The relationships between working memory and long-term memory.
Working memory is a cognitive system with a limited capacity that is responsible for temporarily holding information available for processing. Working memory is important for reasoning and the guidance of decision-making and behavior. Working memory is often used synonymously with short-term memory, but The episodic buffer is also the link between working memory and. We know that LTP (Long-Term Potentiation) in hippocampus is required for the working memory to be functional in mammals (even a most broad search returns . The theoretical concepts short-term memory (STM) and working memory (WM) have been used stages, leading to a permanent storage of information in long- term memory (LTM). Hypothetical models of the relation between STM and WM .
In the conjunction condition, the test trial consisted of either an object-location combination that had been seen before match trial or an object-location recombination mismatch trial, e. Thus, conjunction trials required retention of objects and locations plus the relations between them. Accordingly, and as one might expect, the relational conjunction condition in Olson et al. In two similar experiments, the results were that patients were intact in the feature condition and impaired in the conjunction condition.
Moreover, in one experiment Experiment 2patients were impaired in the conjunction condition even when the study-test delay was as short as 1 sec average delay of 2 sec for all three study items. The selective impairments in retention of relational information in these two studies after short delays raised the possibility that the MTL is critical for retention of relational information, even when working memory is sufficient to support performance Hannula et al.
Indeed, it was suggested that the distinction between memory for single items vs. An alternative possibility is that memory for relational information was impaired because the demands on memory were higher in the conditions assessing memory for relations than in the conditions assessing memory for items, and that these demands on memory exceeded visual working memory capacity Shrager et al.
In the case of Hannula et al. In addition, the structure of the continuous recognition test meant that even at a lag of one item, participants still needed to try to hold in mind a number of previous scenes up to ninebecause the decision to identify each item as old or new sometimes depended on as many as nine previous items Fig.
Moreover, even though the inter-stimulus interval was only 3 sec, the delay between the initial presentation of a study scene and the assessment of memory for object location was as long as 14 sec. In the second task which assessed memory for scene-face associations, participants also had to try to hold in mind a number of previous scene-face pairs even at the lag of 1, because they did not know whether the next trial would consist of a new study trial, a probe trial concerning the most recently presented scene-face pair, or a probe trial concerning a scene-face pair that had been presented up to nine trials earlier.
It is therefore possible as considered by Hannula et al. We recently tested this idea in two experiments that differed in their demands on memory but that assessed retention of the same object-in-scene information Jeneson et al. In the first experiment, we used the same procedure as was used previously Hannula et al.
In the second experiment, we used a conventional test paradigm consisting of separate study-test trials that involved either a brief 3-sec or a relatively long sec retention interval. In this case, participants were required to hold in mind only one scene at a time.
Short-Term Memory and Working Memory - Types of Memory - The Human Memory
If maintenance of object-in-scene information is critically dependent on the hippocampus, one would expect hippocampal damage to impair performance at the 3-sec retention interval as well as at the sec retention interval. Instead, the patients exhibited fully intact memory for object-in-scene information when the retention delay was short 3 secand they exhibited impaired memory when the delay was long 14 sec. Thus, in this study, memory was impaired for object-in-scene information only when the task imposed relatively large demands on memory because several scenes needed to be maintained [Experiment 1], or because the retention interval was long [Experiment 2].
The study by Olson et al. The fact that healthy individuals can sometimes remember single features e. Indeed, in studies directly comparing memory for features and memory for conjunctions, performance is typically poorer when individuals must distinguish combinations of features from recombinations of features than when they must identify single features Mitchell et al.
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- Working memory, long-term memory, and medial temporal lobe function
- Difference Between Short-Term, Long-Term, and Working Memory
One possibility is that detecting recombinations of features is more demanding than detecting changes in single features because recombination test trials interfere with maintenance Alvarez and Thompson or retrieval Wheeler and Treisman of the original feature combinations.
Given that conjunction trials are typically more difficult than single feature trials, the question remains whether the memory load in the conjunction condition in Olson et al.
Note that the serial presentation of study items meant that, on two-thirds of the trials, one or two sample images intervened between study and test.
That is, different correlations between STM and WM on the one hand and intelligence on the other hand may not be directly related to substantive differences between STM and WM, but to differences in the attentional demands that the two concepts address. Indeed, both Baddeley and Cowan et al. This is also included in Figure 1 F. Recently, a change can be observed in cognitive research into the relationship between WM and fluid intelligence.
Several studies have argued strongly against the discrepancy between STM and WM for predicting intelligence. For example, Ackerman et al.
It is questionable how meaningful such small difference is. In addition, Colom et al. Through this hierarchical approach the authors showed that the STM component of both types of tasks is the critical component contributing to intelligence Colom et al. Furthermore, a large overlap of variance between STM and WM tasks was found after factor analysis of 12 diverse memory span tasks in a sample of participants Colom et al.
These results are supported by Unsworth and Engle bwho conducted a meta-analysis and re-analysis of key data sets. They concluded that simple and complex span have correlations with higher order cognitive functions that are similar in magnitude and that WM and STM tasks are similarly affected by several experimental variables such as the phonological similarity between list items.
Furthermore, they stated that both constructs are similar in terms of performance indicators. Unsworth and Engle suggested that the variance common to simple and complex span tasks is responsible for their predictive power and reject the notion that STM and WM are largely different constructs. Thus, according to this study, simple and complex span tasks are likely to measure similar processes i. Another study also demonstrated that WM and STM are hardly distinguishable and even proposed that fluid intelligence is nearly perfectly correlated to both constructs Martinez et al.
Consistent results were obtained in children aged 5—7 years. Finally, STM has also been identified as the construct accounting for the relationship between complex span measures and reasoning Krumm et al. In general, these studies show that by evaluating the contribution of STM performance to intelligence prior to the contribution of WM performance, the residual variance in WM performance is not or only weakly associated with intelligence e.
Yet these findings again raise the question to what degree both constructs differentiate and whether both WM and STM measures are not better explained by one general factor. In that case, model B is correct Figure 1. There are several theories that try to identify the factors responsible for the correlation between performance on WM tasks and cognitive abilities. The concurrent processing required to solve the additional task may use some of the capacity otherwise used for the storage of information.
This results in a diminished reliability of the stored information and a decrease of performance. In other words, persons with more general cognitive capacity, as reflected by fluid intelligence, will perform better on WM tasks. This is quite different from the idea that complex span tasks measure something additional to simple span tasks, such as attention or information processing speed.
However, it is not clear to what process the term cognitive load is referring. According to their resource sharing model the cognitive load of a complex span task is determined by the proportion of time that is spend on the secondary task. That is, attention is captured from the original task during the performance of the interfering activity, resulting in a decay of the to-be-remembered items.
The longer the attention is switched away from the memory task and captured by concurrent activities, the stronger the decrease of WM performance Barrouillet et al.
This would also imply that the cognitive load of STM tasks is depending on internal distractors, since there are no external distractors on these tasks. Unsworth and Engle a reintroduced the terms primary and secondary memory to offer another explanation for individual differences in WM performance. First, they argue that an immediate free recall task can be used to measure WM capacity and is an equally good predictor of higher order cognitive functions as are complex span tasks.
Next, they suggest that performance on this task relies on two factors: Primary memory is considered a limited capacity short-term component. The maintaining process in this store depends on general processes that are also described in other models, such as focus of attention Cowan, or general storage capabilities Colom et al.
Information is displaced from primary to secondary memory when primary memory is fully occupied or when attention is disengaged from the maintained items, for example when performing a distracting secondary task. According to this model, individuals that perform low on WM tasks are either impaired at maintaining information in primary memory i. As demonstrated by Unsworth et al.
However, the effects may be more profound on WM tasks, because of the larger distraction. In the end, these explanations are comparable to a large extent.
The difference between the views is that some consider cognitive load to be a general exhaustible capacity Colom et al. There is substantial evidence for a large association between intelligence and both WM and STM performance, and the underlying construct accounting for this association may be simple short-term storage, attentional processes, or both.
A better approach may be to consider the different tasks as part of a continuum with variations in the mentioned factors.
For instance, patients with isolated lesions in the dlPFC typically show impairment on delayed-response tasks that require an active maintenance of information Gazzaniga et al. Imaging studies have revealed activity during execution of the n-back task in the dlPFC and ventrolateral PFC vlPFClateral premotor cortex, dorsal cingulate and medial premotor cortex, frontal poles, and medial and lateral posterior parietal cortex PPC; Owen et al.
These regions constitute a complex distributed cortical network involved in activation and allocation of resources Khan and Muly, Because the components of maintenance and particularly manipulation are hard to isolate in the n-back task, it is impossible to identify which regions in this extensive network correspond to either WM or STM. Yet, such dissociation is desirable to support a distinction between both processes. To demonstrate a difference in neuronal activation related to both concepts it is necessary to design tasks that can isolate activity related to the manipulation component of WM from activity linked to maintenance.
Because it is beyond the scope of this article to discuss all brain structures linked to STM and WM the remaining of this section will focus mainly on the dlPFC and its relation to maintenance and manipulation.
First, it is important to understand that issues similar to the ones discussed in the previous two paragraphs can also be encountered in imaging studies. For example, it has been shown that activity in the dlPFC is higher during the performance of a manipulation task i.
If we indeed consider STM and WM as two separate systems than the question arises why dlPFC activation was also observed during the maintenance of information. Since the dlPFC is also critically involved in attention Kane et al. Indeed, there are studies showing that increased activity in dlPFC corresponds to an increased maintenance load Veltman et al.
For example, it was shown that variation in maintenance and manipulation load were both related to dlPFC activity and that both tasks tap virtual identical systems Veltman et al. These findings are also in agreement with models that claim that attentional capacities are critical for both WM and intelligence Conway et al. That is, WM tasks in general consist of two interleaved tasks and thus require more dividing of attention reflected by dlPFC activity compared to STM tasks.
Others have suggested that the relationship between WM and fluid intelligence can be partly explained by interference control. These activation patterns were centered on the dlPFC and parietal cortex and reflected the common dependence on interference control during performance of the tasks.
However, as acknowledged by the authors, it was unclear to what degree interference control independently related to processing or storage because the WM tasks used in this study are measuring both Burgess et al. First, they instructed participants to either maintain or alphabetize a sequence of letters.
On the maintaining trials subjects had to reproduce a sequence of letters in the same order, whereas on the alphabetize trials they had to reorder the letters in alphabetical order i. Analysis of the fMRI activity revealed that manipulation-related activity was independent of maintenance-related activity in both the dlPFC and superior parietal lobule SPL.
This procedure yielded a different result. In other words, these results are consistent with a model of segregation of manipulation from maintenance functions in the PFC Postle et al. In agreement with that, Postle argues that the PFC activity observed during WM tasks is not related to short-term retention but to control processes not exclusively limited to WM Postle, According to this view, WM is not a specialized system but an emerging property arising through the coordinated recruitment of different brain systems.
If it is not consolidated, it is discarded. This process of discarding is important to make room for learning and new memories. But once a memory is stored in the long-term memory bank, it is stored there forever. It may not feel like it is stored there forever. Sometimes, you may not be able to recall something that is stored in the long-term memory bank—nevertheless, it is there.
Because once memory is stored, it is permanent. Short-term memory definitely plays a function in working memory but it is not exactly the same thing. Both short-term memory and long-term memory hold information available for working memory usage. However, working memory is a theoretical framework of the structure of how memory manipulation works, in which short-term memory and long-term memory both serve extremely important functions. The central executive region located in the prefrontal cortex seems to play a fundamental role in both short-term and working memory.
The region serves as a temporary storage facility for short-term memory while at the same time making the memory available for recall and manipulation. The ability to manipulate information is essentially the theoretical difference between short-term memory and working memory.