Working memory (Baddeley)

Baddeley, A.D. (1992). Working memory. Science, 255, 556-559.

In the 1960s, a dichotomous view of memory (i.e., short-term and long-term storage) was predominant. Dual-task techniques further probed this model and eventually a tripartite system emerged, which comprises the following components, a main “control tower” and two “slave systems”:

  1. The central executive, which is assumed to be an attentional-controlling system, is important in skills such as chess playing and is particularly susceptible to the effects of Alzheimer’s disease;
  2. The visuospatial sketch pad, which manipulates visual images; and
  3. The phonological loop, which stores and rehearses speech-based information and is necessary for the acquisition of both native and second-language vocabulary.

Working memory is defined as “a brain system that provides temporary storage and manipulation of the information necessary for such complex cognitive tasks as language comprehension, learning, and reasoning” (p.556). As implied by the previous statement, storage and processing of information occurs simultaneously.

In addition, the concept of a short-term memory was replaced by a concept of a “working memory.” This article discusses the components of working memory, what is known about each component’s functionality, and the implications of long-term phonological learning on language acquisition.

[*Note: Much of the following material was excerpted from the chapter…]

There are two main approaches to investigating working memory:

  • Psychometric approach (North America)
  • Focuses on the extent to which performance on working memory tasks can predict individual differences in the relevant cognitive skills.
  • Working memory is seen as necessary for the concurrent storage and manipulation of information; tasks are devised that combine processing and storage, and the capacity of such tasks to predict a range of other cognitive skills, such as reading, comprehension, and reasoning, is tested.
  • Dual task/neuropsychological approach (Europe)
  • Focuses on analyzing the structure of the working memory system. Most effort has been devoted to the two slave systems (less complex than the  central-executive system).

Individual differences in working memory

Daneman and Carpenter’s working memory tasks involved in reading comprehension — subjects to read aloud or listen to a series of short sentences while retaining the last word from each sentence for subsequent immediate recall. The test typically starts with two sentences and increases to a point at which subjects are no longer able to recall all the terminal words. This point is designated the subject’s working memory span.

  • Found a correlation coefficient of about 0.5 or 0.6 between working memory span and reading comprehension
  • Similar correlations are found when simple arithmetic, combined with word recall, is substituted for sentence processing
  • Subsequent tests found that students with high working memory span were better at coping with “garden path sentences,” and that they are better at drawing inferences from text, suggesting that they have a better grasp of its meaning

Another class of experiments involving individual differences in working memory is concerned with the study of reasoning and concentrates particularly on intelligence tasks. Results suggested a very high correlation between working memory capacity and reasoning skill. They concluded, however, that the two concepts, although closely related, were not synonymous; reasoning performance was more dependent on previous knowledge than was working memory, which in contrast appeared to be more dependent on sheer speed of processing.

Components of working memory

Working memory performs the following functions: concurrent storage and processing; coordination of resources, with memory storage being only one of many potential demands that are likely to be made on the system; and coordination of information from two or more slave systems. (Central executive deficit in Alzheimer’s disease).

The slave systems of working memory

The dual-task paradigm has been used to demonstrate the separability of the memory systems responsible for (1) learning by means of visuospatial imagery and (2) of learning by rote repetition.

  • Imagery is disrupted by the requirement of performing a visuospatial task, such as tracking a spot of light moving on a screen, by certain types of eye movement, or by the presentation of irrelevant visual material during learning.
  • Farah has distinguished one imagery component that is principally concerned with the representation of pattern information and that involves the occipital lobes from a second more spatial component that seems to be dependent on parietal lobe functioning.
  • Neuropsychological evidence supports this dichotomy, with some patients having great difficulty in imaging and recalling such visual features as the shape of the ears of a spaniel dog or the color of a pumpkin but having no difficulty in spatial tasks such as describing routes or locating towns on maps; other patients show exactly the reverse pattern of deficits.
  • Tests involving memorization of complex chess positions. Results: expertise correlated highly with memory performance, but all subjects showed the same basic pattern: no disruption from the concurrent verbal task but clear impairment from the tasks occupying the visuospatial sketch pad or the central executive. A second study required subjects to choose the optimum next move from a complex middle-game position and found exactly the same pattern. Disruption of verbal activity had no effect, whereas visuospatial disruption was clear, and this problem-solving task was even more susceptible to central executive disruption than the task in the first study.

The phonological loop

Comprises two components, a phonological store that can hold acoustic or speech-based information for 1 to 2 seconds, coupled with an articulatory control process, somewhat analogous to inner speech. This system serves two functions; it can maintain material within the phonological store by subvocal repetition, and it can take visually presented material such as words or nameable pictures and register them in the phonological store by subvocalization.

1)    The acoustic similarity effect. This is the observation that the immediate ordered recall of items is poorer when they are similar rather than dissimilar in sound.

2)    The irrelevant speech effect. This refers to a reduction in recall of lists of visually presented items brought about by the presence of irrelevant spoken material.

3)    The word-length effect. This provides evidence on the nature of the subvocal rehearsal process. Memory span for words is inversely related to spoken duration of the words. Subjects can generally remember about as many words as they can say in 2 seconds.

4)    Articulatory suppression. It is possible to disrupt the use of subvocal rehearsal by requiring subjects to utter some repeated irrelevant sound, such as the word “the.”

Investigating long-term phonological learning

  • Such as acquiring the vocabulary of one’s native, or even a foreign, language.
  • Short-term phonological storage is important for new long-term phonological learning. Subsequent studies with normal adults have shown that factors that influence the phonological loop, such as articulatory suppression, word length, and phonological similarity, strongly influence foreign vocabulary acquisition yet show no effect on learning to associate pairs of familiar words.
  • Nonword repetition (measure of short-term phonological learning) proved to be highly correlated with vocabulary and to be a powerful predictor of vocabulary.
  • Short-term phonological memory is crucial in the acquisition of vocabulary.
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