CS 3724 Lecture Notes for Sep 4

Human Limitations and Errors

I. Errors

Slips

• Capture errors
• Description errors
• Data-driven errors
• Associative activation errors
• Loss-of-activation errors
• Mode errors

Mistakes

Forcing functions

• Examples: locking keys in car, interlocks on seatbelts, forgetting bank cards, swiping pens
• Methods: interlocks, lockins, lockouts

Design lessons

• Put the knowledge in the world
• Use the power of natural and artificial constraints
• Narrow the gulfs of execution and evaluation

II. Human Limitations

Theoretical foundations

• Limitations of memory
• Miller's 7 +/- 2
• Chunking
• Volatility of memory
• Conditions for optimum problem solving
  • Graphical progress indicators (vs static, blinking, or numeric)
  • Knowledge of objects and actions
  • Few delays
  • Low anxiety
  • Few errors that are easy to handle

Expectations and attitudes

• Miller's 2-second limit
• Task response times: typing/mouse 50-150 ms, simple frequent tasks 1 s, common tasks 2-4 s, complex tasks 8-12 s
• Users prefer shorter response times
• Shorter response times leads to shorter user think time (program compile times now and then, Web page load times)
• Response-time choke and slowing down the user
• Empirical tests help set suitable response times

User productivity

• Repetitive tasks
• Problem-solving tasks

III. Homework 1 Discussion