Limitations of Working Memory

There is a general awareness that the capacity of working memory is limited and has to be shared for holding and operating processes. Overloading occurs when the learner tries to hold too many pieces of incoming data. Thus, if we attempt to do too much at once we simply overload. Barber (1988) argued if the information we are concerned with reaches the upper limits of our working space, an overloading in the capacity of working memory could occur, and a loss in productivity may arise. Studies (Johnstone and Wham, 1982; Johnstone and Letton, 1991) show that overloading of working memory appears when the learner is incapable of discriminating between the “noise” (irrelevant information or that which the teacher considers unimportant) and “signal” (relevant information the teacher thinks are important). As we can see in figure 3-13, it is necessary during an experiment to recall: theory, names of apparatus, and recognise material, recall skills, new written instructions, new skills, new verbal instructions.

The study of Johnstone (1980) showed that a sudden drop in the learner’s performance was apparent when any task load exceeded the upper limit of the learner’s working memory capacity. Johnstone (1999) noted that overload happens very often during lectures. Because all students' working space is devoted to writing notes based on the lecturerspoken words, little space is left for elaborating them and thus understanding them. This is very similar to what Jonhstone and Wham (1982) found with laboratory work . In the science field, Johnstone (1984) indicated there are three aspects which can hinder student learning: the nature of the science; the methods of teaching a science; and the methods by which students learn. Johnstone and El-Banna (1989) examined the relationship between working memory and problem solving success in chemistry. They showed that, if the number of the items of information the students are supposed to hold in

the mind at the same time, in order to solve the problem exceeds their working memory capacity, their performance will drop dramatically.

In the mathematics field, Ashcraft (1994) declared that three aspects of mental calculation could overload working memory; the retention of temporary information, the length of time of that retention, and the number of operations involved in the calculation. The Christou study (2001), which investigated the difficulties of solving algebra story problems, showed that the phenomenon of overloading of working memory capacity could be responsible for students’ difficulties in algebra story problems representation. He found a sharp drop in performance when a task demanded more working memory space than a student possessed.

Student ability to develop techniques to cope with information overload depends heavily on the conceptual framework already established in his long-term memory. It is known that working memory is not expandable but it can be used more efficiently. Miller (1965) put forward the idea of “chunking” which is the process of organising information and uses strategies to bring several items together into meaningful units. Gathercole et.al, (2006) indicated the next step after detecting a student with poor working memory ability is to determine the learning activities that will place heavy memory demands. Some types of learning activities demand storing a considerable amount of material that may be arbitrary in structure (such as a series of numbers or the precise wording of a fairly lengthy sentence), and other activities involve the storing of material while being engaged in another activity (such as spelling or reading a new word or making an arithmetic calculation).

Overall, working memory capacity is limited, so overloading can easily occur. When working memory is overloaded, the processing of information cannot take place unless this information can be effectively chunked. However, as Johnstone and El-Naeme (1991) stated “there is an added limitation which leads to inefficient use of this working/ holding/ thinking space. This can occur at the selection stage in which the sensory input is filtered, to separate out or processing, that which is deemed to be relevant, important or interesting.” Overloading of working memory can lead to memory failures. Gathercole et.al, (2006) illustrated that memory failures occur when forgetting the instructions, failing to cope with Concurrent processing and storage demands, losing track in complex tasks, and episodic forgetting.