The cognitive load theory
The central idea behind the theory of cognitive load is that the human brain can only process a small amount of new information, and a large amount of stored information. Cognitive load theory is about optimising the information load for short term memory, make it easier to process or transfer information to long term memory.
For the average user, high cognitive loads directly translate into 'hard to use'.
There are 3 types of cognitive loads:
- Intrinsic. Inherent difficulty of the task or information at hand. For example, is the topic eigenvectors or simple addition? A 12-step application or a quick feedback form?
- Extraneous. Anything that effects the learning of the intrinsic task, such as jargon, inessential info, distracting elements, confusing interface or more.
- Germane. This is a positive load, mainly to reinforce what the user has learnt so far. In traditional learning environments, it includes things such as spaced learning, quick follow-up quizzes and other desirable difficulties. For usability in the digital world, it could include reinforcing previous choices and confirming decisions among others.
Research in this area has produced a couple of key techniques to improve instructional design:
- Worked example effect. The finding that novice learners perform much better if a worked example of a problem is presented to them along with the instruction.
- Expertise reversal effect. The finding that as learners become more proficient at solving a particular type of problem, they should gradually be given more opportunities for independent problem solving.
- Tailored experiences. Gauge the existing skills and knowledge of the user, and tailor the experience that matches it.
- Present all essential information together. Give users an overview of the entire concept in one go (for usability in the digital world, this strategy could prove counter-productive).
The magical number Seven (7)
One of the most cited cognitive psychology papers is Miller's the magical number seven, plus or minus two. The finding is that the average person can only hold about 7 things in their short term memory, plus or minus 2 things.
But what's the implication for usability? If your interaction demands a long process, where you are counting on your users to remember things, you might want to review the cognitive load on your users. Are you stretching the limits of what the average person can remember in a short span of time? If you are, then you need to optimise their cognitive load.
Can we measure cognitive loads?
For digital experiences, we rely mostly on user-provided feedback to assess cognitive load. This is subjective, as the variability of humans is a constant in this scenario.
However, there has been research into multi-modal scientific studies to measure cognitive loads on students who study difficult-to-grasp concepts such as Integration or Eigenvectors.
Optimising cognitive load for usability
There are a few usability principles that come into play when optimising cognitive loads:
Simply disclose information that is directly needed to do the task at hand.
Write concisely, so users don't entirely skip the text, and stay to the point, as the users in most transactional systems are there to get the job done.
Also make sure that your communications meet the readability scores needed for your audience.
Provide distributed, small and to-the-point explanations of all possible friction points. Use layering such as tooltips or expanders to keep these explanations only for those who seek it.
Allow users only the most essential choices in any particular pathway in your process. Increasing choices makes decision-making harder. With limited choices, their cognitive load will be significantly reduced.
Use recognition rather than recall
This is one of the 10 usability heuristics for interface design by the legendary Jakob Nielsen.
Simply let people recognise familiar information, rather than asking them to provide it from memory. For example, if you want users to select a state from a dropdown control, present them a list of the states, rather than asking them to type in the name of the state.
Provide memory aids
Reinforce previous choices by repeating or displaying them along the way.
Chunking is a cognitive psychology concept, where related things are grouped into chunks that are remembered and processed by users much better than just a linear list or queue.
Chunking depends on the existing knowledge of the user cohort. Expert users have advanced knowledge of how things work, so their cognitive load will be different from the average user.
Subtising is the rapid and accurate recognition that human brain does, usually only for small numbers of items.
An application of subtising is digit grouping. For example, writing one million as 1,000,000 rather than 1000000.
Other things to keep in mind
Contiguity effect suggests that things are better recalled that are in close proximity to each other, primarily because human memory depends on association between items and their mental context.
Use existing mental models, if you can
In cases where it makes sense to use an existing mental model, it would help immensely to build on top of it. For example, as soon as I mention the word tree, you'd immediately understand the related concepts of roots, branches, leaves, watering and more.