Joystick Versus Mouse Communication

For more than 20 years designers what kind of is compared By Vic Kley have puzzled over the problem of with the mouse. KA Design Group how best to enter information into Until recently, there have been Oakland, CA the . They have concluded two kinds of available: the that a device using the controlled absolute and the rate. With an ab- motion of forearm, wrist, thumb and solute, the travel of the joystick cor- index finger to point to graphic pat- responds directly to the scope of terns on the display screen could the display. Moving the absolute substantially facilitate the control joystick to its topmost position and instruction of the computer. places the at the top of the Many believe that pointing devices display. Moving it to its lower left provide the most powerful non-key- position places the cursor at the board way to communicate with a lower left corner of the display, and computer, and even the computing so on. public has recently shown an With the rate joystick, the travel emerging willingness to accept of the joystick imparts a direction of pointing devices as an improved motion to the cursor. Push the rate mode of computer interaction. Al- joystick to the left, and the cursor though the current popular belief is will move from wherever its present that the "mouse" is the only appro- position is. Push it to the lower left, priate pointing device for all appli- and the cursor will move diagonally cations, nothing could be further in that direction. Let the stick return from the truth. to center, and the cursor comes to a In 1967, a classic study estab- halt. Furthermore, in typical de- lished that the digitizing tablet was signs, by varying how far in any di- the best overall pointing device. But rection the rate joystick is moved, this much-quoted study—by Eng- one controls the speed with which lish, Engelbart and Berman—un- the cursor will move. When the rate derstandably did not concern itself joystick is moved up slightly, the with the prohibitively high cost of cursor rises slowly. Push it to the the tablet, since mainframe com- top of its travel, and the cursor puters were the order of the day. moves upward at maximum speed. Even today, the digitizing tablet re- While the Card study did find mains the best general pointing de- marginal advantage in positioning vice in situations where money is no speed for the mouse (Figure 1), this object. was only in comparison to the rate But, with the advent of inexpen- joystick. An absolute joystick was sive microcomputers, studies have not included in this study. In the ear- shifted their attention to low-cost lier English study, the absolute joy- pointing devices. In a 1978 study by stick was found to meet or exceed Card, English and Burr, the joystick, the positioning speed of the mouse. mouse, and text keys It should be noted that, in applica- were compared for text selection tions where it is desirable to inte- and editing performance. The Card grate a pointing device into a key- study (also known as the Xerox board, the mouse is ruled out. In study) concluded that the mouse such cases, an arrow or text key de- was "found to be fastest on all sign could be used, but a joystick counts and also to have the lowest solution would be far superior. error rates." Although proponents of the mouse have relied heavily on A New Kind of Joystick this conclusion, the crucial point is Recently preliminary tests were 69 conducted using a NorthStar Ad- The general relationships between vantage computer and an abso- \.,the digitizing these two groups and the various lute/rate joystick, a hybrid that pointing devices are, of course, in- combines the advantages of both tablet remains herent in the basic designs. Move- traditional designs. A switch on the ment of the forearm/wrist group side of the joystick handle under the the best general generally requires more energy, and thumb (adjustable for left- or right- pointing device is more fatiguing, than movement of hand operation) is depressed to se- the thumb/finger/wrist. lect absolute mode. In this position, in situations The digitizing tablet, in making a motion to the upper left corner of use of forearm and wrist motions, the joystick corresponds to the im- where money is closely approximates the activity of mediate movement of the graphics writing and drawing. And, because cursor to the upper left corner of no object" of the very high lineal resolution of the computer display. Once the tar- the tablet, thumb/index finger mo- get area is reached, the thumb-in- tions can be captured as well. The dex finger pressure is relaxed. The tablet is the only device discussed switch is thus released, and the ten times the precision of the best here that can represent both the joystick reverts to rate operation. mouse available. This hybrid combines the large-mo- tion positioning speed of the abso- The Need for More Research lute joystick with the rate joystick's A pointing device must be compati- Effect of Target Distance small movements and fine control. ble with the requirements of both on Positioning Time As a result, in applications where man and machine. Yet far too little coarse positioning speed predomi- attention has been paid to the joints Arrow nates, it is expected that the abso- and muscles that will have to oper- Keys / lute joystick mode (which is lock- ate the device—often for hours at a able on software request or by time. A thorough examination double-clicking the thumb-actuated should not only focus on the re- state switch) will easily meet or ex- quired positioning precision for the ceed the positioning speed of the specific task, but also on the dura- Text Keys mouse. tion of the task for any muscle For small cursor movements, group and its particular fatigue fac- even the Card study found the rate tor. Such a study would be an im- joystick and mouse essentially iden- portant guide to both the engineer tical (only a 1% to 3% difference) for and the system integrator. In addi- movements of less than an inch tion, studying muscle groups would (Figure 1). Furthermore, in the rate establish evaluation criteria for fu- mode, a 15-degree motion from the ture pointing device development. center of the joystick produces an The two main muscle groups in- 2 468 15 incremental change in the output of volved in pointing devices are fore- Distance in Centimeters the joystick of one part in 4,096— arm/wrist and thumb/finger/wrist. Figure 1

Decision Factors in Pointing Device Selection Pointing Resolution Positioning Fatigue Device Capability Speed Cost Factor Portable? Compact?

Digitizing High High High Medium No No Tablet - ... Absolute High High Low Low Yes Yes Joystick

Rate High Medium Low Low Yes Yes Joystick

Mouse '"High ' "High" Med/High Medium Yes No

Absolute/Rate High High Med/Low Low Yes Yes Joystick

Arrow or N/A Low Low Medium Yes Yes Step Keys

Light Pen Low High Medium High Yes No u Figure 2 70 thumb/finger/wrist motion and The absolute/rate joystick offers forearm/wrist motion. "...for high speed and high resolution The optical or mechanical mouse (100-400 points per inch in absolute uses forearm/wrist motion exclu- comparable mode; 1,000-10,000 points per inch sively (except for switch activation), applications, a in rate mode. The joystick provides while the joystick uses the motion of natural, absolute mapping in the thumb/finger/wrist motion exclu- joystick is absolute mode, and no extra desk sively. area is required. The fatigue factor Operation of arrow or text keys typically 60 to 80 is low, and the device is both porta- requires only the repeated "on/off" ble and compact. For high-resolu- striking motion of the finger and percent less tion applications that are extremely wrist. Since the key is either up or cost-sensitive, the absolute/rate down, this device does not take ad- expensive than joystick is recommended. vantage of the natural human ability a mouse" Medium Resolution: Either a mouse to control and modulate move- or an absolute/rate joystick is rec- ments. ommended for medium-resolution, cost-sensitive applications. For this Text Editing Recommendations gested for other applications, and degree of resolution, the joystick's Although none of these devices is are based primarily on the resolu- rate mode would be adjusted to op- appropriate for every situation, ten- tion and positioning speed required, erate more coarsely. tative guidelines can be suggested as well as on cost sensitivity. How- Low Resolution: For low-resolution, even without the benefit of detailed ever, factors such as space require- cost-insensitive applications, either studies. The most common use of ments, fatigue, compactness, and a mouse or an absolute/rate joy- pointing devices today is for text or portability are also taken into ac- stick would be appropriate. For ap- text-related editing in which a key- count (Figure 2). plications that are cost-sensitive, board is a necessity. A keyboard- The cost of a pointing device will the absolute joystick is recom- mounted pointing device is there- depend, in large measure, on the mended, since at this resolution the fore advantageous, because it degree of resolution required. How- rate mode is dispensable. The ab- always leaves the wrist and forearm ever, for comparable applications, a solute joystick offers high speed, in a known relationship to the key- joystick is typically 60 to 80 percent provides natural, absolute mapping, board. Thus, a return hand motion less expensive than a mouse. and no extra desk area is required. is minimal, direct, and repeatable. A portable device can be incor- The fatigue factor is low, and the By contrast, the return hand motion porated into a portable computer's device is both portable and com- with either the tablet or mouse is in- carrying package, while a "com- pact. determinate and not automatically pact" device can be integrated into For extremely cost-sensitive ap- repeatable. Hence, the editing pro- the computer keyboard. "High" plications, step keys are recom- cess is interrupted and delayed. resolution means the operator's mended. Step keys, which function There is also reason to believe ability to resolve over one part in much like a simple rate joystick, that, for text editing, the absolute/ two thousand (2048 x 2048 picture provide an ultra low-cost pointing rate joystick may actually position elements). "Medium" resolution device. No extra desk space is re- faster and with fewer errors than the corresponds to a 512 x 512 display, quired, the fatigue factor is moder- mouse. Once the joystick in abso- and "low" resolution to 256 x 256 ate, and the device is both portable lute mode has placed the cursor in . and compact. • the region of a text line or character High Resolution: For high-resolution column, the rate mode can be used applications where cost is not a pri- to move it easily in a horizontal or mary consideration, the digitizing References vertical direction. This allows the tablet is outstanding. The tablet of- Card, Stuart. K., William K. English, and rapid selection of a character within fers natural, absolute mapping of Betty J. Burr, 1979 "Evaluation of a line, or a line within a paragraph. the user's motions onto the display Mouse, Rate-Controlled Isometric Joy- space, with resolution as high as stick, Step Keys, and Text Keys for Text And, when moving the cursor along Selection on a CRT," Ergonomics, Vol. a line of text in the rate mode, an in- 500 to 1,000 points per inch. Desk 21, No. 8, 601-613. advertent upward deviation that area must be provided for the tab- English, W. K., D. C. Engelbart, and M. L. does not exceed 15 degrees will not let, and the fatigue factor is moder- Berman, 1967, "Display-Selection push the cursor off the text line of ate. This device is neither portable Techniques for Text Manipulation," IEEE Transactions on Human Factors in interest. Thus, the cursor move- nor compact. Electronics, HFE-8, 1, 21-31. ments tend to adhere to the line- For applications that are cost- and-column grid of written text. sensitive, however, either a mouse With a mouse or tablet, however, an or absolute/rate joystick is recom- inadvertent motion such as this mended. The mouse offers high Vic Kley is president of KA Design I would actually displace the cursor speed and high resolution (100-300 Group, and has been involved in O one or more text lines, resulting in a points per inch), but does not offer computer graphics and design since 1977. He holds six pat- Io positioning error. natural, absolute mapping. Some 5 desk area must be provided, and ents in input device technology and General Application the fatigue factor is moderate. This has two more pending. E Recommendations device is portable, but not com- The following guidelines are sug- pact. 72