How Much Information Can The Brain Hold? Test Your Memory


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The concept of the magic number seven, plus or minus two, has a long, revered place in the history of psychological research. It has been well known since the 19th century when a little observational experiment was done by Scottish philosopher, William Hamilton. Hamilton noted that whenever a handful of marbles were thrown onto the floor, the placement of only about seven of the marbles could be remembered without confusion. G.A. Miller, a Princeton University psychologist, wrote his famous paper, “The Magical Number Seven, Plus or Minus Two,” in 1956. For many years, this was the most cited non-statistical paper in psychology. Miller’s contention was precisely the same as Hamilton’s: most of us can hold in short-term memory approximately seven units of information.

This cognitive process is called digit span, or alternatively, sequential processing. It measures how many digits can be taken in through the eyes or ears and repeated in correct order. The test offers insight into attention span and organization of information. On its most fundamental level, it is a memory test, asking the performer to utilize a specific memory system in the brain that we call short-term memory. It is performed most simply in the form of a tester saying three to seven numbers at one-second intervals, and asking the applicant to repeat back the numbers.

As well as being a memory test, it is also an ordering technique. If we don’t remember the order of information, processing the information would be a cognitively chaotic experience. We might be able to remember all the numbers in a telephone number, for instance, but if we don’t know the order of the numbers, we won’t be able to reach the person we want to call.

Sequential processing takes place almost every time you attend to a new source of information. In fact, it happens right now as you are reading these lines. Think about the complexity of the task of reading. First you have to recognize the words (receiving the information); then, you have to hold each word in memory long enough to link one word to the next (holding the information); next, you have to ascribe meaning to the linked words (processing the information); finally, you use the meaning you have ascribed to the words to make a decision about how you want to use the information — do you want to use it to further the progression of civilization, or do you want to throw it in the garbage can — (utilizing the information)?

It is not mere coincidence that phone numbers have been seven digits since 1959, when AT&T changed over from place-name plus digits to all-digit dialing. So, instead of University 7-8634 (and yes, I am old enough to remember those days — that number was my Cousin Carol’s phone number), the number became 867-8634. When phone numbers included a word, they were easier to remember than they are now. (The newest addition of needing to dial area codes, even when you are calling a number within the same area code, is not an additional memory burden however; the three digits that comprise the area code are already familiar to us; they have been cycled into long-term memory storage, and their familiarity means that they are “chunked” not as three separate items, but as one item of information.)

Traditionally, researchers have thought that as the brain grows, from birth onward, the child can increase his digit span by one item per year. A one-year-old can repeat back one number; a two-year-old can repeat back two numbers; a five-year-old can repeat back five numbers. It has been thought that the ability to retain sequential items in short-term auditory memory ends at seven years of age; thus, prevailing intellectual wisdom (and Miller’s research) has been that most people can repeat back about seven sequential items — plus or minus two, referred to as “7 + or – 2”; yet, as in all things, some people do a little better, and some do a little worse — but the magic number seven is the average, and describes the ability of most of us.

Or does it? Perhaps in 1956, when George Miller wrote his paper, the average digit span memory was seven; but it is likely that average number is lower in today’s population. With external electronic devices replacing our internal memory systems, we are asking our brains to do less memory-work, and thus, it is likely that our brains have become less efficient or skilled at memory-work. Probably more of us function on the low end of the seven plus or minus two scale than the high end. In giving a number of people a digit span test, I have found that for many, memories are taxed in trying to repeat back seven full digits.

Since Miller’s publication, there has been a wealth of research on digit span, and the correlation of sequential processing ability with intelligence and over-all cognitive functioning. Digit span is taught and used as a standard diagnostic tool in all IQ testing as well as in comprehensive cognitive evaluations. It has been shown that digit span has a high correlation with IQ. A 1996 study compared digit spans and standardized test scores for grades K through 12, and showed that there is, on average, a 3.1 year grade-level-difference in achievement between an auditory digit span of five and an auditory digit span of six. (This would be enough, for example, to bring seventh-grade work up to tenth-grade level.)

It is fair to say that any individual with an auditory or visual digit span under seven digits is functioning with a handicap. Low auditory and visual sequential processing ability is a major contributing factor in almost all learning disabilities.

You can assess your own sequencing ability by simply having someone say a random assortment of numbers to you, one digit a second. Then you repeat the numbers. Start with four digits, and with each success, build up to the next level. When you top off at whatever number you achieve, then continue with the experiment, but now repeat the digits fed to you backwards. It’s much harder, but challenges your brain to not just remember, but to actually manipulate items in short-term memory, to re-position them.

In my next blog, you will read how one man, Bob Doman (Director of the National Association for Child Development), has made a game-change for sequential processing by challenging one major assumption that all researchers and clinicians had previously made — that the digit span capability of an individual is a fixed ability (like over-all IQ).

Until Doman, psychologists assumed that digit span capability — once it topped off at the level achieved around age seven — would not vary from year to year, or even from circumstance to circumstance. Yet, Doman has demonstrated with tens of thousands of people that digit span capability can be improved, and when it is, global changes in functioning are witnessed.