Dyslexia: The Double Deficit Theory
Harvard Graduate School of Education
The Recognition, Strategic and Affective Networks:
Dyslexia: Strengths and Success Stories
The Landmark School
Dyslexia is a disorder impacting five to 17% of school-aged children (Shaywitz & Shaytwitz, 2006). It is familial and heritable, with upward to a 60% chance of it being passed from parent to child (Shaywitz, 2006). This paper will focus on a severe form of dyslexia : the double-deficit disorder. Though, still being investigated, evidence has mounted that phonological awareness contributes to a separate discrepancy in reading skills independent of processing speed (Wolf & Bowers, 1999). It appears that among poor readers, there are children who struggle to read and suffer from two separate cognitive disorders (Wolf & Bowers, 1999). One : the inability to hear and/or place in short-term memory phonemes-or small bits of sound. For example, as we speak, these sounds are said very quickly. Phonological processing is the ability to process quickly and accurately these sounds so we can attach meaning to them (Rose & Meyers, 2002.) Studies by Paula Tallal in the 1980’s suggested that, among other neural disruptions, this was due to slow cortical sound processing (Sptizer, 1999). Second : readers must be able to rapidly recognize and retrieve visually presented linguistic stimuli. Difficulty in doing so may imply deficits in processing speed.. As will be reviewed, some children suffer from both. When both deficits are present, there are more limited compensatory routes for reading (Coleman, 2006). This dual disorder impacts reading rate, fluency, and clearly impacts comprehension (Wolf & Bowers, 1999).
In a 1998 study, it was determined that among 83 severely impaired readers, 50% fell into the double-deficit category, 29% in the naming speed group and 14% had phonological difficulties (Wolf & Bowers, 1999). For poor readers, deficits in naming speed processes can be more impairing than phonological deficits (Wolf & Bower, 1999).
Though, the double-deficit disorder is not yet officially categorized, the neuroscience of where the deficits occur in the brain and the behavioral responses are clear (Wolf & Bowers, 1999). This disorder requires different tests for diagnosis and different approaches for remediation (Wolf & Bowers, 1999).
The role of Phonological Processing: Researchers have observed that phonemic sensitivity to hearing sounds can ultimately impact perceptual, cognitive and linguistic processing. For example, a child who doesn’t hear correctly beginnings or ends of words will have trouble identifying those words once in text. Some children have “top-down” deficits and can not attach meaning quickly or correctly to words that they hear perfectly well. Phonological processing deficit, in contrast, impacts “bottom-up” strategies (Rose & Meyers, 2002).
For example, when asked to take the “st” from “stich” in a testing situation, these children struggle to hear and recall the “st” that starts of the word. When asked to repeat long nonsense words like “teebudieshawlt”, they struggle (CTOPP, 1999). These students usually have solid cognitive and linguistic functions involving I.Q., reasoning, vocabulary, and syntax (Shaywitz, 1998), but it is hard to use contextual cues when struggling to sound out words. It is estimated that 88% of children with reading difficulties have trouble with phonological awareness (Shaywitz, 1998.)
The role of Processing Speed (“Naming-Speed”) : An able reader must be able to have high quality representations of the sound-symbol patterns of letters and words, and be equipped with a rapid retrieval system for fluency (Wolf, Miller and Biddle, 2000). Without fluency, comprehension is impaired. If a child can break down words phonetically, but has low fluency in reading it means, cognitively speaking, that the speed of which a letter or word is retrieved is too slow for efficient reading comprehension. (Wolf, Bowers & Biddle, 2000).
The problem may be that these students have deficits in the time it takes to disinhibit from one stimulus (e.g., a letter) and then perceive and recognize the next. Then, they have ongoing difficulty activating lexical access and retrieving processes for the letter’s ‘verbal label’, and then quickly moving to the next stimulus ((Wolf, Miller & Biddle, 2000). A student struggling with processing speed may have trouble reading an array of numbers, colors or letters quickly without slowing down or pausing.
Two reading challenges ~ the Double-Deficit Theory : When both deficits occur together, a student is with difficulty breaking down words that rely on phonological skills an trouble rapidly retrieving and converting the words to symbols of meaning. Even with excellent “higher-order” skills, it may be difficult to create an image of a story when the pieces are so slow coming together. Reading, spelling, writing and math skills may be impacted. To recognize that these two disorders originate from different neurology deficits is the first step in realizing that different treatment and school support will be required.
Language acquisition develops in the temporal lobes in the first four years of life; phonological development in the inferior parietal and temporal lobes from early childhood to eight years (Shaywitz, 1998). To read, we first must understand language and transform the visual features of words into the linguistic sounds they represent (Shaywitz & Shaywitz, 1998). During this process, there are three primary networks-- recognition, strategic and affective--that work together, though they are in different areas of the brain and have different functions. They help us recognize and code visual and auditory input, focus and regulate our attention long enough to hear and see information, and provide the emotional ability to interpret correctly and appreciate fully what we read (Rose & Meyers, 2002).
Summary of major deficits in network areas : The recognition network has the primary task of combining letters and sounds to allow the reader to quickly recognize words. We can see through fMRI imaging how the brain responds to temporal compression of sounds, specifically speech. This tool has helped locate the brain regions involved in the phonological and processing circuitry needed for reading (Poldrack, Temple, Protopapas, Nagarajan, Tallal, Merzenich & Gabriele, 2001). The left hemisphere of the brain, specifically, the left inferior frontal and left superior temporal regions—known as Broca’s and Weinicke’s area, along with the right inferior frontal cortex, respond to speech sounds. These are the main language areas used by typical readers. Within the strategic networks, it appears dyslexics activate the prefrontal and frontal lobes while reading, unlike regular readers who rely on the temporal lobes (Shaywtiz, Shaywitz, & Liberman,1991). The thalamus, located within the affective network region, in the prefrontal region, is used to regulate speed and accuracy of speech-sound processing and direct incoming information. This module, also, appears different in dyslexic readers (Shaywitz, et al., 1991). Research also indicates deficits in the circuitry between the retina to the lateral geniculate nucleus and the visual cortex resulting in slower processing speed (Demb, 1997; Ridder, et.al, 1997 as cited in Feifer, 2005)
Recognition Networks: As mentioned, the posterior system involving the posterior superior temporal gyrus, Weincke’s area, helps with the understanding of words (Shaywitz & Shaywitz, 2006). Studies show that in dyslexics there is disruption in these key language regions, as well as the angular gyrus. This area, in the parietal lobe, is critical to carrying out cross-modal integration needed for reading (Shaywitz & Shaywtiz, 2006). The angular gyrus acts like bridge between visual word recognition and the rest of the language process (Carter, 1999). Evidence exists that disruptions in the posterior region of the brain near the angular gyrus and the occipital and temporal brain regions may also impact the fluency (speed) and word identification (McCandliss and Noble, 2003).
A study by Geschwind & Galaburda (1985) produced evidence that structural deviations of the plana tempolare within the temporal lobe may inhibit phonological processing stems. Geschwind, also, speculated that dyslexics seem to have more occurrences of left-handedness and good math abilities, both right hemisphere controlled attributes Geschwind (Feifer, 2005) Others have reasoned this may be due to the asymmetry caused on the left hemisphere due to high levels of fetal testosterone causing loss of cortical cells in that region. (Feifer, 2005). Overall, in dyslexia, there is a pattern of underactivation of the posterior brain regions and heightened activation in the anterior regions, and the right hemisphere posterior regions (Shaywitz, et al, 1998, Pugh, et al, 2001).
Strategic networks : This region controls planning and task execution, and the ability to attend and retain information (Rose & Meyers, 2002). As mentioned, connections appear problematic in dyslexic readers between the posterior and frontal regions, specifically Broca’s areas, in the inferior frontal gyrus, an area responsible for speech and silent reading (Pugh, et al, 2001). The strategic networks are critical also to listening skills required for phonological processing. However, students with disorders recognizing speech might have strong strategic listening skills that help them retain information to compensate for their slower recognition processes (Rose & Meyers, 2002). Strong “top-down” strategic skills can help a child struggling with rate and fluency reading issues by helping to provide greater gestalt” thinking (Rose & Meyers, 2002).
Affective networks : Within this region, the thalamus helps coordinate sensory input during the reading process (Carter, 1998). In dyslexics, this region can be damaged impacting the ability to process sound (Galaburda, et al., 1985). Most importantly, the limbic system, itself, is connected by millions of connections to cortical parts of the brain (Carter, 1998). The system takes emotional significance events and a response is fed to the cerebral hemisphere where it is processed, impacting the way we perceive situations (Carter, 1998). Children with deficits in phonological and processing speed will likely perceive many academic situations as threatening. This might “kick” the limbic system into frequent “fight or flight” responses, setting the stage for anxiety and depression (Carter, 1998). Disorders impacting mood and feeling, can impede learning, and produce slower word fluency, reduce the energy needed to attend to word-sound recognition, and the ability to commit word meaning to memory. However, by showing engagement and commitment to a particular subject, the affective system can provide the ‘boost’ needed to overcome deficits in the recognition and strategic networks. (Rosalie Fink, as cited in Rose & Meyers, 2002). The impact of the affective networks needs to be fully understood by educators. In fact, one could argue, this system could be most crucial to children struggling with this disorder (Rose & Meyers, 2003).
|Dyslexia: Strengths and Success Stories
Many well-know and successful people have struggled with dyslexia. Their talents frequently reside outside the language domain. Is their success due to having the disorder or in spite of it? Perhaps dyslexic’s talents are a result of nature ensuring cognitive diversity and talent ( Sherman, 2006). Many have strong visual/spatial and perceptual skills due to greater activity in the right temporoparietal region of the brain (Pugh, Mencl, Jenner, Katz, Frost, Lee, et al., 2001). In any case, hard work, an early recognition of their skills and ambition helped them, like other successful people, overcome the hurdles they faced while in school.
Here are well-know examples of people who have struggled with dyslexia, along with the “non-language” neural networks areas they used (and the neuropsychological ones) to develop their skills :
Pablo Picasso, Artist
From an early age, Picasso developed a sense of how people wanted to be seen (affective) and a unique sense of style and beauty (visual spatial.) His abstract artistic style was beyond the skills of most painters from that period (conceptual).
Tom Cruise, Actor
In his early years, Tom was athlete of considerable skill (kinesthetic/motor). Later, he focused his energy on pursuing an acting career. He is well-know for his methodical ability to plan for his roles and his punctuality (strategic), and his focused pursuit in understanding his character’s real intentions and beliefs (affective).
Richard Branson, Actor
Richard Branson failed miserably at tests and school work. However, he was blessed with outstanding personal skills and an innate ability to connect with people (affective/ interpersonal). He also believed in himself (affective/strategic) and after some early success in business, forged forward in a determined way (strategic), and never looked back on his disability.
(Examples taken from :www.dyslexiaonline.com/famous/famous.htm; “Dyslexia – you’re not alone” Neuropsychological descriptions taken from Howard Gardner’s Multiple Intelligence theory, 1989)
As you walk into the entrance of the Admissions Office at the Landmark School, you may be distracted by the turn-of-the-century detail encompassing this elegant property. Set against the north shore landscape, it is easy to forget that this school is not your run-of-the-mill New England prep school. For its students and parents, the school it is liberating departure from the struggles borne from most traditional schools, where reading words on paper defines a student.
The Landmark School serves children with severe dyslexia. Commonly, the children admitted have both phonological and processing deficits (double-deficit). Students come from all over the world who have struggled most of their lives to read. Ironically, only 1/3 of the children who apply are admitted, making it as difficult to get into as many prestigious private schools. On any given week-day the office is filled with families seeking admittance to the school.
On a typical day, children sit with parents waiting to be interviewed or tested. For many, school has been a damaging experience and this school—usually miles from home—may be a last resort. Among the students accepted, their reading challenges have a similar pattern. These students have problems in usually three areas of language processing. Some have trouble recognizing or remembering letters and numbers. Others struggle to hear various letter sounds, and, yet others can have trouble rapidly processing letters and words. A Landmark student usually suffers from at least two of these deficits. The last two are characteristics of children with double-deficit disorder.
The importance in modern society of being able to read and write accurately and quickly is apparent to anyone looking closely at the faces of the children waiting to be interviewed. They are like the farmer’s weakling child from years past—their disability hangs heavy in a world where productivity and worth is measured by one’s ability to acquire knowledge from printed text.
Tools for success – network systems get a boost : The school embraces and strengths these students. The school understands how the recognition, strategic and affective network systems work together for children with dyslexia. As students increase their ability to recognize letters or hear sounds, this impacts their reading and writing skills, which in turn impacts their sense of self allowing them to become, in many cases, more determined and deliberate about how they organize and plan their lives each day. Someday universal design in schools will help these students much earlier in their lives.
Carter, R. (1999). Mapping the Mind. Berkeley: University of California Press.
Coleman, M. (2006). A critical investigation of the etiology of developmental dyslexia: Retrieved on March 22, 2006.
Comprehensive Test of Phonological Processing-CTOPP. (1999). Austin, TX. Pro-Ed.
Feiffer, S. (2005, April 30). The Neurology of Reading Disorders: Diagnosis and Intervention. [Learning and the Brain Conference.] Hotel Sonesta, Cambridge, MA.
Galaburda, A., Sherman, G., Rosen, G., Aboitiz, F.& Geschwind, N. (1985). Developmental Dyslexia: Four consecutive patients with cortical abnormalities. Annals of Neurology. 18, 22-233.
Gardner, H., & Hatch, T. (1989). Multiple intelligences go to school: Educational implications of the theory of multiple intelligences. Educational Researcher, 18(8), 4-9.
Jordan, D. (2002). Overcoming Dyslexia. Austin, TX. Pro-Ed. pp.156-158
McCandliss, B. & Noble, K. (2003). The development of reading impairment: a cognitive neuroscience model. Mental Retardation & Developmental Disabilities Research Reviews, 9,3.
Poldrack, R., Temple, E., Protapapas, A., Nagarajan, S., Tallal, P., Merzenich, J. (2001). Relations between the neural basis of dynamic auditory processing and phonological processing: Evidence from fMRI. Journal of Cognitive Neuroscience. 13: 687-697. Cambridge, MA. The MIT Press.
Pugh, K., Mencl, W., Jenner, A., Katz, L., Frost, S., Lee, J, Shaywitz, S. & Shaywitz, B. (2001). Functional neuroimaging studies of reading and reading disability. Mental Retardation & Developmental Disabilities Research Reviews. 6,3.
Rose, D. & Meyers, A. (2002). Teaching every student in the digital age. Alexandria, VA. ASCD Books.
Shaywitz, B, Shaywitz, S, Liberman, Y, (1991). Neurolinguistic and Biologic Mechanisms in Dyslexia. The Reading Brain: The Biological Basis of Dyslexia," DD Duane and DB Gray, Ed. Parkton: York Press, pp. 27-52,
Shaywitz, S. (1998). Dyslexia. New England Journal of Medicine, 338, 307-312.
.Shaywitz B., Shaywitz S., Blachman B., Pugh K., Fulbright R., Skudlarski P, Mencl W., Constable R., Holahan J., Marchione K., Fletcher J., Lyon G., Gore JC. (2004). Development of left occipitotemporal systems for skilled reading in children after a phonologically-based intervention. Biol Psychiatry. 2004 May 1;55(9):926-33
Shaywitz, S., & Shaywitz, B. (2006). The Neurobiology of Reading and Dyslexia. National Center for the Study of Adult Learning and Literacy. Retrieved on March 27, 2006. www.ncall.net
Sherman, G. (2006) Dr. Sherman offers his version of dyslexia. Charles Schwab Learning.Org. Retrieved on March 25, 2006. www.schwablearning.org/articles
Spitzer, M. (1999). The mind within the net. Cambridge: MIT Press: p. 165
Wolf, M., & Bowers, P. (1999). The double-defict hypothesis for the developmental dyslexias. Journal of Educational Psychology. 91, 3, 415-438.
Wolf, M., Bowers, P. & Biddle, K. (2000). Naming-speed processes, timing and reading: A conceptual review. Journal of Learning Disabilities. 33, 4, p. 387-407.
Dyslexic? You’re not alone. www.dyslexiaonline.com/famous/famous.