Orthographies and dyslexia

Orthographic dyslexia, a subtype of dyslexia, results in difficulty decoding and encoding skills due to slow and inaccurate rates of storing word and letter formations into memory. Orthographic dyslexics have difficulty in storing mental representation of words, especially phonetically irregular words such as word spellings that end in -ight ("light" and "sight"). The problems underlying this type of dyslexia are related directly to memory and coding skills that allow representation of printed letters and words, not to poor phonological processing.[11]

This type of dyslexia is also termed surface dyslexia because people with this type have the inability to recognize words simply on a visual basis. Words that are misspelled cause the readers difficulty because they attempt to sound out the words by looking at each individual letter rather than the word as a whole.[12] So a reader might read the word "cat" and pronounce the "c" as a hard "c" but then read the word "ice" and pronounce the "c" as a hard "c" as well because they are sounding out each individual phoneme rather than just recognizing the word "ice" in its entirety.

Despite intervention, children suffering from orthographic dyslexia continually have lower achievement reading levels when compared to their peers. Additionally, children show a greater difficulty throughout schooling when spelling words with irregular or unusual orthographies when compared to their other children. Research also shows that dyslexic children have primary difficulties in phonological processing and secondary difficulties in orthographic processing, aiding to the distinction of two subtypes.[13]

The complexity of a language's orthography is directly related to the difficulty of learning to read in that language. Orthographic complexity also contributes to how dyslexia manifests in readers of different languages.[14]

Deep orthographies are writing systems, such as those of English and Arabic, that do not have a one-to-one correspondence between sounds (phonemes) and the letters (graphemes) that represent them.

Shallow orthographies, such as Italian and Finnish, have a close relationship between graphemes and phonemes, and the spelling of words is very consistent. With shallow orthographies, new readers have few problems learning to decode words and as a result children learn to read relatively quickly. Most dyslexic readers of shallow orthographic systems learn to decode words with relative ease compared to dyslexics using deep orthographies, though they continue to have difficulty with reading fluency and comprehension.[8] The hallmark system of dyslexia in a shallow orthography is a comparatively slow speed of rapid automatized naming.

Writing and drawing performed by a child with dyslexia, displaying common behavioral symptoms.

For languages with relatively deep orthographies, such as English and French, readers have greater difficulty learning to decode new words than languages with shallow orthographies. As a result, children's reading achievement levels are lower.[15] Research has shown that the hallmark symptoms of dyslexia in a deep orthography are a deficit in phonological awareness and difficulty reading words at grade level.[16] For these dyslexic readers, learning to decode words may take a long time—indeed, in the deepest orthographies a distinctive symptom of dyslexia is the inability to read at the word level—but many dyslexic readers have fewer problems with fluency and comprehension once some level of decoding has been mastered.

Studies between the English and German (which has a shallower orthography than English) languages have shown that the greater depth of the English orthography has a "marked adverse effect on reading skills" among children with dyslexia, though the dyslexics in these studies still mostly underperformed compared to control groups.[8][17] Other research, however, has suggested that all children with dyslexia still suffer the same reading difficulties despite different orthographies, including reading speed deficit and slow decoding mechanisms.[7] These findings suggest that orthographic differences do not significantly impact the main difficulties those with dyslexia experience.

Most of the current research on dyslexia focuses on alphabetic orthography.[9]

Alphabetic writing systems vary significantly in the depth of their orthography. English and French are considered deep orthographies in comparison to Spanish and Italian which are shallow orthographies. A deep orthography like English has letters or letter combinations that do not reliably map to specific phonemes/sound units, and so are ambiguous in terms of the sounds that they represent whereas a transparent or shallow orthography has symbols that (more) uniquely map to sounds, ideally in a one-to-one correspondence or at least with limited or clearly signified (as with accent marks or other distinguishing features) variation. Literacy studies have shown that even for children without reading difficulties like dyslexia, a more transparent orthography is learned more quickly and more easily; this is true across language systems (syllabic, alphabetic, and logographic), and between shallow and deep alphabetic languages.[20]

In cross-language studies, Aro and Wimmer report differences in developmental reading skills across several alphabetic orthographies. Among those tested, English children achieved only 50% accuracy in pseudoword testing by the end of first grade and did not attain high accuracy until fourth grade. However, in the same test, French, German, Dutch, Spanish, Swedish, and Finnish children all achieved scores approaching 85% and 90% in Grade 1 and Grade 4, respectively.[21] This research provides evidence that orthographic irregularities, such as the "complex grapheme-phoneme relations" found in English, present significant difficulties in the reading development of children.[21]

However, there is little evidence that a more "regular" orthographic system would significantly diminish the amount of dyslexia cases. Because there is also a visual aspect to dyslexia, affected children often show symptoms such as mirror letter reversal (e.g. confusing "b" and "d"), which can manifest in any language regardless of orthographic depth.

Logographic writing systems (such as Chinese characters and Cuneiform) differ significantly from alphabetic systems in that the graphemes of a logographic system are logograms; that is, written characters represent meaning (morphemes), rather than sounds (phonemes). As a result, logographic systems require a comparatively large number of unique characters. This means that development of reading and writing skills in logographic systems depends more heavily on visual memorization than in alphabetic systems. Thus dyslexics, who often rely on grapheme memorization to cope with phonological awareness deficits,[22][23] may show reduced difficulty in acquiring a language which uses a logographic system.[24] However, logograms offer fewer phonological cues than alphabets and so have a more irregular orthography/grapheme-to-phoneme correspondence when compared with a more transparent system like an alphabet or syllabary. Literacy/readability studies of children without reading difficulties have shown that children take longer to demonstrate literacy in logographic systems than do children in syllabic systems or alphabetic systems, .[20] These differences in proficiency diminish as age increases, but the findings suggest that more transparent systems are easier to learn as primary languages.

Archaic Chinese logograms

Chinese children can exhibit more severe difficulties due to dyslexia when compared to those using an alphabetic script. Not only are Chinese dyslexic children phonologically at a disadvantage, but visiospatial processing disorder prevents activation of the semantic information.[25]

In alphabetic languages, phonological awareness plays a central role in reading acquisition; while phonological awareness in Chinese is much less important. Rather, reading in Chinese is strongly related to a child's writing skills, which depend on orthographic awareness and on motor memory. In handling alphabetic languages with deep orthographies, the child must cope with having more than one spelling to represent a sound. In spoken Chinese, a single syllable is used in many different words, and a Chinese child must cope with having many written characters that represent the same syllable.[20]

Further complicating the Chinese writing system, the Chinese character is made up of strokes and sub-character components, substantially increasing visual complexity. Thus orthographic processing is an important aspect of reading. Deficient orthography-to-meaning mapping can lead to reading disability. A key strategy in teaching children to read is to have children repeatedly write samples of single characters, thus building the child's awareness of a character's internal structure (orthographic awareness).[19]

Rapid naming is one of the best single predictors of dyslexia in all languages tested, including both alphabetic and character-based writing systems.[19][26] There is some evidence that the means of deciphering characters differs between logographic and alphabetic writing systems differ in the brain: logographic systems echo map-reading skills.

In a syllabary, written characters represent spoken syllables, whereas alphabetic systems use characters/letters to represent separate phonemes.[20] A symbol in a syllabary typically has the canonical shape of a consonant-vowel (CV) combination. In the Japanese syllabaries, hiragana and katakana, there is a nearly one-to-one correspondence between morae and characters. The transparency of these syllabaries is the reason for their use in first teaching Japanese children to read before advancing to the complex logographic system of kanji, and by the age of five, prior to any official reading education, 89% of Japanese children can read the majority (60 or more out of 71) of hiragana characters.[20]

Syllabary orthographies, like English orthography, can also be very irregular. A symbol could mean "i" in one sentence but the same symbol could mean "e" in a different sentence if it is preceded by a different symbol,[27] which can increase the difficulty of reading for people with dyslexia. However, little research has been done on how dyslexia presents in syllabic systems. One possible reason for this is that because of the different ways that dyslexia can present, (i.e. how visuospatial systems are affected in Chinese dyslexics - or how the logographic system is affected by defects/abnormalities in the visuospatial processing regions, which is more likely since written language is a cultural artifact with no genetic predispositions, and so existing structures must be adapted to handle language) the disorder may go unnoticed or not be recognized. On the other hand, a Japanese psychologist wrote that "while dyslexia, reading disability, reading disorder, reading retardation, or whatever you prefer to call it, comprises a formidable portion of psychiatric practice in Western countries, its incidence in Japan is so rare that specialists in Japan do not get any referrals",[28] indicating that the prevalence of dyslexia may vary cross-linguistically. A literacy study on children without reading disabilities found that syllabic scripts like Japanese katakana and hiragana, which are very transparent orthographically, are learned more quickly and with better proficiency than more orthographically opaque languages, followed in ease of use and learning by shallow alphabetic scripts that also have many phonological cues, then by complex alphabetic scripts that have irregular orthography (like English), and then by logographic scripts like kanji which have no phonological cues.[20]