When I was studying cognitive science, one thing that came up several times was the capacity of our working memory. If you are unfamiliar with the term, it goes like this. You have two major memory systems in your head, one is long term memory which stores all of the things you recall about your childhood, your family and friends, where you live and so on. Basically all you remember can be found there. Then there is the working memory that functions like a work bench. When you are reading these words, working memory helps you remember the meaning of the words, putting them together into coherent sentences. You will probably not remember every word when you are done reading, but if I have managed to keep your attention, you will remember the general message. Which is about the capacity of working memory and how to apply it to UX.
Just like a work bench, working memory can’t hold an unlimited amount of information. If you look through a text book on memory, you will most likely see the formula “seven plus minus two” jumping out at you, it is almost like a mantra. What it means is that the average human brain can hold somewhere between 5 to 9 pieces of information in his or her brain at any given moment. Smack in the middle of 5 and 9 are 7, hence “seven plus minus two”.
Now, for some reason the 7+/- 2 rule have been adopted into user experience and interaction design as an explanation as to why a menu should not have more than seven items in it. I do put my pride in making it easy for the user, but this is a red herring. First of all, the 7 +/- 2 rule was not based on research when it first appeared in a paper written by George A. Miller. (Actually it first appeared in a speech were he speculated about this capacity being about seven items and then he wrote a paper on that speculation.) Despite this fact, the 7 +/- 2 rule caught on and has been thriving ever since. Turns out that when Alan Baddeley did some research, working memory holds only about four items as long as they are not too complex.
Secondly those four items regard things and concepts that we have to keep track of, not elements that are visible right in front of us. Now, I’m not saying that working memory is irrelevant in UX and interaction design, I’m saying that menus is not where it’s best applied. When going through a menu, the user have all the options readily available on the screen and research backs up that broad and shallow menus are easier to scan and work with than narrow and deep ones. Working memory is about what people carry in their head – in a user’s case it could be an item he or she is searching for, and keeping track of where they have already looked. With this in mind, it makes more sense to refer to working memory capacity, four items or otherwise, in links visited. On an e-commerce site it might also make sense to offer easy access to the items in the shopping cart for users to keep track of what they’ve already added. In UX it’s simply polite to minimize the cognitive workload.
Don’t be afraid to question authority, and try to keep yourself updated on the research that have been published.
As a bonus, here’s a site with more UX myths I found when doing research for this post.