Introduction

The Dyslexia Syndrome 

Dyslexia - an 'umberella-like' term to cover a range of quite different problems?

Is dyslexia different from normal development?

Secondary effects

Dyslexia - a specific pattern of difficulties?

Physical Problems

Psychological Problems

Teaching Dyslexics

References

© D. J. Brown 1998

Dyslexia: Why are we confused as to what it is and how to deal with it?

Daryl J Brown (1997)

Introduction

    Dyslexia first appeared in the literature about 1886. And "it is a term which, since that time, is replete with widely differing definitions and misunderstood by many practitioners" (Cruickshank, 1986). In the 1960s and 1970s, 'dyslexia' began to be applied to children who did not gain literacy at the same rate as their classroom peers. A group of children were identified who found it difficult to learn their letter sounds and to cope with the phonology of the oral language. These children were also identified as having other, possibly related, difficulties all of which were used to define the symptoms of dyslexia or the dyslexia syndrome.

The Dyslexia Syndrome

    If dyslexia were a specific difficulty then, in a clinical or medical sense, it ought to be possible to identify the symptoms of dyslexia, determine the cause and then prescribe an appropriate treatment. However the disparate problems presented by dyslexic children defy such a simplistic model. The World Federation of Neurology (1968), as quoted by Pumfey and Reason (1991), defined dyslexia as a "disorder in children who, despite conventional classroom experience, fail to attain the language skills of reading, writing and spelling commensurate with their intellectual abilities". Such a definition, often seen in the literature, is a definition by exclusion. The dyslexic child is not identified by a characteristic trait but, instead, by being unable to acquire certain language skills. There could be many causes for a child failing (for example - low intelligence, sensory impairment, social and emotional problems). If there are children with a specific pattern of difficulties it would not be possible to distinguish them from those children on the basis of this or a similar definition. Perhaps this is why it "is possible to find research in which ..... dyslexia is operationally defined as six months behind grade level in reading (Pumfrey and Reason, 1991). Other definitions are also quite vague 'Dyslexia, or Specific Learning Difficulty, is an organising disability which impairs working memory and hand skills, so causing interference in the ordered development of language and sometimes numeracy' (British Dyslexia Association).

    Specific Learning Difficulties (SpLD) subsumes dyslexia (Pumfrey and Reason, 1991) and is often (erroneously) regarded as synonymous. In a chapter on LEA policies and practices, Pumfrey and Reason (1991) quote a list of suggested SpLD characteristics. All the characteristics can be found in various dyslexia definitions. They state that the list has been adopted fully or in part by a number of LEAs. It is important to note that children with SpLD may have one or more of the characteristics described on this list.

• extreme and persisting difficulty in learning to read, write or spell in children who otherwise appear able and well motivated, who have not suffered from protracted absence or ill-health, or from unfavourable environmental conditions;
  

• extreme and persisting difficulty in remembering and dealing with sequences, such as letters in written or printed words, or the sounds of oral words, or the sequence of words in a sentence;
  

• similar difficulties with sequences of numbers, or with arithmetic operations;
  

• problems with the recognition or retention of patterns, particularly where the factors of sequence, direction or organization are important;
  

• spelling errors which are particularly bizarre, unusual or distorted, and which may be wholly inconsistent and irregular or marked by systematic errors, with letter sequence (such as reversals) or which had high levels of skill that represent consistently phonetic versions of words whose correct spelling is regular;
  

• reading errors that are characterised by the persistence of frequent omissions and tabulations of words and part of words, hesitations and repeated amendments;
  

• writing that continues to be very much slower than average or to be marked by extreme irregularity of layout and presentation, or very unusual letter formation;
  

• a wide, often growing gap between the child's level of 'conceptual' understanding, or sophistication of his or her oral language, and his or her level of performance in 'technical' skills such as reading, writing, spelling, drawing, interpreting maps and diagrams, or dealing with mathematical skills involving place value or directional or sequential aspects and processes;
  

• the persistence of difficulties of this kind despite special remedial help.

    Hornsby (1984) lists a number of pointers to dyslexia which "although they are very often found in dyslexic children, they are not necessarily present in all dyslexics", Hornsby (1984). Many of these pointers are also to be found in the above list but there are some notable additions. These include:

• Directional confusion. For example not being able to tell left from right, or to read a map accurately.
  

• Learning late in their development to tell the time or to tie their shoe laces.
  

• Trouble putting names to things and people.
  

• Left handedness or only deciding which hand to use late in their development.
  

• Late development of speech or poor talking with immature speech.
  

• Late in learning to walk or generally having poor coordination.

Figure 1. Heaton and Winterson (1986). "The logical structure of dyslexia. An underlying disorder of language function accounts for all the signs and symptoms of dyslexia." (See text for discussion)

    Comparing definitions of dyslexia with the LEAs list for SpLD would appear to indicate that the two are virtually synonymous and that they are an 'umbrella-like' term for a whole range of difficulties. Do children with a specific pattern of difficulties, called dyslexia, exist? Heaton and Winterson (1986) consider that a single underlying disorder of language function could account for all the signs and symptoms of dyslexia. "The operation of this cause sets up a number of consequential effects which may be mistakenly thought of as casual." Heaton and Winterson (1986). Their model is shown in Figure 1, but attribute difficulties such as scotopic sensitivity and 'clumsiness' to a primary disorder of language function. Even though this model is too simplistic it does indicate how a child may exhibit secondary characteristics which could be confused with a specific or primary cause. Furthermore they may exhibit symptoms which not directly related to their difficulties but as a consequence of how they cope with such difficulties (on obvious example of which is the occurrence of emotional and/or behavioural problems).

Figure 2. The range of difficulties contributing to the dyslexia syndrome.

    Coltheart (1996) makes a similar observation. In any plausible model of reading there will be several different ways in which the model can be damaged. Each point of damage may yield a different group of symptoms. If there are children which have a specific pattern of difficulties then have to be distinguished from within the very broad dyslexia-SpLD definitions described in the preceding paragraphs.

    A schematic representation of potential contributing factors to the syndrome of dyslexia is shown in Figure 2. The symptoms of the syndrome have been described in the previous paragraphs. It has already been stated that dyslexic children may exhibit a number of these symptoms but not necessarily all of them. If a child has dyslexia (a specific pattern of difficulty) it does not preclude them having some additional difficulty which is found in the 'normal' population. Evaluation of the dyslexia syndrome is required to determine which symptoms relate to specific difficulties In the following sections research into these potential contributing factors will be discussed to see if they reveal a specific pattern of difficulties.

Dyslexia - an 'umberella-like' term to cover a range of quite different problems?

Is dyslexia different from normal development?

    Potentially deviation from the normal could occur in two manners - The dyslexic functions like an equal age normal who is not trying hard (Underactivation Model) or like a younger child (Underdevelopment Model), Kinsbourne (1986). In the Underactivation Model the learner finds it hard to maintain the correct strategy for the task and switches to other types of data processing. For example the child may find it hard to maintain the verbal (left hemispheric) mental set. If Kinsbourne (1986) states that the implications of this model would be that:

1) The teacher needs to continually orientate the child to the type of thinking called for by the task in hand

2) The task must be 'over-learned' to the point automaticity.

In the Underdevelopment Model the learner is handicapped by the same constraints that would limit a much younger child's efforts to learn the same skill. Kinsbourne (1986) also describes the remedial implications of the Underdevelopment model:-

1) Instruction is individual, to maintain the child's attention.

2) Potentially distracting stimulation is limited.

3) Learning materials are graduated in difficulty.

4) Learning materials contain no irrelevant features or decorations.

5) At each level of difficulty, the skill is learned to a point of fluency before the next level is attempted.

6) Within each level, additional units of information are phased in one by one. No new item is added unless response to existing items is totally correct.

7) Length of instruction is determined by the needs of the child, not by administrative needs (as long as gains are made, no longer than attention is maintained).

8) Learning is 'nearly errorless' as possible. If the child makes an erroneous response, the form of questioning is changed lest the mistake become habitual.

9) Reinforcement is immediate and tangible

    The direct consequence of this model is to assume that eventually the child will follow all the stages of 'normal' development. The British Medical Association appear to agree, they BMA, 1980 definition (Pumfrey and Reason, 1991) states "It tends to lessen as the child grows older, and is capable of considerable improvement especially when appropriate help is offered.

    The guidance given by Kinsbourne (1986) would be considered to be good teaching practice by most professionals. Both the Underdevelopment and Underactivation models show how a dyslexic child could find aspects of learning difficult. It does not, however, reveal specific patterns of difficulties, a dyslexic child may, for example, have difficulties with arithmetic and not other aspects of normal development. Francis et al. (1996) engaged in a longitudal study of children with reading disabilities but did not find that they were characterised by a developmental delay or lag.

Secondary effects:

    The emotional and behavioural consequences of failing to achieve are well documented. "One study of 'poor readers' shows lower expectations of success, a tendency to give up more easily in the face of difficulty and a tendency to attribute success to external causes such as luck", (Pumfrey and Reason, 1991). Giving up in the face of difficulty could be translated as 'poor attention span', a characteristic which has been attributed to dyslexic children. There are children who "are unable to respond to rote phonological or multi-sensory approach despite skilled teaching and they become frustrated by their lack of achievement", (Lewis, 1996). This frustration may manifest itself in behavioural problems which. The Dyslexia Institute also considers that the organising and learning deficiencies can affect behaviour, (Pumfrey and Reason, 1991) .

    It is also possible that some of the symptoms are actually a result of the intervention. The use of intelligence profiles in defining dyslexia is discussed in a later section but it is worthwhile mentioning that Tyler (1990) comments that "it has been argued that where studies compare good and poor readers who are matched for mental age, the differences in [IQ] profiles may be caused by different reading experiences". Yet it is just such profiles that are used to diagnose dyslexia, (see next section). Whittaker (1981), who is quoted in Pumfrey and Reason (1991) states that "we do not have a medical condition called dyslexia. We have an educational problem about how to teach more effectively."

Dyslexia - a specific pattern of difficulties?

    "Despite the use of the adjective 'specific' [in Specific Learning Difficulties], much of the research on reading difficulties (dyslexia) has involved a somewhat non-specific group of children failing to read at the expected level, Pumfrey and Reason (1991). There is evidence that children labelled as 'Dyslexic' can be subdivided into more homogenous subgroups (Elliot, 1990).

    Intelligence tests such as the Wechsler Scale have been used for a number of years to operationally define dyslexia. The tests are being used to indicate a discrepancy between their presumed intellectual capacity and their achievement as well as to profile their abilities. It "has been argued that the ACID profile (relatively low scores on Arithmetic, Coding, Information and Digit span subtests) is merely a correlate of school achievement" Pumfrey and Reason (1991) referring to van der Wissel (1997).

    There does not appear to be any evidence in the literature for a direct link between IQ (verbal or global) and mechanical reading in 'normal' children, yet it is this very comparison that we are asked to make in order to use an IQ test to label a child as dyslexic. The labelling of dyslexic children using IQ tests is merely a statistical association between IQ scores and various patterns of difficulty - what Pumfrey and Reason (1991) refer to as "psychometric selection effects". Furthermore Tyler (1980) "correlational factors are not necessarily linked causally to reading difficulties and many of the measures used in the initial analysis are apparently remote from the reading/spelling process (Hulme and Snowling, 1988)", Tyler (1980).

    Intelligence testing itself does not reveal whether there are specific patterns of difficulty giving rise to dyslexia. The WISC, as with other tests, is based on measured normal distributions of the various sub-tests and dyslexics are frequently defined on the basis of being below average some of the subtests and above average for others. The ACID profile is an example of this. Given a different set of subtests, however, there might be a totally different group of children who 'fail' the IQ test. The sub-type characteristics may change with age and the stages of learning to read (Elliot, 1990)

    Stanovitch (1991) argues that "a major source of contention and theoretical confusion surrounding the term dyslexia stems from an almost perverse insistence in utilizing the concept of intelligence in definitions of reading disability". The prerequisite of many definitions of dyslexia is that the child must be of at least average intelligence to qualify, yet intelligence is a concept surrounded by deep controversy in the cognitive, developmental, and psychometric literature (Stanovitch ,1991).

    Intelligence testing does not provide the answer to the problem of whether dyslexia is the result of a specific pattern of difficulties although its use has assisted in the generation of the Dyslexia syndrome and the identification of children who may have special educational needs. The major implication is that Teachers need to be aware that the IQ test itself cannot diagnose with certainty that a that a child has dyslexia, but only with a statistical confidence. There are other potential causes for differences in subtest scores, one of which, schitopic sensitivity, is discussed in the next section.

Physical Problems.

    Physical in adequacy in the form of clumsiness (for example - not being able to tie shoe laces) has "been used as a marker for dyslexia by neurologists such as Critchley (1970)" they "have not appeared as significant" although "there is a clear overlap of problems associated with 'clumsy' children and those of speech disordered children" (Pumfrey and Reason, 1991)

    The scotopic sensitivity syndrome - proposed by Helen Irlen - is that there is an array of perceptual anomalies that allegedly cause visual dyslexia, (Pumfrey and Reason, 1991). The syndrome allegedly consists of visual distortions in four categories.

• Light sensitivity : the ability to accommodate high contrast and glare.
• Visual resolution: the ability to see print clearly and without distortions.
• Span of focus: the ability to perceive groups of words at the same time.
• Sustained focus: the ability to do with tasks with the eyes in a relaxed state with the objects in focus

    "Claims have been made that between 50 and 75 percent of learning disabled people suffer from this syndrome" Pumfrey and Reason (1991). However, a significant proportion of the 'normal' population also suffer from this syndrome (Brown pers. com. After attending an Irlen presentation). Pumfrey and Reason (1991) reviewed the literature on the use of lenses and filters, they consider that the evidence "indicates that visual problems do not seem to be a major cause of dyslexia". Dyslexic child suffering from scotopic sensitivity are bound to have their problems exacerbated. Although the Irlen lenses involve over 140 variations "the most significant effect of Irlen lenses is to reduce light overall rather than affect specific colours" (Moseley (1990b) cited by Pumfrey and Reason, 1991).

    Should teachers suspect that a child has scotopic sensitivity the most immediate response would be to reduce the light intensity. Certain blackboards and whiteboards are renowned for giving off a glare when viewed at certain angles. Moving the child to a different part of the classroom may well help. The printed word may be modified by overlaying sheets of coloured acetate such as are used for OHP transparencies. These are available in a variety of colours and intensities. Photocopying material onto coloured paper is another means of avoiding the complications of scotopic sensitivity. It is unlikely that many schools will be able to print specialist handwriting paper in unobtrusive shades as reported by Brown (1990)

Psychological Problems.

    Francis et al. (1996) undertook a longitudinal study testing a variety of skills in disabled readers which were thought to index brain function. Poor readers did not 'catch up', which is what would be expected if their difficulties had been the result of developmental delay. Instead they suggest that reading disability is best characterised by deficit models.

    Examination of the dyslexia syndrome has led workers to define deficits in a whole list of cognitive skills, including visual processing, phonological awareness and short-term memory. Each has been proposed as the fundamental deficit in dyslexia (Ellis, 1993). An example of this is shown in Figure 1(Heaton and Winterson, 1986). A single deficit is obviously an oversimplification of the case and research has centred upon the possible existence of sub-groups with children who were categorised by the original dyslexia syndrome. Though there have been problems in using intelligence to generate classifications of reading ability. (Francis et al.,1996 and Stanovich, 1991).

    At about this time a new term - Specific Learning Difficulties (SpLD) arose. This term encompassed many of the difficulties originally associated with the dyslexia syndrome. In 1991 the United Kingdom Reading Association considered that dyslexia referred specifically to difficulty with words or language symbols but did not include dyscalcula and dysgraphia, (Pumfrey and Reason, 1991). Although the British Dyslexia Association appears to go against this trend in stating that dyslexia "may be accompanied difficulty in number work" but is particularly "related to mastering and using a written language (alphabetic, numeric and musical written language) although often affecting oral language to some degree." Pumfrey and Reason (1991).

    Many of the difficulties originally encompassed in the dyslexia syndrome were separated into dyslexia and dysgraphia. The potential for confusion in redefining the term dyslexia is exacerbated by the use of SpLD which some workers consider to be synonymous with dyslexia (Pumfrey and Reason, 1991). The process of redefining dyslexia and the use of the term SpLD is shown in Figure 3.

Figure 3. A schematic diagram to show the various stages of research into dyslexia.

    Dyslexia is seen as a specific difficulty in activities involving the sounds of speech and the symbols (orthography) of the written language. This is often referred to as phonological dyslexia. Even within this more precise definition there are different sub-groups which exhibit different patterns of difficulty (for example surface dyslexia vs phonological dyslexia). Comparison with the study of acquired dyslexia and the application of information processing models have been used to account for surface dyslexia and phonological dyslexia. "Developmental surface dyslexics lean heavily on phonological letter-sound conversion procedures when attempting to read aloud. As a result they tend to regularise irregular words.", (Ellis, 1993). Acquired phonological dyslexics rely to a very large extent on whole word recognition of written words. They have impaired phonological reading skills and so are very poor at reading aloud unfamiliar words or non words. There is a continuum from phonological to surface dyslexia (Ellis, 1993). This indicates that the two different types of dyslexia could be the result of different children's strategies in coping with an underlying difficulty. 

    Dysgraphia (once included in the dyslexia syndrome) is a specific difficulty in relating sight to hand movements in tasks like writing . It may be akin to Dyspraxia or "Clumsy Child Syndrome" where the eye hand co-ordination is poor.

    Children may have some or all of the above categories (as well as addition problems, for example with mathematics - dyscalcula). This is shown schematically in Figure 4 which shows the possible combinations of these three difficulties. The combination of all three of these difficulties would present a child with a large number of difficulties.

    A schematic representation of the research into dyslexia is shown in Figure 3 but the process of defining dyslexia has been fraught with difficulty. "Despite the use of the adjective 'specific', much of the research on specific reading difficulties (dyslexia) has involved a somewhat non-specific group of children failing to read an expected level", (Pumfrey and Reason, 1991). 

    "Difficulties in agreeing or even making explicit, the theoretical basis for expectations concerning reading attainments and other literacy skills, impede progress in describing, identifying, predicting progress and developing effective interventions.", (Pumfrey and Reason, 1991).

Figure 4. The potential overlap of Dyslexia, Dysgraphia and Dyspraxia

Teaching Dyslexics.

    The teaching methods used with dyslexics tend to place great emphasis on phonics. "In this they are directed at the what is for many dyslexics the greatest area of difficulty", Ellis (1993). It is undoubtedly the case that phonics has assisted many dyslexics to acquire literacy.

    The short term memory and attentional problems of the dyslexic require that there is some form of 'over-learning'. This implies that the work is presented again and again, (Thomson, 1990). This is intended to generate automaticity.

    Unfortunately "there are many children who are unable to respond to rote phonological or multi-sensory approach despite skilled teaching", (Lewis, 1996). Ellis (1993) notes "that several studies have shown that dyslexics can make reasonable progress when given systematic instruction but the dyslexics in these studies are usually engaging in all sorts of reading-related activities. That and the frequent absence of control groups, means it is very difficult to know just what helps most and what does not help at all. Learning to read may not require the memorisation of phonic rules or lists of words. Such subskills could be acquired during the course of reading, (Pumfrey and Reason, 1991).

    "The uniqueness of each child's pattern of abilities, attainments and difficulties is well accepted" (Pumfrey and Reason, 1991). It would therefore appear reasonable to determine the remedial regime on the basis of individual assessments. This would certainly be the logical way to proceed if dyslexia is an 'umbrella-like' term for a range of different problems. However in the first section on the dyslexia syndrome the possibility that many of the symptoms of dyslexia could arise from a small number of specific difficulties. These specific difficulties could manifest themselves as a wide range of characteristics or symptoms many of which are the result of how the dyslexic has come to cope with their difficulty. In this scenario there is a danger that an individual assessments may lead to treating the symptoms rather that the problem.

    Tomson (1990) suggests that "although one could teach to a weakness [the auditory or phonetic deficits of a dyslexic], one should also circumvent the major problem by presenting the written language in alternative forms, namely visual and kinesthetic". Various techniques such as 'simultaneous oral spelling' may have this effect. In simultaneous aural spelling the words are said aloud then spelt individually. The word is then repeated and then written down , each letter being said as it is written individually, then read and cover up and said again. This is still a multisensory approach in that the word is heard, organising the sounds in it. The structure of the word is felt through the pen and the fingers. Finally hearing the sound patterns again enables it to be matched to the visual form of the word.

    It is not possible to consider the performance of a child in isolation from the pedagogic context. Therefore there are factors which ought to be taken into consideration but which cannot. In order to avoid such etiological considerations Brown (1980) examined the attentional style or processing characteristics of the individual when they tried to make sense of the printed word. This approach permits the possibility of "a mismatch between the processing set of an individual apprentice reader and that of the reading pedagogy in his/her classroom."

    One possibility is that dyslexics find it difficult to switch from one modality-bound encoding stage to another (Brown, 1980). Thus dyslexics find the process of reading - which requires the visual recognition of words, phonological encoding and then semantic encoding - very difficult. "Interference between different sounds can create greater difficulties in memory and organisation for the child", (Tomson, 1990). In information processing terms, however, the purpose of reading is the semantic encoding of information. The mediation of phonologic processing is not an essential requisite of the process.

    These ideas could be applied directly into the classroom. If the child finds it difficult to switch modality within a task then the teacher needs to determine the optimum modality for the learning experience and (if possible) remove the potential for distraction away from that modality encoding process. An example which goes some way towards this ideal is the use of sandpaper letters for children learning the orthography of letter shape. If the child was to be blindfolded during this process then potential for confusion caused by switching between sight and kinaesthetic modalities would be reduced. It is possible that the tactile feedback from the sandpaper itself would interfere with the point of the exercise - the generation a kinaesthetic trace of the letter formation within modality specific memory.

    In general terms the teacher needs choose an information processing approach over a deficit approach. This will require to each task to be analysed in terms of essential and non-essential components. Having identified the essential components it is then necessary to determine the optimum teaching strategy. If the target of a particular task is to 'bark at print' then this would require one kind of processing strategy. If the target is reading for meaning then a different kind of strategy would be required. In both cases the role of phonology (the dyslexics area of weakness) would have to be assessed to determine the extent to which it assists or inhibits the successful outcome of the intervention.

    In choosing to teach specific processing strategies for the task in hand we are attempting to modify the dyslexic child's cognitive process. The child is acquiring a new skill and although dyslexia does not seem to be the result of developmental lag (Francis et al., 1996), the child is engaged in a learning experience which most other children have already achieved. The guidelines proposed by Kinsbourne (1986), which have been reviewed earlier in this work, may well prove beneficial in guiding teachers through this process.

    Dyslexia is seen by some to be an 'umbrella-like' term to cover a range of quite different problems but others do perceive underlying specific patterns of difficulties. Perhaps the clearest idea of the nature of the problem is to consider a set of specific difficulties whose nature and severity can be considered a continuum across to the difficulties of normal children with the consequence that more productive focus can be made on the nature of all children's learning strategies conducive or otherwise to the acquisition of literacy. It is suggested that this might best be served by the cultivation of a value-free information-processing approach to the study of the relevant learning strategies rather than the assumption of deficit.

References

Brown E. N. (1980) Attentional Style, Linguistic Complexity, and Treatment of Reading Difficulty. In Knights R. M. and Bakker D. J. Treatment of Hyperactive and Learning Disordered Children. University Park Press, Baltimore 419pp

Brown E. N. (1990) Children with Spelling and Writing Difficulties: An Alternative approach. In Pumfrey P. D. and Elliot C. D. (Eds.) Children's Difficulties in Reading, Spelling and Writing. Falmer Press, London 316p

Coltheart M. (1996) Phonological Dyslexia: Past and Future Issues. Cognitive Neuropsychology 13(6):749-762

Cruickshank (1986) Forward to Pavlidis and Fisher (Eds.) Dyslexia: Its Neuropsychology and Treatment. Wiley

Elliot (1990) The Definition and Identification of Specific Learning Difficulties. Pumfrey P. D. and Elliot C. D. Children's Difficulties in Reading, Spelling and Writing. Falmer Press, London 316p

Ellis A.W. (1993) Reading, Writing and Dyslexia: A Cognitive Analysis. Lawrence Erlbaum Associates, Hove 137pp

Francis J., Shaywitz S., Stuebbing K., Shaywitz B. and Fletcher J. (1996) Developmental Lag Versus Deficit Models of Reading Disability: A Longitudinal, Individual Growth Curves Analysis. Journal of Educational Psychology 88(1):3-17

Heaton and Winterson (1986) Dealing with Dyslexia. Better Books Publishing, Bath. 210pp

Hornsby (1984) Overcoming Dyslexia: A straightforward guide for families and teachers. Martin Dunitz Ltd., London.

Kinsbourne (1986) Models of dyslexia and its subtypes. Pavlidis and Fisher (Eds.) Dyslexia: Its Neuropsychology and Treatment. Wiley

Lewis L. (1996) An Inspection of the practical soundness of the icon methodology as an approach to acquiring literacy skills. Northamptonshire Inspection and Advisory Service.

Manis F. R., Seidenberg M. S., Doi L. M., McBride-Chang C. and Peterson A. (1996) On the basis of two subtypes of development dyslexia. Cognition 58: 157-195

Stanovich (1991) Discrepancy definitions of reading disability: Has intelligence led us astray? Reading Research Quarterly 16(1): 7-29

Thomson (1990) Evaluating Teaching Programs for Children with Specific Learning Difficulties. In Pumfrey and Elliot (Eds.) Children's Difficulties in Reading, Spelling and Writing. Falmer Press, London 316p

Tyler S. (1990) Subtypes of Specific Learning Difficulty: A review. In Pumfrey and Elliot (Eds.) Children's Difficulties in Reading, Spelling and Writing. Falmer Press, London 316p