USER CENTERED SYSTEM DESIGN
`
`NewPerspectives on
`Human-Computer Interaction
`
`Edited by
`
`DONALD A, NORMAN
`STEPHEN W, DRAPER
`
`University of California, San Dievo
`
`[EA LAWRENCE ERLBAUM ASSOCIATES, PUBLISHERS
`
`Hillsdale, New Jersey
`
`London
`
`CHAPTER 15
`
`There's More to Interaction
`Than Meets the Eye:
`Some Issues in Manual Input
`
`WILLIAM BUXTON
`
`Imagine a time far into the future, when all knowledge about our civili-
`zation has been lost.
`Imagine further,
`that in the course of planting a
`garden, a fully stocked computer store from the 1980s was unearthed,
`and that all of the equipment and software was in working order. Now,
`based on this find, consider what a physical anthropologist might con-
`clude about the physiology of the humans of our era? My best guessis
`that we would be pictured as having a well-developed eye, a long right
`arm, a small
`left arm, uniform-length fingers and a “low-fi" ear. But
`the dominating characteristics would be the prevalence of our visual
`system over our poorly developed manual dexterity.
`Obviously, such conclusions do not accurately describe humans of
`the twentieth century, But they would be perfectly warranted based on
`Valve Exhibit 1055
`the available information. Today's systems have severe shortcomings
`when it comes to matching the physical characteristics of their opera-
`Valve v. Immersion
`in recent years there has been a great improvement
`tors, Admittedly,
`in matching computer output
`to the human visual system. We see this
`
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`ISSUES IN MANUAL INPUT
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`legs, hands,
`is with the human's effectors (arms,
`In our example, it
`the greatest distortion occurs. Quite simply, when compared
`to other human-operated machinery (such as the automobile),
`tadays
`computer systems make extremely poor use of the potential of the
`human's sensory and motor systems. The controls on the average
`user's shower are probably better human-engineered than those of the
`computer on which far more time is spent. There are a number ofrea-
`sons for this situation. Most of them are understandable, but none of
`them should be acceptable.
`My thesis is
`that we can achieve user interfaces that are more
`natural, easier to learn, easier to use, and less prone to error if we pay
`more attention to the "body language" of human-computer dialogues.
`|
`the quality of human input can be greatly improved
`(hrough the use of appropriate gestures.
`In order to achieve such bene-
`tits, however, we must
`learn to match human physiology, skills, and
`expechitions with our systems’ physical ergonomics, control structures,
`and functional organization,
`In this chapter I look at manual input with the hope of developing a
`better understanding of howwe can better tailor input structures to fit
`the humanoperator.
`
`A FEW WORDS ON APPROACH
`
`restrict myself to the discussion of
`|
`[due to constraints on space,
`input.
`I do so fully realizing that most of what
`| say can be
`applied to other parts of the body, and | hope that
`the discussion will
`encourage the reader to explore other types of transducers.
`
`Just consider the use of the feet in sewing, driving an automo-
`bile, or in plaving the pipe organ. Now compare this to your
`average coniputer system. The feet aretotally ignored despite
`the fact
`that most users have them, and Surthermore, have
`well-developed motor skills in their use.
`
`I want
`the temptation to discuss new and exotic technologies.
`to stick with devices that are real and available, since we haven't come
`close to using the full potential of those that we already have.
`Finally, my approach is somewhat cavalier.
`I will leap from example
`to example, and just touch on a few of the relevant points.
`In the pro-
`
`the grain of my analysis ts still not fine enough just emphasize
`That
`how much more we need to understand,
`
`is unlikely that we ul
`is so complex that it
`Manaving input
`ever totally understand it. No matter how good our thearies
`are, we will probably always have to test designs through
`actual implementations and prototyping. The consequence w
`this for the designer is that prototyping tools (software anc
`hardware) must. be developed and considered as part of the
`basic environment.
`
`THE IMPORTANCE OF THE TRANSDUCER
`When we discuss user interfaces, consideration of the anna tran
`ducers too often comes last, or near last. And yet, the hi Bers
`ties of the system are those with which the user has Sees : ass
`direct contact. This is not just an issue of comfort. Di ao oe
`have different properties, and lend themselves to different t SS
`if gestures are aS important as I believe, then we mus! pay
`e
`attention to the transducers to which we assign them.
`<iteenaiten
`An important concept in modern interactive eresfail pee sie
`device independence. The idea is
`that
`input devices | a e *
`classes of what are known as virtval devices, such as ae Oe
`"valuators.” Dialogues are described in terms of these tee
`The objective is to permit the easy substitution of ee orn
`for another of the same class. One benefit
`in this is that i .
`experimentation (with the hopeful consequence of iteo
`among the alternatives). The danger, however,
`is
`ae St
`easily lulled into believing that the technical interchangea
`es
`devices extends to usability. Wrong!
`It
`is always parpeas 0 ‘ .
`mind that even devices within a class have various idiosy an -
`often these very idiosyncratic differences that determine t eae :
`ateness of a device for a given context, So, device indepen eae
`useful concept, but only when additional considerations are made
`making choices,
`
`Example 1: The Isometric Joystick
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`VOWEL PAME BUNTON
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`ISSUES IN MANUAL INPUE
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`323
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`
`Two tometric joysticks.
`
`(Measurement Systems. Inc.)
`
`the same, andare electroni-
`the same manufacturer. They cost about
`In fact, they are plug compatible. Howtheydiffer is in
`the muscle groups that
`they consequently employ, and the
`umount of force required to get a given output.
`
`vs, mice or
`Remember, people generally discuss joysticks
`trackhalls. Here we are nor only comparing joysticks against
`jovsricks, we are comparing one isometric joystick to another,
`
`When should one be used rather than the other? The answer obviously
`bopends on the context, What can be said is that their differences may
`olten be more significant than their similarities.
`In the absence of one
`it may be better to utilize a completely different
`type of
`transducer (such as a mouse) than to use the other isometric joystick.
`
`Example 2: Joystick vs. Trackball
`
`is very
`it
`In many ways,
`springloaded joystick shown in Figure 1$.2A.
`similar to the isometric joysticks seen in the previous example.
`It
`is
`made by the same manufacturer, and it
`is plug-compatible with respect
`to the X/Y values that i transmits. However, this new joystick moves
`when it
`is pushed, and (as a
`result of spring action)
`returns to the
`center position when released.
`In addition,
`it has a third dimension of
`control accessible by manipulating the self-returning,
`spring-loaded
`rotary pot mounted on the top of the shaft.
`Rather than contrasting this to the joysticks of the previous example
`(which would,
`in fact, be a useful exercise), let us compare it
`to the 3-
`D trackball shown in Figure 15.2B.
`(A 3-D trackball is a trackball con-
`structed so as to enable us to sense clockwise and counter-clockwise
`“twisting of the ball as well as the amount that it has been "rolled" in
`the horizontal and vertical directions.)
`This trackball
`is plug-compatible with the 3-D joystick, costs about
`the same, has the same "footprint" (consumes the same amount of desk
`space), and uulizes the same major muscle groups.
`It has a great deal
`in common with the 3-D joystick of Figure 15.2A.
`In many ways the
`the joystick in Figure 15.2A has more in common with the trackball
`than with the joysticks shown in Figure 15,1!
`
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`WIL TAM BUNTON
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`1S.
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`ISSUES IN MANUAL INPUT
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`325
`
`the appropriateness of
`/f you are starting to wonder about
`always characterizing input devices by names such as “joys-
`nek" or “mouse,” then the point of this section is getting
`It
`is starting to seem that we should lump devices
`fovether according to some “dimension of maxinnim signifi-
`cance,” rather than by some (perhaps irrelevant) similarity in
`their mechanical construction (such as being a mouse or jovs-
`The prime issue arising from this recognition is the
`problem ofdetermining which dimension is of maxinuin signi-
`ficance in a@ given context. Another is the weakness ofour
`current vocabulary to express such dimensions.
`
`Despite their similarities, these two devices differ in a very subtle, but
`sunificant, way. Namely, itis much easier to simultaneously controlall
`three dimensions when using the joystick than when using the trackball,
`In some upplications this will make no difference. But for the moment,
`we Cure about instances where it does. We look at two scenarios.
`
`Scenario J; We are working on a graphics program for doing VLSI
`The chip on which we are working is quite complex. The only
`the entire mask can be viewed at one time is at a very small
`To examine a specific area in detail,
`therefore, we must "pan"
`over it, and "zoom in.” With the joystick, we can pan over the surface
`the circuit by adjusting the stick position, Panning directionis deter-
`mined by the direction in which the spring-loaded stick is off-center,
`und speed is determined by its distance off-center. With the trackball,
`we exercise control byrolling the ball in the direction and at the speed
`that we want to pan.
`
`Panning ts easier with trackball than the spring-loaded joys-
`tick. This is because of the strong correlation (or comipatibil-
`uv) between stimulus (direction, speed, and amount of roll)
`and response (direction, speed, and amount of panning) in
`this example. With the spring-loaded joystick,
`there was a
`position-to-motion mapping rather than the motion-to-motion
`mapping seen with the trackball, Such cross-modality. map-
`pines require learning and impede achieving optimal human
`performance. These issues address the properties of an inter-
`face that Hutchins, Hollan, and Nerman (Chapter 5) call
`
`is easy to zoomin and out of regions ofinterest while panning. One
`need only twist
`the shaft-mounted pot while moving the stick. Tlow-
`ever, with the trackball,
`it
`is nearly impossible to twist
`the ball at
`the
`same time that
`it
`is being rolled. The 3-D trackball is,
`in fact, better
`described as a 2+1D device.
`Scenario 2: | am using the computer to control an oil refinery.
`pipes and valves of a complex part of the system are shown graphica y
`on the displays, along with critical status information. My job Is to
`monitor the status information and, when conditions dictate, modify
`the system by adjusting the settings of specific valves,
`I do ae
`means of direct manipulation. That is, valves are adjusted by manipu at-
`ing their graphical representation on the screen. Using oe ne
`is accomplished by pointing at
`the desired valve, then twisting u e po
`mounted on the stick. However,it is difficult to twist the joystick-pol
`without also causing some change in the X and Y values. This —
`problems, since graphics pots may be in close proximity on the Oe ay.
`Using the trackball, however, the problem does not occur.
`In or erto
`twist the trackball,
`it can be (and is best) gripped so that the finger tips
`rest against the bezel of the housing. The finger tps thus eeiy
`rolling of the ball. Hence, twisting is orthogonal to motion in
`an
`:
`The trackball is the better transducer in this example precisely because 0
`its idiosyneratic 2+ 1D property.
`Thus, we have seen howthe very properties that gave the
`joystick the advaniage in the first scenario were a liability in
`‘the second. Conversely, with the trackball, we have seen how
`the liability became an advantage. What
`is to be learned
`here is that ifsuch cases exist between these two devices, then
`it
`is most
`likely that comparable (but different) cases exist
`among all devices. What we are most lacking is some rea-
`sonable methodologyfor exploiting such characteristics via an
`appropriate matching of device idiosyncrasies with structures
`of the dialogue.
`
`APPROPRIATE DEVICES CAN SIMPLIFY SYNTAX
`In the previous example we saw howthe idiosyncratic properties
`
`a
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`IS ISSUES IN MANUAL INPUT=327
`WOE TEAM BIEN DOIN
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`SageEt
`
`
`de rit:
`
`the case. Computer systems are more often used by a number of peo-
`a number of
`tasks, each with their own demands and charac-
`leristies. One approach to dealing with the
`resulting diversity of
`to supply a number of input devices, one optimized for
`each type of transaction. However, the benefits of the approach would
`veneraly break down as the number of devices increased. Usually, a
`more realistic solution is to attempt to get as much generality as possi-
`hle from a smaller number of devices. Devices, then, are chosen for
`their range of applicability. This is, for example, a major attraction of
`vraphics tablets. They can emulate the behavior of a mouse. But
`untike the mouse,
`they can also be used for tracing artwork to digitize
`it into the machine.
`| continue to discuss devices in such a way
`Having raised the issue,
`as to focus on their idiosyncratic properties. Why? Because by doing
`| hope to identify the type of properties that one might try to emu-
`ie, should emulation be required,
`is often useful to consider the user interface of a system as being
`mide up of a number of horizontal
`layers. Most commonly, syntax ts
`considered separately from) semantics, and lexical
`issues independent
`from syntax. Much of this way of analysis is an outgrowth of the
`theories practiced in the design and parsing of artificial languages, such
`us tn the design of compilers for computer languages. Thinking of the
`world in this way has manybenefits, not the least of which is helping to
`avoid. “apples-and-bananas"
`type comparisons. There is
`a problem,
`in that it makes it too easy to fall into the belief that each of
`independent. A major objective of this section is
`to
`point out how wrong an assumption this is.
`In particular,
`I
`illustrate
`how decisions at the lowest level, the choice of input devices, can have
`4a pronounced effect on the complexity of the system and on the user's
`
`Example 2: Two children’s toys. The Etch-a-Sketch (shown in Fig-
`is a children’s drawing toy that has had a remarkably long
`life in the marketplace. One draws by manipulating the controls so as
`fy) cause a stylus on the back of the drawing surface to trace out
`the
`desired tmage. There are only two controls: Both are rotary pots. One
`controls left-neht motion of the stylus and the other controls its up-
`
`The Skedoodle (shown in Figure 15.3B) is another toy based on very
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`1S. ISSUES IN MANUAL INPUT=329
`WIELEAM BRUNTON
`
`Sketch has a separate control for each of the two dimensionsof control,
`the Skedoodle has integrated both dimensions into a single transducer:
`
`they offer an
`Since both toys are inexpensive and widely available,
`excellent opportunity to conduct somefield research. Find a friend and
`demonstrate each of the two toys. Then ask the friend to select the toy
`to be the best for drawing. What all
`this is leading to is a drawing
`competition between you and your friend. However, this is a competi-
`tron that you will always win, The catch is that since your friend got
`to
`choose toys, you get to choose what is drawn.
`If your friend chose the
`Skedoodle (as do the majority of people), then make the required draw-
`ing be of a horizontally-aligned rectangle.
`If they chose the Etch-a-
`then have the task be to write your first name, This test has
`two benefits. First,
`if you make the competition a bet, you can win
`hack the money that you spent on the toys (an unusual opportunity in
`research), Second, you can do so while raising the world’s enlighten-
`ment about the sensitivity of the quality of input devices to the task to
`which they are applied,
`
`[f you understand the importance of the points being made
`here, vou are hereby requested to go out and applythis test on
`every person that vou know who is prone to making unilateral
`and dogmatic statements of the variety "mice (tablets, joys-
`trackballs, ete.) are best." What is true with these two
`tovs (as illustrated by the example) is equally true for any and
`all computer input devices: Theyall shine for same task.
`
`We can build upon what we have seen thus far, What if we asked how
`we can make the Skedoodle do well at the sameclass of drawings as the
`hich-a-Sketch?) An approximation to a solution actually comes with the
`tov in the form of a set of templates that
`fit over the joystick (Figure
`18.4), The point
`to make here is that
`if we have a general-purpose
`input device (analogous to the joystick of the Skedoodle), then we can
`provide tools to fit on top of it to customize it for a specific application.
`(An example would be the use of “sticky” grids in graphics layout pro-
`vrams.) However,
`this additional level generally comes at the expense of
`increased cost in the complexity of the control structure.
`lf we don’t need
`
`
`
`FIGURE 15.4, Adding constraints to un input device. Templates on a Skedoodle joys-
`lick,
`
`important
`The nulling problem. One of the most
`Example 4:
`characteristics of input devices is whether they supply absolute or rela-
`tive values to the program with which they are interacting. Mice and
`trackballs, for example, provide relative values. Other devices, such as
`tablets,
`touch screens,
`and potentiometers
`return absolute values
`(determined by their measured position), Earlier,
`I mentioned the
`importance of the concept of the "dimension of maximum importance.”
`In this example,
`the choice between absolute versus
`relative mode
`defines that dimension.
`least) two
`The example comes from process control, There are (at
`philosophies of design that can be followed in such applications.
`In the
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`S300 Wit base HUN TON
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`ISSUESINMANUAL INPUT
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`adjusting P. The job is done and we are in the state shown in Figure
`15.5D.
`From an operator's perspective, the most annoying part of the above
`transaction is having to reset the controller before the second parameter
`can be adjusted. This is called the mulling problem.
`It is common, takes
`lime to carry out,
`time to learn, and is a common source of error.
`Most importantly, it can be totally eliminated if we simply choosea dif-
`ferent transducer.
`that we
`The problems in the last example resulted from the fact
`chose a transducer that returned an absolute value based on a physical
`handle’s position. As an alternative, we could replace it with a touch-
`sensitive strip of the same size. We will use this strip like a one-
`dimensional mouse.
`Instead of moving a handle, the strip is "stroked"
`up or down using a motion similar to that which adjusted thesliding
`potentiometer. The output
`in this case, however,
`is a value whose
`magnitude is proportional to the amount and direction of the stroke.
`In
`short, we get a relative value which determines the amount of change
`in the parameter. We simply push values up, or pull them down. The
`action is
`totally independent of the current value of the parameter
`being controlled. There is no handle to get stuck at the top or bottom.
`The device is like a treadmill, having infinite travel in either direction.
`In this example, we could have “rolled” the value up and down using
`one dimension of a trackball and gotten much the same benefit (since
`it too is a relative device),
`An important point
`in this example is where the reduction in com-
`plexity occurred:
`in the syntax of the control
`language. Here we have
`a compelling and relevant example of where a simple change in input
`device has resulted in a significant change in the syntactic complexity of
`a user interface. The lesson to be learned is that in designing systems
`in a layered manner—first the semantics, then the syntax, then thelex-
`ical component, and the devices—we must
`take into account
`interac-
`tions among the various strata. A// components of the system interlink
`and have a potential effect on the user interface. Systems must begin to
`be designed in an integrated andholistic way.
`
`PHRASING GESTURALINPUT
`It determines the
`Phrasing is a crucial component of speech and music.
`ebb and flowof tension in adialogue.
`It lets us know when a concept
`
`parameters at different stages of an operation.
`Let us assume that we are implementing a system based on time
`multiplexing. There are two parameters, A and B, and asingle sliding
`potentiometer to control
`them, P. The potentiometer P outputs an
`absolute value proportional
`to the position of its handle. To begin
`the control potentiometer is set to control parameter A. The ini-
`lal settings of A, B, and P areall illustrated in Figure 1S.5A. First we
`want Lo raise the value of A to its maximum. This we do simply by
`sliding up the controller, P. This leaves us in the state illustrated in
`Figure 15.5B. We nowwant to raise parameter B to its maximum
`value. But how can we raise the value of B if the controller is already
`in its highest position? Before we can do anything we must adjust the
`handle of the controller relative to the current value of B. This is illus-
`trated in Figure 15.5C. Once this is done, parameter B can bereset by
`
`A
`
`B
`
`P
`
`Be
`
` A
`
`B
`
`1]
`
`iA)
`
`Initial State
`
`(B) Praises A to Max
`
`| A
`
`B
`
`Pp
`
`P
`
`(C} P must maich B
`
`(D) P raises B to Max
`
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`

`S32 Witt base BUX TON
`18. ISSUES IN MANUAL INPUT=333
`
`
`
`Phrases “chunk” related things together. They reinforce their connee-
`In this section | attempt
`to demonstrate how we can exploit
`the
`benefits of phrasing by building dialogues that enable connected con-
`cepts to be expressed by connected physical gestures.
`It you look at
`theliterature, you will find that there has been a great
`deal of study on how quickly humans can push buttons, point at
`text,
`und type commands. What
`the bulk of these studies focus on is the
`smallest grain of the human-computer dialogue, the atomic task. These
`are the "words" of the the dialogue. The problem is, we don't speak in
`words. We speak in sentences. Much ofthe problem in applying the
`results of such studies is that they don’t provide much helpin under-
`stinding howto handle compound tasks. Mythesis is,
`if you can say it
`in words in a single phrase, you should be able to express it to the com-
`puter in a single gesture. This binding of concepts and gestures thereby
`becomes the means of articulating the writ rasks of an application.
`
`Most ofthe tasks which we performin interacting with com-
`puters are compound.
`In indicating a point on the display
`with @ mouse we think of what we are doing as a single task:
`picking @ point, But what would you have to specify if vou
`had to indicate the same point by typing? Your Single-pick
`operation actually consists of two sub-tasks:
`specifving an X
`coordinate and specifying a Y coordinate. You were able ta
`think of the aggregate as a Single task because of the
`appropriate match among transducer, gesture, and context.
`The desired one-to-one mapping between concept and action
`has been maintained. Myclaimis that what we have seen in
`this simple example can be applied to even higher-level tran-
`
`Two useful concepts from music that aid in thinking about phrasing are
`fension and closure. During a phrase there is a state of tension associ-
`ated with heightened attention. This is delimited by periods of relaxa-
`tion that close the thought and state implicitly that another phrase can
`be introduced by either party in the dialogue.
`It
`is my belief that we
`can reap significant benefits when we carefully design our computer
`Uislogues around such sequences of tension and closure.
`In manual
`T will want tension to imply muscular tension,
`
`a state that corresponds
`the dialogue:
`tension throughout
`exactly with the temporarystate of the system. Because of the
`gesture used,
`it is impossible to make an error in syntax, and
`vou have a continual active reminder that you are in an unin-
`terruptable temporary state. Because of the gesture used,
`there is none ofthe trauma normally associated with being in
`a mode. That you are in a modeis ironic, since it is precisely
`the designers of"modeless” systems that make the heaviest use
`of this technique. The lesson here is that it is not modes per
`se that cause problems.
`
`there is a kinesthetic connectivity to
`inpul
`In well-structured manual
`reinforce the conceptual connectivily of the task. We can start
`to use
`such gestures to help develop the role of muscle memory as a means
`through which to provide mnemonic aids for performing different tasks.
`And we can start to develop the notion of gestural self-consistency across
`an interface.
`
`What do graphical potentiometers, pop-up menus, scroll-bars,
`rubber-band lines,
`and dragging all have in
`common?
`Answer:
`the potential to be implemented with a uniform form
`of interaction. Work it out using the pop-up menu protocol
`given above.
`
`WE HAVE TWO HANDS!
`
`the manufacturers of arcade video games seem to
`is interesting that
`It
`recognize something that
`the majority of main-stream computer sys-
`tems ignore:
`that users are capable of manipulating more than one
`device at a time in the course of achieving a particular goal. Now this
`should come as no surprise to anyone who is familiar with driving ar
`automobile. But
`it would be news to the hypothetical anthropologis
`that we introduced at the start of the chapter. There are two question:
`here: “Is anything gained by using two hands?" and “If there is, why
`aren't we doing it?"
`The second question is the easier of the two. With a few excep
`tions,
`(the Xerox Star,
`for example), most systems don’t encourage
`two-handed multiple-device input. First, most of our theories abou
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`Is. ISSUES IN MANUAL INPUT—335
`WHEL EAM BUNTON
`
`effort, and expense is worthwhile. So that is what
`inthe rest of this section,
`
`1 will attempt to do
`
`Example 5: Graphics Design Layout
`
`| am designing a screen to be used in a graphics menu-based system.
`To be effective, care must be taken in the screen layout.
`I have to
`determine the size and placement of a figure and its caption among
`some other graphical items,
`I want
`to use the tablet to preview the fig-
`locations and at different sizes in order to determine
`where it should finally appear. The way that
`this would be accom-
`plished with most current systems is to go through a cycle of position-
`scule-position-...
`actions. That
`is,
`in order to scale,
`I have to stop
`positioning, and vice versa.
`
`This is akin to having to turn off your shower in order to
`adjust the water temperature.
`
`An alternative design offering more fluid interaction is to position it
`with one hand and scale it with the other. By using two separate
`devices | am able to perform both tasks simultaneously and thereby
`uchieve a far more fluid dialogue,
`
`Example 6: Scrolling
`
`A common activity in working with many classes of programis scrolling
`through data, looking for specific items. Consider scrolling through the
`text of a document that is being edited.
`I want to scroll till
`I find what
`I'm looking for, then mark it up in some way. With most windowsys-
`this is accomplished by using a mouse to interact with some
`(usually arcane) scroll bar tool. Scrolling speed is often difficult to con-
`trol and the mouse spends a
`large proportion of its time moving
`between the scroll bar and the text. Furthermore, since the mouse is
`involved in the scrolling task, any ability to mouse ahead (.e,, start
`moving the mouse towards something before it appears on the display)
`If a mechanism were provided to enable us to control
`scrolling with the nonmouse hand, the whole transaction would be sim-
`
`examples and the scrolling of this example. An example of
`space-multiplexing would be the simultaneous use of the serol-
`ling device and the mouse.
`Thus, we actually have a hybrid
`type ofinterface.
`
`Example 7: Financial Modeling
`| am using a spread-sheet for financial planning. The method used to
`change the value in a cell
`is to point at
`it with a mouse and type the
`new entry. For numeric values,
`this can be done using the numeric
`keypad or the typewriter keyboard.
`In most such systems, doing so
`requires that the hand originally on the mouse moves to the keyboard
`for typing. Generally, this requires that the eyes be diverted from the
`screen to the keyboard, Thus,
`in order to check the result,
`the user
`must then visually relocate the cell on a potentially complicated display.
`An alternative approach is to use the pointing device in one hand
`and the numeric keypad in the other. The keypad hand can then
`remain in home position, and if the user can touch-type on the keypad,
`the eyes need never leave the screen during the transaction.
`
`Note that in this example the tasks assigned to the two hands
`are not even being done in parallel.
`Furthermore, a large
`population ofusers—those who have to take notes while mak-
`ing calculations—have developed keypad touch-typing facility
`in their nonmouse hand (assuming that the same hand is used
`for writing as for the mouse), So if this technique is viable
`andpresents no serious technical problems,
`then wity is it not
`in common use? One arguable explanation is that on most
`systems the numeric keypad is mounted on the same side as
`the mouse.
`Thus, physical ergonomics prejudice against the
`approach,
`
`WHAT ABOUT TRAINING?
`Some things are hard to do, they take time and effort before they can
`be performed at a skilled level. Whenever the issue of two-handed
`input come up, so does some facsimile of the challenge, “But
`two-
`handed actions are hard to coordinate.” Well, the point is true. But it ts
`also false! Learning to change gears is hard. So is playing the piano.
`
`

`

`WHEL DAMP TEIN TON
`
`1S
`
`ISSLIESIN MANUAL INPUT
`
`347
`
`and it can actually reduce errors and learning time. Multiple-handed
`input should be one of the techniques considered in design. Onlyits
`approprhiteness fora given situation can determine if it should be used.
`In that, itis no different than any other technique in our repertoire,
`
`Example 8: Financial Modeling Revisited
`
`Assume that we have implemented the two-handed version of the
`spreadsheet program described in Example 7.
`In order to get the bene-
`| suggested,
`the user would have to be a touch-typist on the
`numeric keypad. This is a skilled task that
`is difficult
`to develop.
`There ts a temptation, then,
`to say "don't use it."
`If the program was
`far school children,
`then perhaps that would be right. But consider
`who uses such programs: accountants, for example, Thus, it
`is reason-
`able to assume that
`a significant proportion of the user population
`comes to the system with the skill already developed. By our implementa-
`tlon, we have provided a convenience for those with the skill, without
`miposing any penalty on those without
`it—they are no worse off than
`they would be in the one-handed implementation. Know your user is
`(and important) consideration that can be exploited in
`order to tailor a better user interface.
`
`CONCLUSIONS
`
`| began this chapter by pointing out that there are major shortcomings
`in our ability to manually enter information into a computer. To this
`input has lagged far behind graphical output, And yet, as some
`of our examples illustrate, input is of critical
`importance.
`If we are to
`improve the quality of human-computer interfaces we must begin to
`wpproach input from two different views. First, we must look inward to
`the devices and technologies at the finest grain of their detail, One of
`the main points that
`| have made ts that some of the most potent and
`usetul characteristics of input devices only surface when they are
`analyzed ata far lower level of detail than has commonlybeen the case.
`Second, we must
`look outward from the devices themselves to how
`into a more global, or holistic, view of the user interface. All
`uspects of the system affect the user interface. Often problems at one
`level of the system can be easily solved by making a change at some
`other level. This was shown for example,
`in the discussion of the nul-
`
`SUGGESTED READINGS
`The literature on most ofthe issues that are dealt with in this chapter is
`pretty sparse. One good source that complements many of the ideas
`discussed is Foley, Wallace, and Chan (1984). A presentation on the
`notion of virtual devices can be found in Foley and Wallace(1974). A
`critique of their use can be found in Baecker (1980). This paper by
`Baecker is actually part of an important and informative collection of
`papers on interaction (Guedj,
`ten Hagen, Hopgood, Tucker, & Duce,
`— of
`the notions of “chunking” and phrasing discussed are
`expanded upon in Buxton (1982) and Buxton, Fiume, Hill, Lee, and
`Woo (1983). The chapter by Miyata and Norman tn this book gives a
`lot of background on performing multiple tasks, such as in two-handed
`input, Buxton (1983) presents an attempt to begin to formulate a oe
`onomyof input devices, This is done with respect to the proper