1. CEN3722 Human Computer Interaction Title of Presentation
Dr. Ron Eaglin

2. Outcomes Explain why designers should not blame users for errors.
Describe types of errors, slips, and mistakes.
Describe the various types of slips.
Describe how to design to minimize errors

3. Outcomes Define and provide examples of these types of slips
Capture errors, mode errors, description errors, data-driven errors, associative-activation errors, loss of activation errors
Describe these forcing functions
Gag, warn, do nothing, do what I mean, Let’s talk about it, teach me.

4. Consequences of Human Error
1998 USSR Phobos satellite lost on trip to Mars
Ground controller omitted a single letter in a series of digital commands sent to the space craft.
The omission caused code to be mistranslated to trigger a test sequence stored in ROM.
This also launched hundreds of conspiracy theorists – simply Google “Phobos UFO”

5. Blame
Effects of electrical noise on signal reliability (well known phenomenon).
Designers often use error correction codes.
If Phobos malfunction had caused Phobos loss – would ground control have been blamed?
Error correction codes were standard practice.
Where is blame assigned?

6. Facts People make mistakes
Creativity, adaptability, and flexibility are human strengths
Alertness and precision in action or memory are our weaknesses
We have identified class of errors and conditions likely to evoke them
We can design for error.

7. Humans vs. Computers
Humans deal with human errors and correct all the time
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Machines need precision – do not tolerate errors well

8. Dealing with Errors In Design – devise systems to minimize errors
Make it easier to deal with errors
Provide clear indication of causes and remedies
Provide tools to make correction easier

9. Example

10. Example Outlook 360 will prompt you to ask you if
You mention an attachment in the body of your mail
You don’t attach an attachment to the mail.

11. Types of Errors Mistakes and Slips
A person establishes an intent to act – if the intention is not appropriate this is a mistake.
Misdiagnosis or misinterpretation of the situation.
Example: Incorrectly hitting send on incomplete .
If the intent is appropriate, but action is not what was intended this is a slip.
Example: a typo caused by improper hand placement on keys.

12. Slip – Capture Error
Done when a frequently done activity – takes over the intended action.
Example: Turning wrong direction in car based on habit – when you intended to go other direction
Example: Typing a common word incorrectly based on other words typed with a common letter sequence
Example: Typing the wrong phone number if you have one you commonly dial.

13. Slip – Capture Error (correction)
Avoid using common sequences for infrequent commands (Such as Ctrl-C, Ctl –V – Copy Paste)
Provide feedback mechanism to tell users what they are performing (You are attempting send the message without the attachment)
Have system understand the context of the commands and act/warn user accordingly.

14. Slips – Description Error
Happens when there is insufficient specification of the action
Ambiguity leads to incorrect action being performed
Caused by lack of consistency in command structures

15. Slips - Description Error
Ensure options a clearly differentiated (like a row of switches)
Provide sufficient feedback about action and consequence
Slips that can go unnoticed need to have feedback mechanism

16. Slips – Data Driven Error
Unconscious processing of external data interferes with intention
Typing what you are thinking not what you intended
Calling your wife/child/friend by wrong name
Saving file with wrong name

17. Slips – Data-Driven Error
Minimize distractions when consequences are severe
Provide clues as to intent of user (if predictable)
Give suggestions for things like file name, catch obvious slips

18. Slips – Loss of activation error
You forget what you are doing in mid-flow
Example: talking on phone/forgetting why you called

19. Slips – Loss of activation errors
Use cognitive reminders
Understand common patterns with suggestions
Lists or process flows to stay on track

20. Slips – Mode Error
When you think you are in one state, but actually in another
Example: CAPS LOCK BEING ON AND TYPING IN ALL CAPS

21. Slips – Mode Error Avoid use of modes
Make system states are obvious, many cues
Make it easy to correct or catch
“You just typed an message in all CAPS, did you intend to do this or should I correct it?”

22. Design for Errors Anticipate human errors and prevent then
Forcing Function – prevents the behavior from continuing until the problem has been corrected.
Guarantees detection but not correction
Example: disable buttons
Example: Don’t allow car to lock if keys inside (require keys to lock car)

23. Forcing Functions - Gag
Prevents user from continuing if error state
Computer locks unless computer and monitor are on
Car wheels locked unless key in ignition

24. Forcing Functions - Warn
Warning – File already exists, overwrite?
Seat belt light and audio alarm

25. Forcing Function – Do Nothing
If action is illegal or in error – nothing happens
No user feedback, can cause frustration

26. Forcing Function – Self Correct
System guesses legal action you want to perform
Example: Spell check – provides much humor on cell phones
Do What I Mean – Ultimate self correct function

27. Summary Explain why designers should not blame users for errors
Describe common slips and mistakes and differences
Describe different types of slips and forcing functions