The «Magical Number Seven» describes the very limited capacity of human short-term memory. It is biologically determined and can hardly be increased by training. Most people are able to remember about 7 units of information for a short time after seeing or hearing it. A short-term memory that could hold 8 items would be above average. For people with cognitive disabilities, short-term memory is particularly impaired - they can rarely remember more than 4 objects.
Origin
This finding became popular through the work of psychologist George A. Miller, who published his research in 1956 in the widely cited article «The Magical Number Seven: Limits on Our Capacity for Processing Information». This publication in «Psychological Review» is considered a milestone in cognitive psychology.
But in fact it was John Locke who discovered the so-called «Seven Phenomenon» more than 300 years ago when he examined the comprehension of adults. He found that when subjects were shown a large number of objects for a short period of time and then asked to remember them, they had a hit rate of almost 100% for up to 7 objects. For more than seven objects, the accuracy rate dropped abruptly.
Miller's studies were very thorough and showed in several experiments that this capacity limit occurs in all cognitive tasks and is almost always around 7 items. Miller wryly remarked that he was "haunted by the number seven". The number seven kept popping up in his data (sometimes a little more, sometimes a little less) as the limit.
The subjects heard different high-pitched tones and had to categorize them. Miller found that people could reliably distinguish only about seven different gradations on a one-dimensional scale – with more categories, the ability to discriminate decreased drastically.
Similarly, the so-called «Span of Attention», i.e. the number of objects that can be grasped simultaneously with a quick glance (this is also referred to as Subitizing, the spontaneous grasping of small quantities). Up to about 6-7 elements can be recognized immediately, larger numbers have to be counted or estimated.
It has also been shown that in terms of «Span of Immediate Memory», subjects can remember and immediately reproduce about 7 elements (e.g. numbers or letters in the correct order) without making any mistakes.
Miller's research shows that almost all subjects are able to recall 5 pieces of information that they have seen for a short time without errors. As the graphic shows, the memory performance drops relatively abruptly when more than 7 information units are presented.
Criticism
Critics point out that chunking and mnemonics enable people to retain significantly more information in the short term. This is true, but these improvements are almost always due to the use of long-term memory and memory aids, and not to an actual increase in the capacity of the short-term memory. In other words, we bypass the 7±2 limit by forming chunks, which demonstrates the importance of chunks for structuring information.
Furthermore, an absolute focus on the number 7 as a phenomenon is dubious. Miller already showed that the longer the chunks were, the lower the number of correct reproductions became. The 7±2 applies to single numbers or letters. The amount of recognized information is therefore dependent on the type and, above all, the length of the chunks. According to Baddeley's working memory model, the working memory is not limited by the number of chunks, but by the time span. All chunks that can be spoken in two seconds can be fully processed. In further research by Baddeley, it was shown that chunks that belong together can be remembered more easily. In the experiment, sentences of 15 words or more could be reproduced exactly. On the other hand, it was shown that a lower limit of 4 to 5 chunks is already occupied by simultaneous recording.
Application in UX and UI design
In particular, in connection with Hick's Law, according to which too many options slow down the decision-making process, it is clear that menus should never contain more than 6-8 entries per level. Thus, no grouping of information should consist of more than seven individual elements. This would be very important to keep in mind in the area of Chunking.
Larger groups should definitely be «chunked», i.e. structured into logical subgroups. See the two diagrams below.
This graphic shows how grouping individual pieces of information into meaningful chunks effectively extends the typical capacity limit of around 7 items – a key mechanism for storing more information in the short term.
The illustration shows that "related" elements should be grouped together and presented as a single unit. To support this, they should be visually separated and, if necessary, also visually distinct. According to Baddeley, the easier the information is to remember (distinctive features, recognizable patterns) the shorter the time needed to absorb it and the better the ability to reproduce it.
