The Nature of Dyslexia

The term dyslexia is derived from the Greek dys (difficult) ad lesicos (pertaining to words) and was first used by Berlin in 1887 to describe extreme difficulty reading and spelling words. The World Federation of Neurology defines dyslexia as follows.

Specific developmental dyslexia is a disorder manifested by difficulty learning to read despite conventional instruction, adequate intelligence, and adequate sociocultural opportunity. It is dependent upon fundamental cognitive disabilities which are frequently of constitutional origin (1968; cited in Critchley 1970).

The qualifier developmental refers to a disorder of suspected congenital or hereditary origin, in contrast to acquired dyslexia, a disorder resulting from brain injury after the onset of reading (Frith, 1986). It is important to state that the world developmental does not mean that the disorder will disappear with maturity. A distinguishing characteristic of dyslexia is, in fact, its persistence, although appropriate remedial treatment and the development of compensatory strategies may moderate its effects.

The qualifier specific is intended to connote a disorder limited specifically to reading rather than involving a general learning problem.

There is even evidence that dyslexia is limited not just to reading, but to very specific aspects of reading. Philip Cough's theoretical simple view of reading holds that there are two contributors necessary to skilled reading comprehension: 1) decoding and 2) listening comprehension (Gough & Tunmer, 1986). That is, children with reading problems could be having difficulty at either the word reading level or with understanding what they have read once they have decoded or deciphered written words into spoken words.

Dyslexia is considered a learning disability in the Federal Register under Public Law 94-142. As with other learning disabilities covered under this law, dyslexia involves what is called an exclusionary diagnosis. That is, instead of describing characteristics directly, the definition describes all the conditions that must be ruled out (e.g., low IQ, physical handicaps, environmental factors, etc.) before making a diagnosis.

The more prevalent view for the past 15-20 years involves language problems. Language is a highly complex function, however, and not all aspects of language appear to be implicated as primary causes in developmental dyslexia.

Research substantiates a significant relationship between early language processing and/or production problems and later reading problems. Follow-up studies of children diagnosed with early specific language impairment (SLI) have shown the incidence of later reading disability to be 90 percent or greater. Not all children with dyslexia have histories involving early language disorder.

One recurring question in the field is whether or not difficulty with the phonological aspects of reading is caused by difficulty with auditory perception. No differences have been found between children with and without dyslexia in perception of nonverbal environmental sounds. Possible difficulties appear related to speech sounds alone.

Measure of ability to listen, remember, and repeat auditory stimuli have also been used to assess verbal short-term memory, but Th. stimuli tend to be longer than the single words used above in the auditory perception tasks. Individuals with dyslexia have been found to perform less well than same-age normal readers on tasks requiring them to repeat information verbatim.

The term phonological awareness refers to the metacognitive understanding that spoken language is made up of a series of sounds and that these sounds occupy a particular sequential order.

Several British researchers have provided evidence of a link between deficits in phonological awareness and deficits in reading. While it has been argued that phonological awareness may be an effect of mature reading rather than its cause, it has also been demonstrated that the degree to which phonological awareness is developed prior to reading instruction plays a powerful role in determining reading outcomes.

Keith Stanovich has suggested that the entire range of difficulties often attributed to dyslexia may stem from what he calls the phonological core deficit. He argues that failure to learn to decode words because of phonological processing problems causes subsequent deficits in reading comprehension, vocabulary development, and even IQ through lack of access to print experiences.

Neurological and Biological Correlates

Overt neurological problems have been difficult to substantiate as a common factor among children with dyslexia.

Academic Manifestations of Dyslexia

Significant Problems with:
Word Recognition
Reading Rate
Reading Comprehension
Listening Comprehension
Expressive Writing Problems
Handwriting Problems

Dyslexia is generally perceived first and foremost as a word-reading disorder.

Word Attack Skill: The most pronounced among the reading difficulties that individuals with dyslexia experience is the inability to decode unfamiliar words. This problem appears to be the common denominator in all cases of dyslexia.

Today--primary deficits in phonologically driven word-level reading is recognized as the principal area of deficit in dyslexia.


This document was prepared in 1994 by Nancy Youree Duggin, National Board Certified Teacher and the Instructional and Professional Development Coordinator for Tennessee Education Association.