Introduction to Computer Input Introduction to Computer Input Devices and Their EvaluationDevices and Their Evaluation

Shumin ZhaiShumin Zhai

IBM Almaden Research CenterIBM Almaden Research Center

First Mouse (Douglas Engelbart and First Mouse (Douglas Engelbart and William English, 1964)William English, 1964)

First Mouse Patent (Engelbart)First Mouse Patent (Engelbart)

"A Research Center for Augmenting Human Intellect," "A Research Center for Augmenting Human Intellect," Douglas C. Engelbart, and William K. English, Douglas C. Engelbart, and William K. English, Proc. Proc. 1968 Fall Joint Computer Conference1968 Fall Joint Computer Conference

A Variety of Input DevicesA Variety of Input Devices

MouseMouse StylusStylus TouchscreenTouchscreen TouchpadTouchpad JoystickJoystick ......

Performance EvaluationPerformance Evaluation ““I like it!” / “It is cool!” is not enoughI like it!” / “It is cool!” is not enough

• ““Perception is not always reality”Perception is not always reality”• Conscious articulation is not always behavior Conscious articulation is not always behavior

(describe how to ride a bike)(describe how to ride a bike)

Individual differencesIndividual differences Making HCI an empirical (good) scienceMaking HCI an empirical (good) science

Iterative DesignIterative Design

Observation/ idea

Design/implementation

Product/Knowledge

PerformanceEvaluation

• Evaluation for insights• Evaluator vs. designer

QualitativeQualitative Analysis Analysis

TouchscreenTouchscreen• ProsPros• ConsCons

Stylus / light penStylus / light pen• ProsPros• ConsCons

Quantitative Performance EvaluationQuantitative Performance Evaluation

What to measure? What to measure? • Depending on the task / application scenarioDepending on the task / application scenario

Common measuresCommon measures• Trial completion timeTrial completion time• Error rateError rate• Learning speedLearning speed• Comfort / fatigueComfort / fatigue• etc.etc.

Real task: Interacting with WIMP interfaceReal task: Interacting with WIMP interface Experimental task: target acquisition Experimental task: target acquisition

• abstract, elemental, essentialabstract, elemental, essential

Performance measures: time, error ratePerformance measures: time, error rate

Pointing Device EvaluationPointing Device Evaluation

Fitts’ law Fitts’ law ((Paul Fitts, 1954)Paul Fitts, 1954)

MT MT == a a ++ b b loglog22( +1)( +1)DDWW

IDID

DD

WW

1/b - Index of Performance, Throughput, Bandwidth

Fitts’ lawFitts’ law

““The information capacity of the human The information capacity of the human motor system in controlling the amplitude of motor system in controlling the amplitude of movement”,movement”,

Journal of Experimental PsychologyJournal of Experimental Psychology, , vol 47, 381-391vol 47, 381-391

ID (bits)log2(A/W+1)

Time (sec)

***

**

***

**

***

**

***

**

Experimental DesignExperimental Design

Fairness for the given taskFairness for the given task Wide enough ID combinationsWide enough ID combinations

• W’s: from character size (10) to icon (30 W’s: from character size (10) to icon (30 pixel)pixel)

• A’s: from short (60) to cross screen (800)A’s: from short (60) to cross screen (800) Multiple individuals/subjectsMultiple individuals/subjects Balancing ordersBalancing orders Statistical analysisStatistical analysis Controlling error (about 5%)Controlling error (about 5%)

A BB A

A B CB C AC A B

Task modeling for evaluationTask modeling for evaluation

Bring task modeling to device Bring task modeling to device evaluationevaluation• Card, English, Burr, 1978Card, English, Burr, 1978

“Evaluation of mouse, rate controlled isometric “Evaluation of mouse, rate controlled isometric joystick, step keys and text keys for text selection joystick, step keys and text keys for text selection on a CRT”, on a CRT”,

ErgonomicsErgonomics, vol. 21, , vol. 21, 601-613601-613

Beyond Fitts’ lawBeyond Fitts’ law

Hick’s lawHick’s law Key stroke modelKey stroke model Control theoretic modelingControl theoretic modeling Limitations to Fitts law: pointing onlyLimitations to Fitts law: pointing only

Trajectory-based tasksTrajectory-based tasks Example: hierarchical menusExample: hierarchical menus Is there a “law” to Steering?Is there a “law” to Steering?

Thought experiment...Thought experiment...

2 goals passing2 goals passingIDID = log = log22 ( +1) ( +1)

3 goals passing3 goals passingIDID = 2 log = 2 log22 ( +1) ( +1)

N+1 goals passingN+1 goals passingIDID = = NN log log22 ( +1) ( +1)

goals passinggoals passingIDID = ? = ?

AAWW

AA

2W2W

AANWNW

AA

A/2A/2

A/NA/N

A/2A/2

A/NA/N A/NA/N

WW

AAWW

AA

WW

““Steering law”Steering law”

Steering law (Accot and Zhai 1997)Steering law (Accot and Zhai 1997)• ““Beyond Fitts’ law: Modeling trajectory based HCI tasks”, Beyond Fitts’ law: Modeling trajectory based HCI tasks”,

Proc of CHI’97Proc of CHI’97

dxdxW(x)W(x)

IDIDCC = =

CC

TTCC = a + b ID = a + b IDCC

ResultsResults

AA

WW

Device comparison in steeringDevice comparison in steering tasks tasks(Accot & Zhai, CHI’99)(Accot & Zhai, CHI’99)

Steering Index of Difficulty

Time

5 10 15 20 25 30

Trackball

Touchpad

Trackpoint

MouseStylus

Conferences and Journals Conferences and Journals

CHI: ACM Conference on Human Factors in CHI: ACM Conference on Human Factors in Computing SystemsComputing Systems

INTERACT: IFIP Conference on Human Computer INTERACT: IFIP Conference on Human Computer InteractionInteraction

UIST: ACM Symposium on User Interface Software and UIST: ACM Symposium on User Interface Software and TechnologyTechnology

HFES: Human Factors and Ergonomics Annual HFES: Human Factors and Ergonomics Annual MeetingMeeting

ACM Transactions on Computer Human Interaction ACM Transactions on Computer Human Interaction (TOCHI)(TOCHI)

Lab Assignment Lab Assignment Measure Fitts’ law index of performance with bare Measure Fitts’ law index of performance with bare

hand on paperhand on paper Measure any two devices using Fitts’ law with the Measure any two devices using Fitts’ law with the

Almaden Program Almaden Program Compare performance of the two devicesCompare performance of the two devices Compare devices with bare handCompare devices with bare hand Discuss the validity/benefits of Fitts’ law in your Discuss the validity/benefits of Fitts’ law in your

study.study. Discuss pros and cons of the devices: suggest Discuss pros and cons of the devices: suggest

improvements or new designsimprovements or new designs