Dyslexia: More than a Phonological Deficit

Most problems can be solved once we understand their cause. For example, scurvy claimed the lives of thousands of seamen during long sea voyages. Yet the disease was brought under control relatively quickly once its cause was discovered: a vitamin C deficiency. A logical point of departure, therefore, is to ask: What causes dyslexia?

Although some causes of dyslexia have a genetic origin, and environmental factors play an important role, cognition mediates brain-behavior relationships. Cognition, 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 the search for the Holy Grail: the single cognitive deficit that is both necessary and sufficient to account for all the behavioral characteristics of dyslexia. Until the 1950s, the belief was that dyslexia was 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 his clinical work:

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

Phonological awareness becomes the Holy Grail

In 1957, Noam Chomsky published his seminal book, Syntactic Structures, which transformed the study of language and, with it, reading. The emphasis on visual processing largely disappeared, and dyslexia came to be viewed primarily as 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 with 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 US government investing more than $15 million annually through the National Institute of 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 within 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 knowledge of the alphabet to develop basic phonological awareness.

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 widely regarded as an important foundation for phonics instruction, which plays a central role in learning to read.

Phonological deficit theory gains ground 

The phonological deficit theory gained prominence following studies of preschool children aimed at determining which pre-reading skills best predict 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 in 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 has even been proposed as a predictor of 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, drawing heavily on Stanovich’s research. 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 10 studies and found no significant difference in the effects of phonemic awareness between measures of reading administered immediately after training and those administered up to two or three years later. 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 is not the whole story   

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% 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) note that children with poor phonological abilities can nevertheless develop strong 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 illiterate adults and readers of non-alphabetic scripts 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 were unable to perform a phoneme-deletion task. These findings have helped cement the link between awareness and reading in an alphabetic system, but they have 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 the onset of their study, 16 of 23 early readers (about 70%) scored at the ceiling on 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 use of the term “phonological” and the extent to which it encompasses a range of cognitive processes, such as working memory and rapid naming. Ramus et al. (2013), for example, suggest that many with dyslexia have difficulties with the exercise of phonological skills rather than with 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 instruction made significantly more errors on a visual-search task and a spatial-cueing task than normal readers did in kindergarten. Moreover, several studies show that people with dyslexia exhibit a visual-processing deficit independent of phonological skills.

Conclusion

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 neither necessary nor sufficient to cause reading disability (Catts & Adlof, 2011), current thinking views phonological difficulties as one of multiple deficits that may interact to cause reading disability (Peterson & Pennington, 2012; Pennington, 2006).

The implications for assessment and intervention are clear. Dyslexia is unlikely to be explained fully by any single deficit. Effective assessment should therefore consider the range of cognitive processes that contribute to reading, while intervention should be guided by the individual’s specific strengths and weaknesses rather than a single explanatory model.

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