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Short-term memory is a component of memory that holds a small amount of information in an active, readily available state for a brief period, typically a few seconds to a minute. The duration of STM seems to be between 15 and 30 seconds, and STM’s capacity is limited, often thought to be about 7±2 items.
It’s often likened to the brain’s “working space,” enabling tasks like reasoning and language comprehension. Information not rehearsed or processed can quickly be forgotten.
Short-term memory has three key aspects:
- Limited capacity (only about 7 items can be stored at a time)
- Limited duration (storage is very fragile, and information can be lost with distraction or the passage of time)
- Encoding (primarily acoustic, even translating visual information into sounds).
Capacity: Magic Number 7
The capacity of short-term memory is limited. A classic theory proposed by George Miller (1956) suggests that the average number of objects an individual can hold in their short-term memory is about seven (plus or minus 2 items).
Miller thought that short-term memory could hold 7 (plus or minus 2 items) because it only had a certain number of “slots” to store items.
However, Miller didn’t specify how much information can be held in each slot. Indeed, if we can “chunk” information together, we can store much more information in our short-term memory.
Miller’s theory is supported by evidence from various studies, such as Jacobs (1887). He used the digit span test with every letter in the alphabet and numbers apart from “w” and “7” because they had two syllables.
He found out that people find it easier to recall numbers rather than letters. The average span for letters was 7.3, and for numbers, it was 9.3.
However, the nature of the items (e.g., simple versus complex) and individual differences can influence this capacity.
It’s also worth noting that techniques like chunking can help increase the effective capacity by grouping individual pieces of information into larger units.
Duration
Short-term memory typically holds information for about 15 to 30 seconds. However, the duration can be extended through rehearsal (repeating the information).
The duration of short-term memory seems to be between 15 and 30 seconds, according to Atkinson and Shiffrin (1971). Items can be kept in short-term memory by repeating them verbally (acoustic encoding), a process known as rehearsal.
Using a technique called the Brown-Peterson technique, which prevents the possibility of retrieval by having participants count backward in 3s.
Peterson and Peterson (1959) showed that the longer the delay, the less information is recalled. The rapid loss of information from memory when rehearsal is prevented indicates short-term memory having a limited duration.
If not rehearsed or encoded into long-term memory, the information in short-term memory is susceptible to interference and decay, causing it to be forgotten.
It’s important to note that short-term memory duration can vary among individuals and can be influenced by factors like attention, distraction, and the nature of the information.
Encoding
Encoding in short-term memory primarily involves a transient representation of information, usually based on the sensory attributes of the input. Here’s a breakdown of how encoding works for short-term memory:
- Acoustic Encoding: This is the most common form of encoding in short-term memory. Information, especially verbal information, is often stored based on its sound. This is why, when trying to remember a phone number, you might repeat it aloud or “hear” it in your mind.
- Visual Encoding: Visual encoding is the process of storing visual images. For example, if you glance at a picture briefly and then try to recall details about it a few moments later, you’re relying on visual encoding.
- Semantic Encoding: This involves processing the meaning of information. Although it plays a more dominant role in long-term memory encoding, there are short-term tasks where meaning can influence memory (e.g., remembering words that form a coherent sentence vs. a random list).
- Tactile Encoding: Information can also be encoded based on touch, though this is less common than acoustic or visual encoding for short-term memory tasks.
Various factors, including attention, repetition, and the nature of the information, can influence the effectiveness of encoding in short-term memory.
However, without further processing, the data held in short-term memory can decay or be displaced, emphasizing the transient nature of this memory store.
More durable and elaborate encoding methods, such as deep processing or the formation of associations, are needed to move information from short-term to long-term memory.
Working memory
Baddeley and Hitch (1974) have developed an alternative model of short-term memory, which they call working memory.
Short-term memory and working memory are not the same, although they are closely related concepts. Short-term memory refers to the temporary storage of information, holding it for a brief period of time.
Working memory, on the other hand, involves not just storing, but also manipulating and processing this information. It’s like the brain’s “workspace” for cognitive tasks, such as problem-solving, reasoning, and comprehension.
Working memory is a more dynamic and complex system than mere short-term storage.
References
Atkinson, R. C., & Shiffrin, R. M. (1971). The control processes of short-term memory. Institute for Mathematical Studies in the Social Sciences, Stanford University.
Baddeley, A.D., & Hitch, G. (1974). Working memory. In G.H. Bower (Ed.), The psychology of learning and motivation: Advances in research and theory (Vol. 8, pp. 47–89). New York: Academic Press.
Miller, G. (1956). The magical number seven, plus or minus two: Some limits on our capacity for processing information. The psychological review, 63, 81-97.
Peterson, L. R., & Peterson, M. J. (1959). Short-term retention of individual verbal items. Journal of experimental psychology, 58(3), 193-198.
