Channel Capacity

In ‘The Tipping Point’, author Malcolm Gladwell introduces the concept of Channel Capacity.

“There is a concept in cognitive psychology called the channel capacity, which refers to the amount of space in our brain for certain kinds of information.”

You’d be forgiven for thinking that “the amount of space in our brain for certain kinds of information” is a vague and noncommittal definition. In typical Gladwell style, he uses simple language to introduce an idea before employing more engaging storytelling techniques to expand upon it.

Before we get to that, however, I thought it may be useful to bring in another short definition. This time from Phil Barden, taken from his book Decoded.

“A classic finding in cognitive psychology is that the upper limit of our working memory (…) is 7 +/-2 chunks of information (e.g. numbers, letters, words or faces), which amounts to roughly 40-50 bits in the case of numbers or letters.”

So, Channel Capacity is a measure of the brain’s ability to process and store multiple pieces of new information.

If we’re told to remember the numbers 1 to 50 in order, we’ll succeed without trouble.

However, given a sequence of ten random numbers to remember and we’ll struggle.

The latter example takes up 10 independent “channels” in our working memory rather than 1.

And 10 is slightly above our upper limit.

Gladwell, doing what he does best, explains:

“Suppose, for example, that I played you a number of different musical tones, at random, and asked you to identify each one with a number. If I played you a really low tone, you would call it one, and if I played you a medium tone you would call it two, and a high tone you would call three. The purpose of the test is to find out how long you can continue to distinguish among different tones. Most people can divide tones into only about six different categories before they begin to make mistakes and start lumping different tones in the same category. This is a remarkably consistent finding. If, for example, I played you five very high pitched tones, you’d be able to tell them apart. And if I played you five very low pitched tones, you’d be able to tell them apart. You’d think, then, that if I combined those high and low tones and played them for you all at once, you’d be able to divide them into ten categories. But you won’t be able to. Chances are you’ll still be stuck at about six categories.

This natural limit shows up again and again in simple tests. If I make you drink twenty glasses of iced tea, each with a different amount of sugar in it, and ask you to sort them into categories according to sweetness, you’ll only be able to divide them into six or seven different categories before you begin to make mistakes. Or if I flash dots on a screen in front of you very quickly and ask you to count how many you see, you’d get the number right up to about seven dots, and then you’d need to guess. “There seems to be some limitation built into us either by learning or by the design of our nervous systems, a limit that keeps our channel capacities in this general range,” the psychologist George Miller concluded in his famous essay “The Magical Number Seven.” This is the reason that telephone numbers have seven digits. “Bell wanted a number to be as long as possible so they could have as large a capacity as possible, but not so long that people couldn’t remember it,” says Jonathan Cohen, a memory researcher at Princeton University. At eight or nine digits, the local telephone number would exceed the human channel capacity: there would be many more wrong numbers.”


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