PAPERS
`
`. .....:.o;..........a...:.....:...· ~····'--.:' ._,, •.:. ,. C'. _;
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`CHI 98 •18-23 APRIL1998
`
`A Comparison of
`Three Selection Techniques for Touch pads
`
`I. Scott MacKenzie
`Dept. of Computing & Information Science
`University of Guelph
`Guelph, Ontario Canada N1 G 2W1
`+1 519 824 4120 x8268
`smackenzie@acm.org
`
`Aleks Oniszczak
`Dept. of Computing & Information Science
`University of Guelph
`Guelph, Ontario Canada N1 G 2W1
`+1 519 824 4120
`aoniszcz@uoguelph.ca
`
`ABSTRACT
`Three methods of implementing the select operation on
`touchpads were compared. Two conventional methods -
`using a physical button and using "lift-and-tap" - were
`compared with a new method using finger pressure with
`tactile feedback. The latter employs a pressure-sensing
`touchpad with a built-in relay. The relay is energized by a
`signal from the device driver when the finger pressure on
`the pad surface exceeds a programmable threshold, and
`this creates both aural and tactile feedback. The pressure
`data are also used to signal the action of a button press to
`the application. In an empirical test \vith 12 participants,
`the tactile condition was 20% faster than lift-and-tap and
`46% faster than using a button for selection. The result
`was similar on the !SO-recommended measure known as
`throughput Error rates were higher \vith the tactile
`condition, however. These we attribute to limitations in
`the prototype, such as the use of a capacitive-sensing
`touchpad and poor mechanical design. In a questionnaire,
`participants indicated a preference for the tactile condition
`over the button and lift-and-tap conditions.
`
`Keywords
`Touchpads, pointing devices,
`feedback, Fitts' law
`
`input devices,
`
`tactile
`
`INTRODUCTION
`in
`Since notebook computers are usually operated
`constrained spaces, mice are generally not used as the
`systems' pointing device. Until recently, most notebooks
`included either a trackball or an isometric joystick as a
`pointing device. Apple was the first company to
`incorporate a touchpad in a notebook computer, and many
`other companies have since chosen touchpads over
`joysticks or trackballs. A touchpad implements the select
`operation either using physical buttons (as with mice) or
`
`Permission to make digitalfhard copies of all or part of this material for
`personal or classroom use is granted \\ithout fee provided that the copies
`are not made or distributed for profit or commercial advantage, the copy(cid:173)
`right notice, the title oftl1e publication and its date appear, and notice is
`given that cop) right is by permission of the ACM, Inc. To copy otherwise,
`to republish. to post on servers or to redistribute to lists, requires specific
`permission and! or fee.
`CHI 98 Los Angeles CAUSA
`Cop)right 1998 0-89791-975-0/98/ 4 .. $5.00
`
`using a "lift-and-tap" technique.
`This paper presents an empirical evaluation of a new
`selection technique for touchpads that is based on tactile
`feedback. The work is a continuation of a design described
`in an earlier short paper [II].
`
`TOUCHPADS VS. MICE
`Although
`touchpads are also available for desktop
`computers, most people prefer to use a mouse. So, why is
`a mouse a better pointing device .. than a touchpad when
`space is not an issue? The answer may lie in the
`separation of selection from positioning. Using a mouse,
`the pointer is positioned by moving the mouse on a
`mousepad. The device is gripped between the fingers and
`thumb and movement occurs via the wrist and forearm.
`With a touchpad, pointer movement is accomplished by
`sliding a finger along the touchpad's surface. Both are
`generally used as "relative positioning" devices, where the
`pointer moves relative to its previous position when the
`device or finger moves.
`For a mouse, selecting is the act of pressing and releasing
`a button while the pointer is over an icon or other screen
`object Double clicking and dragging are related
`operations that also require pressing a button. There are
`two common
`implementations
`for
`selecting with
`touchpads: (a) using physical buttons, or (b) using lift-and(cid:173)
`tap. Both inherit problems we are attempting to correct in
`our tactile touchpad.
`
`Physical Buttons
`Most touchpads include physical buttons that are typically
`If an index
`operated with the index finger or thumb.
`finger is used, the finger must move frequently between
`the
`touchpad and
`the buttons and
`this
`impedes
`performance compared with the same procedure using a
`If the thumb is used, then positioning and
`mouse.
`selecting proceed in concert, as with a mouse; however,
`the result may be sulroptimal because of interference
`between the muscle and limb groups engaged. A similar
`problem has been noted for trackballs [12], wherein high
`error rates (particularly for dragging tasks) are attributed
`to the "closeness" of the muscle and limb groups required
`
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`CHl 98 • 18-23 APRIL 1998
`
`for the separate acts of positioning and selecting. With a
`mouse, on the other hand, positioning occurs primarJy via
`the wrist and forearm, While selecting occurs primarily
`through the fingers. Thus, the limbs and muscle groups
`are separate for each task and tend not to interfere.
`
`Lift-and-Tap
`Because of the problem noted above, most touch pads also
`support ..,lift-and-tap" as an alternative to pressing buttons.
`However, this is perhaps replacing one problem with
`another. We'll illustrate this by considering the basic
`transactions with computer pointing devices. According to
`Bm.'ton's three-state model of graphical input [4], these can
`be modeled by three states:
`out-of-range (the device/finger is elevated)
`State 0
`tracking (pointer movement)
`State I
`dragging (movement with button depressed)
`State 2
`These are identified in Figure 1, annotated for mouse
`interaction.
`
`Lift mouse
`
`Button up
`
`Tracking
`
`Out of
`Range
`Figure 1. Buxton,s three state model of graphical
`input with labels appropriate for mouse interaction
`
`Dragging
`
`For touchpads and mice, pointer motion occurs in state I,
`the tracking state. The comparison becomes interesting
`v.ilen we consider the state transitions required for
`-clicking, double clicking, dragging, and clutching.
`(Clutching is the act oflifting'the mouse or finger from the
`mousepad or touch surface and repositioning it.) Figure 2
`identifies the state transitions for the most common
`operations for a mouse and a lift-and-tap touchpad. A few
`observations follow. In general, operations require more
`state transitions ·with a lift-and-tap touchpad than with a
`mouse. A simple click on a mouse begins and ends in
`state 1, Whereas on a touchpad it begins in state 1 and ends
`in state 0. To return to pointer positioning (state 1), the
`finger must resume contact with the pad, and if this occurs
`too quickly a dragging operation occurs. Note as well that
`'Clutching on a lift-and-tap touchpad is confounded with
`clicking and dragging. This is not the case with a mouse.
`
`·- A~•·,
`
`'
`
`,.
`
`PAPERS
`
`Lift-and-tap Touchpad
`Mouse
`Operation
`1
`Pointer Positioning 1
`1-0-1-0
`1-2-1
`Single Click
`1-0-1-0-1-0
`1-2-1-2-1
`Double Click
`1-0-1-0-1
`1-2
`Dragging
`1-0-1
`1-0-1
`Clutching
`..
`Figure 2. State transitions for common operations
`using a mouse and a lift-and-tap touchpad.
`
`THE TACTILE TOUCHPAD
`In view of the preceding discussion, it is worth exploring
`for state
`implementations
`alternate, perhaps better,
`transitions. One possibility is to implement them by
`pressing harder with the pointing/positioning finger. A
`mouse button provides aural and tactile feedback when it is
`pressed, and this is an important component of the
`interaction. Similar feedback may be elicited from a
`touchpad by means of a mechanical solenoid or relay
`positioned under the pad and activated with an electrical
`signal to create a "click" sensation in the fingertip. Since
`a mouse button clicks both When pressed and when
`released, the same response is desirable for a tactile
`touchpad to achieve a more natural feel.
`To prevent spurious clicks, the transitions should include
`hysteresis. That is, the state I-2 pressure level that maps
`to the button-down action should be higher than the state
`2-1 pressure level that maps to the button-up action. This
`is illustrated in Figure 3. The correct thresholds must be
`determined in user tests.
`
`,,
`
`0
`
`1
`State
`
`2
`
`Figure 3. Pressure-state :function. A click is
`generated for state I-2 transitions and for state 2-1
`transitions.
`
`There is prior work on embedding a solenoid under a
`mouse button to create tactile feedback. A study by
`
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`CHI 98 • 18-23 APRIL 1998
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`Akamatsu and MacKenzie [1] found significant reductions
`in movement times for target selection tasks using a
`modified mouse
`incorporating
`tactile
`feedback as
`compared to an unmodified mouse. Using a Fitts' law
`analysis of the data, it was found that the tactile condition
`produced the highest throughput of all tested conditions.
`It was surmised that similar results would be achievable
`with the tactile touchpad. One can provide aural feedback
`through the computer's existing sound system. However,
`we feel the combination of spatially-placed aural and
`tactile feedback at the finger tip is preferable to spatially(cid:173)
`the
`system's
`displaced audio-only
`feedback using
`loudspeaker, although the latter is worthy of investigation.
`Our tactile touchpad is illustrated in Figure 4. For our
`prototype, we cut a hole in the bottom of a Synaptics
`T1002D capacitive touchpad and installed a Potter &
`Brumfield T90N1D12-5 relay. A wooden platform
`attached to base provides space for the relay. The relay is
`controlled by signals sent from the host's parallel port.
`
`~ I·
`
`I
`I
`I
`
`Figure 4. The tactile touchpad. (a) top view. (b)
`bottom view.
`
`(b)
`
`338
`
`The Synaptics touchpad includes· an x-y-z mode in which
`the z-axis information is the applied pressure. Our
`software uses z-axis information to determine when to
`energize and de-energize the relay. In informal tests with
`pilot subjects we determined that, of the 256 pressure
`levels detected by the touchpad, a value of 140 with a
`hysteresis value of 5 produced an acceptable response -
`one similar to the feel of a mouse button.
`
`ISO TESTING OF POINTING DEVICES
`Although there is an abundance of published evaluations
`of pointing devices in the disciplines of human-computer
`interaction and human factors, the methodologies tend to
`be ad hoc, and this greatly diminishes our ability to
`interpret the results or to undertake between-study
`comparisons. Fortunately, there is an emerging ISO
`standard that addresses this particular problem [8]. The
`full standard is ISO 9241, "Ergonomic design for office
`work with visual display terminals (VDTs)". The standard
`is in seventeen parts, and some have received approval as a
`DIS (draft international standard). Part 9 of the standard
`is called "Requirements for non-keyboard input devices".
`As of this writing it is in the CD (committee draft) stage.
`ISO 9241-9 describes, among other things, quantitative
`The
`tests to evaluate computer pointing devices.
`procedures are well described and will allow for consistent
`and valid performance evaluations of one or more pointing
`devices.
`
`The standard quantitative test is a point-select task. The
`user manipulates the on-screen pointer using the pointing
`device and moves it from a starting position to a target and
`selects the target by pressing and releasing a button on the
`device. There are many variations on this test; however, a
`simple reciprocal selection task is easiest to implement and
`allows for a large quantity of empirical data to be gathered
`quickly. The task is "reciprocal" because the user moves
`the pointer back and forth between targets, alternately
`selecting the targets. The selections are ''blocked" with
`multiple selections per task condition.
`As the point-select task is carried out, the test software
`gathers low-level data on the speed and accuracy of the
`user's actions. The following three dependent measures
`form the basis of the subsequent quantitative evaluation:
`time (MT), or task
`Movement Time. Movement
`time in seconds or
`the mean
`completion time,
`is
`milliseconds for each trial in a block of trials. Since the
`end of one trial is the beginning of the next, the movement
`time is simply the total time for a block of trials divided by
`the number of trials in the block.
`,
`Error Rate. Error rate (ER) is the percentage of targets
`selected while the pointer is outside the target.
`Throughput. Throughput (TP) is a composite measure, in
`''bits per second", based on both the speed and accuracy of
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`PAPERS
`
`The experiment used custom software known as the
`Generalized Fitts' Law Model Builder [15]. The software
`executes under DOS and interacts with the system's
`pointing device through the installed mouse driver.
`All three selection techniques used the same device, a
`modified Synaptics T1002D touchpad, as described earlier.
`Standard features of the touchpad include two physical
`buttons and a lift-and-tap button emulation in firmware.
`For each block of trials the experimental software
`presented a new target condition. Two rectangles of width
`W separated by distance D appeared. A crosshair pointer
`appeared in the left rectangle and a red X appeared in the
`opposite rectangle denoting it as the current target (see
`FigureS.)
`
`performance. The measure was introduced in 1954 by
`Paul Fitts [5], and it has been widely used in human
`:fuctors and experimental psychology ever since.1 See [16]
`19] for extensive reviews.
`Throughput, as specified in the ISO draft standard, is
`calculated as follows:
`ID
`Troughput =-e
`MI'
`
`(1)
`
`\\here
`
`(2)
`
`The term IDe is the effective index of difficulty, and carries
`the unit "bits". It is calculated from D, the distance to the
`target, and We. the effective width of the target
`The term MI' is the movement time to complete the task,
`and carries the unit "seconds". Thus, throughput carries
`the unit "bits per second", or just "bps".
`The use of the "effective" width (W.,) is important W., is
`the width of the distribution of selection coordinates
`computed over a block of trials. Specifically,
`W., = 4.133 X SDx
`(3)
`\\here SDx is the standard deviation in the selection
`coordinates measured along the axis of approach to the
`target This implies that W., reflects the spatial variability
`or accuracy that occurred in the block of trials. As a
`result, throughput is a measure of both the speed and the
`In some sense,
`accuracy of the user's performance.
`throughput reflects the overall efficiency with which the
`user was able to accomplish the task given the constraints
`of the device or other aspects of the interface.
`It is important to test the device on difficult tasks as well
`as easy tasks; so, multiple blocks of trials are used, each
`with a different target distance and/or target size.
`METHOD
`Participants
`Twelve participants (5 male, 7 female) were used in the
`study. All participants were right handed, and all used
`computers with graphical user interfaces on a daily basis.
`Two participants had prior experience with touchpads.
`Apparatus
`A 166 MHz Pentium-class system with a 17" color monitor
`was used. The Ctmouse mouse driver for DOS, version
`1.2, was used for all but the tactile touchpad condition.
`For the latter, a custom driver was written to implement
`the special features of the tactile condition.
`
`1 Fitts used the term "index of performance" instead of
`throughput. The term "bandwidth" is also used.
`
`j
`I
`!
`l
`l
`
`~
`I I
`li
`!
`
`!
`!
`l
`
`\\
`
`D
`
`14
`
`+
`
`'\\
`!I
`1!
`II
`I
`I
`j
`
`~I
`
`X
`
`I
`w-.j f.- )
`
`I
`J
`./.
`
`Figure 5. Experimental condition.
`
`Procedure
`Participants were instructed to move the pointer by moving
`their index finger on the touchpad surface. Specifically,
`they were instructed to move the pointer as quickly and
`accurately as possible from side to side alternately
`selecting the target using the current selection technique.
`As each target was selected the red X disappeared and
`This helped
`reappeared in the opposite rectangle.
`synchronize participants though a block of trials. If a
`select operation occurred while the pointer was outside the
`target, a beep was heard to signal an error. Participants
`were instructed to continue without trying to correct errors.
`For each task condition, participants performed 20
`selections.
`Before gathering data, the task and the selection technique
`were explained and demonstrated to the participants.
`Participants were given a block of warm-up trials prior to
`data collection.
`
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`
`Design
`The experiment was a 3 x 3 x 3 x 3 x 20 within subjects
`design. The independent variables were as follows:
`
`button, lift-and-tap, tactile
`1, 2, 3
`
`Selection Technique
`Block
`Target Distance
`Target Width
`
`40, 80, 160 pixels
`10, 20,40 pixels
`1, 2, 3 ... 20
`Trial
`The conditions above combined with 12 participants
`represent a total of 19,440 trials. To minimize skill
`transfer, the presentation of the selection techniques was
`counter balanced. The target distance/size conditions were
`blocked. Each block consisted of nine distance/size
`For each
`combinations presented in random order.
`condition, participants performed 20 trials in succession.
`The distance/size conditions were chosen to create a set of
`tasks covering a range of task difficulties. The easiest task
`combines the largest target (40 pixels) with the shortest
`distance (40 pixels). The index of task difficulty is
`ID=log{~ +I)=log{:~ +1)=1.00bits
`
`(4)
`
`The most difficult task combines the smallest target (10
`pixels) with the largest distance (160 pixels):
`
`m =log{~ +I)= log2C1~0
`
`+I)= 4.o9 bits
`
`slower by 20% for lift-and-tap (1611 ms) and by 46%
`using the physical button (1967 ms). These differences
`were statistically significant (F2,1s = 41.6,p < .0001).
`Exactly the opposite ranking was observed on error rates,
`however. Using a button for the select operation, the error
`rate was 4.I%.
`It was I.4x higher using lift-and-tap
`(5.8%) and 2.4x higher using the tactile condition (9.9%).
`However, these differences were not statistically significant
`(F2,1s = 2.21,p > .05).
`The results for speed and accuracy are shown in Figure 6.
`Overall performance is better toward to bottom-left of the
`figure.
`
`2200
`
`I 2000 e 18oo
`
`j::
`~ 1600
`G)
`E 1400
`
`Button (1967 ms, 4.07%)
`
`•
`
`Lift & 1ap (1611 ms, 5.76%)
`
`Tactile (1345 ms, 9.92%)
`
`•
`
`~ ::!: 1200
`1000 +----....-------.-------.
`15.00
`0.00
`5.00
`10.00
`
`(5)
`
`Figure 6. Results for speed and accuracy
`
`Error Rate(%)
`
`Rest intervals were permitted between blocks of trials. The
`duration of rest intervals was based on participants'
`discretion. All three selection techniques were tested in a
`single session lasting about an hour. At the end,
`participants were given a brief questionnaire on their
`impressions of the three selection techniques.
`
`RESULTS AND DISCUSSION
`Since the experiment employed a within-subjects design, a
`Latin Square was used to balance potential learning
`effects. However, there remained the possibility of
`asymmetrical skill transfer [14] from one selection
`technique to the next based on the order of presentation.
`This was tested for and was found not to have occurred, as
`the effect for order of presentation was not statistically
`significant on all three dependent measures (movement
`time, error rate, throughput, F2,9 < 1).
`The grand means on the three primary dependent
`measures were 164I ms for movement time, 6.6% for error
`rate, and 1.17 bps for throughput. The interaction
`technique and block effects on these measures are reported
`in the following sections.
`
`Speed and Accuracy
`The tactile selection technique had the lowest movement
`time per trial at I345 ms. The other conditions were
`
`Throughput
`A strong analysis of the effect of selection technique is
`obtained by the dependent measure throughput, because it
`reflects both the speed and accuracy of performance and
`because it is the measure recommended in the ISO draft
`standard, 9241-9. The highest throughput was observed in
`the tactile condition at 1.43 bps. The other conditions
`exhibited lower throughputs by 25% for lift-and-tap {1.07
`bps) and by 31% using a button (0.99 bps). See Figure 7.
`The differences were statistically significant (F2,1s = 18.0,
`p<.0001).
`
`1.43
`
`1.60
`Ci) 1.40
`.8" 120
`i 1.00
`_g. 0.80
`§I 0.60
`e o.40
`~ 020
`0.00
`
`Button
`
`lilt& Tap
`
`Tactile
`
`Selection Technique
`
`Figure 7. Throughput by selection technique
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`CHI 98 • 18-23 APRIL 1998
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`PAPERS
`
`Learning Effects
`For each selection technique, participants performed three
`blocks of trials in succession. Each block consisted of 20
`trials on each of the nine randomly presented target
`conditions (180 total trials). It is worthwhile, therefore, to
`examine the effect of ''block" on the three dependent
`this reflects
`measures, since
`the extent
`to which
`participants improved with practice. As well, a block x
`selection technique interaction effect may be present,
`indicating different learning patterns across devices.
`The main effect of block was statistically significant for
`movement time and throughput, but not for error rate. The
`reverse pattern emerged for the block x selection technique
`interaction, which was significant for error rate, but not for
`movement time or throughput. These patterns are best
`illustrated through figures (see Figure 8).
`
`The pattern in all three parts of Figure 8 looks favorable
`for the tactile selection condition. The improvement in
`performance is clearly seen in each figure, and it is most
`dramatic from block 2 to block 3 (although the block x
`effect was not
`interaction
`technique
`statistically
`significant). With continued practice, the tactile condition
`is likely to improve. On error rate- the only measure on
`which the tactile condition faired poorly -
`it might even
`"catch up", although this could only be determined in a
`prolonged study.
`
`These measures for throughput are on the low side when
`compared to other pointing devices. We have conducted
`other unpublisb.ed studies using the same experimental
`conditions, and have obtained measures in the range of
`3.0-4.5 bps for mice and 2.0-3.5 bps for trackballs.
`Published figures for throughput are also higher, in
`general. A 1991 study reported 3.3 bps for a Kensington
`trackball, 4.5 bps for an Apple mouse, and 4.9 bps for a
`Wacom stylus [12], while a 1993 study found throughput
`equal to 4.3 bps for the mouse [13]. Rates less than 4 bps
`are not uncommon, however (e.g., [2, 7, 10, 3, 6]).
`
`-+-Button
`--~:r- Lift & Tap
`...______
`~---.- Tacble
`
`2200
`c;;
`.§. 2000
`& 1800
`E
`i= 1600
`.... c
`& 1400
`E
`& > 1200
`0 :: 1000
`
`(a)
`
`81
`
`82
`
`Block
`
`83
`
`-+-Button
`
`~ -a-lift&Tap
`~-.-Tactre
`
`_
`
`14.00
`12.00
`~ 10.00
`.s s.oo·
`Cll a::
`... 0 ... 4.00
`6.00
`... w
`
`2.00
`0.00
`
`~
`
`Outliers
`Since the error rates were somewhat high, we decided to
`investigate further. We identified a category of response
`called "wrong-side outliers". These are selections that
`occurred on the wrong side of the display. For example, if
`the goal was to select the target on one side of the display
`and the selection occurred before the pointer was halfway
`to the target, the selection was on the wrong side of the
`display. This is a gross error. We call these "outliers"
`because they are outside the normal range of variations
`expected in participants' behavior. A wrong-side outlier
`can occur for several reasons, such as double-clicking on a
`target or inadvertent lifting or pressing with the finger
`during pointer motion.
`
`Overall, button selection had the fewest wrong-side
`outliers (178, 2.75%), followed by tactile (245, 3.78%) and
`lift-and-tap (253, 3.90%). Comparing the percentages
`with the overall error rates given earlier, we see that
`wrong-side outliers, formed a significant portion of the
`overall errors.
`
`(b)
`
`81
`
`82
`Block
`
`83
`
`-+-Button
`
`0 1.8o
`~ 1.60
`i 1.40
`_g. 1.20
`~ 1.00
`] 0.80
`l- 0.60 +------,;------,-------,
`81
`82
`83
`
`(c)
`
`Block
`
`~ --~:r- Lift& Tap
`~ ~---.-Tactile
`~·
`
`Figure 8. Block by interaction technique for (a) movement
`time, (b) error rate, and (c) throughput
`
`The number of wrong-side outliers, by selection technique
`and block is shown in Figure 9.
`.
`
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`CHI 98 •18-23 APRIL1998
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`120
`~ c
`:::1
`0 .e.
`100
`f
`80
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`
`60
`
`40
`20
`
`iii . C)
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`
`c
`
`-o-Button
`-a- Lift & Tap
`-A- Tactile
`
`83
`
`0
`
`81
`
`82
`Block
`Figure 9. Wrong-side outliers by block and
`selection technique
`
`The Potential for a Tactile Touch pad
`The Synaptics touchpad's method of deriving pressure data
`is indirect since it senses the capacitance between the
`finger and the pad. Pressure is derived from the area of
`the user's finger contacting the surface of the pad. Since
`one's finger flattens on the pad with increased pressure,
`the device takes advantage of this correlation. As a
`consequence, users with small fingers must press harder
`than users with
`large fingers.
`Participants with
`particularly large fingers required a more delicate touch
`than they preferred. This may account for the increased
`error rate of the tactile touch pad condition.
`A better version of our touchpad would use true pressure(cid:173)
`sensing technology, and such products are now available
`(e.g., the VersaPad by Interlink Electronics). A future
`replication of this experiment utilizing a calibration
`procedure at the onset would also be interesting, although
`this is generally not considered acceptable as a required
`procedure in commercial pointing devices.
`Another noticeable artifact of the
`tactile
`touchpad
`condition was a tendency for the on-screen pointer to move
`down slightly as the subject pressed down to select a
`target. This was most pronounced with participants who
`held their pointing finger relatively perpendicular to the
`touchpad's surface. When they pressed down, the center
`of the finger's surface area moved towards the bottom and
`the onscreen pointer "dipped" with each press. As the
`targets were long and vertical, this most likely did not
`in the experiment; however,
`have an effect
`it
`is
`noteworthy. One subject suggested that the pointer freeze
`at a certain pressure level prior to a button press
`registering so that the results would be more predictable.
`Another possible solution would be to correct for the
`downward dips as the user pressed on the pad through
`software. That is, as the ''pressure" increased, the
`pointer's vertical value might be slightly increased to
`compensate for the user's tendency to move the pointer
`downwards.
`Our prototype's mechanical design was not of the highest
`quality. The relay was bulky and it was wedged-in against
`the bottom surface of the pad's PC board. A better design
`may assist in reducing error rates.
`For all three selection techniques, the measures for
`throughput were low -
`lower than those typically found
`with trackballs or mice, for example. This begs the
`question, why would one choose a touchpad over a
`trackball or mouse? Besides personal preferences, we have
`no definitive answer to offer. A follow-up study with
`experienced touchpad users, or conducted over a prolonged
`period of time, might shed light on this; it would help
`answer the question, can a touchpad be as good as a other
`pointing devices (using throughput as the criterion)?
`
`The good showing of the button technique is likely due to
`the clear separation of pointer movement from target
`selection.
`Since movement and selection are more
`integrated with the lift-and-tap and tactile conditions,
`higher rates for wrong-side outliers are expected.
`
`Questionnaire
`At the end of the experiment, participants were given a
`questionnaire. For each selection technique, they were
`asked to provide a rating on their speed perception, their
`accuracy perception, and their overall preference. They
`entered a score from 1 {slowest, least accurate, liked the
`least) to 4 (quickest, most accurate, liked the most). The
`results are shown in Figure 10. Each cell is the total score
`for twelve participants, with higher scores preferred.
`
`Selection
`Speed
`Accuracy
`Overall
`Technique
`Perception Perception Preference
`Button
`15
`3
`5
`15
`Lift-and-tap
`15
`13
`19
`Tactile
`15
`17
`Ftgure 10. Questionnarre results. (Note: Scores
`are totals of participants' ratings; higher scores are
`better.)
`
`Participants liked the tactile selection technique.
`(This
`was evident in their comments, as well.) Tactile selection
`ranked 1st for speed perception, 1st (tied) for accuracy
`perception, and 1st for overall preference. It is noteworthy
`that on accuracy participants rated the tactile condition
`equal to, or better than, the other conditions even though it
`had the highest error rate. This could be due to the higher
`measures for throughput, which reflect the overall ability
`of participants to complete their tasks.
`
`342
`
`RingCentral Ex-1028, p. 7
`RingCentral v. Estech
`IPR2021-00574
`
`

`

`'CHI 98 • 18-23 APRil 1998
`
`PAPERS
`
`CONCLUSION
`Although touchpads are not likely to supplant mice on the
`desktop. our results have implications for portable
`computer usage, and further refinements may make the
`tactile touchpad closer to a mouse in performance.
`The tactile touchpad was found superior to both the lift(cid:173)
`and-tap mode touchpad and button mode touchpad in
`terms of movement time and throughput Although the
`error rate was higher than with the other touchpad
`conditions, it was not generally noticed by the participants
`and the overall flow of information (viz., throughput) was
`higher even "ith the increased error rate. With design
`improvements, the use of embedded tactile feedback in a
`touchpad can fucilitate simple interactions such as
`pointing and selecting.
`ACKNOWLEDGEMENTS
`We thank Joe Decker of Synaptics for providing the
`touchpads and technical documentation for our prototype. ·
`Helpful comments and suggestions were provided by
`members of the Input Research Group at the University of
`Toronto and the University of Guelph. These are greatly
`appreciated. This research is funded by NSERC of
`Canada.
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