DOET 5 Human error

Question!

• When I poured the ground up coffee into my coffee cup rather than the French press, what type of Slip was that?

Human error

Mistake or Slip?

• Mistakes are the result of conscious deliberation– Form the wrong goal and then plan and execute the

wrong action

• Slips result from automatic behavior– Intend to do one thing, end up doing another

Mistake

You successfully do the wrong thing.

Hard to detect because, after all, you made the wrong plan to address the problem…

and you were successful at it!

Slips

• Easy to detect: discrepancy between intended result and the actual result– But, only if results of the action are visible

• Show up most frequently in skilled behavior.

Six types of Slips

Capture

Description

Data-driven

Associative activation

Loss-of-activation

Mode errors

Refer to the wiki for this portion

• http://wiki.ggc.usg.edu/mediawiki/index.php/ITEC4130Fall2009NormanSlips%26Errors

How can you handle slips?• Prevent slips from happening by designing

appropriately– For example, if you have modes, reduce the number or

eliminate them by redesign– Make things deliberately different

• Detect and correct them when they do– On hazardous actions ask for confirmation

• Provide for recovery– Trash can does not delete, rather stores for deletion

One small problem:

• When you design an error-tolerant system, people come to rely on that system! (It had better be RELIABLE!)– Anti-skid brakes– Blade guard on circular saw

Human thought• Is dependent on the underlying memory• Is not like logic, it is much messier• Memory

• Not like a photo album, not that neat and orderly

• Two models• Filing cabinet model• Connectionist model

Human thoughtThe filing cabinet

• Thoughts are neatly encoded and organized• Schema theory, frame theory, semantic networks,

propositional encoding…• …all are names used for this model

Human thoughtThe connectionist model

• Connectionist– Memory is represented as patterns of activation and

inhibition– Much is hidden, inaccessible, beneath the surface, with

only the end states available for conscious inspection…– Examples

• Try to sing a song from its middle• What letter comes before Q?

The structure of tasks

• Descriptions of even simple tasks result in wide AND deep structures– Many choices, many levels

• Consider the game of tic-tac-toe• Shallow

– Many, simple choices, few steps– Baskin Robbins Ice Cream

• Narrow– Few choices, many steps– Recipe

Everyday tasks

• Not frequently studied by psychologists

• Generally routine, requiring little conscious thought or planning

• Much of human behavior is subconscious

• Conscious thought– Is slow and serial– Is limited by the small capacity of STM

• The nature of explanations– Easier to predict result AFTER it happens!– “Obvious” only happens after the fact

To increase errors, add a little:

• Social pressure

• Time pressure

• Economic pressures

Designing for error

• Design to minimize error by understanding the causes of errors

• Make actions reversible

• Make error discovery easier

• Make error correction easier

• Change the attitude toward error from “stupid user” to “stupid design”

Dealing with error

• Warning signals should not occur frequently… to attract attention

• Warning signals don’t work when there is the possibility that there will be many at the same time

Forcing functions

• Physical constraint

• Three flavors– Interlocks force a particular sequence– Lockins prevent premature stops (shutting

down word processor without saving)– Lockouts prevents entrance (stairs to basement)

Resultant design philosophy:

• Put knowledge in the world

• Use natural and artificial constraints

• Make stuff VISIBLE!– Narrow the gulf of execution

• Make options visible

– Narrow the gulf of evaluation• Make the results of actions visible

The End!