Big Signal for Common Tasks

The power of visual cues to guide user behavior is well known- size and color, for example, are often employed in various interfaces to call attention to the affordance that most users will be looking for most of the time. Large green “Start” buttons on copiers make them easy to use because the most common task is initiated by the most obvious control. The depth of this connection is always impressive when seen in action.

In an effort to relieve my five year-old’s cabin fever, I asked him to come outside with me to fill up the windshield washer reservoir in my car. It’s a brand new sedan, with a complex engine compartment.





I showed him the windshield washer fluid first, and then I opened the hood and said “Where do you think it goes?”

With less than a half-second’s consideration, almost instantly, he pointed at the lid to the reservoir.

“Why do you think it goes there?” I asked.
“Because it’s the same color as the washer stuff”.

The conscious design choice of the blue color for the lid of the reservoir acts pre-attentively to associate the object with the “washer stuff”, which is in the “locus of attention” (see Jef Raskin for more). Almost everything else in the engine compartment is either black or unfinished metal. Even before working memory can process the query and engage in problem-solving, there is a bias towards the large blue “cap”-object.

So, the motorist is happy because they will almost certainly succeed in their task with little to no effort. The designers applied an appropriate signal to the affordance that will be most frequently used. Other preliminary tasks, like opening the bottle of washer fluid and poking at the foil cover, can actually be more challenging than figuring out where to pour the stuff.

We’ve seen that the brightest signal will co-opt our attentional faculty. There will be a bias towards that signal that will require effort for the user to overcome. Violating that expectation through using a color other than blue for either the reservoir cap OR the fluid will impact the user's experience. Predicting and accounting for this behavior is an important part of user-centered design.