It has been difficult to isolate distinguishing features that would categorize specific dyslexia as a single condition. SLDs have many subtypes with a variety of breakdowns, as suggested by Carlson (1998). He suggested two major distinctions of people as follows:
As mentioned previously, we will focus on dyslexia, which is a general term for reading disorders with many subgroups (i.e. surface, phonological, word-form or spelling, and direct). As a quick note, dysgraphia, writing disorders, has similar subgroups (i.e. surface, phonological, and direct). Basically, writing involves reading with an output expression using visual imagery and phonetics, as well as memory of letter sequence and muscle motor. The dyslexia subgroups can be understood as follows:
Since all dyslexics do not possess the same symptoms, Ingram (1964) suggested dividing dyslexia into three categories,
Persons with visuo-spatial difficulties cannot recognize groups of letters. They may tend to guess words by shape and not by context. People with this form of dyslexia may also confuse reversible letters, transpose letters in syllables and syllables in words and words in phrases. They have trouble reproducing letters in writing and may confuse letter, syllable and word order. They may also read words backwards.
Those with speech sound difficulties have problems in understanding spoken language. Difficulty arises in breaking words into syllables and in forming sentences. Those who have problems correlating are unable to find the appropriate speech sounds for individual letter or sounds in writing (this is seen more commonly with monosyllabic words).
Researchers began to standardize the concept of dyslexia as case studies and investigations increased. The divisions below are listed according to the researcher of dyslexia. (Snowling Margaret, 1972)
Boder's- Reading-Spelling Pattern Dysfunction
Boder developed a diagnostic screening tool for developmental dyslexia from which she divided into three subtypes:
Johnson & Myklebust's- Visual and Auditory
Johnson and Myklebust(1967) standardized reading tests as well as tests for reading diagnosis. They also identified subtypes of dyslexia.
Bateman's-Visual learners, Auditory learners, Visual and Auditory deficits.
Bateson (1968) identified three categories based on the Illinois test of Psycho linguistic Abilities. They are:
Smith's Three Patterns based on WISC and WAIS tests. In 1970 Smith used the Weschler intelligence test and the WISC to draw some conclusions. Smith's inferences were similar to Border's. He detailed three pattern dyslexics:
Mattis, French and Rapin-Language Disorder group, Articulary and Dyscoordination Group and a Visualspatial Verceptual Disorder group.
Mattis French and Rapin conducted a study of 113 children to investigate the cause of dyslexia. They tested all of children on IQ, vision, hearing and academic exposure. They divided the children into three groups: (I) those with brain damage who could read, (II) those with brain damage who were dyslexic and (III) those without brain damage who were dyslexic. Interestingly enough they found a similarity between those with developmental dyslexia and those with brain-damage dyslexia. On the basis of these results and a battery of neuropsychological examinations, they divided dyslexia into three syndromes.