Task Load

Task load is how much information a person can process at once. It is crucial in user experience (UX) design as it helps identify what information to share with users and when.

Too much task load and a user may become overwhelmed, unable to perform tasks, and generally unhappy. NASA originally designed the task load index (TLX) to evaluate how to ensure jobs were not beyond human capabilities. The NASA TLX also includes physical strain as part of the index, which is usually irrelevant for desktop and mobile interfaces. However, with the rise of augmented reality (AR) and virtual reality (VR) interfaces, the TLX is more relevant than ever to UX and an invaluable user research tool.

Why Task Load is Crucial for UX

Task load is an important metric to remember for interface design. Information-heavy tasks like onboarding need to keep the task load in mind, as an overwhelmed user might close the app or ignore valuable information because it was too much at once.

Information architecture, or how to organize information for ideal user comprehension, is another element that should reduce cognitive task load and make a more enjoyable user experience. 

How to Design for Task Load

Here are some tips to help your designs account for task load:

• Clean visual designs can be an excellent way to prevent the user from being overwhelmed.

• User experience designers should ensure their product provides the most relevant information at the most suitable time. Simple tasks are put first, and more complex tasks are introduced when users have understood the basics. This is called progressive disclosure.

• Task load is especially important for high-stress tasks or when a user might be distracted. It’s an excellent way to identify pain points and create a better overall user experience, even for less stressful tasks. Lower your task load threshold for these contexts to account for the extra stress.

• Usability tests can help identify when users might be overwhelmed.

• Drip-feed information instead of flooding the user with too many prompts. Break tasks into manageable steps, and don't ask too much from your user at one time.

• People can only process up to five to seven task items. This limitation also applies to choices presented to users. For example, surveys only include up to five options to choose from.

• Consider temporal demands or how long a task will take. Users might get distracted, interrupted, or give up if a task takes excessive time. It is good UX practice to shorten any task to as few manageable steps as possible.

Task load also applies to physical limitations as well. For most UI's, this is less relevant. For full-body interfaces like AR and VR, this becomes much more important.

• The TLX can help you evaluate whether a task is too physically demanding for most users, and whether a less strenuous interaction might be better. 

• Use simple physical interactions instead of complicated or strenuous ones. Use gaze, simple touch and proximity instead of complex or laborious body movements. Especially for repeated tasks, these will quickly tire your users and possibly injure them.

These tools and guidelines will allow users to enjoy your product or service more comfortably and use them more often with less effort.

Task Load vs Cognitive Load

While cognitive load is a common consideration in UX, it doesn’t account for physical demands. For interfaces like mobile and desktop, those might not be relevant. But, with the rise of AR and VR, which allow for full-body interactions, the TLX is a much more holistic approach.

This allows for a much more flexible perspective on user effort. Some VR apps might want a heavy physical but low mental effort for specific apps—for example, a VR exercise app.

How to Use the TLX

Let's consider the example of a VR exercise app. With the TLX, you can check each stage in the user's journey.

For the onboarding stage, try to keep mental demands as low as possible, but expect a higher mental demand as the user learns the app. You should consider a low temporal demand to keep onboarding short and a low physical demand.

Expect temporal and physical demands to skyrocket for an entire exercise routine and lower mental demands to compensate. A high physical demand is necessary at this stage, but be aware of overexertion. Workouts take time, but it might behoove you to be sensitive to the user's time limits and keep temporal demands in a specific range. Mental demands should be shallow, so ensure instructions are clear. Your users should not do algebra and jumping jacks at the same time (although that would be impressive).

After the workout, keep physical demands low so the user can rest, temporal demands low to move on with their day, and mental demands about average. The user might want to check or share their performance. Make it easy to understand and do without (metaphorically) jumping through hoops.

Beyond Digital

The TLX is a comprehensive rubric that isn't limited to only digital products. It was originally designed for physical processes and is still an invaluable tool for UX in the physical world.

Process engineers, teachers, and, of course, astronauts can use the TLX for a variety of tasks. For example, a product designer might use the TLX to test how the washing machine they are designing performs during usability tests. A fishing vessel might want to test the effort of operating its sonar system in case there is a storm.

The TLX has endless uses and a flexible approach to UX of all types, which makes it an invaluable tool for designers everywhere.

Learn More About Task Load

Take our course on UX Design for Augmented Reality.

See the original TLX from the NASA Task Load Index.

Read the Nielsen Norman article on how to Minimize Cognitive Load to Maximize Usability.