Fluid, expert reading is built upon clearly identified cognitive abilities, in particular relating to processing the sound of speech, but also, as we will see, in processing the order of phonemes (sequentiality). Although this is a necessary condition, however, it is not sufficient. Because, although these capacities are deficient in dyslexic children, they are not lacking in those children who are labelled 'poor readers'. 'These children show no such fundamental difficulties.' explains Poncelet. 'Their representations of the sounds of speech are therefore normal. The problem lies elsewhere. Either they haven't benefited from good learning methods or the necessary support, or they suffer from concentration difficulties or lack of motivation. '

Phonological conscience

Poncelet goes on to specify that establishing the distinction, in adulthood, between dyslexics and poor readers is sometimes difficult. Why? Because a good experience of reading has an influence on the representation of sounds. It isn't unusual for people to say: 'When I hear a word, I see it in its written form' or 'When I hear a word I don't know, I try to imagine it written down'. While phonological representations influence spelling, spelling also influences phonological representations. 'Eventually, the level of understanding the sounds of language is not the same in someone who has learned to read and someone who has not, despite having the required prerequisites', says Poncelet. By adulthood, it is difficult to make a differential diagnosis and a battery of appropriate tests is required, all pointing to the question of evaluating the degree of deficiency in decoding graphemes. The problem is even more taxing when the forest can't be seen for the trees: a dyslexic who has reached university level, having benefited from appropriate support during childhood, often reads better than a poor reader.

There are several theories of dyslexia, but the most solid by far is that of phonological theory. Focussing respectively upon hearing, sight and motricity, other approaches have received less empirical support.

According to phonological theory, the deficiency in the decoding process, i.e. the ability to establish a correspondence between graphemes (letters) and phonemes (sounds) which characterises dyslexia, is directly due to the fact that these representations of the sounds of speech (or phonological representations) are insufficiently fine or detailed. It follows that the person also suffers from poor 'phonological awareness: he or she is unable, or manages much more slowly than a normal child, to divide words up into their different parts, segment them into syllables and, further, into phonemes. These children find it difficult to see that a word such as 'cahier' (French for 'exercise book') consists of two syllables (ca-hier), and particularly that it consists of four phonemes (k-a-i-é).

A deficiency in short-term phonological memory, the system responsible for temporarily storing verbal information, has also frequently been highlighted in dyslexics. The proof is that they appear to experience much greater difficulty than other children in repeating pseudo-words, words with a fairly high number of syllables, or sequences of numbers of a certain length. 'The results obtained from this type of task prior to entry into primary school are predictive of the child's reading level a few years later', notes Poncelet. Systematic application of such tasks would facilitate testing for potential dyslexia.'

The right order

In an article published in November 2010 in the Journal of Cognitive Neuroscience, Steve Majerus, an F.R.S.-FNRS senior scientist working in the Psychology, Cognition and Behaviour Department of the ULg, shows that, in contrast to widely received wisdom, short-term verbal memory is not a specific entity with its own existence (read the article Short term memory revisited). Rather, it can be compared to a verbal information retention function which emanates from the interaction of three more general systems: the language system (in particular long-term verbal memory), attentional control and the system of 'serial order' processing (sequentiality).