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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
2
3
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
2
3
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
0
100
200
300
400
500
600
ball rod vSphere
Ine
fici
en
cy (
pe
rce
nt)
solid
wire
0
1
2
3
4
5
6
7
8
9
10
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