05 January, 2009

Magic Number Seven

The Magical Number Seven, Plus or Minus Two

"The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information" is a 1956 paper by the cognitive psychologist George A. Miller.

concept goes beyond numbers. For example, most of us can remember about seven recently learned chunks of similarly classified data. Keep this in mind when you are presenting information to other people.

The chunking principle requires you to classify the items into groups to reduce the information overload.

BenefitsBy chunking information the author improves the reader's comprehension and ability to access and retrieve the information.

Miller showed a number of remarkable coincidences between the channel capacity of a number of human cognitive and perceptual tasks.

In each case, the effective channel capacity is equivalent to between 5 and 9 equally-weighted error-less choices: on average, about 2.5 bits of information.

Miller hypothesized that these may all be due to some common but unknown underlying mechanism.

He noticed that the memory span of young adults was around seven elements, called chunks, regardless whether the elements were digits, letters, words, or other units.

Later research revealed that span does depend on the category of chunks used (e.g., span is around seven for digits, around six for letters, and around 5 for words), and even on features of the chunks within a category.

In general, memory span for verbal contents (digits, letters, words, etc.) strongly depends on the time it takes to speak the contents aloud, and on the lexical status of the contents (i.e., whether the contents are words known to the person or not).

Several other factors also affect a person's measured span, and therefore it is difficult to pin down the capacity of short-term or working memory to a number of chunks.

Nonetheless, N. Cowan has proposed that working memory has a capacity of about four chunks in young adults (and less in children and old adults).

A variety of studies could be summarized by saying that short term memory had a capacity of about "seven plus-or-minus two" chunks.

Miller wrote that "With binary items the span is about nine and, although it drops to about five with monosyllabic English words, the difference is far less than the hypothesis of constant information would require.

The span of immediate memory seems to be almost independent of the number of bits per chunk, at least over the range that has been examined to date."

Miller acknowledged that "we are not very definite about what constitutes a chunk of information."

Miller noted that according to this theory, it should be possible to effectively increase short-term memory for low-information-content items by mentally recoding them into a smaller number of high-information-content items.

"A man just beginning to learn radio-telegraphic code hears each dit and dah as a separate chunk. Soon he is able to organize these sounds into letters and then he can deal with the letters as chunks.

Then the letters organize themselves as words, which are still larger chunks, and he begins to hear whole phrases."

Thus, a telegrapher can effectively "remember" several dozen dits and dahs as a single phrase.

Naive subjects can only remember about nine binary items, but Miller reports a 1954 experiment in which people were trained to listen to a string of binary digits and (in one case) mentally group them into groups of five, recode each group into a name (e.g "twenty-one" for 10101), and remember the names.

With sufficient drill, people found it possible to remember as many as forty binary digits. Miller wrote:

"It is a little dramatic to watch a person get 40 binary digits in a row and then repeat them back without error. However, if you think of this merely as a mnemonic trick for extending the memory span, you will miss the more important point that is implicit in nearly all such mnemonic devices. The point is that recoding is an extremely powerful weapon for increasing the amount of information that we can deal with".

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Please visit the above Wikipedia pages to gain more comprehensive understanding.

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