301.
`joel.bartlett@compaq.com.
`
`This report is a superset of Rock ’n’ Scroll is Here to Stay,
`published in the May/June 2000 issue of IEEE Computer
`Graphics and Applications.
`
`© 2000 IEEE Computer Society.
`© 2000 Compaq Computer Corporation.
`
`of such a device draws on a long-standing interest in using
`motion sensing for user input and the realization that iner-
`tial sensing systems are the logical type of system to embed
`in small devices[2]. While researchers have anticipated
`tilting a personal digital assistant (PDA) to navigate
`through a document, only in the last two to three years have
`the sensors become small, cheap, and sufficiently low
`power that they can be embedded in a handheld device and
`realize this vision.
`
`Figure 1: As the left edge of the device is dipped, that is,
`rotated about the roll axis, the picture slides to the left of
`the display.
`
`2. Tilt to scroll
`For desktop devices, scrollbars have become the de
`facto control mechanism for paging through documents
`larger than the screen. When user interface designers use
`scrollbars on the smaller display of a handheld device, two
`problems arise: both horizontal and vertical scrollbars are
`often required, and the scrollbars occupy a larger percent-
`age of the screen. Designers can recover the display area
`
`Lenovo EX-1026,
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`WRL RESEARCH REPORT 2000/3
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`ROCK ’N’ SCROLL IS HERE TO STAY
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`used by scrollbars by allowing scrolling by dragging the
`document using a stylus or scrolling via a cursor key.
`However, all these techniques still require the use of both
`hands. One way to free a hand is to use the hand that holds
`the device to control scrolling. As users rotate the device
`in their hand about either or both axes away from a user-
`defined neutral orientation, the device senses the motion
`and the screen contents scroll appropriately, as shown in
`Figure 1.
`As described, scrolling is always on, just like dexterity
`puzzles that you tilt to get the rolling ball in the correct
`hole. This isn’t always the desired behavior, so other sys-
`tems that have investigated “tilt to scroll ”have provided a
`“clutch ” button to engage scrolling[3-6]. When pressed,
`the device’s tilt scrolls the display; otherwise, scrolling is
`disabled.
`The clutch button seems a good solution to accidental
`scrolling, but it comes at some cost. In some simple user
`tests that we conducted at the start of this investigation,
`users complained about having to tilt the device and press
`the button in a synchronized manner. For tasks like reading
`a column of text, users often want to continuously scroll
`and don’t want to keep their hand tensed to hold the button
`down the whole time.
`Finally, any time you provide a button, you make an
`assumption about how the user will hold the device and
`push the button. One solution to this problem is to add
`more buttons. A more elegant one is to make the whole
`device a button, where the user squeezes it to enable
`scrolling[4]. Or, you can make the scrolling behavior mo-
`dal.
`
`Rock ’n ’Scroll uses the last approach. We assume
`scrolling is the device’s normal mode and provide com-
`mands to disable and enable scrolling and to set the de-
`vice’s neutral orientation. However, for this behavior to be
`an improvement over a “clutch ”button, the application
`designer must ensure that frequent mode switches aren’t
`required.
`
`3. Gesture to control
`The commands that control scrolling can be issued in
`any number of ways, including button presses or inter-
`action with a touchscreen. The same inertial sensors that
`control scrolling can also be used to recognize gestures as
`commands - this is the method we chose for Rock ’n’
`Scroll. Levin and Yarin[7] have also investigated this
`method to implement a tilt-and shake-sensitive interface for
`drawing.
`Other possible command gestures include snapping or
`shaking the device, tapping on it with the other hand, or
`fanning it. Unlike Levin and Yarin’s implementation[7],
`we rejected snapping and shaking the device because of the
`strain it places on the user’s hand and wrist. The mass of a
`4-to 6-ounce device proves sufficient to strain users when
`they repeatedly perform such a gesture. Tapping is attrac-
`tive because it doesn’t require users to move the device, but
`
`Figure 2: The first frame of the sequence (top-to-bottom)
`shows the thumbnail photo. In the next three frames, the
`user fans the device. The fifth frame displays the full-size
`picture.
`
`2
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`WRL RESEARCH REPORT 2000/3
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`ROCK ’N’ SCROLL IS HERE TO STAY
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`it does have the disadvantage of requiring a second hand to
`operate.
`We then tried slower fanning gestures about either of
`the device axes. The gentler motion seems easier on the
`hand and wrist than a snap, and the longer duration of the
`gesture makes it easier to separate it from high-frequency
`noise like hand tremors and vehicle vibrations. The se-
`quence of pictures in Figure 2 illustrates how to select a
`picture from the album with a downward fanning gesture
`about the roll axis. The first frame shows the thumbnail
`picture. Then the user smoothly dips and raises the left-
`hand edge of the device to display the desired picture.
`Three other similar gestures - upward about the roll
`axis, downward about the pitch axis, and upward about the
`pitch axis - can also be made. When combined with
`scrolling, they provide a vocabulary of commands more
`than sufficient to implement the rest of the album’s com-
`mands: step from a picture back to the menu of thumb-
`nails, step to the next picture, disable and re-enable scroll-
`ing, and reverse scrolling direction.
`The gestures don’t require a large amount of space to
`execute. For example, they can be performed with a user
`seated with an elbow on a chair’s armrest. When users
`hold the device as shown in Figure 2, the device motion is
`in front of them, and those seated on either side aren’t dis-
`turbed.
`
`4. Hold still to orient
`The final gesture used in the photo album is holding
`the device still for a couple of seconds, which serves two
`purposes. The first is that it reorients the device. In Figure
`3, the user moves the album from landscape to portrait
`mode by positioning it vertically with the new top edge of
`the album up. The user holds the album still in that posi-
`tion for a couple of seconds, then the screen image rotates
`to the new orientation.
`The second purpose of the hold-still gesture is to
`change the album’s neutral orientation. To do this, the user
`first gestures to disable scrolling, then holds the device still
`in the new neutral orientation for a couple of seconds, and
`gestures to enable scrolling. While this operation takes
`three gestures to accomplish, it’s not a burden to users be-
`cause they perform the task infrequently.
`
`5. Implementation
`Now that I’ve demonstrated the mechanics of control-
`ling the device, we can turn our attention towards its im-
`plementation. Verplaetse[2] characterized the motion that
`should be expected as accelerations from 0.1g to 1.0g and a
`frequency of motion of 8 to 12 Hz. The inertial detectors
`must also meet the needs of a personal device: rugged, self-
`contained, small, light, and low power. Finally, we need
`low-cost detectors to meet the manufacturing cost require-
`ments for mass-market digital appliances.
`With these design constraints in mind we chose a two-
`axis, single-chip accelerometer - Analog Devices'
`
`Figure 3: As shown in this sequence, the user positions the
`album in the desired orientation, then holds it for a couple
`of seconds to change the display from landscape to portrait
`mode.
`
`ADXL202 - to measure acceleration on each of the de-
`vice’s axes (see Figure 1). With the addition of one resistor
`and three capacitors, we integrated it into Itsy[8], Compaq
`Research’s experimental platform for “off the desktop
`”computing. Every 10 ms, the ADXL202 reports accelera-
`tion values in the range of íg to +2g for each axis. These
`measurements are averaged in groups of four, so the photo
`album application sees 25 sets of measurements per second.
`These values represent a combination of gravitational ac-
`celeration, user motion, and noise. Initial noise filtering
`occurs by using a low-pass filter in the accelerometer set at
`10 Hz. Exponentially averaging sequential results achieves
`additional filtering. When plotted over time, the values
`look something like Figure 4. At time t0 the user is scroll-
`ing the display by rocking it fore and aft. By time t1, the
`user is holding the device fairly still. At time t2, a gesture
`like that shown in Figure 2 starts and is completed at time
`t3.
`
`Figure 4 illustrates a problem with extracting both
`gesture and scrolling information from the same data
`stream. The user thinks the gesture starts at time t2, but the
`device doesn’t recognize it until t3. During this interval,
`
`3
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`WRL RESEARCH REPORT 2000/3
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`ROCK ’N’ SCROLL IS HERE TO STAY
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`scrolling continues on both axes, so the application may
`scroll from one item to the next in a menu and the gesture’s
`action is applied to the wrong object. This can be seen in
`Figure 2, where in the fourth frame, the thumbnail menu is
`scrolling because the gesture has not yet been recognized.
`To correctly associate the gesture with the right device
`state, the scrolling code is speculatively executed by saving
`the time and current scrolling state before each change oc-
`curs. When the system recognizes a gesture at t3, the sys-
`tem restores itself to the state at t2 (shown in the first
`frame of Figure 2), then applies the gesture’s operation.
`The scrolling state need not be saved indefinitely, since a
`maximum length of a gesture can be defined.
`
`Figure 4: Acceleration versus time for each axis of motion
`is plotted here. Each signal is labeled and shown inde-
`pendently, with the acceleration value on the vertical axis
`and time on the horizontal axis. The vertical gray bars are
`at one-second intervals, and dotted vertical lines denote
`points of interest.
`
`6. But will it work?
`Before implementing Rock ’n’ Scroll for Itsy, we con-
`structed a prototype system to test the ideas. The prototype
`system appears to the user as a handheld computer with a
`cable leading out of it. It consists of a small video liquid
`crystal display (LCD) with a two-axis accelerometer at-
`tached to the back. The accelerometer was made from two
`earlier generation (Analog Devices ADXL05) one-axis
`accelerometers and included a PIC16C73A microcontroller
`to convert the analog outputs from the ADXL05s into
`digital values reported 25 times a second to a PC via an
`RS-232 serial line. The measurements drive a PC applica-
`tion whose output to the screen is converted to a National
`Television System Committee (NTSC) video signal via a
`scan converter, then displayed on the LCD. The prototype
`is decidedly inferior in handling to an Itsy, since it is larger
`and heavier, its screen has a narrower viewing angle, and it
`is tethered to a PC.
`Applications constructed include a viewer allowing us-
`ers to scroll through a number of pictures and text images,
`a game where a cat catches mice, and an interactive map of
`our building. The map application lets users tilt to browse
`
`4
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`a floor and gesture to change floors, set the device’s neutral
`orientation, or disable or enable scrolling. Fifteen members
`of Compaq’s Palo Alto research labs participated in a
`scripted trial that took about twenty minutes per person.
`During the trial the user stood and manipulated the test
`system under my instruction.
`The most important goal of the study as to confirm (or
`reject) the premise that the Rock ’n’ Scroll user interface
`can be rapidly mastered by a larger user community. Test
`users first familiarized themselves with the device by
`scrolling text and pictures. With little practice, they were
`able to start and stop scrolling, find specific articles in the
`text, and center selected items in a picture on the screen.
`Next, we demonstrated the map application, then the users
`tried it. A subjective measure of their ability to operate the
`application as then made based on the three to five minutes
`that they used the application. Three quarters of the users
`found it easy to operate all features of the application. One
`quarter of the users had moderate difficulty making one or
`more of the types of gestures. With some coaching and
`adjusting of the gesture recognizer, all users were able to
`make all types of gestures.
`The more interesting result though, has to do with user
`expectations about how the device would scroll. As the
`prototype hardware and software were being constructed,
`we observed that users have different (and often strong
`expectations) about which way the display should scroll
`when they tilted the device. For example, when the left
`edge of the device is dipped, should the picture on the de-
`vice slide left or right? We designed the user study to ex-
`amine this and found that while a default sensitivity and
`scrolling speed was acceptable, a default scrolling direction
`as not. For each user, the initial scrolling behavior as ran-
`domly selected. As the tests were run, the users were al-
`lowed to change scrolling behavior to a preferred setting,
`while the experimenter encouraged them to try the alterna-
`tive as well. All but two test subjects immediately chose a
`preferred direction and maintained it across the entire test.
`The results, summarized in Figure 5, suggest that the world
`is divided into “sloshers” and “pointers.” Sloshers expect
`that the screen contents have mass and tilting the display
`will cause them to slide down. Pointers expect the opposite
`motion as they point with the edge of the device towards
`the section of the image that they want moved to the center
`of the display.
`However, when presented with a simple game, all
`subjects but one expressed a strong preference for the
`“slosh” mode of operation. The game, shown in Figure 6,
`displayed a cat on the screen. The user tilted the device to
`move the cat around to catch mice. Those who favored the
`“slosh ”mode of operation in the earlier parts of the test
`explained that when they dipped the left edge of the device,
`they expected the cat to go left. Those who “point” ex-
`plained that they were pointing to where they wanted the
`cat to go. Though the test subjects had different explana-
`tions, the end result as that they expected the device to be-
`have in the same manner.
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`ROCK ’N’ SCROLL IS HERE TO STAY
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`Figure 7: Doom on Itsy
`
`down, they’d move up the stairs. Whether they sloshed the
`gun up the stairs or pointed to where they wanted the gun
`to go, the action and expected result were identical.
`Directly manipulating a handheld computer to play
`games fascinated nearly all subjects. The simple cat and
`mouse game on the prototype as surprisingly compelling,
`and users would often continue to play with it for a few
`minutes after their test session ended. When watching us-
`ers play Doom on an Itsy, it’s clear that they had signifi-
`cantly more kinesthetic satisfaction in tilting the device
`than in rocking a cursor key.
`
`7. A limit to embodied user interfaces
`An alternative way to play Doom is to maneuver using
`the diamond-shaped cursor key to the right of the screen.
`This offered an opportunity to determine user input prefer-
`ences for this application. We encouraged users to play the
`game using both input methods and polled them later about
`their preference. The seven respondents to the poll were
`evenly split in their preferences: three preferred the cursor
`key and four preferred tilt-to-scroll. However, when their
`user interface preference was correlated with their level of
`experience playing electronic games, all those with exten-
`sive experience preferred to use the cursor key and the rest
`preferred tilt-to-scroll. Experienced users felt they could
`maneuver with more precision with the cursor key and
`didn’t like the fact that an enthusiastic press of the ¿UH
`button would move the player. Less experienced users
`preferred to tilt-to-scroll and described that method as more
`natural or intuitive than the cursor key.
`While most users had positive things to say about the
`Rock ’n’ Scroll interface, they also noted some problems
`with the display while playing the game. The Itsy display is
`a reflective LCD, so ambient light conditions can cause
`significant changes in screen visibility as the device tilts.
`In addition, enthusiastic play often results in significant tilt
`that exceeds the viewing angle of the display. While LCD
`technology will improve and reduce these effects, some
`experienced users observed one display difficulty inherent
`in embodied user interfaces: perceived motion on the
`screen is the sum of the motion of the embodied device and
`
`Figure 5: In the frame at the top, the picture is in the initial
`position. When the left edge of the device is dipped, seven
`of the fifteen subjects expected gravity to "slosh" the pic-
`ture into the position it has in the center frame, and five of
`the fifteen subjects expected to see the picture like the bot-
`tom frame because they "pointed" with the left edge of the
`device to that corner of the picture.
`
`Figure 6: Cat and mouse game.
`
`We also observed this behavior with the game Doom
`that we ported to Itsy. In Figure 7, virtually all users ex-
`pected that when they tilted the top edge of the display
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`5
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`ROCK ’N’ SCROLL IS HERE TO STAY
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`the changes made to the display by the device. As you
`interact with the device by moving it, the orientation of the
`display to the user changes, then in response to that motion
`the display contents move on the display. For “twitch
`”games like Doom, where the user manipulates the device
`rapidly, tilt-to-scroll results in motion on the screen that
`may be harder to visually track than motion via the cursor
`key. On the other hand, for applications like the photo al-
`bum, where the user is not rapidly manipulating the device
`while trying to track moving fine detail on the screen, this
`should not be an issue. The results from this small test
`suggest an area for further study.
`
`8. Additional ways to Rock ’n’ Scroll
`In the discussion to this point, users always held the
`device in either or both hands. However, since all interac-
`tion occurs by manipulating the device, it could also be
`worn. One promising area for wearing a small gesture-
`controlled device is on the “snuff box ”portion of either
`hand - that is, the area between the thumb and index finger
`on the back of the hand. This area is typically visible when
`using your hands. Gestures can be made on either of the
`device’s axes by moving either your hand or forearm. Fig-
`ure 8 shows how a thermometer that measures the tem-
`perature at the palm of the glove could be mounted. By
`gesturing, the user can change the display to show the
`minimum, maximum, or current temperature. Other ges-
`tures could be used to switch the scale between Fahrenheit
`and centigrade and clear the saved minimum and maximum
`values. While at first this might seem a contrived example,
`consider for a moment the difficulty of trying to push your
`watch’s buttons while you have gloves on.
`
`Figure 8: Industrial glove with hands-free thermometer
`(mock-up).
`
`6
`
`To date this work has focused on interacting with a
`handheld device with a display, but the same techniques
`could be used to control other personal electronics such as
`radios, MP3 players, or cellular telephones. Rather than
`being restricted to play, fast-forward, and reverse buttons
`on a music player, the user could tilt to have fine-grain
`control over playing speed and gesture to step to the next
`track. As fashion plays an increasing role in personal elec-
`tronics, invisible control interfaces could provide desired
`product differentiation. Finally, the inertial sensor doesn’t
`have to be incorporated in the device, but could be in the
`form of a ring or bracelet that communicates with the de-
`vice via a personal wireless network.
`
`9. Evolution of sensors
`Moore's Law predicts continuing improvements in
`digital electronics, equally impressive improvements are
`also occurring in sensors. Three generations of Analog
`Devices' accelerometers were tracked during the design and
`construction of Rock ’n’ Scroll and their key attributes are
`shown in the following table.
`
`axes
`output
`voltage
`current
`height
`area
`
`ADXL05
`1
`analog
`4.75-5.25
`10 mA
`5.8 mm
`70 sq mm
`
`ADXL202
`2
`digital
`3.0-5.25
`0.6 mA
`5.5 mm
`110 sq mm
`
`ADXL202E
`2
`digital
`2.7-5.25
`0.6 mA
`2 mm
`25 sq mm
`
`Our investigation started with the first generation part,
`the ADXL05. Since each part measured only 1 axis, two
`were required for the design, as well as a microcontroller to
`convert the analog outputs to appropriate digital values, and
`a power regulator to convert Itsy's 3.3 volt supply to 5
`volts. Prototype electronics were constructed, but the
`number of components and the power required (~25 mA)
`suggested that the design was not appropriate for Itsy.
`The next generation part improved things significantly.
`Since the ADXL202 measured 2 axes, only one was re-
`quired. Its digital outputs eliminated the microcontroller
`and provided a further reduction in components, but the big
`improvement that enabled Rock ’n’ Scroll's integration into
`Itsy was the 40x reduction in power: 0.6 mA versus ~25
`mA. Package height and area continued to be a problem
`though, and resulted in Itsy's length growing by 10 mm.
`The final generation of the part (which was too late for
`our use), the ADXL202E, significantly reduces the package
`height and area which will simplify its integration into fu-
`ture digital appliances.
`
`10. Conclusion
`The Rock ’n’ Scroll user interface shows how inertial
`sensors in handheld devices can provide additional function
`beyond “tilt-to-scroll.” By also using them to recognize
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`ROCK ’N’ SCROLL IS HERE TO STAY
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`[5] J. Rekimoto, “Tilting Operation for Small Screen Inter-
`faces, ”Proc. ACM Symp. User Interface Software and
`Technology (UIST96), ACM, New York, 1996, pp.167-
`168.
`
`[6] D. Small and H. Ishii, “Design of Spatially Aware
`Graspable Displays”, Proc. CHI97, ACM, New York,
`1997, pp. 367-368.
`
`[7] G. Levin and P. Yarin, “Bringing Sketching Tools to
`Keychain Computers with an Acceleration-Based Inter-
`face”, Proc. CHI98 Extended Abstracts , ACM, New York,
`1998, pp. 268-269.
`
`[8] C. Waldspurger, “The Itsy Pocket Computer,” invited
`talk,
`Int’l
`Symp. Wearable
`Computers
`98,
`http://www.research.compaq.com/wrl/itsy/talk-iswc98/.
`
`gestures, a significantly richer vocabulary for controlling
`the device is available that implements an electronic photo
`album, pager, or other limited function digital appliance
`without any additional input methods. The examples in
`this article offer a glimpse at the freedom for both the de-
`vice designers and users inherent in devices that can be
`held in either hand, at any orientation, operated with mit-
`tens on, or not in the hand at all.
`I hope I’ve communicated some of the excitement that
`surrounds inertial interfaces. What started out as a side
`investigation in our laboratory has captured sufficient inter-
`est that we’ve designed it into the next generation of Itsy.
`We expect others to adopt these interfaces as well and look
`forward to seeing the results of their efforts.
`
`Rock ’n’ Scroll - the movie
`A short movie demonstrating the sample photo album
`is available from the Rock ’n’ Scroll project web page:
`http://www.research.compaq.com/wrl/projects/RocknScroll
`/RocknS.html.
`
`Acknowledgements
`Rock ’n’ Scroll as developed as part of the Itsy pocket
`computer project at Compaq ’s research labs in Palo Alto.
`The work relied on the interest and knowledge of other
`team members including William Hamburgen, Lawrence
`Brakmo, Keith Farkas, Dirk Grunwald, Tim Mann, Robert
`Mayo, Sharon Perl, Barton Sano, Marc Viredaz, Carl
`Waldspurger, and Deborah Wallach. Wayne Mack pro-
`vided electronics assembly assistance. My colleagues at
`Compaq’s research labs in Palo Alto were willing and ar-
`ticulate test subjects. Wendy Bartlett and CG&A’s editors,
`guest editors and reviewers improved the presentation of
`the results. I thank you all.
`
`References
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`7
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`Lenovo EX-1026,
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