Recently, Trecy Martinez Perez, Steve Majerus, Aline Mahot and Martine Poncelet applied this three-pronged strategy to understanding short-term memory impairment in dyslexics. Their work was the subject of two articles, one published in the journal Dyslexia, entitled Evidence for a Specific Impairment of Serial Order Short-term Memory in Dyslexic Children (2), and another published in the journal Research in Developmental Disabilities, entitled Impaired Short-Term Memory for order in adults with dyslexia (3). 'Short-term verbal memory impairments may have several origins', says Steve Majerus. It has been established that one of these, in dyslexics, is the difficulty of creating fine, individualised, well-segmented phonological representations. However, while learning to read requires good phonological awareness, it also requires the ability to connect phonemes in the right order. Because the number of sounds is limited in each language, this order constitutes one of the key factors enabling the distinction between words of the same length and consisting of the same phonemic units to be made.'

The question is therefore as follows: do dyslexics struggle when they have to store the sequence of words in their memory, i.e. the order of phonemes? The answer is yes. In the course of their work, the ULg neuropsychologists have shown not only that retaining 'sequentially ordered' information (the sequence of phonemes) was impaired in dyslexic children and adults, in the same way as phonological knowledge, but, furthermore, this deficiency was generally associated with deeper dyslexic difficulties. 'Moreover, we discovered that in children in the last year of nursery school, their ability to memorise the order of verbal information was the biggest predictor of their reading level one year later', indicates Majerus.

Similarly, their vocabulary level aged six or seven is strongly correlated to their ability to recall 'serially ordered' information. 'According to our predictions, processing sequential information should also prove to be very important for memorising how to spell words, particularly when these have an unusual structure', he continues. Moreover, studies conducted a few years ago at the University of Brighton showed that in adults, the acquisition of vocabulary in a foreign language is better the greater the ability to process 'serially ordered' information. Finally, other work has shown the importance of these abilities in learning numerical calculations in childhood.

Basic capacity

Images obtained during fMRI show that short-term retention of 'serially ordered' information depends upon a specific cerebral circuit: the anterior part of the right parietal lobe. Using this imaging technique, the ULg team focussed on the cerebral processing of sequences of words and sequences of photographs of faces projected onto a screen to dyslexic adults and control subjects. Four words and four faces were initially presented in a specific order. Combinations of two pairs of words or two faces were then projected onto the screen. The participant had to determine, for each pair, which element had previously been presented first. On the one hand, the dyslexic participants made a greater number of errors, both in terms of faces and the order of words. On the other hand, activation of the anterior part of the right parietal lobe in these same subjects was slightly lower. 'These results indicate that the treatment of 'sequentially ordered' information is a basic ability which operates in learning all new codes which are organised according to a certain sequence', states Majerus.

In his opinion, this experimental data further strengthens the value of using the 'phonic method' of learning to read, which is based on the sequential decoding of letters making up words. Moreover, by highlighting the importance of processing sequence information, they open up a complementary avenue for rehabilitation to treat children with dyslexia.

(2) Trecy Martinez Perez, Steve Majerus, Aline Mahot et Martine Poncelet (2012). Evidence for a Specific Impairment of Serial Order Short-term Memory in Dyslexic Children, Dyslexia, 18, 94-109
(3) Trecy Martinez Perez, Steve Majerus, and Martine Poncelet. Impaired Short-Term Memory for order in adults with dyslexia, Research in Developmental Disabilities (in press)