Mistakes, Errors, and Slips + Design Principles: Visibility, Feedback, Mapping, Constraints

2 types of human errors

-unconscious slips

-conscious mistakes

slips

occur when users intend to perform one action, but end up doing another (often similar) action; unconscious

-example: accidentally putting liquid hand soap on one’s toothbrush instead of toothpaste

mistakes

made when users have goals that are inappropriate for the current problem or task (wrong method for achieving your goal/objective); conscious

-example: if someone misunderstood the meaning of the oil-pressure warning light in his car, and thought it was the tire-pressure monitor, no matter how carefully he added air to his tires, it would not fix the issue with his oil pressure

general guidelines for preventing slips

-include helpful constraints

-offer suggestions

-choose good defaults

-use forgiving formatting

general guidelines for preventing mistakes

-gather user data (to understand users’ mental models)

-follow design conventions

-communicate affordances

-preview results

design principles

-visibility

-feedback

-mappings

-constraints

(from Donald Norman’s book, “The Design of Everyday Things”)

visibility

make the state and operations of a system visible and clear to users

-don’t hide controls; craft well-designed displays (like progress bars) and using other senses like sound output, giving users a good indication of the state and operations of the system

bad visibility example

pumping gas shown in picture

-hard to know how to turn pump on, push to start button hard to see among other buttons

good visibility example

starting email message

-easy to see compose button to start email

Microsoft Office Toolbar is also another good example, showing most common options and devoting more screen real estate to more common buttons (like paste)

mappings

used to determine relationships, typically between something you want to control and the thing you use to control it OR between an action and result of that action

-physical analogies/relationships + cultural standards

bad mapping example

cup lids: difficult to tell right size for cups, shown in image

good mapping example

cup lids: easy to tell right size for cups since cups and lids are next to each other for each size, shown in image

bad mapping example

stove burners: how do I know how to map the different burners to different switches?

good mapping example

stove burners: clear which switches are for each burner

bad mapping example

ceiling fans: which string turns on the fan, which turns on the light?

feedback

an action that the system takes in response to a user action

-leads to CAUSAL models (if y happens after x, then x caused y)

-prime mechanism for helping people understand how the system works and build an appropriate model of the system

good feedback example

-hovering over laptop configurations highlights them

-typing numbers in phone and showing the digits entered so far (image)

-Google Now: when tapping the microphone or saying okay google, visual feedback is given with red circle having circles around it, showing Google is interpreting input and that it is listening

constraints

design features that limit the range of possible actions a user can take

-narrow down options a user has to consider, making their task easier

-physical constraints: chargers and VCR tapes can go in only one way

-there are also logical and simple constraints that you can design into a system

good constraints example

grey out or deactivate unavailable menu items (image shows Cut and Copy are unavailable since nothing is selected)

good constraints example

constraining user input (image shows Amazon dropdown menu for how much you want to buy a product, only giving sensible options)

good constraints example

Duolingo: trying to learn Spanish and translating a sentence (image), only a set of words are given at the bottom to choose for translation

-user is not yet ready to type in free text, so clues are given instead to constrain choice and having higher probability for picking right response