Short-term memory - Wikipedia
Neurobiol Learn Mem. Jul;84(1) Relationship between short- and long-term memory and short- and long-term extinction. Cammarota M(1). Storage-oriented memory span tasks with no explicit concurrent processing are usually referred as short-term memory (STM) tasks, whereas tasks involving. Short-term memory is the capacity for holding, but not manipulating, a small amount of The idea of the division of memory into short-term and long-term dates back to . The relationship between short-term memory and working memory is.
As time passes, cellular and molecular changes allow for the strengthening of direct connections between neocortical regions, enabling the memory of an event to be accessed independently of the hippocampus. Damage to the hippocampus by injury or neurodegenerative disorder Alzheimer's disease, for instance produces anterograde amnesia—the inability to form new declarative memories—because the hippocampus is no longer able to connect mnemonic information distributed in the neocortex before the data has been consolidated.
Interestingly, such a disruption does not impair memory for facts and events that have already been consolidated. Thus, an amnesiac with hippocampal damage would not be able to learn the names of current presidential candidates but would be able to recall the identity of our 16th president Abraham Lincoln, of course!
The role of sleep in memory consolidation is an ancient question dating back to the Roman rhetorician Quintilian in the first century A. Much research in the past decade has been dedicated to better understanding the interaction between sleep and memory. Yet little is understood. At the molecular level, gene expression responsible for protein synthesis is increased during sleep in rats exposed to enriched environments, suggesting memory consolidation processes are enhanced, or may essentially rely, on sleep.
Further, patterns of activity observed in rats during spatial learning are replayed in hippocampal neurons during subsequent sleep, further suggesting that learning may continue in sleep. In humans, recent studies have demonstrated the benefits of sleep on declarative memory performance, thus giving a neurological basis to the old adage, "sleep on it.
Similar overnight improvements on virtual navigation tasks have been observed, which correlate with hippocampal activation during sleep. After the final word-pair, subjects had to do the multiplication distractor task for 20 seconds.
In their results, Bjork and Whitten found that the recency effect the increased probability of recall of the last items studied and the primacy effect the increased probability of recall of the first few items still remained. These results would seem inconsistent with the idea of short-term memory as the distractor items would have taken the place of some of the word-pairs in the buffer, thereby weakening the associated strength of the items in long-term memory.
Bjork and Whitten hypothesized that these results could be attributed to the memory processes at work for long-term memory retrieval versus short-term memory retrieval.
Tzeng also found an instance where the recency effect in free recall did not seem to result from the function of a short-term memory store. Subjects were presented with four study-test periods of 10 word lists, with a continual distractor task second period of counting-backward.
At the end of each list, participants had to free recall as many words from the list as possible. After free-recall of the fourth list, participants were asked to free recall items from all four lists.
Both the initial free recall and the final free recall showed a recency effect. These results went against the predictions of a short-term memory model, where no recency effect would be expected in either initial or final free recall. As evidence, they provided the results of their experiment, in which the long-term recency effect disappeared when the distractor after the last item differed from the distractors that preceded and followed all the other items e.
Thapar and Greene challenged this theory. In one of their experiments, participants were given a different distractor task after every item to be studied. According to Koppenaal's and Glanzer's theory, there should be no recency effect as subjects would not have had time to adapt to the distractor; yet such a recency effect remained in place in the experiment. In the end distractor task, the processing context of the final items is no longer similar to the processing context of the other list items.
At the same time, retrieval cues for these items are no longer as effective as without the distractor.
Therefore, the recency effect recedes or vanishes. However, when distractor tasks are placed before and after each item, the recency effect returns, because all the list items once again have similar processing context. As these neurons fire, the available neurotransmitters in their store are depleted and this pattern of depletion is iconic, representing stimulus information and functions as a memory trace.
How Human Memory Works
The memory trace decays over time as a consequence of neurotransmitter reuptake mechanisms that restore neurotransmitters to the levels that existed prior to stimulus presentation. Relationship with working memory[ edit ] The relationship between short-term memory and working memory is described differently by various theories, but it is generally acknowledged that the two concepts are distinct.
Working memory is a theoretical framework that refers to structures and processes used for temporarily storing and manipulating information. As such, working memory might also be referred to as working attention.
Working memory and attention together play a major role in the processes of thinking. Short-term memory in general refers, in a theory-neutral manner, to the short-term storage of information, and it does not entail the manipulation or organization of material held in memory. Thus, while there are short-term memory components to working memory models, the concept of short-term memory is distinct from these more hypothetical concepts.
Within Baddeley 's influential model of working memory there are two short-term storage mechanisms: Most of the research referred to here involves the phonological loop, because most of the work done on short-term memory has used verbal material.
Since the s, however, there has been a surge in research on visual short-term memory and also increasing work on spatial short-term memory.
The decay assumption is part of many theories of short-term memory, the most notable one being Baddeley's model of working memory. Short-term working memory appears to operate phonologically. For instance, whereas English speakers can typically hold seven digits in short-term memory, Chinese speakers can typically remember ten digits. This is because Chinese number words are all single syllables, whereas English are not.
The type or characteristics of the information also affects the number of items which can be retained in short-term memory. For instance, more words can be recalled if they are shorter or more commonly used words, or if they are phonologically similar in sound, or if they are taken from a single semantic category such as sports, for example rather than from different categories, etc.
There is also some evidence that short-term memory capacity and duration is increased if the words or digits are articulated aloud instead of being read sub-vocally in the head.
The relatively small capacity of the short-term memory, compared to the huge capacity of long-term memoryhas been attributed by some to the evolutionary survival advantage in paying attention to a relatively small number of important things e. Chunking is the organization of material into shorter meaningful groups to make them more manageable. For example, a hyphenated phone number, split into groups of 3 or 4 digits, tends to be easier to remember than a single long number.
Experiments by Herbert Simon have shown that the ideal size for chunking of letters and numbers, whether meaningful or not, is three.
Relationship between short- and long-term memory and short- and long-term extinction.
However, meaningful groups may be longer such as four numbers that make up a date within a longer list of numbers, for example. With chunking, each chunk represents just one of the 5 - 9 items that can be stored in short-term memory, thus extending the total number of items that can be held.
The use of mnemonic devices can significantly increase memory, particularly the recall of long lists of names, numbers, etc. It is usually assumed that the short-term memory spontaneously decays over time, typically in the region of 10 - 15 seconds, but items may be retained for up to a minute, depending on the content.
However, it can be extended by repetition or rehearsal either by reading items out loud, or by mental simulationso that the information re-enters the short-term store and is retained for a further period.