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Unlock This CourseShort-term memory (STM) is like your brain's temporary workspace - it holds information for a brief period whilst you're actively using it. In Atkinson and Shiffrin's Multi-Store Model, STM acts as a crucial bridge between sensory memory and long-term memory. Think of it as your mental notepad where you jot down a phone number before dialling it, or hold mathematical calculations in your head whilst solving a problem.
Understanding STM is essential because it affects everything from following instructions to having conversations. When your STM is overloaded, you might forget what someone said at the beginning of a long sentence, or lose track of your place in a complex task.
Key Definitions:
Atkinson and Shiffrin proposed that memory consists of three separate stores: sensory memory, short-term memory and long-term memory. Information flows from one store to the next, with STM serving as the active processing centre where we consciously work with information.
One of the most famous discoveries in psychology is Miller's "Magic Number 7" - the idea that STM can hold approximately 7 (plus or minus 2) items at once. This means most people can remember between 5-9 pieces of information simultaneously.
George Miller conducted extensive research showing that STM has a limited capacity. He found that people could typically recall about 7 digits, 7 letters, or 7 words immediately after hearing them. This limitation applies regardless of whether the items are numbers, letters, or even concepts.
Most people can remember 7 random digits: 4-9-2-8-1-6-3. Try it yourself - look at these numbers, then look away and recall them!
Similarly, about 7 random letters can be held: K-M-R-P-L-D-F. The same principle applies across different types of information.
Interestingly, 7 words can also be remembered: cat, house, blue, run, happy, book, tree. This shows capacity is about items, not total information.
Miller discovered that we can increase STM capacity through "chunking" - grouping information into meaningful units. For example, the number sequence 1-9-9-4-2-0-0-1 is hard to remember as 8 separate digits, but easy as two chunks: "1994" and "2001" (both significant years). This is why phone numbers are often grouped: 020-7946-0958 rather than 02079460958.
Without rehearsal, information in STM fades quickly. The landmark research by Peterson and Peterson (1959) demonstrated that STM duration is surprisingly brief - much shorter than most people expect.
Lloyd and Margaret Peterson conducted a groundbreaking study to measure STM duration precisely. They presented participants with three-letter combinations (trigrams) like "KJR" or "BMX", then asked them to count backwards in threes to prevent rehearsal.
The Method:
The Results:
The rapid forgetting occurs because STM relies on active maintenance. Without rehearsal, the memory trace decays naturally. The counting task prevented participants from rehearsing the letters, revealing STM's true duration of approximately 15-30 seconds.
STM primarily uses acoustic encoding - storing information based on how it sounds rather than what it looks like or means. This was demonstrated through research on acoustic similarity effects.
Conrad showed participants sequences of letters and found that errors were more likely when letters sounded similar (like B, C, D, G, P, T, V) rather than when they looked similar. This suggested that STM stores information as "inner speech" - we hear the information in our heads.
When you try to remember a phone number, you likely repeat it to yourself using your "inner voice". This demonstrates acoustic encoding - you're storing the sounds of the numbers rather than their visual appearance. This is why similar-sounding numbers (like "two" and "too") are easily confused in STM.
Rehearsal is the key mechanism for maintaining information in STM and transferring it to long-term memory. There are two main types of rehearsal that serve different purposes.
Simply repeating information to keep it active in STM. Like repeating a phone number until you can dial it. This maintains information but doesn't necessarily transfer it to long-term memory.
Connecting new information to existing knowledge or finding meaning in it. This is more effective for creating lasting memories and transferring information to long-term storage.
The process of "inner speech" that helps maintain verbal information in STM. When you silently repeat information to yourself, you're using this system.
Understanding STM features has practical implications for education, technology design and everyday life. Here are some key applications:
Teachers can use knowledge of STM limitations to improve instruction. Breaking complex information into smaller chunks, allowing time for rehearsal and using meaningful connections all help students work within STM constraints.
Practical Strategies:
User interface designers apply STM research when creating menus, forms and navigation systems. Most effective menus contain 5-7 options and important information is repeated or highlighted to aid retention. Phone numbers are formatted in chunks and passwords often use memorable patterns.
Whilst Atkinson and Shiffrin's model has been influential, research has revealed several limitations in how it describes STM features.
The model suggests STM is a single, unified system, but research shows it's more complex. Working memory models propose multiple components that handle different types of information simultaneously.
Not everyone has the same STM capacity or duration. Factors like age, attention and expertise can significantly affect performance. Some people can remember 9 digits whilst others struggle with 5.
Factors Affecting STM:
Current research has expanded our understanding of STM beyond the original multi-store model. Working memory theory suggests that STM is more active and complex than originally thought.
Baddeley and Hitch proposed that STM consists of multiple components: a central executive that controls attention, a phonological loop for verbal information and a visuospatial sketchpad for visual information. This explains why you can remember a phone number whilst navigating - different STM systems handle different types of information.
Understanding STM features remains crucial for psychology students because it demonstrates how scientific research can reveal the limitations and capabilities of human cognition. The principles discovered by early researchers continue to influence education, technology and our understanding of memory disorders.