A Multi-Cognitive Deficit Model of Developmental Dyslexia

Six blind men came across an elephant. The first blind man ran into the elephant’s “sturdy side” and declared the animal a wall. The second felt the elephant’s tusk “so very round and smooth and sharp” and pronounced the elephant to be a spear.

The third felt the squirming trunk in his hands and proclaimed the elephant to be a snake. The remaining three blind men declared the elephant as, respectively, a tree trunk (based on the leg), a fan (based on the ear), and a rope (based on the tail).

Scholars in the field of learning disabilities (LD) often invoke the parable of the “blind men and the elephant” to capture the state of the research literature on learning disabilities. Although there is no lack of research on the subject of learning disabilities and especially reading disabilities — or dyslexia as it is commonly referred to — the theories, assessments and treatment are so labyrinthine and contradictory as to cause one to throw one’s hands up in the air (Spear & Sternberg, 1986; MacConville, 2007; Waber 2010; Kapur 2011).

Much of the labyrinthine and confusion may well be the result of researchers touching only a part or parts of the dyslexia elephant, missing the fact that it is actually a multi-cognitive deficit. Learning to read is a complex matter that relies on a conglomeration of cognitive functions, not only on one or two (Pennington, 2006; Tamboer et al., 2016).


The term dyslexia was coined from the Greek words dys, meaning ill or difficult, and lexis, meaning word. It is used to refer to persons for whom reading is simply beyond their reach, accompanied by certain symptoms and signs including reversals of letters like b and d; putting letters in the wrong order (reading felt as left); misreading little words (such as a for and); losing orientation on a line or page; reading aloud hesitantly, word by word; trying to sound the letters of the word, but then be unable to say the correct word (for example, sounds the letters ‘c-a-t’ but then says cold); and reading with poor comprehension. Spelling and writing, due to their close relationship with reading, are usually included.

According to popular belief dyslexia is a neurological disorder in the brain that causes information to be processed and interpreted differently, resulting in reading, spelling and writing difficulties. Historically, the dyslexia label has been assigned to students who are bright, even verbally articulate, but who struggle with reading; in short, whose high IQs mismatch their low reading scores. When children are not as bright, their reading troubles have been chalked up to their general intellectual limitations.

Using brain imaging scans, neuroscientist John D. E. Gabrieli and team at the Massachusetts Institute of Technology recently overturned this long-held IQ-discrepancy definition of dyslexia, when they found no differences between the way poor readers with or without dyslexia think while reading. Research results indicated that poor readers of all IQ levels showed significantly less brain activity in the six observed areas than typical readers. But there was no difference in the brains of the poor readers, regardless of their IQs (Tanaka et al., 2011).

The theory of a neurological deficit has also been questioned. In one study, published online in the Journal of Neuroscience, researchers analyzed the brains of children with dyslexia and compared them with two other groups of children: an age-matched group without dyslexia and a group of younger children who had the same reading level as the children with dyslexia. Although the children with dyslexia had less gray matter than age-matched children without dyslexia, they had the same amount of gray matter as the younger children at the same reading level. Lead author Anthony Krafnick said this suggests that the anatomical differences reported in left-hemisphere language-processing regions of the brain appear to be a consequence of reading experience as opposed to a cause of dyslexia (Krafnick et al., 2013).

Extreme viewpoints exist about dyslexia, which makes it difficult for parents to know how to best help their child. On the one side there is the group who believes dyslexia is a condition that cannot be cured but endured. “Dyslexia is like alcoholism … it can never be cured,” stated Clark and Gosnell (1982, pp. 55-56). According to the British Dyslexia Association dyslexia “is likely to be present at birth and to be life-long in its effects” (Fern-Pollak & Masterson, 2016, p. 224). In her acclaimed book, Overcoming Dyslexia, pediatrician Dr. Sally Shaywitz tells concerned parents the sad news: “Once a person is dyslexic, he is dyslexic for life” (2003, p. 164).

On the other extreme there are those who say diagnoses of dyslexia are a complete waste of time. According to Professor Julian Elliott, from Durham University in the United Kingdom, and Professor Elena Grigorenko, from Yale University in the United States of America, diagnosis of dyslexia adds little value. In their book, The Dyslexia Debate (2014) they write: “Parents are being misled by claims that such dyslexia assessments are scientifically rigorous, and that a diagnosis will point to more effective forms of treatment.” Dyslexia, according to them, is a term which, “confuses, rather than clarifies, and should be discontinued.”

What causes dyslexia?

Most problems can only be solved if we address the causes, which brings us to the most controversial aspect of the dyslexia elephant: its cause(s).

The phonological deficit theory is the most well-developed and supported of the theories of dyslexia. It has been widely researched, both in the UK (York group) and in the US, resulting in a remarkable degree of consensus concerning the causal role of phonological skills in young children’s reading progress. Children who have good phonological skills, or good “phonological awareness”, become good readers and good spellers. Children with poor phonological skills progress more poorly. In particular, those who have a specific phonological deficit are likely to be classified as dyslexic by the time they are 9 or 10 years old (Goswami, 1999). The US researchers have united in adopting the phonological deficit hypothesis since the early 1980s, and this united front has led to the investment of more than $15 million annually by the US government, via the National Institute for Child Health and Human Development (NICHD) (Fawcett, 2001).

Phonological awareness refers to an individual’s awareness of the phonological structure, or sound structure, of language. It is a listening skill that includes the ability to distinguish units of speech, such as rhymes, syllables in words, and individual phonemes in syllables.

Phonological awareness is often confused with phonics, but it is different. Phonics requires students to know and match letters or letter patterns with sounds, learn the rules of spelling, and use this information to decode (read) and encode (write) words. Phonological awareness relates only to speech sounds, not to alphabet letters or sound-spellings, so it is not necessary for students to have alphabet knowledge in order to develop a basic phonological awareness of language.

Phonemic awareness is a subset of phonological awareness that focuses on recognizing and manipulating phonemes, the smallest units of sound. The two most important phonemic awareness skills are segmenting and blending. Segmenting is breaking a word apart into its individual sounds. Blending is saying a word after each of its sounds are heard. If a child can segment, he is able to say fish after hearing the word fish. If he can blend, he’s able to say the word fish after hearing the individual sounds fish. Phonemic awareness is said to be foundation skill for phonics, which in turn is the foundation for reading.

The ability to segment and blend phonemes is said to be critical for the development of reading skills, including decoding and fluency, and even that it predicts reading ability. Adams (1990) concluded that phonemic awareness is the “most important core and causal factor separating normal and disabled readers” (pp. 304-305). It is also claimed that phonological awareness training can prevent and correct reading difficulties (Kilpatrick, 2016, p. 13).

Correlation does not mean causation

Margaret Moustafa, professor emeritus of education at California State University in Los Angeles, points out that correlation does not establish causation. For example, there is a high correlation between being dead and being in a cemetery. However, the cemetery did not cause the death. “In statistics, the word predicts means nothing more than that there is a high correlation between two phenomena” (Moustafa, 2001, p. 248).

Research does not support phonemic awareness training, says Moustafa. Olson et al. (1997) report that in their studies of at-risk children, analysis failed to show an advantage of those who received explicit training in phonological awareness on word recognition over control groups, on two-year follow up tests. Troia (1999) reviewed 39 phonemic awareness training studies and found no evidence to support phonemic awareness training in classroom instruction. Krashen (1999a, 1999b) conducted similar reviews and had similar findings. Taylor (1998) points out that while children’s early cognition develops from concrete experiences to abstract understandings, phonemic awareness training begins with abstract exercises.

Blomert and Willems (2010) investigated children at familial risk for dyslexia in kindergarten and first grade. The familial risk was genuine; 40 percent developed reading deficits in first grade. However, they did not find any relationship between a phonological awareness or other phonological processing deficits in kindergarten and reading deficits in first grade.

A study by Pape-Neumann et al. (2015) investigating whether phonological awareness training is an effective intervention to significantly improve reading in German dyslexic third and fourth graders with a phonological awareness deficit, randomly assigned 30 students to one of three interventions: a phonological awareness training, a phonology-based reading training (phonics instruction), and a visually-based reading training (repeated reading of sight words). A total of 20 training sessions (30 minutes each) were distributed over four weeks. The study concludes that, “despite divergent short-term patterns, long-term improvement of reading comprehension and decoding is similar across all training groups, irrespective of the training method… Phonological awareness may but does not need to be part of reading remediation in dyslexic children with a phonological deficit when learning to read a consistent orthography.”

Some findings indicate that phoneme awareness may develop as a consequence of exposure to reading and writing. Especially persuasive is research showing that adult illiterates and readers of a non-alphabetic script lack awareness of phonemes (Lukatela et al., 1995; Morai et al., 1979; Morais, 1991; Read, 1986). These findings have helped to cement the link between awareness and reading in an alphabetic system, but seemed to call into question the presumption that the chief direction of causal influence is from awareness to reading rather than the reverse (Morais, 1991). However, there are findings which support an intermediate view, “that phonological awareness and alphabetic literacy learning influence each other reciprocally (Burgess & Lonigan, 1998; Lonigan et al., 2000; Wagner et al., 1994)” (Manolitsis & Tafa, 2011, pp. 30-31).

Other dyslexia models

There is evidence of speed problems for dyslexic children in almost all areas, including those where rapid sensory processing is not needed. This has been known since the 70’s based on ‘Rapid Automatized Naming’ (RAN) tests (Denckla & Rudel, 1976), in which dyslexic children show speed deficits in simply saying the names on a page full of simple pictures or colors. Rapid naming is said to facilitate fluent reading and comprehension. However, problems are found even when language is not involved, so children with dyslexia are slower to simply press a button when choosing between a high and a low tone (Nicolson & Fawcett, 1994).

Bowers and Wolf brought together the phonological and speed problems in the double-deficit hypothesis, which suggests that there are two separate sources of difficulty in dyslexia, phonology and processing speed. Children with both speed and phonology problems have the most severe problems (Wolf & Bowers, 1999).

The magnocellular theory holds that dyslexia is a sensory dysfunction (Stein & Walsh, 1997), while the cerebellar deficit hypothesis blames a mild dysfunction of the cerebellum (Nicolson et al., 2001). There are many other models, most of them pointing the finger to only a part of the dyslexia elephant.

A multi-cognitive deficit model of dyslexia

A multi-cognitive deficit model attempts to look at the whole elephant: vocabulary; focused, sustained, divided and visual spatial attention; visual, auditory and phonological processing; rapid naming and processing speed; verbal, visual, auditory, sequential, iconic, short-term, long-term and working memory; logical thinking; et cetera.

Until fairly recently, the role that memory may play in creating the dyslexia elephant has been grossly underestimated and even ignored. Yet, it should clearly be considered as a fundamental skill. Riding and Pugh (1977) found that visual sensory (iconic) memory is significantly related to fluency, accuracy and comprehension. Guthrie and Goldberg (1972) identified significant, positive associations between visual sequential memory and paragraph comprehension, oral reading and word recognition. Stanley, Kaplan and Poole (1975) compared 33 dyslexic and 33 control eight- to 12-year-old children and found the dyslexic children to be inferior to controls on tasks involving visual sequential memory and auditory sequential memory.

A study, published in Dyslexia, compared performances of 60 dyslexic children to that of 65 age-matched normal readers on verbal, visual-spatial and visual-object tasks. Results documented a generalized impairment of long-term memory capacities in dyslexic children and findings indicate that the long-term memory deficit in dyslexia is not limited to the dysfunction of phonological components but also for visual and spatial material, thus suggesting that dyslexia is associated to multiple cognitive deficits (Menghini et al., 2010).

Ahissar and team tested dyslexic and non-dyslexic musicians on auditory processing and auditory memory. Dyslexic musicians scored as well as their non-dyslexic counterparts in auditory processing tasks, and better than the general population, but performed much worse on tests of auditory working memory, including memory for rhythm, melody and speech sounds. Moreover, these abilities were intercorrelated, and highly correlated with their reading accuracy, which means that the dyslexic musicians with the poorest auditory working memory tended to have the lowest reading accuracy (Weiss et al., 2014).

One should also consider the role of mutualism. A mutualistic view suggests that cognitive abilities mutually facilitate growth. For example, better reasoning skills allow individuals to improve their vocabulary more quickly, and better vocabularies are associated with faster improvement in reasoning ability (Kievit et al., 2017). Vocabulary size has also been shown to be strongly related to the child’s degree of phonological awareness (Dickinson et al., 2004; Foy & Mann, 2001; Goodrich & Lonigan, 2014). Likewise, cognitive abilities such as nonverbal intelligence (Goodman et al., 2010; McBride-Chang, 1995) and working memory capacity (McBride-Chang, 1995; Oakhill & Kyle, 2000) have been shown to be related to performance in phonological awareness tasks. Perhaps improving vocabulary, nonverbal intelligence and working memory would improve phonological awareness and vice versa.

The bottom line

The elephant is a very large animal. Each blind man was touching only one part. To learn the truth, they will have to put all the parts together.

Given that a single deficit is not sufficient to explain the cause of developmental dyslexia, hasn’t it perhaps become time for LD practitioners to consider a multi-cognitive deficit model?


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