Abstract
The essay discusses short-term memory (STM) and other aspects that are related to it. There has been considerable research done on STM, however, a lot more needs to be done in certain areas. The short-term memories carry a different process related to long-term memories. Short-term memory is often used in place of working memory, but the two are different. Short-term memory refers to only the temporary loading of information while working memory refers to not only temporary storage, but also manipulating information. The paper looks at different experiments related to STM, the impact of word-length effect and the distinctions between STS and LTS.
Introduction
Short-term memory is also referred to as the active or primary memory. This is the conscious mind in Freudian psychology and is like a scratch-pad used for temporary recall and for processing the information at any point in time. The amount of information stored is small in amount and available for a short period in case of short-term memory (STM). The amount of information in short-term memory can vary and is influenced by several aspects that are discussed in the paper. More recent research proposes that people are capable of storing about four pieces of information in short-term memory.
The short-term memory has a restricted capacity, and this can be readily illustrated by a number of experiments. The humans can hold between five and nine objects in the working memory.
The two parts of memory
There are two parts of memory, short-term and long-term. However, the two-component concept of memory was discarded when psychology turned to behaviorism. The short-term memory system, in particular is given essential importance and this is because the procedures carried out under the short-term are under the immediate control of the subject and control the flow of information in the memory system. "Coding" is a set of control processes where the information is easily retrievable, while “Imaging" is a control process for storing verbal information through visual images (The control of short-term memory, 1971). The overall memory system is described as the flow of data into and out of short-term storage and how the subject controls of that flow of information.
The short-term store cannot recover an image once it is lost. However, the information residing in short-term storage can be copied into long-term store, and this is assumed to be a relatively permanent memory. When the image in short-term storage carrying related information in the long-term store gets activated, the information enters the short-term store too. The short-term store at times acts as a temporary activation of the long-term store. The thoughts and information that one are currently aware of can be considered as part of the short-term store. The short-term store is considered as a working memory as the control procedures get centered in and act through it. The time for retrieval of for information in short-term storage ranges from 10 to 30 milliseconds per character.
The impact of acoustic, semantic and formal similarity on short term memory
One has seen the analogous effects of intra-list similarity in long-term memory (LTM). However, in an experiment, it was difficult to see an equivalent effect of semantic similarity in STM. This suggests that that STM may differ from LTM in relying more on acoustic cues or the function of acoustic, semantic and formal resemblance. The subjects under experimentations were asked to recall 24 sequences of five words and another experiment with 24 five-word sequences, made of eight sequences random sampling. There was third experiment done with twenty-four five-word sequences with random sequences drawn from a set of 10 acoustically similar words. All three experiments concluded that there was an enormous and steady adverse effect of acoustic similarity on ordered STM for words. The subjects showed notable constancy and regularity in using almost exclusively acoustic coding system for the short-term remembering (Baddeley, 1966).
The word-length effect
Under another study, the hypothesis that the STM span varies with the length of the words to be recalled was studied. It is observed that the memory span of a subject correlates highly with the secondary memory as compared to the component of primary memory. A study was done to compare the memory span of subjects for sets of long and short words with comparable frequency of occurrence. There were five lengths for the world lists used, made of sequences of four, five, six, seven, and eight. Naturally, the lists with sample of short words result in better memory span. A number of tests were done to examine the relation between memory span, the number of words, the kind of words and the word length effect. The experiments show that the memory span is sensitive to the length of the word, and the effect remains when the number of syllables and number of phonemes are held constant. There is an orderly relation between delivery time and memory span. The memory span is corresponding to the number of words that can be read out in about 2 sec (Baddeley et al, 1975) and it also correlates with the reading rate across subjects. However, the effect of the word length is abolished when the material is presented visually to the subjects. Most of the experiments here broadly fit the assumption that the word-length effect is the result of the restricted aptitude of the rehearsal loop.
There has been a revived interest in the study of memory with the help of recognition methods and currently, there are several theories of the response process in recognition memory. The procedure by which information gets stored and retained in memory is a discrete one. Under the finite-state decision theory, the theory of signal detection has two distinct parts. The first part concerns the changing of memory characteristics, and the next part applies the statistical decision theory to find out the optimum response strategy. Under the Continuous Strength Theory ( Bernbach, 1967)., the underlying assumption is that the decision to respond to an item is whether the strength of that item is above some principle value. It is this strength measure that will directly reflect the effect of memory factors. A series of recent experiments have established the practicality of a decision-theory model, in accounting for recognition memory data. The finite-state decision theory has a significant insinuation for the study of memory by recognition procedures and the probability of forgetting.Short-term memory and fluid intelligence
There is significant relationship between general fluid intelligence and short-term memory capacity as well as the processing speed, as is evident from the earlier experiments. However, there is a need to do more studies and research in this direction. The recent studies indicate that it is the working memory capacity (WMC), and not the short-term memory capacity or the processing speed that is an indicator of general fluid intelligence. It is essential to understand WMC and STM before going into the complex relationship. The short-term memory acts as a simple storage buffer that is decided by trained skills and strategies. The memory is more complicated in contrast and is made of storage and attention component (Conway et al,2002).
In a study, measures of short-term memory capacity, WMC, fluid intelligence and processing speed were administered to 120 young adults. They were tested on their reading span, Operation span, counting span, and their short-term memory capacity was measured. The group also underwent processing speed tasks and fluid intelligence tests. A significant correlation was found in STM latent variables and the speed. There is indication that suggests that the processing speed is a major factor that can lead to the cognitive ability development in childhood. WMC is the fundamental factor rather than speed that impacts the fluid intelligence.
The distinctions between STS and LTS
It is widely accepted that memory is categorized into three levels of storage, the sensory stores, short-term memory (STM) and long-term memory (LTM). Stimuli enters the sensory stores irrespective of whether the subject is paying attention or not to that source. The differences between STS and LTS are well-documented. While STS has a limited capacity, the LTS has no known limit. STS stores verbal items phonemically and semantically in LTS. It is easy to forget from STS, but the process is slow from LTS. The acoustic confusions seen in short-term memory are based on letters and digits that carry little semantic content. We think of memory linked to the perceptual processing ( Craik et al., 972). If the processing capacity maintains information at one level, the short-term memory will appear.
The dual-store approach to short-term recency
There are different sources underlying short- and long-term recency effects. An activation-based short-term buffer is essential besides a relative recovery process. The presence of the buffer allows an explanation of the observed disconnections as well as a frugal explanation for the shift from recency to primacy. The principle of parsimony has been a debatable one between the single- and dual-store theories of memory. The single-store models need much more complex procedures to account for the same data (Davelaar et al., 2005).
Working memory and Short-term memory Short-term memory retains information for a short time, and the short-term store has a working memory component like a sketchpad in the mind. The working memory is a much more complex construct than short-term memory and is based on a set of activated memory elements. When discussing the relationship between working memory (WM) and short-term memory (STM), WM has a higher level cognitive functioning. The data based on the experiments do suggest that STM does play a role in the unique variance to verbal abilities, but did not contribute to variance in quantitative abilities (Engle et al., 1999)
Labeling effects in short-term memory in children
When the effects of verbalizing labels for stimuli were studied in a short-term memory(S TM), it found that evident labeling enabled STM performance. Use of induced verbal labels has influenced the performance of many different cognitive tasks, when studied on children of different age groups. Memory is no doubt influenced by verbal labels, but there comes a stage in the development, when the verbal responses are there but do not serve as mediators. When the study was done on young children of nursery school, the study of the responses showed that verbal labels offered facilitation for the younger students but not for, the older ones. The effect of verbal labeling on recency performance was constant relatively across age levels. There seems to be a particular optimum range within which labeling aids memory and these finding support mediational-deficiency hypothesis. Labeling in the case of older students may interfere with hidden labeling and hence hindering the primary performance (Hagen & Kingsley, 1968). However, labeling did help performance on recency.
Very little is understood on the basic psychological processes on the forgetting and how it is associated with short-term memory. A new computational model of short-term memory, the Start-End Model (SEM) has been introduced for serial order (Henson, 1998). The core opinions of the model are that the position of an item is relatively coded to the beginning and end of the sequence. The items get stored as position-sensitive tokens and can be retrieved by restoring positional codes for each response. Additional assumptions are that the response selection is based on transient phonological information. There are three theories on how we retain order in memory and the errors made by people when recalling. Start-End Model (SEM) is looked upon as a significant improvement on previous models and is unique in predicting the pattern of errors found between different length sequences.
Word frequency
It has been clearly established that verbal short-term memory relies heavily on some form of phonological coding. The verbal short-term memory is limited in capacity, and people can recall more of the shorter than longer words. Moreover, it is easier to recall similar words as compared to the dissimilar words. Word frequency is known to affect both long- and short-term memory tasks. The performance for long-term memory tasks is usually better on high-frequency words as compared to low-frequency words. The short-term memory task procedures are sensitive to the properties of items held in lexical memory ( Hulme et al., 1997). The word frequency impacts the recall through its lexical representations. High-frequency are more easily recognized in speech as compared to the low-frequency words. However, in case of short-term memory tasks, the effects of frequency are not well understood as they are complex.
Verbal short-term memory deficits
Studies show that individuals with Down syndrome suffer from poor verbal short-term memory. When experiments done on children with Down syndrome and their verbal, mental age-matched controls, it was confirmed that there is poorer verbal short-term memory performance as compared to control in these children. The impairments inside and outside of the phonological loop system in Down syndrome offer the basic explanation. The verbal short-term memory deficit might explain the learning difficulties faced by individuals with Down syndrome. Hearing difficulties are common in Down syndrome (Jarrold et al., 2000). The result of the experiments points out that individuals with Down suffer from a decreased capacity phonological store, and these are consistent with the evidence of poorer short-term recall of verbal information.
The past decade has seen serious advances made in the neurosciences and psychological theories about short-term memory. When examining the major psychological theories of short-term memory critically, it is kept in mind as to how to separate short-term from long-term memory. The processes of encoding, maintenance, and retrieval, as well as forgetting from short-term memory have been looked into (Jonides et al.,2008).
Why Do We Forget?
Forgetting is a puzzling problem, especially in STM. How can one forget what was heard or seen a few seconds ago? The two major explanations for forgetting are placed in time-based decay and similarity-based interference. The central assertion of decay theory is that the information in memory decays with the passage of time. However, there have been many questioning over the years regarding the theory as the decay explanations are controversial. There is no explanation of how decay occurs, and there are alternative explanations available. Neural findings of delay-period have also been used to support the theory of decay.
According to Interference Theories, the interference effects play numerous roles in memory theory and are the dominant explanation of forgetting. Secondly, it has been suggested that
the ability of an individual to overcome interference control the STM capacity.
Based on the mind of short-term memory, it is said that memory is made of bundles of stored information, and these may vary in activation and the dormant state. At a time, attention is focused on only a single chunk of information at a time. Forgetting occurs when the items leave the focus of attention and compete with other items to regain the focus.
Auditory and visual presentation
Modality effects and the structure of short-term verbal memory. Memory A model of the structure of short-term memory is presented to explain the consequences of auditory and visual presentation upon short-term retention of verbal stimuli. The model states that the verbal information is processed in separate streams that carry different capabilities. The auditory items get encoded processed in acoustic code and a phonological code. The visual items are reserved in both the phonological code and a visual code. The term modality effect was used for short-term memory tasks that always resulted in higher recall as compared to the visual presentation. Recent experiments show that in comparison to the auditory modality, where the echo continues for a longer period of time, there is little proof to show that sensory-based visual code contributes considerably to recital in typical short-term memory tasks ( Penney, 1989). Instead, it seems that a phonological or P code gets generated that allows for rehearsal and a performance.
The first difference between the auditory and visual streams is that the visual has a greater three-dimensional component and a relatively weaker temporal one as compared to the auditory stream. There is really no suitable spatial analogy in the auditory modality. As compared to the auditory modality, the simultaneous presentation can make the memory task a bit more difficult. However, there is indication that in the visual mode, simultaneous presentation can improve serial recall. Strong links occur between successive items in the auditory modality, as compared to the visual modality, where concurrently presented items are related strongly. Visual interference effects can be verified more easily with simultaneous presentation of visual stimuli as compared to the sequential presentation.
Disruption of short-term memory
A lot of research has been done on the association between short-term memory and speech in the past two decades. Memory span is inversely related to the length of words. There has been a stable trickle of evidence over the years to suggest that there might be some link between short-term memory and the acoustic store. Indication of the phonemic similarity effect seems to be less forthright. The articulatory suppression may demolish the phonemic similarity for visually presented material. However, it seems to have no effect on when the material is offered auditorally. This again asks for a separate auditory and visual memory stores. When experiments were done to study the effect of unattended speech on immediate memory for Visual digits, it was found that memory performance showed clear deficiency. The level of impairment was related to the function of the phonological similarity (Salamé & Baddeley, 1982) of the unrelated words to the visual digits. However, the performance was not influenced by the semantic characteristics of the unattended speech. There is a very coherent evidence in the results of the experiments that suggests that unattended speech can lead to a considerable decrement in immediate memory for visually presented digits.
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