Elevators and Description Errors

I was about to take the elevator down to the lobby today, but when the doors opened on my floor, a curious incident gave me pause. A girl walked briskly out of the elevator, looked around, said "Wait a minute...", realized she was on the fifth floor, and walked back into the elevator to accompany me downstairs. This probably isn't too unusual -- I think a lot of people have gotten off elevators on the wrong floor before (I know I have). But, haven't you ever wondered why that happens?

The elevator-wrong-floor mistake falls into a category of slips called "description errors" (at least, that's what they're called in Norman's excellent primer "The Design of Everyday Things"). What's actually happening here is that the elevator user is matching characteristics of their environment to their mental description of how the situation should appear. So, the elevator rider is looking to step into the elevator, ride it for some period of time, then exit when the door opens on the desired floor. In my example, all these things were happening normally to the girl in the elevator, except that the elevator opened on 5 instead of the lobby. Since the environment matched her mental model pretty well, she performed what she thought was the appropriate action: exiting the elevator.

Although it might sound like I'm hanging this unknown girl out to dry, I'm really not. Description errors can happen to anyone, in a variety of circumstances -- have you ever thrown a dirty shirt in the trash instead of the laundry? picked up a toothbrush instead of a razor? or pressed "power" on the wrong remote? In all these situations, the right action is happening, it's just being performed on the wrong object.

An important note here is that description errors, like all mental slips, are more likely to occur under cognitive load. It's important to realize, though, that this doesn't mean solving calculus problems in your head while whistling a tune -- cognitive load can be as simple as thinking about what you'll be doing later in the day.

Finally, to relate this to design, it's tough to make a system follow useful conventions while still making it immune to description errors. I think it's doable, though, by identifying key decision points (like when the elevator opens) and including salient notifications to help the users keep track of what they're doing. For example, a voice could quietly say the number of the current floor when the door opens. Would this stop all description errors? Definitely not, but I'm sure it would help cut down on the number of embarrassing elevator situations.