Dyslexia and Perception

 It is important to realise that the brain is the organ of perception – it tells us what we see and hear. Neurological processing underlies our perception and Darwinian natural selection over countless generations has shaped our sense organs. It seems common sense to assume that they have been shaped to give us a ‘true’ picture of the world as it ‘really’ is. However, Dawkins states: ‘it is safer to assume that they have been shaped to given us a useful picture of the world, to help us to survive. What sense organs do is to construct a useful model of the world…a kind of virtual reality simulation of the real world’¹. Only scientific research can go beyond the frontiers of our perception and this is where the difficulties begin as it is very difficult to free oneself from the shackles of pre-conception and ‘common sense’.

Professor John Stein, Magdalen College, Oxford, states that ‘dyslexia has an organic neurological basis and, contrary to previous strongly held beliefs, it is not 'purely psychological’². He sees a definite correlation with abnormal magnocellular neurones. These create difficulties independent of intelligence, in particular with reading and spelling. ‘Reading requires the child to identify and order letters visually and to match them with the phonemic sound segments that they represent, whereas speech naturally segments into syllables, not phonemes’³.

The Phonological Model

The phonological model of dyslexia defines it in terms of difficulties associated with converting phonemes (‘smallest meaningful segments of language’) into symbols (letters).^4[1] The mental activity associated with reading can be divided into word identification, phonological processing and cognitive reasoning. A deficit in phonological processing will reduce a person’s ability to convert symbols into sounds (reading) and/or sounds into symbols (writing) thus preventing them from exhibiting their true cognitive ability and preventing them from producing written work commensurate with their underlying ability.

Speaking is carried out at an automatic and unconscious level by a biologically determined phonological module in the brain. First, the relevant phonemic structures are selected and assembled. These individual phonemes are then co-articulated – that is over-lapped and merged - by the speech apparatus. Co-articulation permits the rapid production of phonetic strings but obscures the underlying segmental nature of speech.

In READING, the word ‘cat’ is first decoded into its phonological form (‘Kuh, ahh, tuh) and identified. Once it is identified, higher-level cognitive functions such as intelligence and vocabulary are applied to understand the word’s meaning (‘small furry mammal that ‘purrs’). In people who have dyslexia, a phonological deficit impairs decoding, thus preventing the reader from using his or her intelligence and vocabulary to get to the word’s meaning. To understand how the phonological model works, one has first to consider the way in which language is processed in the brain. Researchers conceptualise the language system as a hierarchical series of modules or components, each devoted to a particular aspect of language. At the upper levels of the hierarchy are components involved with semantics (vocabulary or word meaning), syntax (grammatical structure) and discourse (connected sentences). At the lowest level of the hierarchy is the phonological module, which is dedicated to processing the distinctive sound elements which constitute language.

Before words can be identified, understood, stored in memory or retrieved from it they must first be broken down or parsed into their phonetic units by the phonological module of the brain. In spoken language, this process occurs automatically, at a pre-conscious level. Noam Chomsky and more recently Steven Pinker of the Massachusetts Institute of Technology have argued that language is distinctive (having become so as we evolved, i.e. spoken language was an evolutionary advantage allowing us to work as a team, etc.). It should be noted that there is no overt clue to the underlying segmental nature of speech - speech appears seamless, i.e. an oscilloscope would register the word ‘cat’ as a single burst of sound – only the human language system is capable of distinguishing the three phonemes embedded in the word.

Reading is not natural as it is a human invention which must be learned at a conscious level. A child has to learn that orthography (the sequence of letters on the page) represents the phonology. This is what occurs when a child learns to read. When a child has dyslexia, a deficit within the language system of the phonological module impairs his/her ability to segment the written word into its underlying phonological components. The deficit in phonological processing can prevent word identification. This basic deficit in what is essentially a lower-order linguistic function blocks access to higher order linguistic processes involved in comprehension and meaning which consequently cannot be called into play.

Most children become aware of the phonological structure of words between the ages of four and six years. By the age of six, most children have had at least one full year of schooling, including instruction in reading. Thus, the development of phonological processing parallels the acquisition of reading skills and it appears the two processes are related.

The Optometric Correlates of Dyslexia

It is important for assessors to be aware of the optometric correlates of dyslexia as these are often not mentioned in diagnostic assessments and/or are not part of a standard eye test. Some people experience visual perceptual distortions when they look at certain materials, particularly text. The distortions of text include blurring, movement of letters, words doubling, shadowy lines, shapes or colours on the page, and flickering. These distortions are characteristic of a condition that is often referred to as Meares-Irlen Syndrome, Irlen Syndrome or Scotopic Sensitivity Syndrome. Meares suggested that some children’s perception of text and reading disabilities ‘are influenced by print characteristics’⁵. She found that in some cases the white gaps between words and lines masked the print and caused perceptual anomalies, such as words blurring, doubling and jumping. Coloured filters (either coloured sheets placed on the page - overlays - or with coloured glasses) are an effective treatment and it is claimed that the required colour differs from person to person and is very specific. Wilkins took this research a step further by developing the Intuitive Colorimeter, which enabled a double-masked randomised placebo-controlled trial [RCT].⁶ An RCT confers scientific validity on a treatment or intervention. Children experiencing Meares-Irlen Syndrome were tested with the Intuitive Colorimeter to determine the precise colour of filter that most improved their perception of text. The optimal and control tints were each worn for a period of four weeks, in random order, and the children reported significantly fewer symptoms with their optimal rather than their control tints. Wilkins confirmed Meares’ observation that some people’s reading is affected by print characteristics and he observed that the effects of colour depend critically on typography: ‘colour has its greatest benefit with text that is small and closely spaced. With conventional text the effects on reading speed take time to appear, and do so only when the reader is beginning to tire’⁷.

Stein goes further and states: ‘The visual magnocellular system also plays a leading part in controlling eye movements; hence dyslexics' ocular instability and poor ability to sequence letters visually may be the result of the abnormal development of their magnocellular system. We have found that we can often help children to overcome their ocular instability by means of fixation exercises or in some cases reading with only one eye. Also some children are helped by using either blue or yellow filters, probably because these alter the balance of magnocellular and parvocellular activity.  We have found that we can more than double children's reading progress by treatment of their visual instability using these techniques’⁸.

An assessor should be aware of both of these models and apply his/her understanding when assessing the needs of students with a complex perceptual difference. A number of key points should be borne in mind:

Studies have shown a high prevalence of ocular anomalies in patients presenting the symptoms of Meares-Irlen Syndrome and the responsible assessor should recommend that students be referred to an eye care practitioner who is skilled in the assessment of people with reading difficulties prior to providing coloured overlays/spectacles.

Assessors should be aware of the need for any new scientific development to be accompanied by a Placebo Controlled Trial. This is because of the well known power of the placebo effect which can distort findings. It is because of the placebo effect that these trials take place – if the treatment/strategy has been reviewed in a peer-reviewed journal and a PCT has taken place, it is no longer ‘alternative’.