(based on Shneiderman chapter 1)

[ lecture notes | CSC 397 | Pete Sanderson | Computer Science | SMSU ]

execution and evaluation : getting things done

Source: Donald Norman : The Psychology of Everyday Things (1988) - later "Design"

Norman's Seven Stages of Action
1. form the goal
2. form the intention (task, actions that have to be done)
3. specifying an action
4. executing the action
5. perceiving the state of the world
6. interpreting the state of the world
7. evaluating the outcome

Steps 2 thru 4 form the execution aspect of action.
Steps 5 thru 7 form the evaluation aspect of action.

It is possible for a Gulf to form between users mental model of system and its physical state.
- Gulf of Execution: system does not provide actions that correspond to user intention
- Gulf of Evaluation: effort required to interpret system state and evaluate success

What allows Gulfs to form?

For goal to be achieved effectively, the user's mental model of system must match designer's.
- But user does not interact directly with designer!
- User forms system image based on interactions with system.
- System image may not correctly communicate designer's model to user! Poor mapping.
(diagram on Norman p 16)

Norman's basic principles of good design:
1. visibility (can determine state and alternatives by looking)
2. good conceptual model (p 16) -- designer's model
3. good mappings (e.g. between actions and results)
4. feedback (continuous feedback concerning results of actions)

 If System Image is INCOMPLETE, INCOHERENT, INAPPROPRIATE, then user's model will not match design model.

VCR example. Do you know how to program your VCR without reading instruction manual?

Whose fault it that?

Do you internalize or externalize failures?? Many poor designs not recognized/improved because we do not externalize (let designer know).

Tim DeClue's work recognizes tendency of females to internalize and males to externalize (1997 Central Plains Small College Computing Conference).

 Donald Norman : latest book is "The Invisible Computer" (Nov 1998)
- Relate to HCI.
- User has goal, and uses device to achieve goal.
- If mental focus is on goal, device (computer) is invisible.
- When mental focus has to shift back to device, is no longer invisible.
- Winograd and Flores book Understanding Computers and Cognition; "readiness at hand"

Marshall McLuhan: "The medium is the message" Relate to HCI. What is the message from the designer to the user?

Sensitivity vs adaptability

Strategy depends on ease of human adaptability. See next 3 examples.

Example: hand sizes are as individual as foot sizes, yet nearly every computer user can use same size keyboard. Low sensitivity to size and device not adaptable. One-size-fits-all.

Example: individual foot sizes require different shoe sizes. Sensitivity to size, and device not adaptable.

Example: different sized people work most comfortably in different sized chairs. Chairs can adapt seat height, angle of back etc. Sensitive to size, and device IS adaptable.

Some physical abilities relevant to interaction:
1. static measures (height, finger length)
2. dynamic measures (reach, strength, speed)
3. vision (differentiate objects, sensitivity to high/low intensity, sensitivity to colors, effect of flicker, depth perception for 3D, sensitivity/selectivity with motion, peripheral vision)
4. touch (keyboard, touch screen)
5. hearing (ability to hear different frequencies, differentiate sources)

Ergonomics: physical design of workplaces

Some cognitive processes
1. short term memory
2. long term memory
3. Learning
4. problem solving
5. time perception
6. decision making

Some factors affecting performance
1. Fatigue
2. mental load
3. knowledge of results (e.g. knowledge of application domain)
4. sleep deprivation
5. Anxiety
6. Drugs
7. age

male-female
left-right brain
risk taking-avoidance
introvert-extrovert
feeling-thinking
impulsive-reflective
assertive-passive

visual scan methods: left-right, right-left, top-bottom
formats for time, date, weights, phone numbers, currency
etiquette and formality

Physical impairments: sight, hearing, speech, mobility
Learning disabilities

Abilities are diminished: speed, motion, vision, hearing, speed of comprehension, learning

[ lecture notes | CSC 397 | Pete Sanderson | Computer Science | SMSU ]

Peter Sanderson ( pete@csc.smsu.edu )