Figure

Phonological loop system as envisaged by Baddeley (1990).

Why was PV's letter span with auditory presentation affected by phonological similarity even though she did not use subvocal articulation? The effects of phonological similarity occurred because the auditorily presented letters entered directly into the phonological store even in the absence of subvocal articulation.

Does subvocal articulatory activity within the phonological loop require use of the speech musculature? Baddeley and Wilson (1985) studied patients, all but one of whom suffered from dysarthria, in which damage to the system controlling the speech musculature greatly restricts speech. The remaining patient had the even more serious condition of anarthria, which totally prevents speech. All the patients engaged in subvocal rehearsal or articulation. Baddeley (1986, p. 107) concluded: "The loop and its rehearsal processes are operating at a much deeper level than might at first seem likely, apparently relying on central speech control codes which appear to be able to function in the absence of peripheral feedback."

Smith and Jonides (1997) used two tasks designed to differ in their demands on the phonological store and the articulatory process. They obtained PET scans during task performance. There was heightened activity in the parietal lobe when the phonological store was being used, and increased activity in Broca's (language) area when the articulatory process was being used. Thus, the two subsystems of the phonological loop depend on different parts of the brain.

Evaluation

The theory accounts well for the word-length effect, the effects of articulatory suppression, and the performance of various brain-damaged patients. In addition, the theory accounts for two other effects:

1. The irrelevant speech effect: the finding that irrelevant or unattended speech impairs immediate recall is explained by assuming that all spoken material necessarily enters the phonological store.

2. The phonological similarity effect: the finding that immediate recall is impaired when the memorised items are phonologically similar is explained by assuming that this reduces the discriminability of items in the phonological store.

According to the model, irrelevant speech and phonological similarity both affect only the phonological store. This leads to two predictions:

1. Irrelevant speech and phonological similarity should both affect the same brain area.

2. The effects of irrelevant speech and phonological similarity should be interactive rather than independent.

Martin-Loeches, Schweinberger, and Sommer (1997) tested these predictions. They recorded event-related potentials (ERPs), and obtained evidence against the first prediction: "Irrelevant speech and phonological similarity caused ERP effects with clearly different scalp topographies, indicating that these factors influence different brain systems" (Martin-Loeches et al., 1997, p. 471). They also failed to support the second prediction (as had some previous researchers).

Another problem was identified by Cowan et al. (1998). Memory span was affected by the rate of retrieval from short-term memory as well as by the rate of rehearsal, although only the latter factor is regarded as important within the model. This led Cowan et al. (1998, p. 152) to conclude that, "the leading model of working memory, the phonological loop model.. .has merit, but is an oversimplification."

What is the value of the phonological loop? It increases memory span, but this is far removed from the activities of everyday life. It also aids the reading of difficult material, making it easier for readers to retain information about the order of words in text (see Chapter 12). However, individuals with a severely deficient phonological loop generally cope very well, suggesting that the phonological loop has little practical significance. Baddeley, Gathercole, and Papagno (1998, p. 158) disagreed, arguing that "the phonological loop does have a very important function to fulfil, but it is one that is not readily uncovered by experimental studies of adult participants. We suggest that the function of the phonological loop is not to remember familiar words but to learn new words."

Evidence supporting this viewpoint was reported by Papagno, Valentine, and Baddeley (1991). Native Italian speakers learned pairs of Italian words and pairs of Italian-Russian words. Articulatory suppression (which reduces use of the phonological loop) greatly slowed the learning of foreign vocabulary, but had little effect on the learning of pairs of Italian words.

Trojano and Grossi (1995) studied SC, a patient with extremely poor phonological functioning. SC showed reasonable learning ability in most situations, but was totally unable to learn auditorily presented word-nonword pairs. Presumably SC's poorly functioning phonological loop prevented the learning of the phonologically unfamiliar nonwords.

Which component of the phonological loop is more involved in the learning of new words? According to Baddeley et al. (1998), the phonological store is of more relevance than subvocal rehearsal. Subvocal rehearsal is only used by children to maintain the contents of the phonological store from about the age of 7. However, children as young as 3 years old show a close link between phonological memory performance and vocabulary learning (Baddeley et al., 1998). Such evidence suggests that subvocal rehearsal is not needed for vocabulary learning.

Visuo-spatial sketchpad

The characteristics of the visuo-spatial sketchpad are less clear than those of the articulatory loop. However, it is used in the temporary storage and manipulation of spatial and visual information. Baddeley et al. (1975) studied the visuo-spatial sketchpad. Participants heard the locations of digits within a matrix described by an auditory message that was either easily visualised or was rather hard to visualise. They then reproduced the matrix. When this task was combined with pursuit rotor (i.e., tracking a light moving around a circular track), performance on the easily visualised message was greatly impaired, but there was no adverse effect on the non-visualisable message.

The most obvious interpretation of these findings is that the pursuit rotor involves visual perception, and thus interferes with performance on the visualisable message. However, Baddeley and Lieberman (1980) found that a specifically visual concurrent task (making brightness judgements) actually disrupted performance more on the non-visualisable message. The results were very different when a spatial task with no visual input was performed while the message was being presented. This involved participants trying to point at a moving pendulum while blindfolded, with auditory feedback being provided. This spatial tracking task greatly reduced recall of the visualisable messages, but had little effect on the non-visualisable messages. Thus, recall of visualisable messages of the kind used by Baddeley et al. (1975) and by Baddeley and Lieberman (1980) is interfered with by spatial rather than by visual tasks, implying that processing of such messages relies mainly on spatial coding.

Visual coding can also be of importance within the visuo-spatial sketchpad. Quinn and McConnell (1996) told their participants to learn a list of words using either visual imagery or rote rehearsal. This learning task was performed either on its own or in the presence of dynamic visual noise (a meaningless display of dots that changed randomly) or irrelevant speech in a foreign language. It was assumed that dynamic visual noise would gain access to the visuo-spatial sketchpad, whereas irrelevant speech would gain access to the phonological loop.

The findings were clear (see Figure 6.7): "Words processed under mnemonic (imagery) instructions are not affected by the presence of a concurrent verbal task but are affected by the presence of a concurrent visual task. With rote instructions, the interference pattern is reversed" (Quinn & McConnell, 1996, p. 213). Thus, imaginal processing used the visuo-spatial sketchpad, whereas rote rehearsal used the phonological loop.

Logie (1995) argued that visuo-spatial working memory memory can be subdivided into two components:

• The visual cache, which stores information about visual form and colour.

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