working memory working memory working memory is a cognitive system with a limited capacity that can hold information temporarily. it is important for reasoning and the guidance of decision-making and behavior. working memory is often used synonymously with short-term memory, but some theorists consider the two forms of memory distinct, assuming that working memory allows for the manipulation of stored information, whereas short-term memory only refers to the short-term storage of information. working memory is a theoretical concept central to cognitive psychology, neuropsychology, and neuroscience. history the term "working memory" was coined by miller, galanter, and pribram, and was used in the 1960s in the context of theories that likened the mind to a computer. in 1968, atkinson and shiffrin used the term to describe their "short-term store". the term short-term store was the name previously used for working memory. other suggested names were short-term memory, primary memory, immediate memory, operant memory, and provisional memory. short-term memory is the ability to remember information over a brief period (in the order of seconds). most theorists today use the concept of working memory to replace or include the older concept of short-term memory, marking a stronger emphasis on the notion of manipulating information rather than mere maintenance. the earliest mention of experiments on the neural basis of working memory can be traced back to more than 100 years ago, when hitzig and ferrier described ablation experiments of the prefrontal cortex (pfc); they concluded that the frontal cortex was important for cognitive rather than sensory processes. in 1935 and 1936, carlyle jacobsen and colleagues were the first to show the deleterious effect of prefrontal ablation on delayed response. theories numerous models have been proposed for how working memory functions, both anatomically and cognitively. of those, the two that have been most influential are summarized below. the multicomponent model baddeley and hitch's model of working memory in 1974 baddeley and hitch introduced the multicomponent model of working memory. the theory proposed a model containing three components: the central executive, the phonological loop, and the visuospatial sketchpad with the central executive functioning as a control center of sorts, directing info between the phonological and visuospatial components. the central executive is responsible for, among other things, directing attention to relevant information, suppressing irrelevant information and inappropriate actions, and coordinating cognitive processes when more than one task is simultaneously performed. a "central executive" is responsible for supervising the integration of information and for coordinating subordinate systems responsible for the short-term maintenance of information. one subordinate system, the phonological loop (pl), stores phonological information (that is, the sound of language) and prevents its decay by continuously refreshing it in a rehearsal loop. it can, for example, maintain a seven-digit telephone number for as long as one repeats the number to oneself repeatedly. the other subordinate system, the visuospatial sketchpad, stores visual and spatial information. it can be used, for example, for constructing and manipulating visual images and for representing mental maps. the sketchpad can be further broken down into a visual subsystem (dealing with such phenomena as shape, colour, and texture), and a spatial subsystem (dealing with location). in 2000 baddeley extended the model by adding a fourth component, the episodic buffer, which holds representations that integrate phonological, visual, and spatial information, and possibly information not covered by the subordinate systems (e.g., semantic information, musical information). the episodic buffer is also the link between working memory and long-term memory. the component is episodic because it is assumed to bind information into a unitary episodic representation. the episodic buffer resembles tulving's concept of episodic memory, but it differs in that the episodic buffer is a temporary store. working memory as part of long-term memory central executive long-term memory the central executive of working memory is retrieving memory from long-term memory. anders ericsson and walter kintsch have introduced the notion of "long-term working memory", which they define as a set of "retrieval structures" in long-term memory that enable seamless access to the information relevant for everyday tasks. in this way, parts of long-term memory effectively function as working memory. in a similar vein, cowan does not regard working memory as a separate system from long-term memory. representations in working memory are a subset of representations in long-term memory. working memory is organized into two embedded levels. the first consists of long-term memory representations that are activated. there can be many of these—there is theoretically no limit to the activation of representations in long-term memory. the second level is called the focus of attention. the focus is regarded as having a limited capacity and holds up to four of the activated representations. oberauer has extended cowan's model by adding a third component—a more narrow focus of attention that holds only one chunk at a time. the one-element focus is embedded in the four-element focus and serves to select a single chunk for processing. for example, four digits can be held in mind at the same time in cowan's "focus of attention". when the individual wishes to perform a process on each of these digits—for example, adding the number two to each digit—separate processing is required for each digit since most individuals cannot perform several mathematical processes in parallel. oberauer's attentional component selects one of the digits for processing and then shifts the attentional focus to the next digit, continuing until all digits have been processed. capacity working memory is widely acknowledged as having limited capacity. an early quantification of the capacity limit associated with short-term memory was the "magical number seven" suggested by miller in 1956. miller claimed that the information-processing capacity of young adults is around seven elements, they were referred to as "chunks", regardless of whether the elements are digits, letters, words, or other units. later research revealed this number depends on the category of chunks used (e.g., span may be around seven for digits, six for letters, and five for words), and even on features of the chunks within a category. for instance, attention span is lower for longer words than short words. in general, memory span for verbal contents (digits, letters, words, etc.) depends on the phonological complexity of the content (i.e., the number of phonemes, the number of syllables), and on the lexical status of the contents (whether the contents are words known to the person or not). several other factors affect a person's measured span, and therefore it is difficult to pin down the capacity of short-term or working memory to a number of chunks. nonetheless, cowan proposed that working memory has a capacity of about four chunks in young adults (and fewer in children and old adults). in the visual domain, some investigations report no fixed capacity limit with respect to the total number of items that can be held in working memory. instead, the results argue for a limited resource that can be flexibly shared between items retained in memory (see below in resource theories), with some items in the focus of attention being allocated more resource and recalled with greater precision. whereas most adults can repeat about seven digits in correct order, some individuals have shown impressive enlargements of their digit span—up to 80 digits. this feat is possible by extensive training on an encoding strategy by which the digits in a list are grouped (usually in groups of three to five) and these groups are encoded as a single unit (a chunk). for this to succeed, participants must be able to recognize the groups as some known string of digits. one person studied by ericsson and his colleagues, for example, used an extensive knowledge of racing times from the history of sports in the process of coding chunks: several such chunks could then be combined into a higher-order chunk, forming a hierarchy of chunks. in this way, only some chunks at the highest level of the hierarchy must be retained in working memory, and for retrieval the chunks are unpacked. that is, the chunks in working memory act as retrieval cues that point to the digits they contain. practicing memory skills such as these does not expand working memory capacity proper: it is the capacity to transfer (and retrieve) information from long-term memory that is improved, according to ericsson and kintsch (1995; see also gobet & simon, 2000). measures and correlates working memory capacity can be tested by a variety of tasks. a commonly used measure is a dual-task paradigm, combining a memory span measure with a concurrent processing task, sometimes referred to as "complex span". daneman and carpenter invented the first version of this kind of task, the "reading span", in 1980. subjects read a number of sentences (usually between two and six) and tried to remember the last word of each sentence. at the end of the list of sentences, they repeated back the words in their correct order. other tasks that do not have this dual-task nature have also been shown to be good measures of working memory capacity. whereas daneman and carpenter believed that the combination of "storage" (maintenance) and processing is needed to measure working memory capacity, we know now that the capacity of working memory can be measured with short-term memory tasks that have no additional processing component. conversely, working memory capacity can also be measured with certain processing tasks that don't involve maintenance of information. the question of what features a task must have to qualify as a good measure of working memory capacity is a topic of ongoing research. recently, several studies of visual working memory have used delayed response tasks. these use analogue responses in a continuous space, rather than a binary (correct/incorrect) recall method, as often used in visual change detection tasks. instead of asking participants to report whether a change occurred between the memory and probe array, delayed reproduction tasks require them to reproduce the precise quality of a visual feature, e.g. an object's location, orientation or colour. in addition, the combination of visual perception such as within objects and colors can be used to improve memory strategy through elaboration, thus creating reinforcement within the capacity of working memory. measures of working-memory capacity are strongly related to performance in other complex cognitive tasks, such as reading comprehension, problem solving, and with measures of intelligence quotient. some researchers have argued that working-memory capacity reflects the efficiency of executive functions, most notably the ability to maintain multiple task-relevant representations in the face of distracting irrelevant information; and that such tasks seem to reflect individual differences in the ability to focus and maintain attention, particularly when other events are serving to capture attention. both working memory and executive functions rely strongly, though not exclusively, on frontal brain areas. other researchers have argued that the capacity of working memory is better characterized as the ability to mentally form relations between elements, or to grasp relations in given information. this idea has been advanced, among others, by graeme halford, who illustrated it by our limited ability to understand statistical interactions between variables. these authors asked people to compare written statements about the relations between several variables to graphs illustrating the same or a different relation, as in the following sentence: "if the cake is from france, then it has more sugar if it is made with chocolate than if it is made with cream, but if the cake is from italy, then it has more sugar if it is made with cream than if it is made of chocolate". this statement describes a relation between three variables (country, ingredient, and amount of sugar), which is the maximum most individuals can understand. the capacity limit apparent here is obviously not a memory limit (all relevant information can be seen continuously) but a limit to how many relationships are discerned simultaneously. experimental studies of working-memory capacity there are several hypotheses about the nature of the capacity limit. one is that a limited pool of cognitive resources is needed to keep representations active and thereby available for processing, and for carrying out processes. another hypothesis is that memory traces in working memory decay within a few seconds, unless refreshed through rehearsal, and because the speed of rehearsal is limited, we can maintain only a limited amount of information. yet another idea is that representations held in working memory interfere with each other. decay theories the assumption