The Number Seven Plus or Minus Two

Miller starts his paper by catching our attention stating that there is a number that has been following him around and that is the number seven, plus or minus two. He then goes on to explain that when you are dealing with a communication system there is the input and the output. The amount of information is called the “variance”, and the amount of transmitted information is called the “correlation”. As with any communication system there is a limit to the amount of information that can be put through with accuracy; this limit is called the “channel capacity”. He then defines a “bit” of information which can be understood as the amount of binary decisions that have to be made to achieve the possible outcomes. For example, if there are four possible outcomes, then it would take two bits (two binary decisions) to be made in that process.

The type of communication system that he talks about in his paper is that of the human being. When someone is asked to make absolute judgments about a one-dimensional stimuli, he finds that over many experiments, there is about seven, plus or minus two distinguishes that can be made. Some examples that he gave to illustrate his point were studies that involved someone being asked to distinguish between different pitches, different loudnesses, different tastes, different visual positionings, and even different points of touch on the human body.

He goes on to show that in the real-word we can distinguish between many different peoples faces, and the thousands of words found in the English language. This is why he was careful to explain that the first experiments were only dealing with one-dimensional stimuli. When dealing with mulit-dimensional stimuli, he found that our ability to distinguish goes up. There was only one study that had been done to show this and that was a study that included different pitches,