Clicks & Notes

05 April 2005

Working Memory and (So-Called) Magic Numbers

Spotted this quick news release via kottke (a while back now – this blog post has been sitting in my “Drafts” folder for a couple weeks):

EurekAlert! - How much can your mind keep track of?

  • new research has shown that, when someone is trying to solve a new problem or do an unfamiliar task, the number of individual variables that they can handle is relatively small; four variables are difficult, while five are nearly impossible
  • when problems are more familiar, people are able to break a larger number of variables into more manageable chunks, treating several variables as a single chunk

Which, of course reminded me of this (in)famous article:

The Psychological Review - The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information by George A. Miller (1956, vol. 63, pp. 81-97)

Everybody knows that there is a finite span of immediate memory and that for a lot of different kinds of test materials this span is about seven items in length. I have just shown you that there is a span of absolute judgment that can distinguish about seven categories and that there is a span of attention that will encompass about six objects at a glance.

Which has since been repudiated in its applicability to interface design:

Internetworking - Three Numbers That (Should) Have Nothing To Do With User Interface Design

(E)ven when it is cited correctly, Miller’s work is discussed as if the scientific understanding of short-term memory had not advanced at all in the last half century… More contemporary experiments show that an individual’s capacity for short-term remembering depends heavily on the nature of what is being remembered.

At best, Miller’s 7 ± 2 figure applies to immediate serial recall for a sequence of familiar, easy-to-pronounce, unrelated, verbal stimuli presented auditorily with no distracting sounds within earshot.

Net Return - Seven, plus or minus two. What’s the relevance for web design? (PDF, 90 kb)

  • it is information scent, and not a user’s ability to remember a list of items, that determines their success in using a navigation structure that presents a large number of links
  • information scent arises from wording used in labels and links that clearly conveys to the user what sort of information can be found if they click link

See also:

Also picking up on the news release from EurekAlert!:

beyond bullets - 7 x 20 = Overload

Many people justify 7 bullet points per slide by citing the George Miller article, but what’s always missing in the arithmetic is the total number of bullet points across all of the slides; e.g., 7 bullets per slide times 20 slides equals 140 bullet points.

In turn, beyond bullets links to these two items:

⇒ Filed under:  by jen @ 10:30 pm


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© Jennifer Vetterli, 2005