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Dyslexia: More than a Phonological Deficit

Phonological deficit
Science does not advance by consensus. Science is not an exercise in democracy. – Author unknown
Most problems can be solved once we know what causes that particular problem. For example, a disease such as scurvy claimed the lives of thousands of seamen during long sea voyages. However, the disease was cured fairly quickly once the cause was discovered: a vitamin C deficiency. A viable point of departure would therefore be to ask the question, what causes dyslexia?

Although some causes of dyslexia have a genetic origin and environmental factors play an important role, cognition mediates brain-behavior relationships. It, therefore, offers a sufficient explanation for the development of principled interventions. In short, we need to understand the cognitive difficulties that underpin reading problems, regardless of whether their origin is constitutional or environmental (Snowling & Hulme, 2011, p. 4).

Since the beginning of the twentieth century, dyslexia research has been dominated by a search for the Holy Grail: the single cognitive deficit that is necessary and sufficient to cause all behavioral characteristics of dyslexia. Until the 1950s, the belief was that dyslexia is attributable to visual processing problems.

Samuel Orton, arguably the key figure in setting the stage for the study of reading disabilities in the United States, linked mixed dominance to the symptoms he frequently observed in the clinic where he was hired:

  1. Reversals of letters such as p and q and b and d;
  2. Reading from right to left, manifested by reversals of paired letters, syllables within words, or whole words within sentences;
  3. A propensity to mirror-read and/or write.

From these observations, Orton proposed his “strephosymbolia,” or twisted symbols theory. He suggested that people with dyslexia had a deficient visual perception of letters caused by the inheritance of mixed cerebral dominance.

Phonological awareness the Holy Grail

In 1957 Noam Chomsky published his seminal book, Syntactic Structures, which transformed the study of language and, with it, reading. Any role for visual processing was abandoned, and dyslexia became a linguistic, phonological problem. In an influential book, Dyslexia: Theory and Research, Vellutino (1979) argued that many of the apparent visual problems could be attributed to language difficulties — especially to deficient phonological awareness.

The phonological deficit theory became the most well-developed and supported theory of dyslexia. It has been widely researched in the UK and the US, resulting in a remarkable consensus concerning the causal role of phonological skills in young children’s reading progress. Children with good phonological skills, or good “phonological awareness,” become good readers and spellers. Conversely, 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 nine or ten years old (Goswami, 1999). 

The US researchers have united in adopting the phonological deficit hypothesis since the early 1980s. 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).

What is phonological awareness?

Phonological awareness refers to an individual’s awareness of a language’s phonological or sound structure. It is a listening skill that distinguishes speech units, 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 spelling rules, and use this information to decode (read) and encode (write) words. Phonological awareness relates only to speech sounds, not alphabet letters or sound-spellings. Therefore, students do not need alphabet knowledge 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 sound units. 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 is heard. For example, if a child can segment, they can say f-i-sh after hearing the word fish. If they can blend, they can say the word fish after hearing the individual sounds f-i-sh. Phonemic awareness is said to be a foundational skill for phonics, which, in turn, is the foundation for reading.

Phonological deficit theory gains ground 

The phonological deficit theory gained prominence following studies of preschool children seeking which pre-reading skills are the best predictors of reading and writing ability. Phonological awareness emerged as an important factor (Elliott & Grigorenko, 2014). For example, Bradley and Bryant (1983) found high correlations between preschool children’s initial rhyme awareness and their reading and spelling development over three years. This link held even after controlling for other variables, such as IQ and memory. Other studies comparing older backward readers with younger children without difficulties reading at the same level showed significant phonological deficits for the older groups (Bradley & Bryant, 1978; Olson, 1985; Rack, Snowling, & Olson, 1992).

The ability to segment and blend phonemes is said to be especially critical for the development of reading skills, including decoding and fluency, and even that it predicts reading ability (Taylor, 1998; Moustafa, 2001). In one of the landmark articles on phonemic awareness research, “Matthew effects in reading: Some consequences of individual differences in the acquisition of literacy,” which received the Albert J. Harris Award from the International Reading Association, Keith Stanovich (1986) argued that phonological awareness is causally related to the early development of reading skill, and concluded that the solution for reading failure is to “identify early, remedy early, and focus on phonological awareness” (p. 394). As the “most convincing” evidence for his proposal, Stanovich cited several studies “where phonological awareness skills were manipulated via training, and the manipulation resulted in significant experimental group advantages in reading, word recognition, and spelling (Bradley & Bryant, 1983, 1985; Fox & Routh, 1984; Olofsson & Lundberg, 1985; Torneus, 1984; Treiman & Baron, 1983)” (p. 363).

In the late 1980s, the US Department of Education’s Office of Education Research and Improvement (OERI) commissioned Marilyn Jager Adams to survey the entire body of reading research. She produced Beginning to Read: Thinking and Learning About Print, relying heavily on the research studies conducted by Stanovich. She discusses no fewer than eight of his articles in her report, and in her bibliography makes 26 references to his work, including “Matthew effects in reading.” She concluded that phonemic awareness is the “most important core and causal factor separating normal and disabled readers” (1990, pp. 304-5). According to Kilpatrick (2016), phonological awareness training prevents and corrects reading difficulties (p. 13).

Correlation does not equal 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 sick and being in a hospital. However, the hospital did not cause the illness. “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. Krashen (1999a) reviewed ten studies and found no significant difference between the effects of phonemic awareness for measures of reading administered immediately after training or delayed by up to two or three years. After reviewing another 15, he concluded that training in phonemic awareness has a larger effect on tests of phonemic awareness than on tests of real-word reading and reading comprehension (1999b).

Pape-Neumann et al. (2015) investigated whether phonological awareness training could improve the reading ability of 30 German third- and fourth-graders with dyslexia. 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.”

Taylor (1998) points out that while children’s early cognition develops from concrete experiences to abstract understandings, phonemic awareness training begins with abstract exercises. She also points out that when “Matthew effects in reading”-references are checked, “they are often problematic” (p. 12). For example, the “convincing” results of the study by Olofsson and Lundberg (1985, p. 21) read:

The children who participated in the phonemic training program seemed to have benefited from it to some extent. At least they improved their scores on phonemic synthesis tests in school.

The problem, says Taylor, is that “Matthew effects in reading” was relied upon by Adams and many other scholars, as well as the state of California, to justify the “ABC Bills” and to mandate that children receive phonemic awareness training. In addition, the NICHD has used the article in a report that John Silber sent to every school superintendent in the state of Massachusetts, commanding teachers to “begin teaching phonemic awareness directly at an early age (kindergarten)” (Taylor, 1998, p. 5).

Phonological awareness may not be as important   

Some researchers say phonological factors may be less important than is generally accepted (Byrne, 2011). Not all children with reading disabilities demonstrate a phonological deficit. 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 phonological awareness or other phonological processing deficits in kindergarten and reading deficits in first grade.

Catts and Adlof (2011) and Howard and Best (1996) point out that children with poor phonological abilities can nevertheless develop good reading skills. Phonological awareness appears to be a better predictor of reading ability in general than reading disability in particular (Scarborough, 1998).

Studies of adults with reading disabilities suggest that phonological awareness appears to be rather less important for older poor readers than it is for children, with other processes such as verbal memory, vocabulary, and naming speed playing an equally significant role in differentiating between those with and without reading disability (Swanson & Hsieh, 2009).

Precursor or consequence?

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. Berthelsen and De Gelder (1989) reviewed several studies of speakers of Portuguese, Belgian, Japanese, and Chinese demonstrating that adult non-readers and readers of non-alphabetic scripts are unable to segment phonemes but can do so after learning to read alphabetic scripts. In a study by Lukatela et al. (1995), truly illiterate adults could not do a phoneme deletion task. These findings have helped cement the link between awareness and reading in an alphabetic system but questioned the presumption that the prevailing direction of causal influence is from awareness to reading rather than the reverse (Morais, 1991).

A major methodological limitation of longitudinal studies showing an association of preschool phonological awareness with later reading is that early reading abilities were typically not assessed at the first assessment point. Thus, it is unclear what the association between early phonological awareness and later reading is. For example, Wimmer et al. (1991) showed that at their study onset, 16 of 23 early readers (about 70%) scored at the ceiling in a phoneme awareness task, whereas only 10% of the 105 non-readers reached such high scores. Neglecting the fact that a certain percentage of children can read at the onset of schooling may induce faulty interpretations of predictive patterns.

Some findings support an intermediate view, “that phonological awareness and alphabetic literacy learning influence each other reciprocally (Burgess & Lonigan, 1998; Lonigan, Burgess & Anthony, 2000; Wagner et al., 1994)” (Manolitsis & Tafa, 2011, p. 31).

As correctly stated by Elliott and Grigorenko (2014), much depends on the breadth of the use of the term “phonological” and the extent to which it includes a variety of cognitive processes such as working memory and rapid naming. Ramus et al. (2013), for example, suggest that many of those with dyslexia have difficulties with the exercise of phonological skills rather than poor phonological representations. For these authors, phonological skills are understood as the “things that one can do with one’s phonological representations, but that require additional skill: awareness and meta-cognitive skills, short-term or working memory, rapid and serial retrieval” (p. 639).

Franceschini et al. (2012) showed that visual-spatial attention in preschoolers is an important predictor of reading development. Children who had poor reading abilities during the first or second year of reading education made significantly more errors on a visual-search task and a spatial-cueing task than normal readers had when they were in kindergarten. Moreover, several studies show that people with dyslexia present a visual-processing deficit independently of phonological skills.


A study by Lipowska et al. (2011) concludes: “The presented research constitutes another piece of evidence showing that children with dyslexia are afflicted with both phonological problems and visuospatial deficits connected with the right posterior parietal cortex. Diagnosis limited only to the linguistic aspect may produce an incomplete picture of the actual pathogenic mechanisms. … omitting [visual perception and visuospatial deficits] in the process of diagnosis may lead to a distortion of the picture of a child with developmental dyslexia and thus diminish the chance for effective therapy.”

Given that a single phonological deficit is not necessary or sufficient to cause reading disability (Catts & Adlof, 2011), current thinking sees this as one of multiple deficits that are likely to interact to cause reading disability (Peterson & Pennington, 2012; Pennington, 2006).

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