Subtypes Based on Nature of Word Recognition Deficits

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Another body of research suggests that individual differences specific to word recognition abilities may be a useful way to classify poor readers. There are two routes for word recognition. One is the visual route in which words are recognized directly on the basis of their spelling or orthographic patterns. The other is the phonological route in which words are recognized indirectly by using sound-letter correspondence rules to decode the word. Much attention has been devoted to individual differences in children's abilities to use these word recognition routes.

Reading Styles

A popular view in "folk psychology" and education is that children can be divided into two distinct subgroups based on whether they learn to read more easily by the visual route or phonological route (Carbo, 1987, 1992; Dunn, 1990). Carbo (1992), for example, divides children into global learners and analytic learners. Global learners or readers are argued to learn to recognize words best through a sight-word approach that makes use of the visual route. Analytic readers, on the other hand, learn to read best by a phonics method that takes advantage of the phonological route. Many in early education also refer to these groups as visual and auditory learners and believe that teachers should identify a child's learning style and teach to that style.

Despite the widespread appeal of reading/learning styles, the evidence is not very compelling that children can be divided into homogeneous subgroups on the basis of their reading strengths (or preferences), or that teaching to these strengths is an effective strategy for improving reading ability (Kavale, Forness, & Bender, 1987; Stahl, 1988; Stahl & Kuhn, 1995; Turner & Dawson, 1978). Relatively few studies have actually addressed this issue. Those studies that have offered some support for reading style subgroups and instruction (Holt & O'Tuel, 1990; Thomasson, 1990) have typically been reported outside the peer-review process. As a result, this work has not had the level of scrutiny and evaluation that is needed in order to effectively guide educational practice. This view is also contrary to most current theories of reading development. Most research suggests the importance of both the visual and the phonological routes in learning to read (Share, 1995; Share & Stanovich, 1995). Children need to have good phonological decoding skills to break the alphabetic code (i.e., self-teach) as well as good orthographic skills to develop accurate and automatic word recognition.

Dysphonetic, Dyseidetic, and Alexic Subgroups

Although evidence supporting the existence of word recognition subgroups in the population as a whole is not strong, there is converging research that indicates that such a classification system may be of value for subgrouping poor readers. There is a long history of poor readers being classified on the basis of individual differences in reading by the phonological versus the visual route (Boder, 1971, 1973; Ingram, 1964). Ingram (1964), for example, grouped poor readers into audio-phonetic dyslexics and visuo-spatial dyslexics. The audio-phonetic dyslexics were argued to have problems in sound discrimination and blending and to be poor in phonological decoding. The visuo-spatial dyslexics, on the other hand, were proposed to have difficulties in visual discrimination and spatial skills and problems reading by the sight-word route.

Elena Boder (1971, 1973) developed a classification system that recognized three subgroups of poor readers based on misreadings and/or misspellings: the dysphonetic, dyseidetic, and alexic. The dysphonetic subgroup has a primary deficit in auditory analytic skills. Children in this subgroup have great difficulty learning and using the phonological route. These children display misreadings and misspellings that are phonetically inaccurate. For example, the dysphonetic reader might pronounce block as book or spell scramble as sleber. Dyseidetic readers, on the other hand, have a deficit in the visual route. Consequently, they have particular problems with exception words (e.g., have, colonel). These words are misspelled or misread as phonetic renditions: for example, reading talc for talk or spelling laugh as laf. Finally, the alexic subgroup have a deficit in both phonetic and visual reading/spelling skills. This subgroup is the most handicapped of the three groups.

The primary evidence for the validity of these subgroups comes from a study of 107 dyslexic children (Boder, 1973). Using an in-depth analysis of reading and spelling abilities, 100 of these children were divided into one of the three subgroups. Boder reported that 67 of the dyslexic children were dysphonetic, 10 were dyseidetic, and 23 were alexic. Boder and a colleague (Boder & Jarrico, 1982) later developed a diagnostic screening test for subtyping dyslexia. Researchers, utilizing this test, have provided some evidence of behavioral and electrophysiological differences between subtypes of dyslexics (Dalby & Gibson, 1981; Flynn & Deering, 1989). Flynn and Deering (1989), for example, found that dyseidetic children demonstrated greater EEG activity in the left temporal-parietal region during reading than did dysphonetic children. They suggested that this was evidence of different processing capabilities between these subgroups. Others, however, have failed to uncover reading-related differences between these subgroups of poor readers (Godfrey, Lasky, Millag, & Knox, 1981; van den Bos, 1982). Godfrey and colleagues (1981), for example, failed to find an advantage in speech perception abilities among dyseidetic dyslexics as compared to dysphonetic dyslexics. Such a difference would be expected if dysphonetic dyslexics had a phonological processing problem.

Deep, Phonological, and Surface Dyslexia

Cognitive neuropsychologists have also considered subgroups similar to those proposed by Boder (Coltheart, Patterson, & Marshall, 1980; Marshall & Newcombe, 1973). This work, however, has used terminology and procedures borrowed from the study of acquired dyslexia. Acquired dyslexia is a reading disability in previously literate individuals following neurological damage. Three syndromes are often identified: deep, phonological, and surface dyslexia. Individuals with deep and phonological dyslexia have considerable difficulty in phonological decoding. They are identified primarily on the basis of their problems pronouncing nonwords such as zun or vope. Such words cannot be recognized by the visual route and must be sounded out using sound-letter correspondence rules. Individuals with deep dyslexia, unlike those with phonological dyslexia, also make semantic errors in reading. For example, when asked to read a word like tulip they might say "crocus" or they might read "sun" for moon. Other symptoms include visual errors (confusing words like wife and life), morphological errors (misreading prefixes or suffixes), and greater facility recognizing content words as opposed to function words (Thomson, 1984). Finally, individuals with surface dyslexia have problems with the visual route. They are identified on the basis of their misreading of exception words. Whereas the terms phonological and surface dyslexia roughly correspond to dysphonetic and dyseidetic readers, the former terms have become more popular in recent years.

Using primarily case studies, cognitive neuropsychologists have subtyped individuals with developmental reading disabilities as phonological or surface dyslexics (Coltheart, Materson, Byng, Prior, & Riddoch, 1983; Holmes, 1978; Marshall, 1984; Temple & Marshall, 1983; see Rayner & Pollatsek, 1989, for review). For example, Temple and Marshall (1983) described a case of developmental phonological dyslexia. This student, a 17 old girl, had considerable difficulty reading nonwords compared to real words. Her responses to nonwords were typically real words that were visually similar to the target words. Marshall (1984) noted that this developmental case was very similar to the case of acquired phonological dyslexia reported by Patterson (1982). Coltheart and colleagues (1983) and Holmes (1978), on the other hand, identified a number of cases of developmental surface dyslexia. Holmes reported on four boys, between 9 and 13 years of age, who had great difficulty reading exception words. They often made phonetic errors, regularizing words like bread as "breed." Coltheart and colleagues (1983) identified a 15-year-old dyslexic girl who had many problems with homophones. For example, she was noted to read "pane" correctly, but to define it as "something that hurts."