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Article Excerpt
Memory updating refers to the act of modifying the content of memory. In daily life we are usually requested to update memory when encountering conflicting information or when old information has to be substituted (Bjork, 1978). In the context of working memory, the updating of memory content is usually particularly demanding in terms of attentional resources since the mind is required quickly to substitute old with new information. For example, while looking for the cheapest food on the shelves of a grocery store we need to substitute price information when we find a more advantageous item. If there is the same product in several different packages (i.e. with different weights) we also need to calculate the net prices. The importance of updating can be considered also with reference to complex cognitive abilities. An example is reading comprehension in which the reader is required continuously to substitute information which has become less relevant with new more important information (Palladino, Cornoldi, De Beni, & Pazzaglia, 2001).
Despite its frequency, it is not completely clear how the updating process actually works. Although different updating tasks can be found in the literature (see for example Miyake et al., 2000; Oberauer, 2002; Verhaeghen & Basak, 2005), in many studies the criteria for updating are simply represented by item recency. For example, in one of the first studies on memory updating, participants were presented either with certain-length or with uncertain-length lists of items in order to measure their running memory span, described as a measure of the ability to manipulate memory content fluidly over an allocated period of time (Pollack & Johnson, 1963; Pollack, Johnson, & Knaff, 1959). In the certain-length lists condition, in which participants were informed of the length of the to-be-presented list, they received instructions to report 'as many items as possible' from the final portion of each list. In the second version of the running memory span task (uncertain-length), participants received the same instruction but they ignored the length of the list (see also Crowder, 1969; Morris & Jones, 1990; Parkinson, 1980). Thus in the latter case participants did not know when they would encounter the target information. The two versions of the task lead to a different level of performance with a benefit for the certain-length condition. In addition, Pollack et al. highlighted differences in carrying out the two types of tasks. In the first case, participants were prone to adopt certain strategies in the attempt to recall target items, for example ignore the initial portion of the list, and then actively focus on a small section of the list. Two further strategies, observed by Pollack et al., were the grouping of the presented information and the overt repetition of the digits. In contrast, in the second case (uncertain-length list), the procedure of the task partially prevented the use of any strategy and seemed to involve an updating process. Indeed, participants had initially to store the first items and then update the memory content by dropping the oldest item and inserting the new one in the pool of the most recent ones. Pollack et al. suggested that to carry out this version of the running memory span task effectively participants have to control for proactive interference, especially for long, uncertain lists. Pollack et al. also found that an increase in the speed of presentation was associated with an impairment of performance both in certain- and uncertain-length lists.
Commenting on these first results, Morris and Jones (1990) suggested that the central executive could be involved in the execution of the uncertain-length list updating task devised by Pollack et al. (1959). With Baddeley and Hitch's working memory model (1974; Baddeley, 2000) in mind, they provided evidence of central executive involvement, demonstrating that tasks interfering with the articulatory loop component of working memory (articulatory suppression and irrelevant speech) impaired only the order component of the updating performance, but did not damage the updating component. Thus, according to Morris and Jones, the updating process requires central executive resources but not the phonological loop. Conversely, the serial recall component of the task requires the phonological loop but not the central executive. This result was further confirmed by Van der Linden, Bredant, and Beerten (1994), who demonstrated that elderly participants' recall was affected to a greater extent than young participants' recall by the increase in the number of updates. In contrast, serial recall was weakly damaged in older adults and their decline in performance was comparable to that of younger participants.
However, some authors have pointed out that the classical memory updating task does not necessarily imply an updating process since participants could adopt a more passive strategy waiting until the end of the presentation and then retrieving the correct items on the basis of a recency criterion (Carretti, Cornoldi, De Beni, & Romano, 2005; Palladino et al., 2001; Ruiz, Elousa, & Lechuga, 2005). Ruiz et al. demonstrated, with a variant of the Morris and Jones' task, that the probability of memory intrusions increased for items closer to the target positions (pre-target items). They interpreted this result as showing a major involvement of the articulatory loop compared with that of the central executive. Furthermore, they suggested that Morris and Jones's (1990) task is not well-suited for analysing the memory updating process, intended as an executive function, because the performance in this task could be attributable to passive maintenance mechanisms.
Similar considerations to those of Ruiz et al. (2005) had been previously made by other authors (Palladino et al., 2001) attempting to create a task that could measure the process of updating information in working memory, rather than the simple recall of the last presented items. Palladino et al. devised a task that required selecting items on the basis of a criterion which was not simply based on item recency, but introduced a relevance principle. In their task, participants were required to listen to a list of words (objects and animals) and then to remember the three smallest items, thus assuming that the relevance was defined by the item size. In fact, participants were required to recall the smallest presented items according to their presentation order, differently from other working memory tasks where reordering is required (e.g. Conway et al., 2005). In the case of Palladino et al.'s task, participants had to consider each item included in the list, storing the smallest ones and comparing each new item with those maintained in memory, thus involving more clearly the comparison and substitution functions of updating. The comparison mechanism is a necessary aspect of updating, since it allows the correct selection of items available in working memory through the comparison of old items with new incoming information. It could be hypothesized that the similarity between items affects this process. The more similar the items (for example in size), the more difficult the judgment becomes. This confusion effect could occur in either the decision phase or the retrieving phase, in both cases leading to an interference effect. The substitution mechanism necessarily follows the comparison, since it allows the updating of the memory content. To substitute the old information with the new, old relevant items have to be maintained in a higher state of activation, whereas irrelevant items have to be inhibited. The substitution mechanism is mainly affected by the suppression request, related to the level of activation of items and the number of updates required. In fact, it has been suggested (Palladino et al., 2001) that a critical variable in working memory and updating tasks is represented by the effort required to reduce the activation of...
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