Working Memory

Baddeley and Hitch (1974) argued that the concept of the short-term store should be replaced with that of working memory. Their working memory system has three components:

• A modality-free central executive resembling attention.

• An articulatory loop (now known as phonological loop) holding information in a phonological (speech-based) form.

• A visuo-spatial scratch pad (now known as visuo-spatial sketchpad) specialised for spatial and/or visual coding.

The key component of working memory is the central executive. It has limited capacity, and deals with any cognitively demanding task. The phonological loop and the visuo-spatial sketchpad are slave systems used by the central executive for specific purposes. The phonological loop preserves the order in which words are presented, and the visuo-spatial sketchpad is used for the storage and manipulation of spatial and visual information.

Every component of the working memory system has limited capacity, and is relatively independent of the other components. Two assumptions follow:

1. If two tasks use the same component, they cannot be performed successfully together.

2. If two tasks use different components, it should be possible to perform them as well together as separately.

Numerous dual-task studies have been carried out on the basis of these assumptions. For example, Robbins et al. (1996) considered the involvement of the three components of working memory in the selection of chess moves by weaker and stronger players. The main task was to select continuation moves from various chess positions while performing one of the following concurrent tasks:

• Repetitive tapping: this was the control condition.

• Random number generation: this involved the central executive.

• Pressing keys on a keypad in a clockwise fashion: this used the visuo-spatial sketchpad.

• Rapid repetition of the word see-saw: this used the phonological loop.

The findings are shown in Figure 6.4. Selecting chess moves involves the central executive and the visuo-spatial sketchpad, but not the phonological loop. The effects of the various concurrent tasks were similar on stronger and weaker players, suggesting that both groups use the working memory system in the same way.

Phonological loop

Baddeley, Thomson, and Buchanan (1975) studied the phonological loop. Participants' ability to reproduce a sequence of words was better with short words than with long words: the word-length effect. Participants produced immediate serial recall of as many words as they could read out in 2 seconds. This suggested the capacity of the phonological loop is determined by temporal duration like a tape loop, and that memory span is determined by the rate of rehearsal.

Baddeley et al. (1975) obtained evidence that the word-length effect depends on the phonological loop. The number of visually presented words (out of five) that could be recalled was assessed. Some participants were given the articulatory suppression task of repeating the digits 1 to 8 while performing the main task. The argument was that this task would make use of the phonological loop and prevent it being used on the word-span task. Articulatory suppression eliminated the word-length effect (see Figure 6.5), indicating that the effect depends on the loop.

Weaker chess players Sfij Stronger chess players

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