Working Memory Model

Cognitive activities, such as reasoning and learning need a mental space to control and operate. Working memory model raised by Baddely and Hitch (1974) firstly gave the idea that a central executive in the brain coordinates the activities of two slave systems which are phonological loop and visuospatial sketchpad, to manipulate cognitive information. Based on that, a huge number of researchers were then trying to explore how cognitive activities are manipulated mentally in terms of information storage and their production. Phonological loop, or in other words, verbal working memory, was intensely investigated throughout the years. In this essay, I would indicate two main functions of phonological loop in everyday lives, one is mental arithmetic

and the other is language acquisition. At the same time, I would discuss the characteristics of phonological loop that linked with each of these two functions.

The first function of phonological loop that I am going to talk about is mental arithmetic. The current model of the phonological loop consists of two components: the phonological short-term store and an articulatory control process (ACP) which is a mechanism by which subvocal rehearsal of contents of phonological store prevents decay (Baddeley, 1986). When we try to solve arithmetic problem, for example to calculate the total number of students in grade five of an elementary school, we need to sum up the numbers of students in each grade-five classes. The sum of the first two numbers needs to be held in the brain and then the third and fourth number can be added on to get the final answer. To hold the sum of the first two numbers in short term memory, phonological loop in working memory (short-term memory) transferred the number to the short-term phonological store via articulatory control process, or in other words, via rehearsal. Similar to this example, in AJ FÜrst, GJ Hitch`s (2000) experiment, participants were asked to do multidigit additions. Problems either were presented briefly, and therefore had to be remembered in order to complete the answer, or remained visible. The result indicated that the number of errors was significant larger when problems were presented briefly than that when problems were presented continuously visible. It then can be concluded that the phonological loop appears to be involved in storing problem information in mental arithmetic.

However, it is interesting to notice that the numbers or information can be received visually or auditorily and phonological loop processes differently in different information forms. Conrad and Hull investigated it in 1964. The participants were asked to recall sequences of consonants that were phonologically similar (for example: B D T G C P) and phonologically distinct (for example: F K Y W R Q). The result showed that phonologically distinct letters are easier to recall than letters sounded similar, and this phenomenon is named as phonological similarity effect. Due to the explosion of similarity effect, it was also found that people tend to subvocal the letters to rehearse and memorize in whatever the ways the letters are presented (in visual or auditory form). Following that, it has suggested that for auditory form, the information is coded phonologically directly into phonological store as they have automatic access to it. If the words presented visually, the words are subvocalised and recorded into phonological information before it can access the phonological store. In short words, coding within phonological store is due to the phonemes of words or numbers as opposed to semantic. Back to mental arithmetic with this coding characteristic, if numbers are presented auditorily, they have automatic access to store in phonological loop; if the numbers are presented visually, the information will be subvocalised to phonological form before transferring into phonological store. Furthermore, according to phonological similarity effect, if all numbers appeared in the arithmetic have similar sounds such as five, nine, it might be harder for people to solve the problem than that with distinct sounds such as two and six, since it is harder to hold numbers that sounds similar than numbers sounds distinct .

Apart from mental arithmetic, phonological loop also plays an important role in language acquisition which includes learning new words and complex sentence comprehension.

At a conservative estimate, the average 5-year-old child will have learned more than 2,000 words (Smith, 1926) and will learn up to 3,000 more per year in the coming school years (Nagy & Herman, 1987). Refer to the working memory model; phonological loop raise the function of dealing with spoken and written materials, providing temporary storage of unfamiliar phonological forms. Before explaining this function, it is important to point out a phenomenon that many individuals with specific deficits in short term phonological memories appear to have few problems in coping with everyday cognition: they have normal abilities to produce spontaneous speech (Shallice & Butterworth, 1977) and encounter few significant difficulties in language comprehension (Vallar & Shallice, 1990). Hence, phonological loop might only contribute to learn new words, rather than familiar vocabulary. Take it back to learning in daily lives, if a patient has impaired phonological loop, then it might be impossible for him or her to learn new words even though he or she is capable to learning familiar words. A patient P.V. who has only two digit span proved this idea. In the experiment carried out by Baddeley, Papagno and Vallar (1988), P.V. showed a normal learning patterns when she acquired to learn pairs of meaningful words (Italian and Italian words). However, when the experiment examined her capacity to learn to associate a familiar word with an unfamiliar item from another language (Italian and Russian words), she is completely unable to perform this task in both auditory and visual presentation. It was suggested that short-term phonological storage is important for learning unfamiliar verbal material, and disrupting of phonological loop impairs the learning of second language, whereas, it is not essential for forming

associations between meaningful items that are already known. Therefore, phonological loop take part in learning new words.

Furthermore, similar to other memory stores, the capacity of phonological store is limited. Baddeley et al. (1975) investigated the effect of the length of words on recalling and found that as the words get longer, the performance of short-term recall of these words gets worse. This experiment illustrates that the phonological store is limited in capacity and may significantly affects the learning of new vocabulary for language development. The influence of word length in leaning new words is called word length effect. In addition, Gathercole and Baddeley 1990 investigated the relationship between phonological loop and speed of new-word learning. It was suggested that in both the repetition of single spoken nonwords and the serial recall of lists of spoken words, the disordered group (children with impairment of immediate phonological memory) performed more poorly than an even younger group of normal children with equivalent vocabulary and reading skills. In short words, people with low capacity of phonological loop learn new words more slowly. Besides, short term memory has relatively brief duration. In term of phonological loop, the verbal working memory has only two-second duration. Plus the limited capacity of phonological store, rehearsal is needed to avoid the information is fading especially for language acquisition. Internal rehearsal such as sobvocal is the most common type of rehearsal in language learning. Also, according to the structure of phonological loop, the rehearsal trace is described as a loop and the rehearsal always follows serial order, which means when people need to rehearse a list of words, they always rehearse in the same order. File, S. E., & Lister, R. G. (1982) investigated whether induced deficits in learning result from impaired rehearsal. Participants were required to recall sixteen words they have seen in any order after a 90-second delay. During the 90 seconds, participants were either allowed to free recall or given a counting task to prevent rehearsal. It was suggested that in both the verbal and nonsense-syllable learning tasks, prevention of rehearsal significantly impaired performance. Therefore, in terms of language acquisition or new words learning, serial rehearsal process in phonological loop has a huge impact to facilitate the sounds of words to store in short-term memory, and the limited capacity of phonological store indeed causes the forgetting of information which subsequently affects the word learning.

For language acquisition, complex sentence comprehension is also a part of it. However, the exact role of the phonological loop in sentence processing has been the subject of numerous neuropsychological studies, and much debate, over the past 15 years (Martin, R. C., & Romani, C. 1994). Baddeley and Wilson (1988) test the sentence span of a brain-damaged patient T.B., who had impairment in the capacity of phonological store; the digit span is 1-2. The maximum length of words that she was able to repeat was only three. Similarly, Caramazza, Basili, Roller, Berndt (1981) and Saffran and Marin (1975) also found that their patients with very restricted memory spans also performed poorly on comprehension and repetition tasks using reversible sentences. Thus, they argued that phonological storage plays an important role in syntactic analysis. (Martin, R. C., & Romani, C. 1994) However, in more recent research, it is suggested that phonological loop does not necessary for complex sentence comprehensive. Patient P.V., who also have low digit span, was able to repeat sentence of up to seven in length( Baddeley, A., & Wilson, B. 1988); Besides, Patient R.E. who had a developmental disorder affecting phonological storage but showed normal comprehension for all kinds of syntactic constructions (Butterworth, Campbell, & Howard, 1986). Thus, it might be possible that the poor performance on complex sentence comprehensive is just coexisting with the deficits in phonological loop. But undoubtedly, phonological loop may interact and support other components (semantic and syntactic) in normal comprehensive.

In conclusion, there are mainly two functions of phonological loop that I have talked about, which are mental arithmetic and language acquisition. Those two functions base on the two sub-parts of the phonological loop which are short-term phonological store and articulatory control process. Also, there are several features of phonological loop that contribute to or have negative influence on the function operation, including phonological coding as opposed to semantic, the direct access of phonological information and the limited capacity in the phonological store. The only exception of the certain relationships between phonological loop and the function is the complex sentence comprehensive, which needs to be investigated further to show the relationship with phonological loop.