What is Cognitive Load?
Cognitive load is the demand a task places on working memory, which can hold only a few items at once. John Sweller's cognitive load theory argues that learning fails when this limited capacity is consumed by unnecessary processing, so instruction and study should minimize distraction and build knowledge in manageable steps.
Sweller introduced the theory from studies of problem solving, showing that the search strategies novices use can consume so much working memory that little capacity remains for learning the underlying pattern. What separates experts is not larger working memory but rich knowledge structures, called schemas, stored in long-term memory, which let them treat whole configurations as single items.
Later versions of the theory distinguish load that is inherent to the material, which depends on how many interacting elements must be held in mind at once, from load added by poor presentation, such as split diagrams, redundant text, or surrounding clutter. The design goal is to spend scarce capacity on the structure of the ideas, not on the packaging.
For readers, the theory explains why difficult material demands different tactics: shorter passes, notes that externalize intermediate steps, and summaries in your own words that compress detail into chunks. Highlighting can serve the same function when it is selective, marking the load-bearing sentences so a later pass can skip the rest.