Working Memory Model Essay Link

Executive System

The central executive monitors the control processes in WM. There have been a number of cognitive activities assigned to the central executive, including coordination of subsidiary memory systems, control of encoding and retrieval strategies, switching of attention in manipulation of material held related to the verbal and visual spatial systems, and the retrieval of information from LTM (e.g., Baddeley, 1996; Miyake, Friedman, Emerson, Witzki, & Howerter, 2000). Although the executive function has separable operations (e.g., inhibition, updating), these operations share some underlying commonality (e.g., see Miyake et al., 2000, for a review). Several of these activities have been reduced to three functions: (a) inhibition of irrelevant responses; (b) updating and monitoring of working memory representations; and (c) shifting between mental sets (Miyake et al., 2000). The research appears to support the notion that children with LD suffer from problems with two processes of the executive system: the suppression of irrelevant information and updating.

One activity related to the central executive that has been implicated as a deficit in children with LD is their ability to suppress irrelevant information under high processing demand conditions (e.g., Chiappe, Hasher, & Siegel, 1999; De Beni, Palladino, Pazzaglia, & Cornoldi, 1998; Swanson & Cochran, 1991). These studies have investigated whether children with LD had greater trade-offs and weaker inhibition strategies than average achievers on divided attention tasks. For example, Swanson designed three experiments to reflect attentional demands on both the verbal and visual-spatial system. In one of the experiments (Swanson, 1993b, Exp. 1), a concurrent memory task, adapted from Baddeley (Baddeley, Eldridge, Lewis, & Thomas, 1984) was administered to LD and skilled readers. The task required subjects to remember digit strings (e.g., 9, 4, 1, 7, 5, 2) while they concurrently sorted blank cards, cards with pictures of nonverbal shapes, and cards with pictures of items that fit into semantic categories (e.g., vehicles—car, bus, truck; clothing—dress, socks, belt). Demands on the central executive capacity system were manipulated through the level of difficulty (three vs. six digit strings) and type of sorting required (e.g., nonverbal shapes, semantic categories, blank cards). The results showed that readers with LD could perform comparably to chronological age (CA)-matched peers on verbal and visual-spatial sorting conditions that involved low demands (i.e., three digit strings), and that only when the coordination of tasks became more difficult (e.g., six digit strings) did ability group differences emerge. More important, the results for the high memory load condition indicated less recall for readers with LD than for CA-matched (and achievement-matched) peers during both verbal and nonverbal sorting. Because recall performance was not restricted to a particular storage system (i.e., verbal storage), one can infer that processes other than a language-specific system accounted for the results.

Several studies (e.g., Swanson, 1994, 1993a,b; Swanson & Ashbaker, 2000; Swanson, Ashbaker, & Lee, 1996; Swanson & Sachse-Lee, 2001b) on executive processing have focused on updating. Updating requires monitoring and coding of information for relevance to the task at hand, and then appropriately revising items held in WM. Thus, studies have included tasks that follow the format of Daneman and Carpenter’s Sentence Span measure, a task strongly related to student achievement (see Daneman & Merikle, 1996, for a review) that requires simultaneous juggling of storage and processing requirements. For example, in the reading span task by Daneman and Carpenter (1980), participants are required to read sentences and verify their truthfulness (processing requirement) while trying to remember the last word of each sentence (storage requirement). These studies have consistently found LD readers to be more deficient than skilled readers in WM performance using this task format, which taps central executive processes related to updating (Miyake, Friedman, Emerson, Witzki, & Howerter, 2000).

In general, a number of studies show that some participants with LD matched to NLD participants on IQ are deficient on tasks that measure specific components of executive processing. For example, a cross-sectional study (Swanson, 2003) compared skilled readers and LD readers across four age groups (7, 10, 13, 20) on phonological, semantic and visual-spatial WM measures administered under conditions referred to in Swanson et al. (1996): initial (no probes or cues), gain (cues that bring performance to an asymptotic level), and maintenance conditions (asymptotic conditions without cues). The results clearly showed that the LD readers had less WM recall than skilled readers for all task conditions, tasks that involved the processing of phonological, visual-spatial, and semantic information. Further, the study provided no evidence that LD readers’ WM skills “catch up” with skilled readers as they age, suggesting that a deficit model rather than a developmental lag model best captures such readers’ age-related performance. Further studies (Swanson, 1992, 1993b; Swanson et al., 1996) have found evidence of domain general processing deficits in children and adults with LD, suggestive of executive system involvement.

Those components of the executive system deficient in individuals with LD are related to updating (e.g., Siegel & Ryan, 1989; Swanson, Ashbaker & Lee, 1996) and the inhibition of irrelevant responses (e.g., Chiappe, Hasher, & Siegel, 2000; Carretti et al., 2009). Some alternative explanations to these findings on executive processing (Swanson, 2001a,b), for example that deficits are due to ADHD, domain specific knowledge, and/or low-order processes (such as phonological coding), have been addressed elsewhere (see Swanson, 2005, 2011; for a review of studies).

A01: Outline the features of the Working Memory Model

The working memory model was proposed by Baddeley & Hitch (1974) as an alternative to the multi-store model of memory. It has been developed to directly challenge the concept of a single unitary store for short-term memories. The working memory model is based upon the findings of the dual-task study and suggests that there are four separate components to our working memory (STM). 

The most important component is the central executive; it is involved in problem solving/decision-making. It also controls attention and plays a major role in planning and synthesizing information, not only from the subsidiary systems but also from LTM. It is flexible and can process information from any modality, although it does have a limited storage capacity and so can attend to a limited number if things at one time.  

 Another part of the working memory model is the phonological loop, it stores a limited number of speech-based sounds for brief periods. It is thought to consist of two components - the phonological store (inner ear) that allows acoustically coded items to be stored for a brief period and the articulatory control process (the inner voice) that allows sub-vocal repetition of the items stored in the phonological store.

Another important component is the visuo-spatial scratch pad; it stores visual and spatial information and can be thought of as an inner eye. It is responsible for setting up and manipulating mental images. Like the phonological loop, it has limited capacity but the limits of the two systems are independent. In other words, it is possible, for example, to rehearse a set of digits in the phonological loop while simultaneously making decisions about the spatial layout of a set of letters in the visual spatial scratchpad.  

Finally in 2000 Baddeley proposed an additional component, the episodic buffer.  It is responsible for integrating & manipulating material; it has limited capacity and depends heavily on executive processing. It binds together information from different sources into chunks or episodes, hence the term ‘episodic’. One of its important functions is to recall material from LTM & integrate it into STM when working memory requires it (e.g. imagining an elephant ice-skating).

One strength of the WMM is that there is evidence to support the phonological loop.

Baddeley (1975) word length effect (short words easier to recall than long). 
Prevention from being able to rehearse words by repeating an irrelevant sound. The word length effect was lost as articulatory suppression fills the phonological loop.

A second strength of the WMM is that there is evidence to support the visuo-spatial scratch pad. 

Baddeley (1973) PPts hold a pointer with a moving spot of light whilst visualising the block capital letter F. 
Tracking and letter imagery tasks were competing for the limited resources of the visuo-spatial scratch pad. Where as the tracking and verbal tasks use separate components.

One weakness of the working memory model is that the Central Executive is difficult to quantify.
Little research has been done to understand the central executive.
Nobody knows the  capacity limitations of the central executive? 
Richardson (1984) Problems specifying the precise function of the central executive. 
It cannot be falsified.

A second weakness of the WMM is that the research is lab based.whilst this in itself is not a problem, there is the possibility of lack of ecological validity, especially the artificial setting. However, the model could be argued to have mundane realism since the tasks given to participants COULD potentially represent experienced in daily life (e.g. riding your bike & listening to your ipod). 
Robbins (1996) Chess players.

Aim:To study the role of the Central Executive in remembering chess positions by investigating the effect of generating random letter strings.

20 chess players- given 10 seconds to remember the position of 16 pieces from a chess game.
When memorizing participants either:1. used the central executive by generating random number sequences while avoiding meaningful combinations (H, G, P)or2. carried out articulatory suppression task ( said 'the, the, the' in time with a metronome)
After 10 seconds, memory was tested as ppts were asked to arrange the pieces as they first memorized them.

The letter generation = poor memory and performance.
The articulatory suppression task = good memory and performance.
The central executive not the  phonological loop plays a role in remembering chess positions.

The design of the controlled experiment allows the researcher to claim cause and effect. This mean that we can say that the letter generation task causes poor memory recall.
Randomly generating letter sequences are a valid way of engaging the central executive.
Further conditions have shown that the visuo-spatial scratchpad is used in recalling chess positions.


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