CEN3722 Human Computer Interaction Title of Presentation Dr. Ron Eaglin

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

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.

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”

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?

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.

Humans vs. Computers Humans deal with human errors and correct all the time Yu cn stll rd ths Sntnc bt a mchn cnt. Machines need precision – do not tolerate errors well

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

Example

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.

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 email. 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.

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.

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.

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

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

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

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

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

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

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

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 email message in all CAPS, did you intend to do this or should I correct it?”

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)

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

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

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

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

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