Consistency is a curious design heuristic standing in a point of tension between maintaining traditional design approaches and exploring new innovative ones.
The consistency heuristic goes something like this: when designing an interface feature or an interaction process make sure you don’t confuse users by assigning new meanings to familiar concepts. Features, terminology, controls, and graphics, etc. should also be consistent throughout the designed system. So, presumably, the more consistent a feature or a process is, the easier it is to use because consistency decreases learning overheads.
On one my journeys on an East Midlands train between Nottingham and London my attention was drawn to one of the signed messages that we are increasingly surrounded with everywhere we go … you know, the kind that tell us how to behave and what to do in the world: Please stand on the left when on the escalator, don’t use the lift when the fire alarm is sounding, pull/push door, No smoking, etc.
In this case it was a sign that tells you what to do once you pull on the train emergency handle. You can see it on the picture below.
So, the idea of this “interface” is to allow a commuter to speak directly to the train driver after having pulled the alarm, and to help them manage their communication by conveying the status of their verbal exchange; if the “wait” light is on then don’t speak, if the “speak” light is on then speak.
But notice the choice of representation used here. There are tiny holes forming a circular shape next to the handle; clearly the speaker phone, below of which there are two small lights; a green light labelled with the text “Wait” in red, and an orange light labelled with the text “Speak” also in red.
This means that the commuter should STOP talking when the green light is on and START talking when the orange light is on… could this cause unwanted confusion during an “alarming” situation? Could it be redesigned with more consistency?
I’m sure it could.
The next picture is of my keychain. It has two buttons labelled with opposing arrow heads, one green, one red. Pressing either buttons triggers a tiny small red light on the keychain. I was given this when I moved into my house in Nottingham and was told that I can use it to get into the private parking area…
This is the gate to the parking area…
I have lived in this house for just over a year, pressing the green arrow-headed button to open the gate, and the red one to close it, until I accidently discovered that the gate actually closes automatically, and that the red arrow-headed button actually opens the small door on the left of the gate!
Two buttons with opposing arrow heads, and to my mind this meant green = open, red = close, it just made sense, but it was wrong. Was it my simplemindedness or is it a design flaw?