Case studies related to the multi-store model

Transcription

1 Case studies related to the multi-store model The cases of HM and Clive Wearing are related to the multi-store model, in that both cases support the functioning of STM and LTM as independent mechanisms operating in sequence. The basic idea is that HM's anterograde amnesia evidenced severe malfunctioning of STM, and that in turn meant that any new memories could not be encoded into LTM, just as the multi-store model suggests. The same goes for Clive Wearing. Further, the fact that both men retained some procedural memories and a few episodic memories (especially those with some emotional connection) supports the idea that memory exists in separate cognitive stores. Basically, both cases suggests that amnesia results from the breakdown of the encoding sequence from STM to LTM, which is exactly what the multi-store model predicts. By contrast, Shallice and Warrington's (1970) case study of KF, who was a neuropsychological patient who had lost almost all of his STM capacity due to a motorcycle accident, but was yet still able to form some new long term memories. According to the multi-store model, KF should not have been able to form new LTM, because of the damage to his STM which should have prevented encoding. However, through a series of experiments, Shallice and Warrington were able to establish first that KF's STM system was defective, while his LTM was normal this supports the existence of separate stores of memory, just as the multi-store model suggests (Shallice and Warrington 1970). However, these findings also suggest that the multi-store model might be too simple, and that verbal memories may be encoded directly to LTM, without processing in LTM, if the inputs are processed semantically. This suggests that rehearsal in STM might not be necessary for meaningful verbal inputs, which go straight to LTM their results basically indicate that there might be other ways to access LTM than the multi-store model suggests. Page 1 Figure 6. A suggested model for processing in verbal memory experiments. (The ABC circuit indicates the rehearsal loop in STM). Source: Shallice and Warrington 1970

2 Shallice and Warrington didn't specify how verbal memory might be processed from LTM to speech, for example. Their research suggested another possible pathway for memory processing, but it didn't specify how those memories might be retrieved. It's all in the spirit of science, and ultimately the case of KF clearly shows the segregation of STM and LTM, and suggests an alternative pathway for verbal memory to LTM it both challenges and supports the multi-store model. Theoretical evaluation of the multi-store model Beyond the many studies that support and challenge the multi-store model, there are also many theoretical considerations with the model itself. First, the multi-store model is a bit reductionist. This is sometimes a good thing, because reductionist explanations boil a complex phenomenon (like memory) down to simpler components, and that overall makes the complex process easier to understand. However, this also means that important details can be lost in the oversimplification. For example, the process for encoding verbal memory into LTM might be more complex than the multi-store model suggests, as evidenced by the case of KF. The multi-store model might also be overly simplistic in its depiction of encoding from STM to LTM. The model itself suggests that rehearsal is the main process involved in encoding, but this doesn't explain incident learning (when people learn something without any rehearsal), and it also doesn't explain the difference between types of rehearsal. Elaborative rehearsal refers to thinking about the meaning of a stimulus item like a word, and that semantic element may be involved in LTM encoding. Maintenance rehearsal, by contrast, refers to the simple repetition type of rehearsal that keeps a stimulus item cycling through STM, and is not thought to be effective for LTM encoding. The point is that the multi-store model makes no distinction between these types of rehearsal, and so may be too simplistic. A related problem with the model is that it sort of suggests that LTM is some kind of bottomless memory pit, and everything in there was encoded through rehearsal. There's no question that memory is way more complex than that, so the multi-store model is limited by its simplicity on several levels. LTM is well-understood to be composed of several subsystems or subprocesses and types of memory. Explicit memory (also known as declarative memory), for example, is memory that requires some level of conscious thought, like remembering an elementary school teacher or the details of a study on an IB exam. Explicit memory is further subdivided into semantic memory for facts, events, and accumulated knowledge, and episodic memory for autobiographical details and so on. Again, the multi-store model doesn't account for this complexity, framing LTM too generally. Page 2

3 Figure 7. The main strengths and limitations of the multi-store memory model. Furthermore, the multi-store model suggests that memory is linear, but schema theory challenges this Bartlett's (1932) research shows how cultural schemas may interfere with the retrieval and reconstruction of memory, and Loftus and Palmer's (1974) study showed how memory might be altered by verbs used during questioning. Both of these studies demonstrate that memory might not be as linear as the multi-store model suggests. Also, cognitive processes like memory are also affected by a range of social factors and biological influences, so it's not all about the cognitive processing memory is influenced by multiple processes. Models of cognitive processes the working memory model The multistore model of memory might be the foundation for modern memory research, but it's far from the only model. The working memory model has emerged in recent years as a leading contender for theories of short-term memory, and it goes into a whole lot more detail than the multi-store model. The working memory model is focused on the same cognitive process (memory) in general, but it theorizes a lot more specifically about processing in STM. When psychologists talk about "working memory", they're really referring to the cognitive processes involved in conscious awareness right here, right now. Working memory is basically like ongoing cognition. Working memory is important to psychological functioning, every day, from moment to moment. It's also limited, and that leads to certain challenges. Check it out: Page 3

4 As Doolittle says, working memory "allows us to make sense of the world around us" (TED 2013), but it's also limited in capacity, duration, and focus. On the one hand working memory allows for communication, problem solving, and critical thinking, and it somehow manages multiple processes at once. A student for example can listen to a teacher's lecture, evaluate its pros and cons, and ask questions about it, all while monitoring messages on a social platform or something. The trouble is that most people can really only handle about four of those tasks at a time STM capacity is traditionally thought to be 7 +/- 2, but Doolittle argues that fmri research says that capacity is closer to four (TED 2013). These limits to working memory have all sorts of implications for individuals (TED 2013): Conscious awareness, and what people do from moment to moment. Practice rehearsal and practice can increase working memory capacity. Thinking elaboratively and illustratively working memory function is improved by making connections through imagery. Organization and support humans are "meaning making machines", so organization helps structure knowledge and experience. Teachers and textbooks are useful for this kind of thing. To put it even more simply: "What we process, we learn. If we're not processing life, we're not living it." (TED 2013) Maybe it's just a cognitive process, but it's difficult to imagine anything more important to individual identity and being than memory and conscious awareness, and...that's exactly what the working memory model is all about. Working memory model Building on Atkinson and Shiffrin s research, Baddeley and Hitch (1974) developed an alternative model of short-term memory which they called the working memory model. They were motivated to develop a more complex model of memory by the findings of researchers like Shallice and Warrington (1970), whose findings challenged the structure of the multi-store model. They argued that short-term memory is not a static store, but a complex and active information processor composed of several dynamic subsystems. It's important to note that Baddeley and Hitch's model is not a model of the complete process of memory, but just of short-term memory. This is how working memory fits into the multi-store model: Page 4

5 Figure 1. Working memory model in the big picture the model itself focuses on STM processing (Baddeley and Hitch 1974). As originally conceived, the working memory model is composed of three main parts (Baddeley and Hitch 1974): The central executive is the most important component of the model, although little is known about how it functions. It is responsible for monitoring and coordinating the operation of the visuo-spatial sketchpad and the phonological loop, and it relays their information to long-term memory. The central executive decides which information is attended to, and where in working memory to send it. The central executive basically functions like the "boss" of short-term memory processing. The phonological loop is the part of working memory that deals with spoken and written material. This is the part that has the articulatory control, whereby numbers or words can be rehearsed or repeated for retention in short-term memory, or transferred to the phonological store. The material is rehearsed again and again in a loop. The visuo-spatial sketchpad deals with what things look like and spatial awareness. It comes into action with visual stimuli like a map, or a diagram, or a painting, or somebody's face. The working memory model makes several clear departures from the multi-store model. First, it specifies a lot more activity in STM than simple rehearsal instead, STM enables Page 5

6 complex cognitive activities related to the integration and manipulation of multiple mental representations, all at once. Second, the working memory model allows for multiple processes in STM at once, which actually makes a lot of sense when the model's held up against STM processing in the real world most people are dealing with multiple inputs, almost all the time. Finally, the working memory model specifies a fundamental relationship between LTM and STM, theorizes as the central executive this is what actually enables STM to be an effective "workspace" for memory processing. The central executive basically manages memory processing, and therefore, conscious awareness to at least some extent. Testing working memory capacity Working memory capacity varies quite widely from person to person, so memory researchers are interested in both why this happens, and where the differences in capacity lie. Some tests of working memory are deliberately designed to isolate verbal and visual inputs. For example, check out this dual task procedure for testing working memory capacity. Participants are asked to complete it one line at a time, saying "yes" or "no" aloud in response to the arithmetic question, all while memorizing the words (Smith and Kosslyn 2007): IS (6 X 2) + 3 = 15? SHIRT IS (3 X 5) + 2 = 17? COAT IS (5 X 5) - 5 = 20? PENCIL IS (8 X 4) - 2 = 34? DOG IS (7 X 3) + 4 = 25? EARTH IS (4 X 9) ? SCHOOL The idea is that the task makes two demands on working memory: the arithmetic question is processed by the visuospatial sketch pad, and the word is processed by the phonological loop. Most people are able to remember around 2 or 3 of the words, and very few people have a working memory capacity as high as 6. Updated working memory model The working memory model spawned its own body of research into STM processing, testing various components like phonological processing, word length effects, serial position effects, visual STM, spatial STM, episodic memory, links between working memory and LTM, and...the list goes on. More importantly, all of this research has led to revisions of the working memory model, because it gradually became clear that the working memory model didn't capture all of the phenomena associated with STM processing. For example, some episodic memories are both visual and phonological at the same time, so memory may be more integrated than the model suggests (as framed Page 6

7 above), the working memory model says that visual and phonological information would be stored separately. Baddeley (2000) eventually accounted for some of these missing pieces and updated the model, adding an episodic buffer between the central executive and LTM. This acts as a 'backup' store which communicates with both long term memory and the various components of working memory, with a focus on integrating multimodal memories (Baddeley 2000). An updated model of course calls for an updated diagram. This is what the working memory model looks like now: Figure 3. The working memory model, after the inclusion of the episodic buffer (Baddeley 2000). The long-term knowledge systems basically refer to LTM, and are theoretically subdivided into three main components: Language, which interacts with the phonological loop. Episodic LTM, which interacts with the episodic buffer. Visual semantics (meaningful visual knowledge), which interacts with the visuospatial sketchpad in STM. Essentially, the subsystems in long-term storage link up with matching processing systems in short-term storage, and those STM systems, along with the central executive, are what make up working memory. It's an incredibly flexible system, and it's running Page 7

8 almost all of the time. It's a bit abstracted probably, but in the long run working memory plays the major role in conscious awareness it's that important. Evaluation of the working memory model Just like any model, the working memory model is far from perfect. There's lots of evidence to support it, but it faces many challenges too. That shouldn't be surprising, because memory is a complex cognitive process, and although research has come a long way in the past few decades, psychologists still aren't really all that close to cracking the mysteries and machinations of memory. It is generally agreed that short-term memory is a working memory with processing and filtering powers. The model is based on two premises: if two tasks make use of the same component of working memory, they cannot be performed successfully together, but if two tasks make use of different components, it should be possible to perform them as well together as separately. This seems to hold true in real life as well as in psychology experiments. Reading a text while trying to hold a conversation, for example, will often result in reading the words from the text aloud. Empirical support for the working memory model is impressive there are literally hundreds and hundreds of empirical studies out there related to the working memory model. While the studies below generally support the working memory model, it's important to note that they also influenced it, and some of the results have been used to modify and improve the model over the years. Limitations of the working memory model The first criticism of course is that the working memory model isn't really a complete theory of memory, because it focuses on STM. There may be a whole other set of processes going in LTM that have any number of unknown impacts on STM processing, so the working memory model is sort of like a close-up of an incomplete picture or something. It's a good theory, but it doesn't cover everything. Sensory memory is probably important too, and the working memory model doesn't really touch on it. Further, it still might not be precise enough. There's general agreement that the phonological loop should be split into two separate components: a phonological store and and an articulatory control system. A similar argument is made against the visuospatial sketchpad, with some theorists arguing that it too should be split into separate components for visual and spatial memory. The argument for this is built on studies investigating spatial awareness in blind people. Jones (1975) conducted a meta-analysis of experiments on spatial awareness in blind people, and concluded that "vision is not a necessary condition for spatial awareness" (Jones 1975). Therefore, the visuospatial sketchpad might not be specific enough to how STM actually works, because visual and spatial inputs appear to be processed independently. Page 8

9 There's also very little evidence for how the central executive works and what it does. Its functioning can be inferred, as seen in some of the dual-task experiments, but the central executive is exceedingly difficult to isolate, probably because it's so multi-functional. Another limitation is that the working memory model doesn't really explain how processing abilities can change with practice or time. The Strobach and Schubert 2015 study discussed above is a good example of this, because it shows how executive functioning improved in the non-gamers after 15 hours of practice. The working memory model doesn't explain this, so there's still a lot to learn about how it functions. Strengths of the working memory model Arguably, the working memory model as it currently stands is the product of decades of research and criticism. It has been modified and updated on the basis of research findings over the years, and in this way the working memory model stands as an almost ideal example of scientific inquiry it all comes down to data and an open mind. Baddeley, for his part, has revised the model multiple times, so it's in a state of constant refinement. It's also supported by a seemingly never-ending range of empirical studies, only a few of which are described above. Further, the working memory model is more realistic than the multi-store model of memory because it allows for dynamic processing. STM capacity, for example, is not static or fixed, but changes according to variables like word length or input modality (visual, spatial, verbal, etc.). While computer analogies might work to a very limited degree in explaining cognitive processing, the reality is that human mental processes are far more dynamic than computer processing, and the working memory model at least accounts for this, even if it can't fully explain it. Similarly, the multi-store model of memory suggests that STM is a unitary system, kind of like a hopper for all short-term inputs, regardless of their modality. The working memory model provides a much more complete explanation of STM, and the independent visuospatial, phonological, and executive components are much more in line with the complexity of cognitive processes in humans. When it comes down to it, this means that the working memory model has more ecological validity than the multistore model. Further, the multi-store model over-emphasizes rehearsal in STM, and the working memory model goes way beyond that to allow for several types of cognitive processing within STM. Finally, the working memory model passes the "application test", meaning that the model can be used to explain all kinds of cognitive tasks, including verbal reasoning, comprehension, reading, problem solving, visual processing, spatial processing, and so on. The multi-store model was a good start, but the working memory model is taking things to the next level. Page 9

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