Memory Span
Introduction
In this activity, you will test your own short-term memory using a paradigm called the memory span. By examining your results, you will be able to evaluate claims by cognitive psychologists who argue that short-term memory can only hold a limited amount of information for a short period of time. This stands in contrast to sensory memory that you learned in previous activity can hold a relatively larger amount of information for a relatively shorter time. Before you investigate your own short-term memory, it is worthwhile noting the work of George Miller who in 1956 wrote about the magical number seven, plus or minus two, which is interpreted to mean that the number of “objects” an average person can hold in their short-term memory is 7 give or take two. After you complete the experiment and look at your own results, do you agree or disagree with this statement?
Description of Activity
Trials in this activity begin with the usual fixation “+”. Focus on it and then press the space bar when you are ready to begin. You will then see either a series of digits, letters, or words. At the end of the series presentation, you will see a matrix of boxes with individual digits, letters, or words within each box. Click on the boxes showing the items in the order you saw them. If you were shown “v, j, a, t”, then you would click the boxes “v, j, a, t” in that order. You are being asked to do a forward memory span in this activity, whereas a variation of this task that is sometimes used is to click the items in reverse order (e.g., “t, a, j, v”), which is called the backward memory span. When only containing trials with digits, this task is called the digit span. Try to remember as many of them as possible. Another important point about span tasks is that their presentation format may vary, and with it performance, depending on whether you see or hear the digits, letters, or words.
Short-Term Memory Capacity
The limit to the amount of information that you can hold online, be it in the visual, auditory, or even tactile domain, is sometimes referred to as your short-term memory capacity. Simple digit-span tasks are commonly used to test number storage capacity partially because performance is not affected by things like semantics, complexity, and frequency of everyday occurrence and therefore it is not surprising that digit-span performance is often included as a component of intelligence quotient (IQ) tests. However, performance on the digit span is also closely linked to language learning ability.
Short-Term & Long-Term Memory Interactions
The operational definition of memory span is the longest list of items (i.e., digits, letters, or words) that a person can repeat back in the correct order on 50% of trials beginning immediately after presentation. George Miller noted that memory span was about seven (plus or minus two) for young adults. That means the average range is from five to nine. In reviewing your results, did your performance differ on trials consisting of digits, letters, and words? If so, was your memory span on one type of item much better than another or better than the other two? Or was your span about the same across the three item types? Miller noticed surprisingly that span is about the same for stimuli with different amounts of information. Most item sets that include seven words contain in total among them more than seven letters. But span for words is about seven and span for letters is about seven. Why is this? Miller concluded that span is not counted in terms of basic units of information (i.e., a computer bit) but by what he called “chunks,” or units of knowledge. The word “authentic” does not take up nine total units of our memory span because we use our long-term memory that contains knowledge of the single word “authentic,” which we have encountered in many conversations and books we have read and only requires one unit, or chunk. We can also cleverly use knowledge from our long-term memory to break down letter strings like “CIAFBINSA” into “CIA,” “FBI,” and “NSA.” That is of course if we have knowledge about government agencies like the Central Intelligence Agency, the Federal Bureau of Investigation, and the National Security Agency. Chunking is a critical ability that draws on long-term memory (i.e., semantic knowledge) to fit more things into our memory span.