7.2 Short Term Memory
Short Term Memory: Atkinson-Shiffrin Model
Overview of Short Term Memory
Short-term memory (STM) is a vital component of the Atkinson-Shiffrin model.
Analogy of STM as a bucket of water: holds information longer than the rapidly draining pool of sensory memory.
Duration of STM is typically short, generally less than a minute for most types of information.
The capacity of STM is significantly smaller than sensory memory.
Only capable of holding approximately one bucket's worth of information.
Capacity of Short Term Memory
Commonly referred to as the "magic number" of seven plus or minus two.
This indicates that the typical capacity of short-term memory is between 5 to 9 items of information.
Digit Span Task: A Method for Testing Memory Capacity
Involves reading a sequence of numbers aloud to subjects.
Subjects repeat the numbers back.
Example sequence: 7, 4, 9.
Initially easy tasks involve fewer digits; difficulty increases with more digits (4, 5, 6, 7).
Typical struggles observed around the count of seven digits, indicative of STM capacity.
Enhancing Short Term Memory
Capacity can be improved through techniques such as chunking.
Chunking is the process of organizing individual units of information into larger, more meaningful chunks.
Example of letters:
Random list (e.g., H, J, X, A, N, T) holds little meaning, hard to remember more than 7.
Recognizable patterns such as CBC, HBO, ABC allow for chunking into 3-letter units, significantly increasing effective capacity.
Using chunking allows subjects to remember up to 7 chunks, where each chunk represents multiple letters.
Research Example: Ericsson et al. Experiment
An experiment conducted by Ericsson et al. demonstrated the effectiveness of chunking.
Subject: A marathon runner with average short-term memory capacity (initially around 7 plus or minus 2).
Trained using a digit span task incorporated with his hobby of running as a mnemonic device.
Instead of memorizing numbers like 3, 4, 9, 2, he recalled these as a running time (3 hours, 49 minutes, 2 seconds).
Practiced for several months, resulting in a substantial increase:
Ability to remember sequences of approximately 80 numbers by creating meaningful connections through chunking.
Demonstrates growth from average STM capacity to significant improvement when relevance is found in the information.
Graph of Results: Digit span performance over practice sessions illustrated substantial improvement as a function of time.
Limitations of Short Term Memory
If the task involves unchunked letters (e.g., a random sequence), the memory capacity falls back to the typical 7 plus or minus 2 limit.
Duration of Short Term Memory
Duration of STM is also fairly limited.
Can be extended through mental rehearsal (actively refreshing memory).
Example: Repeating "platypus" internally to maintain access to that information.
Brown-Peterson Task: Testing Decay of STM
Examines the effects of preventing rehearsal on memory accuracy:
Method: Participants asked to remember a trigram (e.g., letters B, K, G).
Immediately instructed to count backwards by threes (e.g., 3, 6, 9) to prevent rehearsal of the trigram.
Results showed rapid decay of information as time increases without rehearsal:
Accuracy of recalling B, K, G significantly decreased with the length of the counting task.
Conclusion: Rehearsal is critical for retaining information in short-term memory and aids potential transfer to long-term memory for more stable access.
Implications
Understanding short-term memory and its limitations is essential for strategies in education, cognitive psychology, and improving learning techniques.
Effective chunking and rehearsal techniques can enhance memory capacity and retention in various practical applications such as studying, data management, and oral communication.