Cognition in the virtual world

Which is easiest to read?

What is the time?

What is the time?

What is the time?

What is the time?

What is the time?

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.

General principles of human information processing

Reaction time Power Law of Practice Fitt's Law Principle of uncertainty GOMS - an approach to task

analysis

The Model Human Processor

• Perceptual system(sensors)

• Cognitive system(processors)

• Motor system(effectors)

(Card, Moran,

& Newell, 1983)

Important parameters

Memory capacity Decay Representation Processing cycle time

Sample times

Eye-movement = 230 [70~700] ms

Typical time = 230 ms“Fastman” = 70 ms“Slowman” = 700 ms

Perceptual processor: 100 [50~200]Cognitive processor: 70 [25~170]Motor processor: 70 [30~100]

Model of simple RT problem:

Task: Press button when symbol appears.

Model of simple RT problem:

Task: Press button when symbol appears.1. Perceptual processor captures it in the visual image store & represents it in working memory. 100 [50~200]

Model of simple RT problem:

Task: Press button when symbol appears.2. Cognitive processor recognizes the presence of a symbol. 70 [25~170]

Model of simple RT problem:

Task: Press button when symbol appears.3. Motor processor pushes the button70 [30~100]

Model of simple RT problem:

Task: Press button when symbol appears.

1. The perceptual processor captures it in the visual image store and represents it in working memory. 100 [50~200]

2. The cognitive processor recognizes the presence of a symbol. 70 [25~170]

3. The motor processor pushes the button

70 [30~100]Total time?

Each of these action primitives takes some small amount of time (in msec.).

The Model Human Processor provides a range of parameters you can use to predict precisely how long something will take, or to compare the time needed for alternative actions

More complex RT example

Task: you see one symbol, then another. Push yes if they match, no if they don’t.

Same first step as in simple RT problem:1. The perceptual processor captures

symbol #1 in the visual image store and represents it in working memory

100 [50~200]

Complex RT example, cont.

2. Ditto for symbol #2 100 [50~200] 3. If symbol #1 is still in the visual store,

the cognitive processor can compare the two symbols 70 [25~170]

4. If they match, the cognitive processor decides to hit “yes” 70 [25~170]

5. The motor processor hits “yes”

70 [30~100]How long from step #2 until the end?

Something to think about:

If you’re driving down the highway at 60 mph, how quickly can you react to an emergency?

Mean RT in simplest situation is 240 sec.

You travel 5280 * 60 = 316,800 ft./hr.

1 hour = 60 * 60 = 3600 sec.

So you travel 88 ft./sec.,

or over 21 ft. in 240 sec.

What about Fastman & Slowman?

If you’re driving down the highway at 60 mph, how quickly can you react to an emergency?

Mean RT in simplest situation is 240 sec.

You travel 5280 * 60 = 316,800 ft./hr.

1 hour = 60 * 60 = 3600 sec.

So you travel 88 ft./sec.,

or over 21 ft. in 240 sec. [~11~41 ft.]

General principles of human information processing

Reaction time Power Law of Practice Fitt's Law GOMS - an approach to task

analysis Principle of uncertainty

Power Law of Practice

When something is done again and again, performance follows a power law

(You keep improving with practice, but as you become an expert, you improve less and less.)

Power Law of Practice

Note:

The power law of practice describes quantitative changes in skilled behavior (both cognitive and motor), but not qualitative changes (changes in strategies).

GOMS (Card, Moran, & Newell)

Goal - what the user wants to achieve Operator - elementary perceptual, motor, or

cognitive act Method - a series of operators that forms a

procedure for doing something Selection rule - how the user decides

between methods (if...then...). Skill is particularly important here.

See PRS, Ch 14, 448-455

GOMS (continued)

Examples: Goal - editing a paper (high level)

cutting and pasting text (low level) Operator - typing a keystroke Method - set of operators for cutting Selection rule - how the user chooses

a method

Advantages of GOMS

very general purpose allows for individual differences much predictive power about

timing good at predicting "ideal"

performance

Disdvantages of GOMS

not so good at predicting errors takes a long time to conduct

analysis whole may not be the sum of the

parts ignores the nature of internal

symbolic representations - focus is very low-level

Skill acquisition and transfer

Transfer (positive transfer) Interference (negative transfer)

Hick’s principle of uncertainty

Predicts how long a response will take in a given situation, based on how likely (or uncertain) the different possibilities are

Hick’s principle of uncertainty A secretary has a telephone console with 10 buttons

for answering calls on 10 lines. When a light behind a button comes on, his job is to push the button and answer the phone.

Which of these situations is going to be faster to react to?

A: where each line gets an equal number of calls

B: where two lines are used heavily, getting 50% and 40% of the calls, with the other 10% divided evenly among the other eight lines.

Hick’s principle of uncertainty

T = I * log2(n+1)

T = time

I = a constant

n = number of possible responses,

assuming all are equally probable+1 is due to uncertainty whether to respond

Hick’s principle of uncertainty

A: where each line gets equal number of calls 3.46 units

B: where two lines are used heavily, getting 50% and 40% of the calls, with the other 10% divided evenly among the other eight lines.

2.14 units

So the RT for B is 62% of the RT for A. (2.14/3.46)

Writing for the Internet (Nielsen)

How users read on the Web

(Read about the different variables that influence readablity; follow the links to the full report of the study.)

Sample Heuristics (used for Assign. #2)

1. Visibility of system status

2. Match between system & real world

3. User control and freedom

4. Consistency & standards

5. Error prevention

6. Recognition rather than recall

7. Flexibility & efficiency of use

8. Minimalist design

9. Help error recovery

10. Help & documentation

Sample Heuristics (modified for Web)

1. Provide feedback

2. Match between system & real world

3. User control and freedom

4. Internal consistency

5. Prevent errors (same as before)

6. Minimize the user’s memory load

7. Enable shortcuts

8. Simple dialogue (covers “minimalist design” and #2)

9. Internal locus of control

10. Help & documentation

(PRS pp. 412-413)