People & Devices: (Inputs & Outputs)

Startlingly small child using computerHistory of human-computer interactionAnother 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 2 6.5

Digitizing tablet 3 2

Trackball 4 1(best)

Force joystick 5 3

Position joystick 6 4

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

KeyboardsAlphabeticQWERTYDvorakChord

Text input

Keyboards Potentially:QWERTY SlowestAlphabeticDvorakChord Fastest

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.