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 Devices Adapted from Wallace, "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 objects The 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(T n ) = log(T 1 ) - .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 of Diminishing Returns Applicable to Choice reaction Typing Many skilled behaviors

Fitt’s Law for position selection MeanTime = C 1 + C 2 log 2 (D/W + 0.5) (1) MeanTime = C 1 + C 2 log 2 (D/W + 1.0) (2) Index of difficulty = log 2 (D/W + 1.0) Index of performance = 1/C 2 About 5-8 bits per second (many devices)

Modified Fitt’s Law MeanTime = C 1 + C 2 (Human + Machine)ID

Control loop

Ar Fish Tank VR (is head pos important) is stereo important. Arsenault and Ware (2001) TOCHI

Effects of incorrect perspective

Task: Tapping from target to target

Effects of stereo in eye hand coordination Approx 3 bits per second (best case)

Effects of correct perspective (HT) No Stereo Stereo No HT HT Index of Performance Summary In bits per second

Factors in input device design Degrees of Freedom Order of control (Milgram) p = a + bt + ct 2 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 Virtual Ware and Rose

Real Object Rotations Hand in the same place as an object helps

Where, between real and virtual does performance break down? Mirror Monitor

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 Color result confirms Hypothesis No major difference In 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