Psychology Breakthroughs Worth Knowing: The Magical Number Seven
Undergraduate psychology majors and students in general will benefit from understanding the groundbreaking concept driving George Miller’s classic essay, The Magical Number Seven, Plus or Minus Two: Some Limits on our Capacity for Processing Information.
Published in 1956, Miller’s theory was the first to articulate that the average human’s working memory could only contain seven objects (plus or minus two). In the article, Miller focuses on two primary cognitive limitations: absolute judgment and memory span, although he also provides a few other interesting insights.
Miller starts from the proposition that the more variance that is observed, the more information will be gained. He explains that when there is great variance in a distribution, it is hard to predict what will happen next, and so, in that sense, the observer is ignorant; however, this ignorance provides the opportunity for gaining more information, simply by further observation. On the other hand, when the variance is small (so everything observed is similar to each other), it is easy to predict what will happen; in this situation, very little information is gained by further observation.
When perceptions are compared, they typically result in one of two judgments: comparative or absolute. Comparative judgments happen when two stimuli are perceived at the same time; one stimulus is called the standard (the level to measure the stimulus against) and the other is called the comparison. And, as the names suggest, the stimuli are compared to each other.
With absolute judgments, only one stimulus is perceived and the standard only exists in the observer’s memory. With this type, the observer compares the remembered standard to the comparison stimulus directly perceived.
For example, when asked which of two directly perceived lights is brighter, the observer will make a comparative judgment. When asked if the directly perceived light is brighter than a light previously, but no longer, seen, the observer makes an absolute judgment.
Miller notes that there are limits to the amount of information a person can perceive and still make correct judgments. Known as the channel capacity of the observer, Miller defines this as the â€œgreatest amount of information that he can give us about the stimulus on the basis of an absolute judgment.â€
Absolute Judgments of Uni-Dimensional Stimuli
Relying on a study that assigned numbers to tones, Miller found that when only two or three tones were used, the listeners’ responses were nearly always correct, but when more than six tones were used, there were more mistakes – making six the channel capacity. Miller looked at other experiments using loudness, taste and visual stimuli and found that the channel capacity for each was five, four and seven, respectively.
Absolute Judgments of Multidimensional Stimuli
Miller found that the more dimensions a stimuli has (up to a point), the easier it is to make absolute judgments about it. He noted that as opposed to only correctly identifying about 7 positions of a point on a line, people could identify 24 distinct positions in a square. Rather than making the determination more difficult, the additional information improved accuracy and increased channel capacity.
In this short section, Miller addressed attention span. He found that, visually at least, when there were less than seven objects observed, the test subject was actually counting and remembering (or subtizing), but over that, the subject was merely estimating.
The Span of Immediate Memory
Miller concludes that the span of absolute judgment of a one dimensional stimulus as â€œsomewhere in the neighborhood of seven.â€ He argues that humans get around this limit in three ways: (1) by making relative judgments; (2) by increasing the number of stimuli (as discussed above); and (3) by rearranging the problem so that instead of making a single absolute judgment with a high magnitude, they make a sequence of absolute judgments, each with a smaller magnitude.
Focusing on the third option, Miller characterizes memory as â€œthe handmaiden of discrimination.â€ He notes that the span of immediate memory is about seven items, mirroring that of absolute judgment. He warns, though, to not read too much into this coincidence. Miller explains that absolute judgment is limited by a total amount of information (what he refers to as bits, as in computer processing) and immediate memory is limited by a number of items (what Miller calls chunks), where each chunk may hold a lot more information than a few bits.
Miller notes that immediate memory may be increased simply storing even more information into each chunk, in a process he refers to as recoding.
Shortly after publication of the article, Miller helped establish the psychological field of cognitive studies. With this new focus on the science of the mind, Miller is credited â€œmore than anyone elseâ€ with changing psychological inquiry from intangible, untestable theories of behavior to verifiable, experiment-based theories based upon the scientific method.
As a direct result of Miller’s â€œmagic 7 + 2,â€ many educators adopted this theory as fact, and since then have based their curriculum and expectations on this limit. Various psychologists have warned against this, despite the fact that the article remains one of the most cited in modern psychology. Using other experiments, and limiting or adding stimuli in varying ways, these professionals have found that the channel capacity and span of memory of individuals to be either higher or lower. Today, consensus remains hard to come by, but many seem to be settling upon four chunks being the limit, rather than seven.