Dyslexia: Phonological Loop Components

A discussion of new notions on the phonological loop, which was first proposed as an articulatory loop and later reformulated, follows (Gathercole and Baddley, 1989). New elaborations are offered by Burgess and Hitch (1999). In their extensive and comprehensive review, two relevant concepts are the two components of the loop— rehearsal and phonological store. Recent brain imaging research, as well as traditional brain lesion data, supports this division.

Rehearsal activity is associated with Broca’s area, whereas the phonological store is either in Wernicke’s area or in an area slightly behind it. The review by Burgess and Hitch (1999) confirms what has been known for some time—that phonological coding and rehearsal have separate cortical locations. Its implication for the present discussion, however, is important. Consult Figure 16.1, which is an elaboration mostly of phonological store, rather than rehearsal.

Reading is related to STM and rehearsal via the phonological store. Simply, we can suggest that STM, as captured in memory span, is a function of the number of items that can be rehearsed in a unit of time (articulation), and that itself must depend on the length of the word, on the one hand, and the speed of phonological encoding of the word, which must precede articulation, on the other. Remembering a short list of familiar words is distinguished from repetition of an infrequently occurring long word; these two operations are connected with rehearsal and phonological store (Burgess and Hitch, 1999).

Listening to one’s own speech is a necessary step in accommodating rapid automatized naming of objects, as well as in reading aloud. We can suggest that RAN essentially requires a successive processing activity, in addition to being modulated by phonological encoding. Thus, RAN is both a separate and a correlated operation, combining mechanisms that end in articulation and rehearsal.

Two kinds of dyslexia are suggested by Harm and Seidenberg (1999), namely, phonological and delayed dyslexia. Both can be related to phonological store and rehearsal mechanisms as well. Phonological dyslexia is the typical and more frequent kind of dyslexia. It is theoretically explained as a damage or deficit to the phonological store; such weakness impedes rehearsal due to poor phonological representation of a word that is required to be read and recalled.

In the case of the delayed dyslexia, the dyslexic may have an underdeveloped knowledge base for exceptional or irregular words (for example, touch, though, isle, knead). The orthography and pronunciation of such words require more rote learning than phonological coding of grapheme to phoneme. The exact reason for the delayed development of the phonological knowledge store is, however, unclear. What happens, to be reasonable, is that the exceptional words are to be processed as whole words, and require lexical rather than sublexical processing.

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