History of developmental dyslexia
Encyclopedia
Identified by Oswald Berkhan in 1881,
the term 'dyslexia' was later coined in 1887 by Rudolf Berlin,
an ophthalmologist practicing in Stuttgart
, Germany
.
He used the term to refer to a case of a young boy who had a severe impairment in learning to read and write in spite of showing typical intellectual and physical abilities in all other respects.
In 1896, W. Pringle Morgan, a British physician, from Seaford, East Sussex
published a description of a reading-specific learning disorder in a report to the British Medical Journal
titled "Congenital Word Blindness". This described the case of a 14-year-old boy who had not yet learned to read, yet showed normal intelligence and was generally adept at other activities typical of children of that age.
In 1925 Samuel T. Orton
, a neurologist who worked primarily with stroke victims, met a boy who could not read and who exhibited symptoms similar to stroke victims who had lost the ability to read. Orton began studying reading difficulties and determined that there was a syndrome unrelated to brain damage that made learning to read difficult. Orton called his theory strephosymbolia
(meaning 'twisted signs') to describe individuals with dyslexia had difficulty associating the visual forms of words with their spoken forms.
Orton observed that reading deficits in dyslexia did not seem to stem from strictly visual deficits.
He believed the condition was caused by the failure to establish hemispheric dominance
in the brain.
He also observed that the children he worked with were disproportionately left- or mixed-handed
, although this finding has been difficult to replicate.
Influenced by the kinesthetic work of Helen Keller
and Grace Fernald
, and looking for a way to teach reading using both left and right brain functions,
Orton later worked with psychologist and educator Anna Gillingham
to develop an educational intervention that pioneered the use of simultaneous multisensory instruction.
In contrast, Dearborn, Gates, Bennet and Blau considered a faulty guidance of the seeing mechanism to be the cause. They sought to discover if a conflict between spontaneous orientation of the scanning action of the eyes from right to left and training aimed at the acquisition of an opposite direction would allow an interpretation of the facts observed in the dyslexic disorder and especially of the ability to mirror-read.
To this end the authors asked four adults to read a text reflected in a mirror for ten minutes a day for five months. In all subjects, the words were not perceived in their globality but required a meticulous analysis of the letters and syllables. They also demonstrated total or partial inversions even sometimes affecting the order of the words in a sentence. They revealed a curious impression of not just horizontal but also vertical inversions. These are errors that exist amongst people with dyslexia and they suffer from the aggravating circumstance inherent in all learning.
In the 1970s, a new hypothesis emerged that dyslexia stems from a deficit in phonological
processing, or difficulty in recognizing that spoken words are formed by discrete phoneme
s, (for example, that the word CAT comes from the sounds [k], [æ], and [t]). As a result, affected individuals have difficulty associating these sounds with the visual letters that make up written words. Key studies of the phonological deficit
hypothesis include the finding that the strongest predictor of reading success in school age children is phonological awareness
,
and that phonological awareness instruction can improve decoding skills for children with reading difficulties.
In 1979 Galaburda and Kemper, and Galaburda et al. 1985, from the examination of post autopsy brains of people with dyslexia. Observed anatomical differences in the language center
in a dyslexic brain, showing microscopic cortical malformations known as ectopias and more rarely vascular
micro-malformations and in some instances these cortical
malformations appeared as a microgyrus
. These studies and those of Cohen et al. 1989, suggested abnormal cortical
development which was presumed to occur before or during the sixth month of foetal brain development.
1993 Castles and Coltheart describe developmental dyslexia as two prevalent and distinct varieties using the subtypes of Alexia, Surface and Phonological Dyslexia. Understanding these subtypes is useful in diagnosing learning patterns and developing approaches for overcoming visual perception
impairments or speech discrimination deficits.
Surface Dyslexia is characterized by subjects who can read known words but who have trouble reading words that are irregular.
Phonological Dyslexia is characterized by subjects who can read aloud both regular and irregular words but have difficulties with non-words and with connecting sounds to symbols, or with sounding out words. Phonological processing tasks predict reading accuracy and comprehension. Manis et al. 1996, concluded that there were probably more than two subtypes of dyslexia, which would be related to multiple underlying deficits.
1994 From post autopsy specimens Galaburda et al., reported : Abnormal auditory processing in people with dyslexia suggests that accompanying anatomical abnormalities might be present in the auditory system. They measured cross-sectional neuronal areas in the medial geniculate nuclei (MGN
s) of five dyslexic and seven control brains. In contrast to controls, which showed no asymmetry, the left-side medial geniculate nucleus
(MGN) neurons were significantly smaller than the right in the dyslexic sample. Also, as compared with controls, there were more small neurons and fewer large neurons in the left dyslexic MGN. These findings are consistent with reported behavioral findings of a left hemisphere-based phonological defect in dyslexic individuals.
The development of Neuroimaging
technologies during the 1980s and 1990s enabled dyslexia research to make significant advances. Positron emission tomography
(PET
) and functional magnetic resonance imaging
(fMRI) studies have revealed the neural signature of adult normal reading (e.g.,Bookheimer et al., 1995; Fiez and Petersen, 1998;
Price, 1997; Pugh et al., 1996; Turkeltaub et al., 2002)
and phonological processing (e.g., Gelfand and Bookheimer, 2003;
Poldrack et al., 1999;
Price et al., 1997; Rumsey et al., 1997a). Brain imaging studies have also characterized the anomalous patterns of neuronal activation associated with reading
and phonological processing in adults with persistent or compensated developmental dyslexia (e.g., Brunswick et al., 1999; Demonet et al., 1992; Flowers et al., 1991; Horwitz et al., 1998; Ingvar et al., 1993; Paulesu et al., 1996; Pugh et al., 2000; Rumsey et al., 1997b; Shaywitz et al., 1998). Employing various experimental approaches and paradigms (e.g., the detection or judgment of rhymes, nonword reading, and implicit reading), these studies have localized dysfunctional phonological processing in dyslexia to left-hemisphere perisylvian regions. Differences in task-related signal change in the left temporoparietal and occipitotemporal cortices have emerged as the most consistent findings in studies of dyslexia in the alphabetic writing system
(Paulesu et al., 2001; for review, see Eden and Zeffiro, 1998). However, it has been demonstrated that in nonalphabetic scripts, where reading places less demands on phonemic processing and the integration of visual-orthographic
information is crucial, dyslexia is associated with under activity of the left middle frontal gyrus
(Siok et al., 2004).
-to-phonology
mapping is transparent, or even opaque
, or any language whose orthographic unit representing sound is coarse (i.e. at a whole character or word level) should not produce a high incidence of developmental phonological dyslexia, and that orthography can influence dyslexic symptoms
2001 Temple et al. Suggest that dyslexia may be characterized in childhood by disruptions in the neural bases of both phonological and orthographic processes important for reading.
2002 Talcott et al. reported that both visual motion sensitivity and auditory sensitivity to frequency differences were robust predictors of children's literacy skills and their orthographic and phonological skills.
2003 Turkeltaub et al., reported: "The complexities of pediatric brain imaging have precluded studies that trace the neural development of cognitive skills acquired during childhood. Using a task that isolates reading-related brain activity and minimizes confounding performance effects, we carried out a cross-sectional functional magnetic resonance imaging
(fMRI) study using subjects whose ages ranged from 6 to 22 years. We found that learning to read is associated with two patterns of change in brain activity: increased activity in left-hemisphere middle temporal and Inferior frontal gyrus
and decreased activity in right inferotemporal cortica areas. Activity in the left-posterior superior temporal
sulcus
of the youngest readers was associated with the maturation
of their phonological processing abilities. These findings inform current reading models and provide strong support for Orton's
1925 theory of reading development."
(A guide to the areas of the brain List of regions in the human brain, Cerebral hemisphere
. and Cerebral cortex
)
2003 Current models of the relation between the brain and dyslexia generally focus on some form of defective or delayed brain maturation
. More recently, genetic research
has provided increasing evidence supporting a genetic origin of dyslexia.
2004 A University of Hong Kong study argues that dyslexia affects different structural parts of children's brains depending on the language which the children read.
2007 Researchers are searching for a link between the neurological and genetic findings, and the reading disorder. There are many previous and current theories of dyslexia, but one that has much support from research is that, whatever the biological cause, dyslexia is a matter of reduced phonological awareness, the ability to analyze and link the units of spoken and written languages.
2008 S Heim et al. This is one of the first studies not to just compare dyslexics with a non dyslexic control, but to go further and compared the different cognitive sub groups with a non dyslexic control group.
Different theories conceptualise dyslexia as either a phonological, attentional, auditory, magnocellular, or automatisation deficit. Such heterogeneity suggests the existence of yet unrecognised subtypes of dyslexics suffering from distinguishable deficits. The purpose of the study was to identify cognitive subtypes of dyslexia. Out of 642 children screened for reading ability 49 dyslexics and 48 controls were tested for phonological awareness, auditory discrimination, motion detection, visual attention, and rhythm imitation. A combined cluster and discriminant analysis approach revealed three clusters of dyslexics with different cognitive deficits. Compared to reading-unimpaired children cluster no. 1 had worse phonological awareness; cluster no. 2 had higher attentional costs; cluster no. 3 performed worse in the phonological, auditory, and magnocellular tasks. These results indicate that dyslexia may result from distinct cognitive impairments. As a consequence, prevention and remediation programmes should be specifically targeted for the individual child's deficit pattern.
the term 'dyslexia' was later coined in 1887 by Rudolf Berlin,
an ophthalmologist practicing in Stuttgart
Stuttgart
Stuttgart is the capital of the state of Baden-Württemberg in southern Germany. The sixth-largest city in Germany, Stuttgart has a population of 600,038 while the metropolitan area has a population of 5.3 million ....
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
.
He used the term to refer to a case of a young boy who had a severe impairment in learning to read and write in spite of showing typical intellectual and physical abilities in all other respects.
In 1896, W. Pringle Morgan, a British physician, from Seaford, East Sussex
Seaford, East Sussex
Seaford is a coastal town in the county of East Sussex, on the south coast of England. Lying east of Newhaven and Brighton and west of Eastbourne, it is the largest town in Lewes district, with a population of about 23,000....
published a description of a reading-specific learning disorder in a report to the British Medical Journal
British Medical Journal
BMJ is a partially open-access peer-reviewed medical journal. Originally called the British Medical Journal, the title was officially shortened to BMJ in 1988. The journal is published by the BMJ Group, a wholly owned subsidiary of the British Medical Association...
titled "Congenital Word Blindness". This described the case of a 14-year-old boy who had not yet learned to read, yet showed normal intelligence and was generally adept at other activities typical of children of that age.
1900-1950
During the 1890s and early 1900s, James Hinshelwood, a British ophthalmologist, published a series of articles in medical journals describing similar cases of congenital word blindness, which he defined as "a congenital defect occurring in children with otherwise normal and undamaged brains characterised by a difficulty in learning to read." In his 1917 book Congenital Word Blindness, Hinshelwood asserted that the primary disability was in visual memory for words and letters, and described symptoms including letter reversals, and difficulties with spelling and reading comprehension.In 1925 Samuel T. Orton
Samuel Orton
Samuel Torrey Orton was an American physician who pioneered the study of learning disabilities. He is best known for his work examining the causes and treatment of reading disability, or dyslexia....
, a neurologist who worked primarily with stroke victims, met a boy who could not read and who exhibited symptoms similar to stroke victims who had lost the ability to read. Orton began studying reading difficulties and determined that there was a syndrome unrelated to brain damage that made learning to read difficult. Orton called his theory strephosymbolia
Strephosymbolia
Strephosymbolia was first coined in 1925 by Samuel Orton as being an answer to the implications the term word blindness makes. Specifically this new word was created to make a distinction between itself and word-blindness, but no reasons are given for what these distinctions arise from, or what...
(meaning 'twisted signs') to describe individuals with dyslexia had difficulty associating the visual forms of words with their spoken forms.
Orton observed that reading deficits in dyslexia did not seem to stem from strictly visual deficits.
He believed the condition was caused by the failure to establish hemispheric dominance
Lateralization of brain function
A longitudinal fissure separates the human brain into two distinct cerebral hemispheres, connected by the corpus callosum. The sides resemble each other and each hemisphere's structure is generally mirrored by the other side. Yet despite the strong anatomical similarities, the functions of each...
in the brain.
He also observed that the children he worked with were disproportionately left- or mixed-handed
Handedness
Handedness is a human attribute defined by unequal distribution of fine motor skills between the left and right hands. An individual who is more dexterous with the right hand is called right-handed and one who is more skilled with the left is said to be left-handed...
, although this finding has been difficult to replicate.
Influenced by the kinesthetic work of Helen Keller
Helen Keller
Helen Adams Keller was an American author, political activist, and lecturer. She was the first deafblind person to earn a Bachelor of Arts degree....
and Grace Fernald
Grace Fernald
Grace Fernald – A Pioneer in Literacy Instruction.Noted educational psychologist, Grace Fernald was an influential figure in early twentieth century literacy education. Fernald established “the first clinic for remedial instruction in 1921 at the University of California, Los Angeles”...
, and looking for a way to teach reading using both left and right brain functions,
Orton later worked with psychologist and educator Anna Gillingham
Anna Gillingham
Anna Gillingham was an educator and psychologist. Working with Dr. Samuel Orton, she trained teachers and published instructional materials regarding reading instruction, producing the Orton-Gillingham approach to reading instruction...
to develop an educational intervention that pioneered the use of simultaneous multisensory instruction.
In contrast, Dearborn, Gates, Bennet and Blau considered a faulty guidance of the seeing mechanism to be the cause. They sought to discover if a conflict between spontaneous orientation of the scanning action of the eyes from right to left and training aimed at the acquisition of an opposite direction would allow an interpretation of the facts observed in the dyslexic disorder and especially of the ability to mirror-read.
To this end the authors asked four adults to read a text reflected in a mirror for ten minutes a day for five months. In all subjects, the words were not perceived in their globality but required a meticulous analysis of the letters and syllables. They also demonstrated total or partial inversions even sometimes affecting the order of the words in a sentence. They revealed a curious impression of not just horizontal but also vertical inversions. These are errors that exist amongst people with dyslexia and they suffer from the aggravating circumstance inherent in all learning.
1950-2000
1949 research conducted under Clement Launay (thesis G. Mahec Paris 1951) went further. In adult subjects, the reading of a series of 66 tiny lower-case letters, 5 mm high, spaced 5 mm apart, first from left to right, and then from right to left, was more easily and quickly done in the left to right direction. For former dyslexic children, a substantial number read a series of 42 letters with equal speed in both directions, and some (10%) read better from right to left than from left to right. The phenomenon is clearly linked to the dynamics of sight, as it disappears when the space between letters is increased, transforming the reading into spelling. This experience also explains the ability to mirror-read.In the 1970s, a new hypothesis emerged that dyslexia stems from a deficit in phonological
Phonology
Phonology is, broadly speaking, the subdiscipline of linguistics concerned with the sounds of language. That is, it is the systematic use of sound to encode meaning in any spoken human language, or the field of linguistics studying this use...
processing, or difficulty in recognizing that spoken words are formed by discrete phoneme
Phoneme
In a language or dialect, a phoneme is the smallest segmental unit of sound employed to form meaningful contrasts between utterances....
s, (for example, that the word CAT comes from the sounds [k], [æ], and [t]). As a result, affected individuals have difficulty associating these sounds with the visual letters that make up written words. Key studies of the phonological deficit
Phonological deficit
The phonological deficit hypothesis is a prevalent neurological explanation for the cause of reading difficulties and dyslexia. It stems from evidence that individuals with dyslexia tend to do poorly on tests which measure their ability to decode nonsense words using conventional phonetic rules,...
hypothesis include the finding that the strongest predictor of reading success in school age children is phonological awareness
Phonological awareness
Phonological awareness refers to an individual's awareness of the phonological structure, or sound structure, of spoken words. Phonological awareness is an important and reliable predictor of later reading ability and has, therefore, been the focus of much research.- Overview :Phonological...
,
and that phonological awareness instruction can improve decoding skills for children with reading difficulties.
In 1979 Galaburda and Kemper, and Galaburda et al. 1985, from the examination of post autopsy brains of people with dyslexia. Observed anatomical differences in the language center
Language center
The term language center refers to the areas of the brain which serve a particular function for speech processing and production.- Current scientific consensus :...
in a dyslexic brain, showing microscopic cortical malformations known as ectopias and more rarely vascular
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
micro-malformations and in some instances these cortical
Cortex (anatomy)
In anatomy and zoology the cortex is the outermost layer of an organ. Organs with well-defined cortical layers include kidneys, adrenal glands, ovaries, the thymus, and portions of the brain, including the cerebral cortex, the most well-known of all cortices.The cerebellar cortex is the thin gray...
malformations appeared as a microgyrus
Microgyrus
A microgyrus is an area of the cerebral cortex that includes only four cortical layers instead of six.Microgyria are believed by some to be part of the genetic lack of prenatal development which is a cause of, or one of the causes of, dyslexia....
. These studies and those of Cohen et al. 1989, suggested abnormal cortical
Cortex (anatomy)
In anatomy and zoology the cortex is the outermost layer of an organ. Organs with well-defined cortical layers include kidneys, adrenal glands, ovaries, the thymus, and portions of the brain, including the cerebral cortex, the most well-known of all cortices.The cerebellar cortex is the thin gray...
development which was presumed to occur before or during the sixth month of foetal brain development.
1993 Castles and Coltheart describe developmental dyslexia as two prevalent and distinct varieties using the subtypes of Alexia, Surface and Phonological Dyslexia. Understanding these subtypes is useful in diagnosing learning patterns and developing approaches for overcoming visual perception
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
impairments or speech discrimination deficits.
Surface Dyslexia is characterized by subjects who can read known words but who have trouble reading words that are irregular.
Phonological Dyslexia is characterized by subjects who can read aloud both regular and irregular words but have difficulties with non-words and with connecting sounds to symbols, or with sounding out words. Phonological processing tasks predict reading accuracy and comprehension. Manis et al. 1996, concluded that there were probably more than two subtypes of dyslexia, which would be related to multiple underlying deficits.
1994 From post autopsy specimens Galaburda et al., reported : Abnormal auditory processing in people with dyslexia suggests that accompanying anatomical abnormalities might be present in the auditory system. They measured cross-sectional neuronal areas in the medial geniculate nuclei (MGN
Medial geniculate nucleus
The Medial Geniculate Nucleus or Medial Geniculate Body is part of the auditory thalamus and represents the thalamic relay between the inferior colliculus and the auditory cortex...
s) of five dyslexic and seven control brains. In contrast to controls, which showed no asymmetry, the left-side medial geniculate nucleus
Medial geniculate nucleus
The Medial Geniculate Nucleus or Medial Geniculate Body is part of the auditory thalamus and represents the thalamic relay between the inferior colliculus and the auditory cortex...
(MGN) neurons were significantly smaller than the right in the dyslexic sample. Also, as compared with controls, there were more small neurons and fewer large neurons in the left dyslexic MGN. These findings are consistent with reported behavioral findings of a left hemisphere-based phonological defect in dyslexic individuals.
The development of Neuroimaging
Neuroimaging
Neuroimaging includes the use of various techniques to either directly or indirectly image the structure, function/pharmacology of the brain...
technologies during the 1980s and 1990s enabled dyslexia research to make significant advances. Positron emission tomography
Positron emission tomography
Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
(PET
Positron emission tomography
Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
) and functional magnetic resonance imaging
Functional magnetic resonance imaging
Functional magnetic resonance imaging or functional MRI is a type of specialized MRI scan used to measure the hemodynamic response related to neural activity in the brain or spinal cord of humans or other animals. It is one of the most recently developed forms of neuroimaging...
(fMRI) studies have revealed the neural signature of adult normal reading (e.g.,Bookheimer et al., 1995; Fiez and Petersen, 1998;
Price, 1997; Pugh et al., 1996; Turkeltaub et al., 2002)
and phonological processing (e.g., Gelfand and Bookheimer, 2003;
Poldrack et al., 1999;
Price et al., 1997; Rumsey et al., 1997a). Brain imaging studies have also characterized the anomalous patterns of neuronal activation associated with reading
Reading (process)
Reading is a complex cognitive process of decoding symbols for the intention of constructing or deriving meaning . It is a means of language acquisition, of communication, and of sharing information and ideas...
and phonological processing in adults with persistent or compensated developmental dyslexia (e.g., Brunswick et al., 1999; Demonet et al., 1992; Flowers et al., 1991; Horwitz et al., 1998; Ingvar et al., 1993; Paulesu et al., 1996; Pugh et al., 2000; Rumsey et al., 1997b; Shaywitz et al., 1998). Employing various experimental approaches and paradigms (e.g., the detection or judgment of rhymes, nonword reading, and implicit reading), these studies have localized dysfunctional phonological processing in dyslexia to left-hemisphere perisylvian regions. Differences in task-related signal change in the left temporoparietal and occipitotemporal cortices have emerged as the most consistent findings in studies of dyslexia in the alphabetic writing system
Alphabet
An alphabet is a standard set of letters—basic written symbols or graphemes—each of which represents a phoneme in a spoken language, either as it exists now or as it was in the past. There are other systems, such as logographies, in which each character represents a word, morpheme, or semantic...
(Paulesu et al., 2001; for review, see Eden and Zeffiro, 1998). However, it has been demonstrated that in nonalphabetic scripts, where reading places less demands on phonemic processing and the integration of visual-orthographic
Orthography
The orthography of a language specifies a standardized way of using a specific writing system to write the language. Where more than one writing system is used for a language, for example Kurdish, Uyghur, Serbian or Inuktitut, there can be more than one orthography...
information is crucial, dyslexia is associated with under activity of the left middle frontal gyrus
Middle frontal gyrus
The middle frontal gyrus makes up about one-third of the frontal lobe of the human brain....
(Siok et al., 2004).
2000s
1999 Wydell and Butterworth reported the case study of an English-Japanese bilingual with monolingual dyslexia. Suggesting that any language where orthographyOrthography
The orthography of a language specifies a standardized way of using a specific writing system to write the language. Where more than one writing system is used for a language, for example Kurdish, Uyghur, Serbian or Inuktitut, there can be more than one orthography...
-to-phonology
Phonology
Phonology is, broadly speaking, the subdiscipline of linguistics concerned with the sounds of language. That is, it is the systematic use of sound to encode meaning in any spoken human language, or the field of linguistics studying this use...
mapping is transparent, or even opaque
Wiktionary
Wiktionary is a multilingual, web-based project to create a free content dictionary, available in 158 languages...
, or any language whose orthographic unit representing sound is coarse (i.e. at a whole character or word level) should not produce a high incidence of developmental phonological dyslexia, and that orthography can influence dyslexic symptoms
2001 Temple et al. Suggest that dyslexia may be characterized in childhood by disruptions in the neural bases of both phonological and orthographic processes important for reading.
2002 Talcott et al. reported that both visual motion sensitivity and auditory sensitivity to frequency differences were robust predictors of children's literacy skills and their orthographic and phonological skills.
2003 Turkeltaub et al., reported: "The complexities of pediatric brain imaging have precluded studies that trace the neural development of cognitive skills acquired during childhood. Using a task that isolates reading-related brain activity and minimizes confounding performance effects, we carried out a cross-sectional functional magnetic resonance imaging
Functional magnetic resonance imaging
Functional magnetic resonance imaging or functional MRI is a type of specialized MRI scan used to measure the hemodynamic response related to neural activity in the brain or spinal cord of humans or other animals. It is one of the most recently developed forms of neuroimaging...
(fMRI) study using subjects whose ages ranged from 6 to 22 years. We found that learning to read is associated with two patterns of change in brain activity: increased activity in left-hemisphere middle temporal and Inferior frontal gyrus
Inferior frontal gyrus
The inferior frontal gyrus is a gyrus of the frontal lobe . It is labelled gyrus frontalis inferior, its Latin name...
and decreased activity in right inferotemporal cortica areas. Activity in the left-posterior superior temporal
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
sulcus
Sulcus (neuroanatomy)
In neuroanatomy, a sulcus is a depression or fissure in the surface of the brain.It surrounds the gyri, creating the characteristic appearance of the brain in humans and other large mammals....
of the youngest readers was associated with the maturation
Erikson's stages of psychosocial development
Erikson's stages of psychosocial development as articulated by Erik Erikson explain eight stages through which a healthily developing human should pass from infancy to late adulthood. In each stage the person confronts, and hopefully masters, new challenges. Each stage builds on the successful...
of their phonological processing abilities. These findings inform current reading models and provide strong support for Orton's
Samuel Orton
Samuel Torrey Orton was an American physician who pioneered the study of learning disabilities. He is best known for his work examining the causes and treatment of reading disability, or dyslexia....
1925 theory of reading development."
(A guide to the areas of the brain List of regions in the human brain, Cerebral hemisphere
Cerebral hemisphere
A cerebral hemisphere is one of the two regions of the eutherian brain that are delineated by the median plane, . The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres has an outer layer of grey matter called the cerebral cortex that is...
. and Cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
)
2003 Current models of the relation between the brain and dyslexia generally focus on some form of defective or delayed brain maturation
Developmental biology
Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...
. More recently, genetic research
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
has provided increasing evidence supporting a genetic origin of dyslexia.
2004 A University of Hong Kong study argues that dyslexia affects different structural parts of children's brains depending on the language which the children read.
2007 Researchers are searching for a link between the neurological and genetic findings, and the reading disorder. There are many previous and current theories of dyslexia, but one that has much support from research is that, whatever the biological cause, dyslexia is a matter of reduced phonological awareness, the ability to analyze and link the units of spoken and written languages.
2008 S Heim et al. This is one of the first studies not to just compare dyslexics with a non dyslexic control, but to go further and compared the different cognitive sub groups with a non dyslexic control group.
Different theories conceptualise dyslexia as either a phonological, attentional, auditory, magnocellular, or automatisation deficit. Such heterogeneity suggests the existence of yet unrecognised subtypes of dyslexics suffering from distinguishable deficits. The purpose of the study was to identify cognitive subtypes of dyslexia. Out of 642 children screened for reading ability 49 dyslexics and 48 controls were tested for phonological awareness, auditory discrimination, motion detection, visual attention, and rhythm imitation. A combined cluster and discriminant analysis approach revealed three clusters of dyslexics with different cognitive deficits. Compared to reading-unimpaired children cluster no. 1 had worse phonological awareness; cluster no. 2 had higher attentional costs; cluster no. 3 performed worse in the phonological, auditory, and magnocellular tasks. These results indicate that dyslexia may result from distinct cognitive impairments. As a consequence, prevention and remediation programmes should be specifically targeted for the individual child's deficit pattern.