People & Devices: (Inputs & Outputs) Startlingly small child using computer History of human-computer interaction Another history video

Human performance and input devices An input device is a kind of transducer - it converts one kind of signal into another. Device independence - when a program is written in such a way that you can switch input devices without changing the program

Input devices - spatial input switches keyboards speech recognizers mouse, trackball, joystick light pen, tablet, touch screen data glove and other body trackers eye trackers etc.

Spatial input (positioning) devices specify spatial location (ex: mouse) mappings can be absolute or relative  full touchscreen, most knobs are absolute  mouse, trackball, joystick, touch pad are relative  some devices can be both (e.g., stylus) can be spatially coincident or not  (touchscreen vs. most others) many programs are device independent

Speed vs. accuracy: A tradeoff This tradeoff affects many human actions! People can choose to favor speed over accuracy, or vice versa. Input devices are sometimes biased toward either speed or accuracy, depending on the task.

Positioning devices (Albert, 1982) Device Speed Accuracy Touch screen 1(fastest)6.5 Light pen 26.5 Digitizing tablet 32 Trackball 41 (best) Force joystick 53 Position joystick 64 Keyboard 7(slowest)5 (from Sanders & McCormick)

Which input device is “best”? It depends on the context of use! (Bill Buxton) (our categories for input devices are not necessarily good ones) Input devices chunk things differently. Interfaces typically deal with only serial input, not parallel input.

Speed vs. accuracy: A tradeoff This tradeoff affects many human actions! Human factors example: moving a mouse to a target: What are the relevant factors?

Fitt’s Law Moving a mouse to a target: What can vary?

Fitt’s Law Moving a mouse to a target: What can vary? how long it takes how far you have to move how big the target is

Fitt’s Law Moving a mouse to a target: What can vary? how long it takes = T how far you have to move = D how big the target is = S How are these variables related? T = ??

Fitt’s Law Moving a mouse to a target: What can vary? how long it takes = T how far you have to move = D how big the target is = S T = D*S? T = S/D?? T = D/S??

Fitt’s Law Moving a mouse to a target: What can vary? how long it takes = T how far you have to move = D how big the target is = S T = D/S

Fitt’s Law moving a computer mouse to a target: how long it takes = T how far you have to move = D how big the target is = S how long it takes you to get started ~.5 s T = (D/S +.5 s)

Fitt’s Law moving a computer mouse to a target: how long it takes = T how far you have to move = D how big the target is = S how long it takes you to get started ~.5 s how fast you are, as an individual = k T = k log (D/S +.5 s)

Fitt’s Law moving a computer mouse to a target: T = total time D = distance S = size of target k = a constant (individual differences) plus, some time to get started

Fitt’s Law moving a computer mouse to a target: T = total time D = distance S = size of target k = a constant (individual differences) plus, some time to get started T = k log (D/S +.5 sec)

Fitt’s Law A quiz designed to give you fitts! (Bruce Tognazzini)

Text input Keyboards Handwriting recognition Speech recognition

Text input Keyboards  Alphabetic  QWERTY  Dvorak  Chord

Text input Keyboards Potentially:  QWERTY Slowest  Alphabetic  Dvorak  ChordFastest

Text input Keyboards Handwriting recognition Speech recognition

Text input Keyboards Handwriting recognition  PRO: better than small keys, integrated with sketching, preferred by some users  CON: may need training, recognition errors; slower than typing for some Speech recognition

Text input Keyboards Handwriting recognition Speech recognition (to be continued)

Input devices (some conclusions) Different controls or input devices chunk things differently Why shouldn’t we use more than just our hands? Choosing input and output devices involves making tradeoffs Remember: The best input device for the job depends on the context of use.