Experts have more procedural knowledge, then laymen. When asked to solve problems, experts retrieve knowledge from long term memory to "long term working memory". Then they have to integrate current information to the working memory to result a solution. Laymen need to load both current information and procedural knowledge into the working memory, thus resulting higher load on the working memory. This overload can be detected by the speed of the solution process, as well as the speed of finding the next step in the solution<ref>[http://www.anitacrawley.net/Articles/Kalyuga%20Measuring%20Knowledge%20to%20Optimize%20Cognitive%20Load%20Factors.pdf Measuring Knowledge to Optimize Cognitive Load Factors During Instruction.‏, S Kalyuga, J Sweller - Journal of educational psychology, 2004‏ - psycnet.apa.org‏]</ref>, and I think someone measured it by pupil dilation.