Cognitive Load Theory [1] breaks down our mental processes as storing schemata (information) in long-term memory. As of now, this is thought to be unlimited as its been difficult to disprove. Short-term memory, or working memory, involves retreival of information from long-term memory. Faster retreival is what we'd consider expertise. While long-term memory is used for the storage of knowledge, the actual information processing during problem-solving takes place in short-term.
Unlike long-term memory, working memory has a limited capacity and duration. This limits the number of schema (information) that can be managed at one time. CLT was originally designed to describe the interconnected-ness of worked examples when it comes to learning. Visual elements should have context, otherwise you are imposing more things for the mind to process (for example, an unnecessary puppy on a PowerPoint would require the mind to process its a puppy, determine it is not relevant to the information, and continue to ignore it). Long-term is uneffected by this process, but the stress imposed in working memory requires effort to maintain.
To answer the question of "What are the sources and/or studies that justify this claim?" - that's what modern Psychology is trying to figure out.
Unlike long-term memory, working memory has a limited capacity and duration. This limits the number of schema (information) that can be managed at one time. CLT was originally designed to describe the interconnected-ness of worked examples when it comes to learning. Visual elements should have context, otherwise you are imposing more things for the mind to process (for example, an unnecessary puppy on a PowerPoint would require the mind to process its a puppy, determine it is not relevant to the information, and continue to ignore it). Long-term is uneffected by this process, but the stress imposed in working memory requires effort to maintain.
To answer the question of "What are the sources and/or studies that justify this claim?" - that's what modern Psychology is trying to figure out.
[1] https://scholar.google.com/scholar?hl=en&as_sdt=0%2C34&q=cog...