You are paying bills at your online banking website. You have to think about what bills need to be paid when, look up your balance, decide how much to pay on your credit cards, and push the right buttons to get the payments processed. As you do this task, you are thinking and remembering (cognitive), looking at the screen (visual), and pressing buttons, typing, and moving the mouse (motor).
In human factors terminology these are called “loads”. The theory is that there are basically three different kinds of demands or loads that you can make on a person: Cognitive (thinking and remembering), Visual, and Motor.
Not all the loads are equal — Each of the loads uses up different amounts of mental resources. You use up more resources when you ask people to look at something or find something on a screen (visual) than when you ask them to press a button or move a mouse (motor). You use up more resources by asking people to think or remember or do a mental calculation (Cognitive), than when you ask them to look at something on a screen (Visual). So from a human factors point of view, the order of the loads from most “expensive” to least is:
- Cognitive (most “expensive”)
- Visual
- Motor (least “expensive”)
It’s all about trade-offs — From a human factors point of view, when you are designing a product, application, or website, you are always making trade-offs. If you have to add a few clicks, but by doing so the person doesn’t have to think or remember as much, that is worth it. Clicking is less of a load than thinking. I once did some research on this topic. People had to go through more than 10 clicks to get the task done, and at the end they would look up and smile and say, “That was easy!” because each step was logical and gave them what they expected. They didn’t have to think. Clicking is less of a load than thinking.
Reduce loads to make it easier — Most of the time when considering loads in design we are looking to reduce the loads (especially cognitive and visual) to make the product easier to use.
Increase loads to grab attention — But sometimes you want to increase the load. For example, to grab someone’s attention you might put more visual information (pictures, animation, a video) and thereby increase the visual load of the product.