Partial recall

How easy do you find it to remember your bank account number? Have you ever forgotten someone’s phone number given to you verbally almost immediately? Or have you ever been in a conversation and been formulating a devastatingly witty contribution then lost the thread of what was being said completely? None of these are signs of mental deterioration; they are part of the natural function of memory. For half a century it has been thought that there is a “magic” number of memory chunks that your brain can handle at one time but now that magic number has been revised and it has been revised down.

In 1956 psychologist George Miller published a paper in the journal The Psychological Review titled “The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information”. The title itself was enough to grab attention and the paper’s central idea that we can only hold a maximum of seven chunks in our “working memory” had a magic in itself and caught on. In recent times though this magic number of “seven” has been questioned and in a new paper Gordon Parker, Professor of Psychiatry at the University of New South Wales, has reported that the human brain can cope with “four” chunks of information rather than “seven”.

Parker’s paper is confirming evidence that has been around for quite a while suggesting that Miller’s original magic number “seven” was an over-estimate. All of this relates not to long-term but to “working memory”. If long-term memory is like library of books, working memory is a whiteboard on which your brain can rapidly record and then erase information. The whiteboard provides continuity from one thought to the next and is a place for quick and rough calculations. It turns the spoken words that make up a telephone number into chunks of digits that can then be written down or used. Working memory helps you carry on conversations and copy moves in a yoga class. Yet it appears to have a limit of between three to five chunks at a time and the reason for this may lie in how how your brain works at a neural level.

If you want to recall a sentence like, “The meerkat tap-danced in the white wine sauce”, each word is represented by the firing of a cluster of neurons. Each cluster must fire in sequence but to avoid remembering each word at the same time the firing of one cluster must suppress the firing of the other clusters. The problem is that the energy required to suppress the firing of other neuron clusters increases exponentially with each added word. Remembering seven items requires about 15 times the suppression needed to recall three. Ten items requires 50 times the suppression needed for three and 20 items would require suppression hundreds of times stronger. This is why the magic number for working memory is now generally agreed to be between three and five chunks, and that makes “four” the new magic number.

Now you have an explanation for those embarrassing conversational lapses. In a conversation you have to hold in mind concurrently the main topic of the conversation, the point or points made by others, and whatever you want to say. When this involves more than four or five chunks of information you are likely to lose track and then…um, what was I saying?

Anyway, next time you do have a conversational phase-out there’s no need to feel bad: it’s a common and natural enough event. Simply explain to your conversational partners, “Sorry man, I chunked out there.”