Design of Everyday Things - Norman, Don [60]
TYPES OF SLIPS
Some slips result from the similarities of actions. Or an event in the world may automatically trigger an action. Sometimes our thoughts and actions may remind us of unintended actions, which we then perform. We can place slips into one of six categories: capture errors, description errors, data-driven errors, associative activation errors, loss-of-activation errors, and mode errors.
CAPTURE ERRORS
“I was using a copying machine, and I was counting the pages. I found myself counting ‘1, 2, 3, 4, 5, 6, 7, 8, 9, 10, Jack, Queen, King.’ I have been playing cards recently. ”3
Consider the common slip called the capture error, in which a frequently done activity suddenly takes charge instead of (captures) the one intended.4 You are playing a piece of music (without too much attention) and it is similar to another (which you know better); suddenly you are playing the more familiar piece. Or you go off to your bedroom to change your clothes for dinner and find yourself in bed. (This slip was first reported by William James in 1890.) Or you finish typing your thoughts on your word processor or text editing program, turn off the power, and go off to other things, neglecting to save any of your work. Or you get into your car on Sunday to go to the store and find yourself at the office.
The capture error appears whenever two different action sequences have their initial stages in common, with one sequence being unfamiliar and the other being well practiced. Seldom, if ever, does the unfamiliar sequence capture the familiar one.
DESCRIPTION ERRORS
A former student reported that one day he came home from jogging, took off his sweaty shirt, and rolled it up in a ball, intending to throw it in the laundry basket. Instead he threw it in the toilet. (It wasn’t poor aim: the laundry basket and toilet were in different rooms.)
In the common slip known as the description error, the intended action has much in common with others that are possible. As a result, unless the action sequence is completely and precisely specified, the intended action might fit several possibilities. Suppose that my tired student in the example formed a mental description of his intended action something like “throw the shirt into the opening at the top of the container.” This description would be perfectly unambiguous and sufficient were the laundry basket the only open container in sight; but when the open toilet was visible, its characteristics matched the description and triggered the inappropriate action. This is a description error because the internal description of the intention was not sufficiently precise. Description errors usually result in performing the correct action on the wrong object. Obviously, the more the wrong and right objects have in common, the more likely the errors are to occur. Description errors, like all slips, are more likely when we are distracted, bored, involved in other activities, under extra stress, or otherwise not inclined to pay full attention to the task at hand.
Description errors occur most frequently when the wrong and right objects are physically near each other. People have reported a number of description errors to me.
Two clerks in a department store were both on the telephone to verify credit cards while simultaneously dealing with a customer and filling out a credit card form. One sales clerk had passed in back of the other to reach the charge forms. When this clerk finished preparing the sales slip, she hung up the handset on the wrong telephone, thereby terminating the other clerk’s call.
A person intended to put the lid on a sugar bowl, but instead put it on a coffee cup (with the same size opening).
I had a report of someone who planned to to pour orange juice into a glass but instead poured it into a coffee cup (adjacent to the glass).
Another person told me of intending to pour rice from a storage jar into a measuring cup, but instead pouring cooking oil into the measuring cup (both the oil and the rice were kept in glass containers on the counter).