Once, there was a time that the phone company was the most powerful purveyor of information technology and research. The venerable Bell Labs employed thousands of people doing primary research, in exchange for their monopoly status as the only phone carrier.
In 1956 (a very good year, by the way), psychologist George Miller published a paper entitled The magical number seven, plus or minus two: Some limits on our capacity for processing information [1]. He had been tasked to empirically find how many random digits a person could remember at any time, so Ma Bell could figure out how many numbers to use for defining the concept of the telephone number. It turned out most people can only remember 5-9 things at any given time without resorting to tricks, such as chunking. This is sometimes referred to as working memory, and its contents are typically lost within 20 seconds without some sort of active rehearsal.
This fact alone has significance for people who create presentations, visualizations, instruction, and almost any kind of media. If people can only keep a limited amount of information at any given time, and you want them to follow what you’re showing, you have to manage which of those 7 items should be top of mind at any given time.
The research on memory and perception of information got a bit more nuanced as time went on. In 1988, John Sweller extended Miller’s observations and applied them to instruction. His Cognitive Load theory suggested that memory is comprised of 2 primary structures — short-term and long-term — both of which are controlled by a central executive, which is our explicit attention — an even more precious commodity of one. Long-term memory is where instruction goes, once it is actually learned by usage. In that sense, the aim of all instruction is to alter long-term memory, but information must pass through short-term memory first. [2]
Sweller viewed long-term memory as "sophisticated structures that permit us to perceive, think, and solve problems", rather than a group of rote-learned factoids. These structures are chunked into things called schemas, which organize a group of individual facts into a single element, taking up one of the precious 7 slots in short-term memory.
Richard Mayer’s later work in Multimedia Learning studied the effects of combining various forms of media and their effects on understanding. He proposed that we have 2 primary pathways for sensing information. This is called the Dual-Coding theory, actually an auditory path, which takes information from the ears, and a visual path, which takes information from the eyes.
The distinction gets fuzzy when reading is involved. Even though words are initially processed by the eyes, the internal mechanisms of the auditory path are used to make sense of the words. Coupled with the fact that we have a limited number of things we can focus on at any given time, care needs to be taken to keep from overloading a single pathway with too much information.
Having two pathways doubles the amount of information that is in play at any given time, but it can be tricky to connect the right kind of information to the right pathway in order to maximize the amount of communication. Written words complicate this even further because they involve both channels. This is why putting a lot of text in PowerPoint slides will dramatically compete with the spoken words for the audience’s attention. [3]
One of the primary goals of information communication of any kind is to present information in a comprehensible manner. Designers must respect the limitations and make use of people’s ability to accept information in order to reach that goal.