Dyslexia

Definition

The definition of dyslexia used by the National Institutes of Health and the International Dyslexia Association: Dyslexia is a specific learning disability that is neurological in origin. It is characterized by difficulties with accurate and/or fluent word recognition, and by poor spelling and decoding abilities. These difficulties typically result from a deficit in the phonological component of language that is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction. Secondary consequences may include problems in reading comprehension and reduced reading experience that can impede growth of vocabulary and background knowledge.

Subtypes and Symptoms

ORTHOGRAPHIC DYSLEXIA

    Orthographic awareness is the ability to perceive and recall letters, letter strings and words.  This ability helps students to establish detailed visual or mental representations of letter strings and words and to have rapid, fluent access to these representations.  Orthographic dyslexia is a term used to describe students whose reading and spelling problems are characterized by poor memory of letter strings.  The following are characteristics of orthographic dyslexia:

Symbol Recognition and Recall Difficulties

• Difficulty learning how to form symbols
• Confusion of symbols similar in appearance (e.g., b and d, n and u, 2 and 5)
• Trouble with near-point and far-point copying tasks
• Tendency to reverse letters or numbers past the age of 7

Word Identification (Decoding)

• Trouble with accurate and rapid word recognition
• Trouble reading exception or irregular words
• Trouble remembering how words look
• Trouble remembering letter sequences
• Over-reliance on phonological and contextual strategies as aids in word identification
• Slow reading speed

Spelling (Encoding)

• Tendency to reverse and transpose letters (eg, grils for girls)
• Tendency to use different spellings for the same word (eg, Pual and Paul)
• Tendency to over-rely on phonological rather than visual features of words
• Tendency to omit word endings

 Calculating 

• Tendency to reverse and transpose digits (eg, 12 for 21)
• Trouble learning and retaining basic math facts
• Difficulty counting in a sequence (eg. counting by 2)
• Trouble solving multistep problems

PHONOLOGICAL DYSLEXIA

   The auditory block consists of two major components: verbal short term memory and phonological awareness.  Verbal short-term memory is the ability to repeat information immediately after hearing it.  Poor verbal short term memory is one of the most frequently reported cognitive characteristics of individuals with severe reading disabilities.  Phonological awareness is an oral language ability that refers to the ability to attend to various aspects of the sound structure of speech.  This metacognitive understanding involves the realization that spoken language is made up of a series of sounds that are arranged in a particular order.  Some students have weaknesses in both short-term memory and phonological awareness.

     Phonological dyslexia refers to a problem with the acquisition of decoding or encoding skills that is caused by difficulty with manipulating and integrating the sounds of a language effectively.  These impairments comprise the most common characteristics of individuals with dyslexia.  Students with phonologically based reading impairments perform poorly on measures of phonological awareness, as well as measures involving the application of speech sounds to letters, such as non-word reading and spelling tests.  Phonological skills are related significantly to spelling performance through high school.  The following are characteristics of phonological dyslexia:

Early Speech/Language Difficulties

• Articulation errors
• Mispronunciations of multi-syllabic words

 Word Identification (Decoding)

• Trouble with remembering sound-symbol relationships
• Confusion with similar-sounding sounds (eg. /b/ and /p/)
• Over-reliance on whole-word and contextual cues
• Difficulty sequencing sounds in words
• Trouble with pronouncing multi-syllabic words
• Trouble pronouncing phonically regular nonsense words
• Difficulty applying phonics to pronounce unfamiliar words
• Slow reading rate

Spelling (Encoding)

• Confusion of sounds (eg. vowels, voiced and unvoiced consonant pairs)
  
• Difficulty sequencing sounds
• Tendency to include a few unnecessary sounds
• Tendency to omit some sounds
• Difficulty representing each syllable
• Tendency to rely on the visual features of words rather than letter-sound relationships

     Students can also demonstrate weaknesses in verbal short-term memory that are likely to affect the development of computational skill.  A student may struggle to follow directions, memorize counting patterns, and keep pace with oral drills in the classroom.

Source:  (Mather & Goldstein, Learning Disabilities and Challenging Behaviors).