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Task Analysis (continued). Task analysis. Observations can be done at different levels of detail fine level (primitives, e.g. therbligs, keystrokes,GOMS - the “micro” level) intermediate level (flow charts, plans, or steps for sequences of actions)

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task analysis
Task analysis

Observations can be done at different levels of detail

  • fine level (primitives, e.g. therbligs, keystrokes,GOMS - the “micro” level)
  • intermediate level (flow charts, plans, or steps for sequences of actions)
  • high level (cognitive goals; social impact - the “macro” level)
general principles of human information processing
General principles of human information processing
  • Fitt's Law
  • Reaction time (the Model Human Processor)
  • Power Law of Practice
  • Principle of uncertainty
  • GOMS - an approach to task analysis
the model human processor
The Model Human Processor
  • Perceptual system

(sensors)

  • Cognitive system

(processors)

  • Motor system

(effectors)

(Card, Moran,

& Newell, 1983)

important parameters
Important parameters
  • Memory capacity
  • Decay
  • Representation
  • Processing cycle time
sample times
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
Model of simple RT problem:

Task: Press button

when symbol appears.

model of simple rt problem8
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 problem9
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 problem10
Model of simple RT problem:

Task: Press button

when symbol appears.

3. Motor processor

pushes the button

70 [30~100]

model of simple rt problem11
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?

slide12
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
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
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
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 msec.

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

1 hour = 60 * 60 = 3600 sec.

You travel 88 ft./sec. or > 21 ft. in 240 msec.

before you can even react (let alone stop)!

what about fastman slowman
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.

You travel 88 ft./sec. or > 21 ft. in 240 sec.

[between ~11 and~41 ft.]

before you can even react (let alone stop)!

general principles of human information processing17
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
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.)

slide21
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
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.
goms continued
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
Advantages of GOMS
  • very general purpose
  • allows for individual differences
  • much predictive power about timing
  • good at predicting "ideal" performance
disdvantages of goms
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
Skill acquisition and transfer
  • Transfer (positive transfer)
  • Interference (negative transfer)
hick s principle of uncertainty
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 uncertainty28
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 uncertainty29
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 uncertainty30
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)

miscellaneous points to review
Miscellaneous points to review
  • Experiment design
  • Breadth-first vs. depth first in menus and in spoken dialog design
  • Writing
  • VoiceXML info
improve your writing
Improve your writing
  • Everyone can write better (and you are no exception!)
    • Advice from Clark
    • Addendum: Brennan
  • Writing for the Internet (Nielsen)
    • How users read on the Web