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.
Increase loads = gaming — The best example of purposely increasing loads is gaming. A game is an interface where one or two or three of the loads has been intentionally increased in order to provide challenge. Some games have high cognitive loads, some have high visual loads, some have high motor loads, and some have purposely increased more than one load.
Have you evaluated a website or product from this point of view? Have you designed a product or website from this point of view?
Interesting stuff Susan, can you link to the research behind this?
Very interesting. The notion of trade-off is key and people tend to forget it.
Hi Susan,
I am enjoying your series of posts. This one is timely. I’m writing a large e-learning project using Articulate authoring software. Your three loads concept is good guidance: down the load scale for ease; up the scale for attention.
Jack
Great post, Susan – great food for thought! It’s always a hard trade-off between cramming in everything that you want, and removing everything non-essential!
Very nice article. This makes perfect sense, and gives a more thorough understanding of web usability than, “the fewer clicks the better.” I like it! Thanks.
Interesting, but what about the fact that most – simple – cognitive tasks can be continued no matter what the added load is- up to a certain extend? (e.g. remembering your name while looking for the place on the screen to fill it in; will not slow down your searching or thinking…)
The idea of ‘increasing the load’ is not completely correct either. It has been showed in earlier studies that people will remember/find/like things more easily or better when visual stimuli are added.
What about the cognitive load of a visual versus voice user interface… in something like a vehicle?
Asking someone to read something would be more distracting clearly, but then again interrupting them and asking them with a vui to hold things in memory would have high cognitive load. How does one take into consideration these kinds of trade-offs?
Thank you and thanks for sharing all these insights…
I definitely subscribe to this methodology. Taking it a step further it might also be worth mentioning the different layers of any particular ‘load’. For instance: are you asked to provide information you’ve given time and time again (ie name) vs a brand new value (ie capcha). I think to a certain extend modern browsing trends and UI standards continue to evolve – as we get lazier we’ll demand more complex tasks to be completed in fewer loads. A combination of all 3 types.
It sounds logical and intuitive, but is it?
In some cases it goes against Jacob Nielsen’s research on web usablity (http://www.useit.com/)
I think it would be important to sort out the most appropriate medium for low investment systems, particularly if it were to be used for marketing. If marketing is one’s reason to lighten the ‘load’ then it may not be that useful on the web.
True as it may be in systematic terms (simple is easier) people are more complicated when it comes to purchasing products or services. The web is an information medium and the written word (content is king) is still the main pursuit that people online engage in.
Investing levels:
For important purchases we look for more information and are willing to invest more time to find the right product or service… and then we choose by way of emotion. But we put the work into the research because we believe we are going to make a logical choice even though our emotions take over.
For impulsive purchases the lighter loads may be perfect.
This sounds very plausible but is there any research to support it? I came across this idea in your book and was looking for references to support some design decisions I would like to make, but the only thing I found on the web was your own blog. Is this just a hypothesis?