Here's a good read with practical tips for VR designers. Adrienne Hunter of Tomorrow Today Labs just posted "Reducing Cognitive Load in VR: 6 Ways to Improve your VR UX."
Cognitive load has to do with how much information you are trying to hold inside of your working memory at any given time. Information is filtered in working memory as a transient step before being encoded in short-term or long-term memory (or forgotten).
We're really just talking about attention. People have a finite capacity to pay attention, which is why it's difficult to manage two complicated tasks at once, such as texting and driving. The more attention that you are paying, the more that your working memory is being used. That makes it harder to learn or to solve puzzles. But, it also has substantial effects on decision-making. Here's a few ways that people made decisions differently when they were under high cognitive load and had to divide their attention:
- Time is judged as moving more quickly
- Performance on physical tasks worsens, specifically spatial search
- Increased acceptance of product feature trade-offs
Only ask your users to do one thing at a time. Setting them up to do a sequence a tasks is preferred to having them do anything simultaneously.