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Working : The Interfhce between Memory and Cognition

Alan Baddeley MRC Applied Unit Cambridge, Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/4/3/281/1754997/jocn.1992.4.3.281.pdf by guest on 18 May 2021

Abstract may be defined as the system for the system is proposed within a broad and relatively speculative

1 Downloaded from http://direct.mit.edu/jocn/article-pdf/4/3/281/1932205/jocn.1992.4.3.281.pdf by guest on 28 September 2021 temporary maintenance and manipulation of information, nec- overview of memory that emphasizes the putative role essary for the performance of such complex cognitive activities of working memory. This is followed by a brief account of a as comprehension, , and reasoning. Used in this , particular model of working memory, and a more detailed the term refers to an area of research that may or may not discussion of the way in which the various subcomponents of prove to be dependent on a single coherent system. Such a the model relate to other aspects of memory and cognition.

HUMAN MEMORY A SPECULATIVE ness provides a convenient way of simultaneously OVERVIEW representing such diverse streams of information about a common , although it is almost certainly not the I assume that memory, along with other cognitive capac- only way (see Baddeley, 1992a,b for a discussion). ities, has evolved to allow the organism to cope with a complex but structured world. The world is never en- Aspects of Learning tirely predictable, but has sufficient regularity to make it advantageous for the organism to use the past in order Whereas a working memory system that coordinates in- to predict the , that is, to make use of learning and formation from a number of sources is likely to aid memory. perceptual organization of the world, it woiild not nec- essarily benefit from . Hence, it would not form such as would be necessary to recognize Working Memory and a cat as such, nor would it allow one to learn that cats Before learning can take place, an organism must be able tend to hiss rather than bark. More importantly perhaps, to perceive the world, and preferably take advantage of it would not allow one to know whether cats were dan- the fact that the information from the range of sensory gerous, or indeed to recognize one’s own cat, or of channels is likely to be correlated. Objects have not only course to remember whether it had already been fed or visual and spatial characteristics, but are likely also to not. It is now widely accepted that long-term memory is have associated tactile features, and quite possibly to have not a simple unitary system, although there is consider- a characteristic smell and . It seems likely that per- ably less agreement as to how it should be conceptual- ceiving and integrating these various sources of infor- ized (Richardson-Klavehn & Bjork, 1988). mation would benefit from at least a temporary form of There are two major dimensions along which it has in , both to allow for extended processing, and also the past been proposed to dichotomize long-term mem- for the fact that the evidence from the various channels ory: one is the proposed distinction between semantic may not always be available simultaneously. Indeed in and episodic memory, and the other uses a rather some cases, such as the subsequent taste of an orange, broader range of terminology of which the implicit and or the sound emitted by cat, information on one channel explicit memory distinction is one of the most widely such as vision, may arrive substantially before that of adopted. is the term applied by Tul- others. It could be argued that this capacity to integrate ving to the storage of information about the world, the sensory information requires some form of working name of the capital of France, or the chemical formula memory, particularly if the system is one that actively for salt, for example. Episodic memory, on the other attempts to build up information about a perceived ob- hand, refers to the recollection of a personally experi- ject. Furthermore, it can be argued that conscious aware- enced event. In its earlier formulations, the theoretical

0 1992 Masachusetts Institute of Technology Journal of Cognitive Volume 4, Number 3 emphasis tended to be on the basic separability of the learning of the varied probabilities of events can readily underlying systems (Tulving, 1972). Later developments be simulated using connectionist networks, employing have tended rather to emphasize the more phenome- one of a range of possible learning algorithms (Rumel- nological aspects of episodic memory, which is assumed hart, 1991). to be associated with the conscious recollection of the earlier episode (Tulving, 1983). Episodic Memory The implicit-explicit memory distinction, which is also sometimes described as a procedural4eclarative or The limitation of such basic accumulative learning pro- direct-indirect memory distinction, has developed more cesses, however, is that they do not allow the organism recently to reflect the observation that certain types or to select one specific episode from the agglomeration of aspects of memory (implicit) appear to differ markedly prior experience. For this a different form of associative from the pattern of function typically observed in labo- learning is required (Rumelhart, 1991), which I would

ratory learning and memory studies (explicit). Such tra- like to suggest corresponds to episodic memory. If the Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/4/3/281/1754997/jocn.1992.4.3.281.pdf by guest on 18 May 2021 ditional studies are typically concerned with the subject’s organism is to retrieve a specific episode, then it must explicit capacity to or recognize material; they have a means of specifying that episode. The most likely show that performance is a function of variables such as mechanism would seem to be via the use of context. It the depth of processing of the material, its meaningful- is assumed that the episodic learning mechanism is ca- ness, and its degree of active organization. pable of very rapidly forming links between stimuli that Downloaded from http://direct.mit.edu/jocn/article-pdf/4/3/281/1932205/jocn.1992.4.3.281.pdf by guest on 28 September 2021 In contrast, implicit or indirect memory measures are are experienced at the same time. Such a link will allow able to reveal other aspects of learning, which appear to one such experience to evoke the other, hence if I met be insensitive to depth of processing, and much less Charlie and Gladys together at the Green Dragon pub, influenced by strategies and organizational variables. then meeting Charlie is likely to remind me of both This latter type of learning also tends to be relatively Gladys and the pub. intact in a wide range of neuropsychological patient Clearly the extent of such retrieval needs to be limited, groups who typically have impairment in explicit declar- otherwise the regulars at the Green Dragon, on entering ative or directly tested memory. Although there is con- the pub, would be overcome by a bombardment of mem- siderable agreement as to the existence and importance ories of everyone they had ever met there, potentially of such distinctions, there is considerably less agreement causing serious interference with the main purpose of as to the best way of theoretically interpreting this rich their visit. The study of the utilization and operation of and rapidly growing research area. Broadly speaking, such retrieval cues has, of course, formed one of the proponents fall into two categories; the first attempt to most active and successful areas of recent memory re- explain the data as reflecting different aspects of a unitary search (Tulving, 1983). memory system (e.g., Jacoby, Baker, & Brooks, 1989; I assume that this process of retrieval from episodic Roediger, 1990), and typically concentrate on data from memory makes a representation of an earlier episode normal subjects. On the other hand, those who argue accessible to working memory, allowing the central ex- for two, or possibly more separate memory systems (e.g., ecutive component of workmg memory to reflect on its Squire & Zola Morgan, 1988; Tulving & Schacter, 1990) implications and choose an appropriate action. Suppose are typically concerned to account for both normal and that I had chatted to Gladys and been told that Charlie neuropsychological evidence. As will become clear, my always went to that particular pub on Tuesday evenings, own views tend to be of this kind, then recollection of that experience would be rather Given that the world is to some extent a predictable useful if I wanted to make sure that I met him. In contrast, place, then it makes sense for the organism to be able a learning mechanism that simply strengthened the as- to capitalize on such predictability, to learn, for example, sociation between Charlie and the pub would be much that food of one kind is typically found in one location, less helpful. water in another, while a third may be associated with danger. The organism will also find it advantageous to Predicting the Future be able to acquire novel skills, allowing hunting to be carried out more effectively, or in the case of So far we have discussed the role of memory as providing for to develop. At a rather more basic level, information about the past; however, the principal there may be advantages to priming, whereby the oper- of such information is for the light it throws on the future, ation of a particular cognitive process may facilitate the and here again working memory becomes crucial in two subsequent operation of that process (positive priming), ways. First, it provides a system for representing the past or may cause it to be inhibited (). Al- in a way that allows the organism to reflect on it, and though these various forms of learning may employ dif- actively choose a further action, rather than simply re- ferent underlying neural systems, they tend to have in sponding to the highest probability. Second, it offers the common the fact that they can in principle be acquired capacity to up and utilize models to predict the future. by a process of gradual accumulation of experience. Such Johnson-Laird (1983) has argued that mental models play

282 Journal of Volume 4, Number 3 an important role in comprehension, thinking, and prob- I have a similar problem in accepting the proposal lem solving. In cases such as the problem of trying to made by Tulving and Schacter (1990) that perceptual meet Charlie, the model of his visiting the pub every priming represents the operation of a single system, week is so simple as to hardly constitute thinking, but it apparently extending across modalities and across pro- does of course involve most of the elements of problem cessing levels. The neuropsychological evidence alone solving, identifying the problem, retrieving the relevant seems to argue for separate perceptual processing mod- information, setting up a simple model, and extrapolating ules for visual and auditory processing, which themselves to the solution of going to the pub on Tuesday. appear to be fractionable into separable subsystems. I assume, therefore, that episodic memory relies on a Priming refers to a particular experimental paradigm that rather special hnd of learning that is capable of associ- happens to be useful for detecting the persisting after- ating arbitrary events, that happen to be present at the effects of earlier processing. The fact that it can be used same time in conscious . This allows the ca- in broadly analogous ways within different perceptual pacity for the recollection of individual episodes, and the systems is, of course, important, but to refer to the

as- Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/4/3/281/1754997/jocn.1992.4.3.281.pdf by guest on 18 May 2021 use of such episodes to plan future behavior, again sumed underlying process as a single system seems un- through the operation of worlung memory. necessary and potentially rather misleading. Semantic memory in this framework is assumed to If the many implicit and procedural tasks that have result from the accumulation of many episodes. Whereas been studied do indeed reflect different processes and

the recollection of an individual episode requires the subsystems, then one might expect to find differential Downloaded from http://direct.mit.edu/jocn/article-pdf/4/3/281/1932205/jocn.1992.4.3.281.pdf by guest on 28 September 2021 differentiation of that from other , more ge- disruption and preservation of aspects of this form of neric semantic recall does not require the separation of learning in neuropsychological patients, and such data the many experiences that came together to build up are indeed beginning to appear (Butters, Heindel, & that aspect of . If one thinks of experiences as Salmon, 1990). being piled one on top of the other, then episodic mem- ory requires the more or less accurate access to the A MODEL OF WORKING MEMORY residue of a single experience, whereas semantic mem- ory is analogous to viewing the pile of experiences from The overview of human memory just given assigns an above and abstracting what the various instances have in important and central role to working memory. The next common. section gives a brief account of a preliminary model of a working memory system that might play such a role. More detailed descriptions are given elsewhere (Bad- deley, 1986, 1992a-c). Amnesic patients are assumed to have a deficit in the The model evolved from the modal model of the 1960s episodic learning mechanism, a problem that creates that assumed a short-term store that acts as a working difficulties in adding to existing semantic memory. memory system. The most influential version of the Hence, they are typically unable to update their se- modal model was that of Atkinson and Shiffrin (1968), mantic memory, and are unaware of who is the current which assumed a unitary short-term store of limited ca- US. President, and are not able to keep up with current pacity that is responsible for a range of memory phe- developments in sport or to follow the plot of a play. nomena including and the recency effect They may however, still be able to retrieve old infor- in . This limited capacity store was also as- mation from semantic memory, since this has already sumed to be essential for both learning and retrieval. been laid down. In short, I opt for a learning, rather than The model received initial support from neuropsycho- retrieval interpretation of the classic amnesic syndrome, logical evidence that indicated a double dissociation be- while not, of course, denying that damage may also tween long- and short-term storage deficits (Baddeley & cause retrieval deficits in some cases. Warrington, 1970; Shallice & Warrington, 1970). How- I assume that the mechanism that is impaired in am- ever, the modal model also encountered problems in nesia is not necessary for implicit or procedural learning, dealing with the neuropsychological evidence. Patients since this is typically preserved in most patients. This with grossly defective short-term storage appeared to does not of course necessitate the assumption that im- show normal long-term learning, and indeed exhibited plicit learning forms a unitary system; it is sufficient to none of the gross cognitive impairment that one might assume that all implicit learning tasks have in common have expected from an impairment in the functioning of the fact that they do not need to rely on episodic learn- an all important working memory system (Shallice & ing. Indeed, it seems highly unlikely that classical con- Warrington, 1970). ditioning, perceptual priming, pursuit tracking, and the Baddeley and Hitch (1974) investigated this issue acquisition of logical rules such as the Fibonacci series through a series of experiments in which a short-term all depend on a single unitary system, despite the fact memory deficit was simulated by requiring subjects to that all are preserved in amnesic patients (Richardson- rehearse a sequence of digits while performing simul- Klavehn & Bjork, 1988; & Zola Morgan, 1988). taneous reasoning, comprehension, and learning tasks.

Baddeley 283 Since the digit sequences were assumed to fill the work- because subjects rehearse in real time; long words take ing memory system to capacity, performance on the con- longer to recycle, allowing a greater degree of trace current cognitive tasks was predicted to be markedly decay to occur before the next rehearsal cycle. Subvocal impaired. Across the range of tasks, a similar pattern of rehearsal can be prevented by artzculatoy suppression, results occurred; concurrent digit span clearly impaired the requirement for the subject to utter some irrelevant performance, but the degree of disruption was far from sound. This prevents the material being rehearsed, and catastrophic. also interferes with any attempt to encode visual material To account for these and other results, Baddeley and by . Articulatory suppression thus forces Hitch proposed to abandon the of a single unitary the subject to abandon the phonological storage of vis- working memory system, proposing instead a tripartite ually presented material, reducing the level of perfor- model. This assumed an attentional controller termed mance and also abolishing any effect of phonological the central executive, aided by two active slave systems, similarity or irrelevant . Suppression also removes the articulatoy or phonological loop, which maintained the effect of word length, in this case, whether presen- Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/4/3/281/1754997/jocn.1992.4.3.281.pdf by guest on 18 May 2021 speech-based information, and the visuospatial scratch- tation is auditory or visual, since the word-length effect pad or sketchpad, which was capable of holding and relies on subvocalization (Baddeley, Lewis, & Vallar, manipulating visuospatial information. Patients with de- 1984). fective digit span were assumed to have an impairment Vallar and Baddeley (1984) studied a patient, PV, with

in the functioning of the phonological loop; since the a very pure short-term phonological memory deficit, Downloaded from http://direct.mit.edu/jocn/article-pdf/4/3/281/1932205/jocn.1992.4.3.281.pdf by guest on 28 September 2021 central executive and sketchpad were assumed to be finding a pattern of results that was consistent with the unimpaired, they were still able to learn, and did not assumption of a defective short-term phonological store. show any overwhelming problems in everyday cognition. This pattern has subsequently been shown to be char- The deficits they did show were broadly consistent with acteristic of such patients (see Vallar & Shallice, 1990 for the proposed model of the phonological loop as de- a review). scribed below (Vallar & Baddeley, 1984). Although the phonological loop model gives a - ably good account of the performance of both normal subjects and neuropsychological patients on a range of The Phonological Loop memory span tasks, the question remained as to the This is assumed to have two components, a brief speech- functional role of this subsystem. There is some evidence based store that holds a memory trace that fades within to suggest that it plays a role in speech comprehension, approximately 2 secs, coupled with an articulatory con- although most STM deficit patients are impaired on pro- trol process. This process, which resembles subvocal cessing only relatively complex sentences (Vallar & Shal- rehearsal, is capable of maintaining the material in the lice, 1990). phonological store by a recycling process, and in addi- This finding is open to at least two interpretations; one tion is able to feed information into the store by a process possibility is that the system is used only as an optional of subvocalization. One final assumption is that auditory back-up mechanism for dealing with particularly de- spoken information gains automatic and obligatory ac- manding materials. The other possibility is that sufficient cess to the store. phonological storage is preserved in most patients to This simple model is able to account for a relatively allow an experienced user of the language to cope with rich array of laboratory findings. The phonological sim- most sentences. Typically, although such subjects have a ilarity effect, whereby memory span for similar sounding digit span of only one or two items, their span for struc- items such as the letters B C G V T is smaller than for tured sentential material tends to be six or seven words, dissimilar items (F W Y K R), is interpreted as reflecting which may provide a sufficiently wide “win- the fact that the store is speech-based. Similar items have dow” to allow the comprehension of all but very complex fewer distinctive features, and hence are more suscepti- material. A third possibility, that the phonological loop ble to trace decay (Baddeley, 1966a; Conrad & Hull, is not necessary for comprehension, is advocated by 1964). The phonological memory trace can also be dis- Butterworth, Campbell, and Howard (1986), who report rupted by the irrelevant speech effect, whereby the pres- the case of a subject with a developmental impairment entation of unattended spoken material disrupts recall in short-term memory who appears to have no compre- (Colle & Welsh, 1976; Salami. & Baddeley, 1982); such hension problems. Interpretation of this case, however, material is assumed to obtain obligatory access to the remains controversial (see Howard & Butterworth, 1989; phonological store, corrupting the memory trace and Vallar & Baddeley, 1989). leading to impaired performance. Baddeley, Papagno, and Vallar (1988) suggested that Evidence for the articulatory control process comes an important function of the phonological loop might be form the word length effect, whereby memory span for to facilitate long-term phonological learning. They dem- long words is poorer than that for short (Baddeley, onstrated that patient PV, with a very pure short-term Thomson, & Buchanan, 1975). This is assumed to occur phonological memory deficit, showed normal paired as-

284 Journal of Cognitive Neuroscience Volume 4, Number 3 sociate learning for pairs of meaningful words, together Shallice and Warrington (1970) had previously seemed with a severely impaired capacity to learn the novel to rule out STS as a necessary stage in long-term learning. words, needed to acquire items of Russian vocabulary. The observation that such patients have a specific deficit Subsequent work using normal subjects showed that the in working memory, which is clearly linked to a parallel acquisition of novel phonological material was substan- deficit in long-term learning, reopens this question. tially more disrupted than meaningful paired associate There is, in addition, parallel evidence for the impor- learning by articulatory suppression (Papagno, Valentine, tance of both the visuospatial sketchpad and the central & Baddeley, 1991), and by the effects of length and executive components of working memory in long-term phonological similarity (Papagno & Vallar, 1992), results learning, as we shall see below. that reinforce the conclusion that the phonological loop is particularly important for the acquisition of novel vo- cabulary. The Visuospatial Sketchpad If the phonological loop has evolved principally for Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/4/3/281/1754997/jocn.1992.4.3.281.pdf by guest on 18 May 2021 the acquisition of language, then the failure to find major This again is assumed to involve a brief store, together impairments in everyday functioning in STM patients with control processes responsible for registering visuo- becomes readily understandable, since they have already spatial information, and for refreshing it by rehearsal. acquired a language, and typically would not be required There is, however, rather less evidence as to the nature

to learn a new language following their brain damage. of this encode and refresh mechanism, and nothing Downloaded from http://direct.mit.edu/jocn/article-pdf/4/3/281/1932205/jocn.1992.4.3.281.pdf by guest on 28 September 2021 One might, however, expect deficits in the phonological equivalent to the word-length effect in phonological store to be particularly problematic in children. This memory has so far been discovered. However, storage possibility was explored by Gathercole and Baddeley may be disrupted by both irrelevant visually presented (1990a) in a sample of children who had been selected items such as pictures or even patches of color (Logie, as having a specific language disability, which involved a 1986), and by concurrent spatial processing. Such dis- combination of normal or above-average nonverbal in- ruption may occur in the absence of visual input, as with telligence, coupled with a delay of at least 2 years in the demonstration by Baddeley and Lieberman (1980) language development. The children did indeed prove using blindfolded subjects, whose capacity to take advan- to have a particularly marked impairment in the capacity tage of a visual imagery mnemonic was disrupted by the to repeat back material, whether assessed by conven- requirement to track a moving sound source. tional memory span measures, or in terms of their ca- The two types of interference, pattern-based and spa- pacity for repeating back nonwords, varying in length. tial, may be associated with separate subcomponents of Gathercole and Baddeley (1989) argued that nonword the sketchpad. The evidence for this is reviewed by Farah repetition provides a better estimate of phonological (1988), who presents evidence from studies of both nor- storage than digit span, since it does not rely on knowl- mal subjects and neuropsychological patients, using both edge of digits or other lexical items, and is functionally memory and psychophysiological measures, and argues more similar to the material involved in learning new for the anatomical and functional separation of the pat- vocabulary than the strings of unrelated lexical units that tern-based and spatial components of visual short-term constitute the standard span procedure. Nonword repe- memory. The pattern-based system appears to be partic- tition proved to be the best predictor of vocabulary ac- ularly dependent on the occipital lobes, while the spatial quisition in children tested over a range of ages between component appears to depend more on parietal pro- 4 and 8 years, and for the 4 year olds at least, cross- cessing. Subsequent work by Goldman-Rakic based on lagged correlation suggests that good nonword repeti- single cell recording in awake monkeys performing a tion leads to good vocabulary, rather than the reverse. visual STh4 task suggests that there may also be a frontal Service (1989) showed in a study of Finnish children lobe involvement which may possibly be associated with that their capacity for learning English was better pre- the executive control of (Goldman-Rakic, dicted by their capacity for nonword repetition than by 1988; Kojima & Goldman-Rakic, 1984). any of a range of other cognitive measures, while Gath- As in the case of the phonological loop, there is evi- ercole and Baddeley (1990b) showed in a simulated dence for an involvement of the sketchpad in long-term vocabulary learning task that children who were low in memory. Baddeley and Lieberman (1980) showed that a nonword repetition skills performed more poorly than concurrent visuospatial tracking task disrupted the verbal high repetition children of equal nonverbal . learning performance of subjects using a spatial imagery This pattern of results not only argues for an important mnemonic, while having no effect on their capacity for role of the phonological loop in , learning an equivalent list by rote rehearsal. Similarly, but also casts new light on the question of the role of Logie (1986) found that presenting visual material such short-term and working memory in long-term learning. as color patches or pictures that the subject was in- The fact that patients with STS deficits appeared to show structed to ignore interfered with verbal paired-associate normal long-term learning in studies such as that of learning based on a visual imagery pegword mnemonic,

Baddelq 285 while again having little or no effect on learning by verbal strategy becoming automated. The capacity of the super- rote rehearsal. visory system to function in this way is therefore directly challenged, with the randomness of the output providing an indication of its capacity. When used as a secondary The Central Executive task, random generation proves to be very disruptive of This is the most important but least well understood executive processes such as are, for example, involved component of working memory. It was initially neglected in assessing a chess position and choosing an optimal on the grounds that the peripheral slave systems offered next move (Baddeley, 1992b). more tractable problems, but has subsequently begun to A good deal of recent work on the analysis of executive attract considerably more research. Baddeley (1986) pro- processes has been concerned with a study of patients posed to use the Norman and Shallice (1980) model of with frontal lobe damage. In a typical study, patients with as a workmg hypothesis for the central known frontal lesions might be required to perform a

executive. This model assumes that action can be con- wide range of tasks that is expected to test different Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/4/3/281/1754997/jocn.1992.4.3.281.pdf by guest on 18 May 2021 trolled at either of two levels, by the operation of a series . The hope is to find one or two tasks of existing schemata, or via the Supervisory Attentional that best characterize this deficit, and that might then System (SAS), which takes control when novel tasks are throw light on the nature of the underlying executive involved, or when existing habits have to be overridden, processes. In practice, such studies tend not to have for example, when danger threatens. A detailed account produced evidence pointing to certain crucial tasks; typ- Downloaded from http://direct.mit.edu/jocn/article-pdf/4/3/281/1932205/jocn.1992.4.3.281.pdf by guest on 28 September 2021 of the model is presented by Shallice (1992), and its ically, the studies find very considerable variability application to working memory is discussed by Baddeley among subjects in terms of both the nature and severity (199213). of their impairment, suggesting a constellation of sub- Shallice’sprincipal concern was to provide a model of processes rather than a single controlling module (Dun- the very characteristic pattern of deficits shown by certain can, 1992; Shallice, 1992). Given the size and complexity patients with bilateral damage to the frontal lobes. Such of the frontal lobes, and their richness of connection patients show marked problems in planning and in at- with other parts of the brain, such a result is perhaps tentional control, sometimes perseverating on a single not surprising. It suggests, however, that the central ex- response, while in other situations they appear to be ecutive itself will need to be fractionated into a number captured by whatever they encounter. Shallice of separable executive processes. argues that the frontal lobes are necessary for the oper- Given the probable complexity of the central execu- ation of the SAS. In its absence, patients may become tive, one approach is to attempt to isolate particular locked into an existing , or, conversely have their functions that are assumed, on a priori grounds, to be captured by any available triggering stimulus. an important feature of the executive, and to design tasks Within the working memory framework, Baddeley has that will measure these capacities. One example of this used the Shallice model to explain existing data on the is given in the attempt to test the hypothesis that patients limited capacity for random generation. When subjects suffering from Alzheimer’s disease (AD) show a partic- are asked to produce a random string of items such as ularly marked impairment in the functioning of the cen- letters of the alphabet, they are capable of performing tral executive (Spinnler, Della Sala, Bandera, & Baddeley, the task well, provided the required rate is slow. As they 1988). speed up, however, they become progressively more The working memory model assumes that one very biased in letter selection frequency and more stereo- important function of the executive is to coordinate in- typed, producing sequences from the alphabet such as formation from separate subsystems. This was studied by PQR and RST, and familiar such as USA and combining pursuit tracking, which is assumed to load on BBC (Baddeley, 1966b). The requirement to perform a the sketchpad, with concurrent digit span, expected to concurrent task also decreases randomness. The capacity make heavy demands on the phonological loop. Tracking for random generation tends to be associated with over- speed and digit sequence length were adjusted so as to all intelligence, and to decline with age. give an equivalent level of performance in three groups, Although the data in this area are highly consistent patients suffering from AD, normal elderly subjects, and and clear, they did not prove easy to interpret. However, young controls. Subjects were then required to perform the Norman and Shallice model offers a clear explanation the two tasks simultaneously. as follows: The task of retrieving a sequence of letters in While the normal elderly were no more impaired than random order places the subject in a conflict situation; the young by the requirement to coordinate two tasks, the names of letters of the alphabet are readily retriev- the Alzheimer patients showed a marked deterioration able by reciting the alphabet, but this clearly infringes in performance, supporting the view that their executive on the requirement to be random. Consequently, the capacity was seriously impaired (Baddeley, Logie, Bressi, subject must continually attempt to develop new retrieval ’Della Salla, & Spinnler, 1986). In a subsequent longitu- strategies, at the same time as avoiding the existing al- dinal study, patients suffering from AD showed a steady phabetic , and avoiding the danger of any deterioration in their capacity to combine tasks as the

286 Journal of Cognitive Neuroscience Volume 4, Number 3 disease progressed, in contrast to their performance on Baddeley, A. D. (1992~).Is working memory working? Quar- the individual tasks, which remained relatively stable terly Journal of , 44A, 1-3 1. Baddeley, A. D., Bressi, S., Della Sala, S., Logie, R., & & (Baddeley, Bressi, Della Sala, Logie, Spinnler, 1992). Spinnler, H. (1991). The decline of working memory in Al- This latter approach has something in common with zheimer’s Disease: A longitudinal study. Brain, 114, 2521- that adopted by Daneman and Carpenter (1980, 1983), 2542. who define working memory as the capacity to simulta- Baddeley, A. D., & Hitch, G. (1974). Working memory. In neously store and process information. They have de- G. A. Bower (Ed.), i%epsychology of learning and motiva- tion (Vol. 8, pp. 47-89). New York: Academic Press. vised a number of tasks that combine storage and Baddeley, A. D., Lewis, V. J., & Vallar, G. (1984), Exploring the processing, and have shown that performance on these articulatory loop. Quarterly Journal of Experimental Psy- tasks correlates with important cognitive skills such as chology, 36, 233-252. language comprehension and , with subjects who Baddeley, A. D., & Lieberman, K. (1980). Spatial working are low in working memory capacity having difficulty in memory. In R. S. Nickerson (Ed.), Attention and perfor- mance (pp. 521-539). Hillsdale, NJ: Lawrence Erlbaum. coping with complex material such as that presented by Baddeley, A. D., Logie, R., Bressi, S., Della Sala, S., & Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/4/3/281/1754997/jocn.1992.4.3.281.pdf by guest on 18 May 2021 garden path sentences, or by texts requiring inference Spinnler, H. (1986). and working memory. Quur- for their comprehension (Daneman & Carpenter, 1980, terly Journal of Experimental Psychology, 38A, 603-618. 1983). Baddeley, A. D., Papagno, C., & Vallar, G. (1988). When long While Carpenter and her colleagues would not ex- term learning depends on short-term storage. Journal of Memoy and Language, 27, 586-595. plicitly adopt the particular model of working memory Downloaded from http://direct.mit.edu/jocn/article-pdf/4/3/281/1932205/jocn.1992.4.3.281.pdf by guest on 28 September 2021 Baddeley, A. D., Thonison, N., & Buchanan, M. (1975). Word just described, they do not deny the existence of more length and the structure of short-term memory. Journal of peripheral systems such as the phonological loop. Their Verbal Learning and Verbal Behavior, 14, 575-589. work does, however, concentrate on the more executive Baddeley, A. D., & Warrington, E. K. (1970). Amnesia and the aspects of working memory, typically using individual distinction between long- and short-term memory. Journal of Verbal Learning and Verbal Behavior, 9, 176-189. differences as a tool for analyzing the role of working Butters, N., Heindel, W. C., & Salmon, D. P. (1990). Dissocia- memory in complex cognitive skills such as comprehen- tion of implicit memory in dementia: Neurological implica- sion and reasoning. Such an emphasis on individual dif- tions. Bulletin of the Psychonomic Society, 28, 359-366. ferences has the further advantage of linking up with Butterworth, B., Campbell, R., & Howard, D. (1986). The uses more traditional psychometric approaches. This appears of short-term memory: A case study. Quarterly Journal of Experimental Psychology, 38A, 705-738. to be meeting with some success, since working memory Colle, H. A,, & Welsh, A. (1976). Acoustic masking in primary measures appear to correlate very highly with perfor- memory. Journal of Verbal Learning and Verbal Behavior, mance on a range of reasoning tasks that have tradition- 15, 17-32. ally been used for measuring intelligence (Kyllonen & Conrad, R., & Hull, A J. (1964). Information, acoustic confw Chrystal, 1990). sion and memory span. British Journal of Psychology, 55, 429-432. 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