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Working Memory

Whatever information is held in attention at a given moment is said to be in working memory. That is the information you are thinking about at any given moment.

Working memory is also called primary memory and short-term memory. It is also more or less the same thing people call attention.

What is working memory? What are its two components?

Brain scans show that working memory involves at least two components: short-term storage that lasts only for a few seconds, and longer-term "executive processes that operate on the contents of storage" (Smith & Jonides, 1999).

Zelinsky & Murphy (2000) describe the short-term process as a visual scratchpad which briefly preserves the visual appearance of a scene. The longer-term process, they concluded, is a verbal storage system used when people rehearse or repeat something to them­selves again and again to remember it.

Rehearsal

Rehearsal is an example of an executive process in working memory. It is con­sciously controlled allocation of infor­mation processing resources. It must be learned; little children do not do it without training.

When people try to remember an unfam­iliar telephone number, they typically repeat the number to themselves. This is what memory researchers call rehearsal.

Several forms of evidence indicate that silent language rehearsal is much like re-hearing something. For one thing, silent rehearsal takes the same time as spoken speech (Landauer, 1962).

Also, errors made during language rehearsal involve confusions between similar sounds as would happen with spoken speech. A subject might remember the nonsense syllable "DNW" as "TNW" because "D" and "T" both contain the "ee" sound.

Sound-based errors presumably occur during rehearsal because the auditory image starts to fade. People grasp at the fading image and make an error when reconstructing it. Errors based on similar sounds are called acoustic confusions.

What is evidence that rehearsal is like an internal voice? What are acoustic confusions?

A student provides this example:

Recently, I experienced an acoustic confusion. A friend of mine called and asked if I would like to come over. He gave me his room number, which was North 205, and I kept rehearsing it over and over in my head.

By the time I reached Dorman Hall, I was saying North 209. I went to room 209, knocked on the door, and went in. I asked where Jeff was, and they said he was not in that room; he was in 205.

I was really embarrassed, but when we studied about acoustic confusions during rehearsal I realized what I had done. [Author's files]

The student's example shows an acous­tical error because 5 and 9 share the hard "I" sound. Perhaps the student was distracted while rehearsing the number 205, grasped at the fading sound, and reconstructed the number as 209, all in a split second.

The Magical Number Seven plus or minus Two

One of the best-documented character­istics of working memory is its limited capacity. The short-term storage process of working memory can hold only about seven items at a time.

To deal with more information than that, the information must be organized into larger chunks. For example, words can be combined into sentences; then more than seven words can be held in working memory.

Psychologist George Miller pointed out the limitation of working memory in a classic 1956 article, "The magical number seven, plus or minus two: Some limits on our capacity for processing information."

As you can see from date, this journal article was published in the early days of the encoding revolution. In fact, some people say this article started the whole idea of using computer concepts like information processing to understand human memory.

What is a chunk?

The magic number seven is the number of chunks of information a person can hold in working memory at the same time. A chunk is a unit of some kind. It could be a letter, a word, or a short sentence.

Miller examined short-term memory tasks and found that typical subjects could hold about 7 chunks in memory at once. This was true whether they were holding 7 letters in memory at once, 7 numbers at once, or 7 words at once. Miller wrote in a humorous tone that he was being "persecuted by an integer" (the number 7) in these studies.

Old-time psychologists, before the encoding revolution, probably would have assumed that fewer words could be held in memory than letters. After all, each word contains many letters.

But this was not the case. Miller's big discovery was that an organized whole (a chunk) functions as one item in primary memory.

What was Miller's "big discovery?"

Miller realized the profound implications of this simple insight. If items can be grouped and treated as chunks in memory, then the capacity of memory can be increased by organizing and grouping things.

To demonstrate this to yourself, try holding the following sequence of numbers in memory, all at once.

7 4 1 4 9 2 1 9 4 5

If you interpret this as a string of ten separate numbers, it exceeds the capacity of working memory. Few people can hold ten items at the same time in primary memory.

However, if you interpret the string of ten digits as two meaningful dates following two digits, then there are only four chunks, and you easily hold the string of 10 digits in working memory.

How can you reduce the string of 10 numbers to 4 chunks?

Chunking points to the importance of organization in overcoming the limits of memory. If short term, working memory is limited to about 7 chunks, the only way to improve its capacity is to organize larger chunks.

This turns out to be a common theme in memory research. Memory is improved by organizing small pieces into larger wholes.

In his original article, Miller des­cribed a 1954 experiment by psychologist Sidney Smith. Smith memorized sets of four binary digits.

Those are numbers expressed in base 2, all ones and zeros, such as (0 0 1 0). Each four-number set of binary numbers is equivalent to one decimal digit (0 0 1 0 equals the number 2).

This meant that a string of 16 binary numbers could be converted into 4 decimal numbers. Once Smith learned to make the 4-to-1 conversion easily and auto­matically, his memory span for binary digits increased from 10 to about 40.

In other words, he could memorize 10 decimal numbers in a row. Then he would convert them back into 0's and 1's to reconstruct a list of 40 binary digits.

How did Smith quadruple his memory capacity?

Ericsson, Chase and Faloon (1980) decided to see how far this "recoding" idea could be pushed. They had an undergraduate student memorize random strings of decimal digits an hour a day, 3 to 5 days a week, for more than a year and a half, paying him for his effort.

At the end of this period his mem­ory span had increased from 7 to 79 digits. In other words, he could repeat back a string of 79 random digits immediately after hearing it without any error.

His long-term memory for the digits also im­proved. By the end of the experi­ment, he often remembered many sequences from previous days.

The subject was not instructed in any particular coding scheme; he invented his own. Being a runner, he found it easiest to translate number sequences into running times.

The number 3492 was recoded as "3 minutes and 49 point 2 seconds, near world-record mile time." Later this was supple­mented with ages; e.g. 893 became 89 point 3, very old man. (Ericsson, Chase & Faloon, 1980).

How did an undergraduate use recoding to improve his memory for digits, in an experiment lasting more than a year?

This might remind you of example from Miller, Galanter, and Pribram described earlier. I assume it was fictitious (they did not refer to an actual published study) but it was realistic.

What sort of "burden" seems to improve, rather than harm, memory?

A subject memorized "BOF" and "MIB" by composing a sentence about a man named BOF who was in "false misery" (MIB). Human memory works better, not worse, when a person adds elaborate encoding schemes, as long as the organization aids memory retrieval.

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References:

Ericsson, K. A., Chase, W. G., & Faloon, S. (1980). Acquisition of a memory skill. Science, 208, 1181-1182.

Landauer, T. K. (1962) Rate of implicit speech. Perceptual & Motor Skills, 15, 646.

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

Smith, E. E., & Jonides, J. (1999). Storage and executive processes in the frontal lobes. Science, 283, 1657-1661.

Zelinsky, G. J., & Murphy, G. L. (2000). Synchronizing visual and language processing: An effect of object name length on eye movements. Psychological Science, 11, 125-131.


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