1. Norman Chapter 3 Knowledge in the Head (+ Mental Models)
Jeff Offutt
SWE 205
Software Usability and Design

2. Where is Our Knowledge ? Some knowledge for using a UI is in our heads
Try arranging letters on a keyboard without looking
We use software correctly by merging our knowledge with external influences :
Information in the world—what we see
We often do not need to be precise
Good UIs constrain our use with syntax—legos, electronic connections, radio buttons
Our culture constrains us—volume and headphones
9-Nov-18
© Offutt

3. 1. Information In The World
Who knows whose face is on a $20 bill ? $50 ?
We do not need a map to go somewhere we are familiar with
But we might not be able to give directions
And what if we can’t read street signs ?
I often forget my classroom numbers after the first week, so use information in the world to find them
How do you remember your 50+ passwords ?
I remember to bring my pointer to class by putting it with my notes when I prepare for class
9-Nov-18
© Offutt

4. Information In the Head Information In the World
Information that we memorize
Our own name
Our address
World
Information that we see or look up
Time
Courses offered next semester
We often move information from one place to another
Our class schedule
The room number for SWE 205
9-Nov-18
© Offutt

5. Two Types of Knowledge Declarative knowledge : knowledge “of”
Facts and rules : Class starts at 10:30, double click the PPT icon to open powerpoint
Easy to write down and teach
Usually requires memorization
Procedural knowledge : knowledge “how”
Allows somebody to accomplish a task
How to get to class by 10:30
How to find the icon and double click
Much harder to teach and learn
Taught by demonstration and learned through practice
Requires deeper understanding
9-Nov-18
© Offutt

6. 2. Precision is Not Needed
People are not good at being precise
The one dollar coin was almost the same size as a quarter—The US made this mistake twice in my life!
Remembering 10-digit phone numbers is hard … so my phone has a contact list and voice activation
The French & Indian war occurred about 20 years before the US revolutionary war … but which year?
We learn to be precise in our field only after years of learning and practice
A good UI must not require precision
But should help the user find precision when required
9-Nov-18
© Offutt

7. 3. Syntactic Constraints
Spelling is hard … but made easier by patterns
What consonants can precede an “h” ?
“ch”, “gh”, “ph”, “rh”, “sh”, “th”, “wh”
Singers, musicians, dancers and martial artists don’t memorize so much as recreate based on patterns that “make sense”
The syntax of a UI must make syntactic constraints clear
In PPTX, if I highlight text, lots of actions are immediately enabled
9-Nov-18
© Offutt

8. Mapping Syntax to Semantics
This arrangement has a natural mapping … fewer mistakes !
How can we remember which control maps to which burner ?
Mistakes are encouraged
9-Nov-18
© Offutt

9. 4. Mental Models Mental : Users’ perception of reality
Example distributed file system: files
Implementation : How a machine, virtual or otherwise, is actually built
Example: Network protocols
Manifest : How the machine represents the implementation to the user
Example: Local disk
9-Nov-18
© Offutt

10. Example: Driving a Car When we push the gas pedal, the car goes faster
Mental : Pushing makes it go faster
Implementation : More gas to the engine, more pressure, pistons go faster, tires go faster …
When we turn the wheel, the car turns
Mental : Turning the wheel turns the tires
Implementation : Turning the wheel turns something else (with the help of a motor for power steering), which causes something else to turn, which puts the tires into a different angle
9-Nov-18
© Offutt

11. Interfaces should conform to the user’s mental model
UIs and Mental Models
Telephones : I want to call Mom, not XXX-XXXX
First we must put the phone number into the “world”
Compile : I want to Run my program, not compile, link, run
File Manager : Dragging a file from window to window is :
Move on the same disk
Copy from disk to external devise (USB thumb drive or backup)
Dropbox?
Calendars : Paper calendars require paging, online calendars can scroll
Interfaces should conform to the user’s mental model
9-Nov-18
© Offutt

12. UIs and Mental Models Predicting storms Dice Patriotweb
Does the prediction “30% chance of snow” mean
It will snow in 3 of 10 locations in the area
Less snow than if 50% chance, but more than if 10%
On 3 days out of 10 with these “weather conditions,” it has snowed in the past
Dice
If I roll a 6 five times in a row, what is the probability that my next roll will be a 6 ?
Patriotweb
Login-Faculty&Advisor-Summary Class List-Submit-Submit … Roster …
I expect : Faculty&Advisor-Summary Class List-Submit-Submit … Roster … but no!
9-Nov-18
© Offutt

13. Typical Paging Calendar
Sun
Mon
Tue
Wed
Thu
Fri
Sat 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
This makes perfect sense … for a paper calendar
9-Nov-18
© Offutt

14. This is closer to the user’s mental model
Scrolling Calendar
Sun
Mon
Tue
Wed
Thu
Fri
Sat 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Feb 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
scroll
This is closer to the user’s mental model
9-Nov-18
© Offutt

15. Adapting to user’s mental models causes cognitive dissonance
Mental Model Summary
Engineers are very comfortable thinking in terms of the implementation model
Users are not
Adapting to user’s mental models causes cognitive dissonance
9-Nov-18
© Offutt