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Working memory: the magic number 7 or is it 4?

June 28, 2010

I am always haunted by the limits of my memory…its limitations have been made even more apparent as I struggle with some of the working memory exercises in the Posit Science programs. However in everyday life I can easily remember to buy bread, milk, and masses of other things I need provided I have made (or built) a list in preparation for shopping. I don’t need to take the list into the shop (it may get left in the car), but I find I can recall the piece of paper, and most of the items. Likewise if I am going to several locations in the car, I can plan the quickest route, list the associated items to be picked up, memorize the sequence of spatial locations, and envision a route formed from the locations. Easy. I can handle many items in memory with a bit of central planning….and a little updating as I get into the car. (Presumably my items/locations are considerably rehearsed and are also richly associated with other things in memory which aids recall).

Working memory limitations: it lasts less than a minute

But working memory is different. My earlier post “The Magical Number Seven Bottleneck” described past and current thinking about the limitations of working memory: it lasts less than a minute, and has clear capacity limits, depending on the information. George Miller (1956) demonstrated that one can repeat back a list of no more than around 7 randomly ordered, meaningful items or chunks (which could be letters, digits, or words). During the Posit Science exercise such as “Listen and Do” I struggled to keep track of 3 or 4 items (sometimes only one or two) and made little progress even after long training. Some other people that I spoke to however were able to improve their memory capacity with training, but not often beyond 5 items. All felt fatalistic about their lack of improvement however hard they tried, not realising that they were really performing at their best given the accepted limited capacity of human working memory.

Doing arithmetic

We use working memory in arithmetic when we carrying a digit from the ones to the tens column while remembering the numbers. When talking to people you might have to hold in mind concurrently the main topic of the conversation, the point made by someone, and a fact and an opinion that you are introducing. Only when all of these elements have been integrated into a single chunk can you successfully continue the conversation. Forgetting one of these things may lead to losing track……eh, what were we talking about?

Like many of our abilities, working memory normally declines precipitously with age, beginning early in adulthood and affects our ability to remember simple things like lists, names and the specific details of events in our everyday life. I have tried some of the working memory games available on the internet that provide columns of paired word lists to learn (a hateful task). I can’t get near the expected 7 plus or minus 2.  The N-back task shows some promise in terms of increasing working memory. The Farmer’s Challenge is another version of it.

New research: 3 to 5 items in working memory capacity

Recently, research has yielded different results. I was glad to discover that young adults can recall only 3 to 5 chunks in memory from a presented word list and only 3 or 4 longer verbal chunks, such as idioms or short sentences.

“with similar results across many types of materials and tasks, we believe there truly is a central working memory faculty limited to 3-5 chunks in adults, which can predict mistakes in thinking and reasoning (Halford, Cowan, & Andrews, 2007).

The difference in the research findings seems to be that the young adults were prevented from rehearsing the words by being given some distraction. Perhaps my low working memory capacity is really a distraction problem…..actually that feels right, as I find I get easily distracted….other things slip into my mind as I carry out tasks of all kinds.  I may be filling working memory with distractions (say, what one is planning to do) when I should be remembering what I am doing…. I am attending to other things irrelevant to the task in hand and storage capacity gets filled up.

The attention mechanism must need attention.

Anyway a 3-5 item working memory capacity feels much better to a low-span individual like me….

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