Input: Devices and Theory

Input for Selection and Positioning

Devices Power Law of Practice Fitt’s Law (2D, 3D lag) Eye hand coordination Two handed Methods and Metaphors

5 Virtual DevicesAdapted from Wallace, 1976.

"The Semantics of Graphic Input Devices"

Button - Indicates Choice (binary)- radio buttons are an extension of this concept.

Keyboard - Alpha numeric strings- a lot of buttons (voice)

Pick Device - For selection of graphic objectsThe canonical example of this is a light pen.

Locator - For specifying screen coords- x, y position(e.g. mouse)

Valuator - generating floating point values:A potentiometer.

Power Law of Practice

Time to perform a task is proportional to the log of the number of times the task has been carried out.

log(Tn) = log(T1) - α.log(n)

The law is usually expressed in terms of blocks of trials since the time to perform a single trial is too variable.

Law ofDiminishingReturns

Applicable to Choice reaction

Typing

Many skilled behaviors

Fitt’s Law for position selection

MeanTime = C1 + C2log2(D/W + 0.5) (1) MeanTime = C1 + C2log2(D/W + 1.0) (2)

Index of difficulty = log2(D/W + 1.0)

Index of performance = 1/C2

About 5-8 bits per second (many devices)

Modified Fitt’s Law

MeanTime = C1 + C2(Human + Machine)ID

Control loop

Update display Measurehand position

Judge distanceto target

Effect handmovement

Yes

No

Human Processing

Machine Processing

Detect startsignal

InTarget?

On to next task

Ar

Fish Tank VR (is head pos important) is stereo important.

Mirror

Virtual Image of Screen

Stereo Glasses

Head Position Tracking

Phantom

Arsenault and Ware (2001) TOCHI

Effects of incorrect perspective

Task: Tapping from target to target

Effects of stereo in eye hand coordination

0

1

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4

0 1 2 3 4 5 6

Index of Difficulty (bits)

Me

an

Tim

e (

sec)

No Stereo

Stereo

Approx 3 bits per second (best case)

Effects of correct perspective (HT)

0

1

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4

0 1 2 3 4 5 6

Index of Difficulty (bits)

Me

an

Tim

e (

sec)

No HT

HT

No Stereo 1.58 1.75Stereo 2.41 2.70

No HT HTIndex ofPerformanceSummary

In bits per second

Factors in input device design

Degrees of Freedom Order of control (Milgram) p = a + bt + ct2

Position (0) Velocity (1) Acceleration (2)

Mappings between devices and tasks S-R compatibility Integral/separable

Isometric/compliant

Direct Manipulation

Visibility of objects and actions Rapid reversability < 100 msec lag in visual feedback Users

Feelings of mastery and control Ease of learning Perceived Transparency “The user is able to apply

intellect directly to the task; the tool itself seems to disappear”. (Rutowsky, 1982)

3D Rotations with a 2D interface

Virtual Trackball (Chen, 17.5 seconds, Hickley 26 sec.)

Arcball 26 seconds (Hinckely, 1997 Shoemake 1992)

Rotations 3dof

Ware: 55 seconds accuracy, 14 seconds speed

Hinckley 3ball 20.7 f sec 14 m sec Zhai 18 sec. Wang: real object rotations of 45 deg in

less than a second Ware and Rose: real object rotation <

2sec virtual objects, real handles

Handles Real and VirtualWare and Rose

Real Object Rotations

Hand in the same place as an object helps

Where, between real and virtual does performance break down?

MirrorMirror

MonitorMonitor

Ware and Rose: results

Hand in the same place as an object helps (30 %).

Random end harder than random start. Sphere vs shape match is a minor factor

Experiment

Two objects: Wire-frame, color coded tetrahedron Solid shape

Results

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200

300

400

500

600

ball rod vSphere

Ine

fici

en

cy (

pe

rce

nt)

solid

wire

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ball rod vSphere

Tim

e (

seco

nd

s)

solid

wire

Color result confirmsHypothesis

No major differenceIn efficiency

Radical solutions

Gadget methods Screen space methods

Props: Physical Objects that Support Interaction (Hinckley)

Guiard’s Kinematic Chain Theory The left and right hands make up a functional

kinematic chain: for right-handers, the right hand moves relative to the output of the left hand. General principles:

1. Right-to-left reference: The right hand performs its motion relative to the frame of reference set by the left hand.

2. Asymmetric scales: Different temporal-spatial scales of motion.

3. Left hand precedence: The left hand precedes the right: for example, the left hand first positions the paper, then the right hand begins to write.

Two Handed Interaction

Props Toolglasses and magic lenses Tool use, e.g. rulers and guides

Gestures

Gestures can speed up input Can be iconic Sketch beautification Erase, create objects, etc.

Dynamic Querie (Schneiderman)

Interactively expose an hide multi-dimensional discrete data.

One slider per data dimension.

Frames of Reference

Retinocentric (2df) look at something Head centered (2df) pan and tilt Torso centered (2df) turn move forward Hand centered (6df) object orientation

Exocentric: Object centered point direction, intersection, docking, ROV control