The Visual Model of Reading

The Visual Model of Reading

By Stuart Warren, MSc(Optom) (Hons)

The Current Model

The majority of consensus is that reading problems such as dyslexia are due to difficulties converting the visual components of words into their sound components.Vellutino, Fletcher, Snowling, Scanlon (2004)

Consider the word “cat”…

c / a / t > “c” / “a” / “t”

The visual components are called “graphemes” & the sound components are called “phonemes”.

There are about 44 phonemes in the English language. Difficulty making this conversion underlies the “Phonological Model” of

reading. This can be helped by teaching phonemic awareness (word sounds) and

phonics (mapping sounds to letters or parts of words).

The Phonological Model

Research by Professor Sally Shaywitz at Yale University using fMRI brain scans on students with dyslexia has shown numerous areas of the brain are involved in reading but that there are 3 areas in the left hemisphere that dominate. Shaywitz et al (1998). These include a Visual Word Form Area (yellow), a Word Analysis Area (red) and a Speech Area (green).

(Front) (Back)

The Phonological Model

The Word Analysis Area (WAA) is located in the temporal parietal cortex. The Visual Word Form Area (VWFA) is located in the occipital cortex. The speech area, also known as Broca’s Area, is located in the frontal

cortex. The WAA is important for phonological processing and works together with the

speech area for saying words. It is the slower “sub-lexical” route important for decoding words.

The VWFA is important for storing words that have been added to our sight word vocabulary and also works together with the speech area for saying (or subvocalizing) words. It is the faster “lexical” route for normal reading.

These areas comprise the key neural circuits for reading. Other areas in the brain important

for reading include the Auditory Cortex for processing auditory information and Wernicke’s Area for language comprehension.

Problems with the Phonological Model

Although the evidence shows that phonological skills correlate the most highly with reading disabilities this does not prove it is the cause. Castles & Coltheart (2004)

Phonics training helps with non-word reading skills, word accuracy and letter-sound knowledge but may not be helpful for reading fluency, spelling, phonological output and reading comprehension. McArthur et al (2012)

Not all students with dyslexia have a phonological problem. Not all students who require learning support have a reading problem. If other factors are shown to be deficient further upstream (such as vision)

this weakens the phonological model as being a cause for learning disabilities.

If a school phonics programme is successful is this because students have learned better phonological skills or because they have developed better word identification skills associated with the phonics programme?

The Case for Vision

Vision is the dominant sense

The symptoms suggest it

Reading starts with vision

The science shows a problem

Visual interventions are effective

Vision is the dominant sense

It is estimated that at least 80% of learning is derived from vision. Try closing your eyes and think about all you couldn’t do in the classroom!

The Case for Vision

Vision is the dominant sense

The symptoms suggest it

Reading starts with vision

The science shows a problem

Visual interventions are effective

The Symptoms Suggest it

When most children start school they are fine with mapping sounds to pictures & objects. The same part of the brain however is also believed to be used for written language (referred to as “neuronal recycling”) which suggests that the problem of written language may be more to do with processing of visual symbols (ie. letters and numbers).

Young (or impaired) readers need bigger text and wider spacing. Losing place, skipping words and lines is common. Words appear to move on the page for some readers. Missing the start or ends of words is common. Persistent letter reversals.

The Case for Vision

Vision is the dominant sense

The symptoms suggest it

Reading starts with vision

The science shows a problem

Visual interventions are effective

Visual Skills for Reading

Consider the visual skills required for reading. A reader needs to:

Estimate the number of letters in a word (eg. a 2 or 5 letter word?) Position their eyes in the correct position on the word (about a third of the

way along the word). Keep the words stable on the page. Extract multiple letters per look (eg. 2 letters, 4 letters etc) Ensure the correct orientation and order of the letters. Identify the exact shape, colour and detail of the letters.

Visual Skills for Reading

These visual skills can be describes as follows:

Estimate the number of letters in a word – “visual counting” Position eyes in the correct position on the word – “saccades” or “voluntary

eye movement control” Keep the words stable on the page – “fixation” Extract multiple letters per look – “visual span” Ensure the correct orientation and order of the letters – “spatial attention” Identify the exact shape, colour and detail of the letters – “visual acuity”

Visual Skills for Reading

But there’s a problem….

Estimate the number of letters in a word – “visual counting” Position eyes in the correct position on the word – “saccades” or “voluntary

eye movement control” Keep the words stable on the page – “fixation” Extract multiple letters per look – “visual span” Ensure the correct orientation and order of the letters – “spatial attention” Identify the exact shape, colour and detail of the letters – “visual acuity”

When children’s eyes are tested at school only the skills at the bottom in grey (“visual acuity” and “colour vision”) are tested. The skills shown above in blue are NOT included however these are the ones thought to be a problem with reading! They also happen to be supported by the same neural pathways – the “Magnocellular Pathway”.

The Case for Vision

Vision is the dominant sense

The symptoms suggest it

Reading starts with vision

The science shows a problem

Visual interventions are effective

Magnocellular Visual Pathways

The science shows there are 2 main visual systems referred to as the “Magnocellular Pathway” (M-Pathway) and the “Parvocellular Pathway” (P-Pathway).

Both of these pathways originate from the eyeball and extend all the way to the back of the brain called the “visual cortex” & remain anatomically separated.

What Do these Pathways Do? M-Pathways: make up only 10% of the visual pathway but are much bigger in size. They conduct information more quickly and are important for motion, spatial coding and temporal (rapid) processing.

P-Pathways: make up much of the remaining visual pathway and are smaller in size. They conduct information more slowly and are important for high contrast, colour vision and fine detailed (static) processing.

Subcortical M-Pathways

Only one system however, the M-Pathway, has been found to be a problem in dyslexia.

The M-Pathway has been studied by scientists for over 30 years. It is much easier to study BEFORE it reaches the visual cortex (at a “subcortical level”) as it is anatomically distinct from the P-Pathway. Livingstone, Rosen, Drislane, Galaburda (1991)

Examples of tests used to look for an M-Pathway deficit are:

coherent motion sensitivity critical fusion frequency contrast sensitivity anatomical appearance

There are over 300 studies on the Magnocellular Pathways with 90% of them showing a problem in dyslexia. This has become known as the “Magnocellular Deficit Theory” of dyslexia.

Cortical M-Pathways

Once the M-Pathways & P-Pathways reach the primary visual cortex (V1) they diverge in two separate directions.

The P-Pathways track down to follow the “Ventral Pathway”. This has an input into the VWFA.

The M-Pathways track up to follow the “Dorsal Pathway”. This has a large input into the WAA in the Parietal Cortex and continues through to the Frontal Cortex - the region of the brain that controls voluntary eye movements for reading.

(Front) (Back)

Cortical M-Pathways

The M-Pathway helps us to know “where” we are on the page and captures critical information rapidly, co-ordinates this with voluntary eye movements, and determines early characteristics of the letters including their spatial arrangement. This information is combined with information from the P-Pathway in order to identify “what” the letters are.

In addition to feedforward pathways (blue) there are also many feedback pathways (red) which makes the M-Pathways harder to study at the cortical level.

(Front) (Back)

Cortical M-Pathways

In order to test for an M-Pathway deficit at the cortical level we need to consider the type of skill being tested and the region of the brain that’s involved. The use of fMRI brain scans can help with this. Demb (1998)

Skills supported by the M-Pathway include: Voluntary eye tracking (saccades) Spatial coding of letters Temporal processing tasks (eg. visual counting & visual span) Motion stability

A high M-Pathway input to the Cerebellum means that a deficit could potentially also affect visual motor co-ordination. Stoodley & Stein (2013)

There is evidence an equivalent M-Pathway may exist for auditory processing as well.

This creates the possibility of a pansensory deficit across multiple domains or there may be a predilection for just one domain only (eg. eye tracking). Stein (2001)

A standardized battery of tests that target M-Pathway functions essential for learning would be helpful for clinicians and educators.

Eye Tracking

It is well known that students with dyslexia have an eye tracking problem (ie. they make more backwards eye movements and pauses) but this has often been attributed to a language problem rather than a primary eye disorder.

This is because early studies found no problem with eye tracking known as “saccades”.

The reason was they only measured saccade reaction times for students ages 10 to 13 years old.

Research by Professor Burkhart Fischer at the Freiburg University shows that saccade reaction times are only significant for younger and older students for the two main types of saccades, “pro-saccades” and “anti-saccades” (see below).

Eye Tracking

Furthermore, when testing using an anti-saccade strategy (ie. one that requires the student to look the other way from the test stimulus) it can be shown that students with dyslexia have a significant problem with eye movement control independently of language. Fischer & Hartnegg (2000), Fukushima (2005), Bucci (2008)

Graphs: Fischer & Hartnegg (2000)

Eye Tracking

Studies show that “pursuit” eye movements are also associated with learning difficulties including dyslexia. Callu et al (2005), Eden, Stein, Wood (1994)

This is often overlooked because we do not use pursuit eye movements to read.

It is known however that pursuit eye movements can share similar (and sometimes the same) neural pathways as saccades! Krauzlis (2005), Rosano et al (2002)

Above: Pursuit eye movements in non-dyslexics compared to dyslexics using a Tobii eye tracker. Presentation from Dr. Anikar Haseloff (2009), University of Hohenheim.

Visual Counting

This includes a skill called “subitizing” (the ability to know the number of items present in a look) and also the ability to count larger numbers of items from memory.

It requires students to say how many spots were flashed on a small central screen.

This visual perceptual capacity tests our concept of “number” and can be deficient in students with dyscalculia as well as in dyslexia.

A problem with this task correlates strongly with students struggling to acquire basic arithmetic skills but it can also affect reading since we estimate the number of letters in a word when we read (see next slide).

Visual Counting

It has been shown by Fischer and Hartnegg that students with dyslexia & dyscalculia have a problem with visual counting – both in terms of accuracy and reaction times. Fischer & Hartnegg (2008)

Visual Span

The “visual span” is our window of visual attention. The further we can attend to visual information per look the greater the

visual span. There are a number of different methods used to test visual span (eg. Form

Resolving Field, the Trigram Method, Letter Strings).

If only one item is presented to the side of fixation this places a relatively low demand on visual attention and so may not be deficient in dyslexia.

If more than one item is presented to the side (or if items are presented on both sides) of fixation this places a higher demand on visual attention (as the information must be processed in parallel) and is more likely to be associated with dyslexia.

Trigram Method Letter String Method

Visual Span

Bosse et al (2007) found the number of dyslexic students with a visual span disorder was at least as high as the number with a phonological disorder and that around 23% had a visual span disorder alone.

A reduced visual span in dyslexia is not due to phonological processing, short term memory (using letter strings) or lack of reading experience. Bosse, Valdois, Tainturier (2007), Lobier, Zoubrinetzky, Valdois (2012)

There is a relationship between the visual span and reading speed. A smaller visual span leads to slower reading speeds (see graph below). Kwon, Legge, Dubbels (2007)

Slow reading speed is a hallmark of dyslexia. Tressoldi, Stella, Faggella (2001) Dyslexics often exhibit a reduced visual span and slow reading.

Dubois et al (2010)

Visual Spatial

Early studies of spatial awareness focused on “lateral preference” (handedness and eye/hand dominance) as a basis for learning problems. Belmont & Birch (1965) found that lateral preference was not significant but confusion of left & right side was.

Studies show that poor readers make more letter and word reversals which may be linked to visual spatial confusion. Boone (1986), Jordan & Jordan (1990), Badian (2005)

As a child gets older they can use various linguistic mechanisms (eg. phonological, semantic and syntactic) as well as other external cues to compensate for a visual spatial deficit that may be contributing towards letter reversals. Hence the reversals may no longer be obvious but the underlying spatial problem may still exist and continue to affect academic performance. McMonnies (1992)

The Florida Longitudinal Project found perceptual-motor factors are more important at predicting reading performance for primary school aged children whereas cognitive factors become more important for older students. Fletcher, Satz (1980)

To understand the role of visual spatial development on reading we can turn to brain imaging techniques which have become a useful tool for studying the effect of spatial encoding on letter features. Pammer et al (2006)

Visual Spatial

It has been found that the more disrupted the spatial qualities of the text becomes the more active the spatial region of the brain as shown by MEG neuroimaging. This places a higher demand on the M-Pathway. A deficiency would therefore make it more difficult to encode letter features.

Eg. 1: “hAvInG iNcOsisTeNt FoNt can severely disrupt reading speed”.

Eg. 2: The ‘Cambridge Effect’ shows us that “lteters can be a taotl mses and you can still raed wothiut a porbelm”.

The above statement is not exactly true since reading a page of text like this would severely decrease reading speed, even for a good reader. It would also be very difficult for someone learning to read!

Consider the difficulty that a dyslexic student (or beginner reader) may have with phonological processing (converting graphemes to phonemes) if they have trouble encoding the letters!

Visual Spatial

In addition, poor readers and students with dyslexia (over the age of 8) are more likely to fail on the “Clock Drawing Test” - a medically recognized test of spatial awareness. Eden, Wood & Stein (2003)

Although dyslexics are often thought to have superior spatial abilities, a study by Winner (2001) involving multiple spatial tasks found that dyslexics performed the same or worse on all tasks except for one when compared to non-dyslexics.

Dyslexics do appear to have better “global visual spatial ability”. Karolyi (2003)

It has been argued that dyslexia may be a problem of visuo-spatial attention caused by a deficiency in the visual dorsal stream. Vidyasagar (2010)

Side: Auditory Discrimination

This is the ability to perceive differences in sound. It has been shown to be a problem in dyslexia by numerous investigators and has been linked to problems with decoding (phonological processing). Tallal (1980), Heiervang et al (2002), Wang et al (2010)

Fischer and Hartnegg (2004) show a systematic difference for dyslexics compared to controls in auditory discrimination, especially for “frequency” and “time order” tasks (see next slide).

This may have a greater affect on skills such as spelling (converting sounds to letters) and following instructions rather than on reading (converting letters to sounds).

Side: Auditory Discrimination

Fischer and Hartnegg (2004)

The Case for Vision

Vision is the dominant sense

The symptoms suggest it

Reading starts with vision

The science shows a problem

Visual interventions are effective

Visual Interventions are Effective

Interventions to enhance the visual skills presented in this discussion usually involve training in the form of daily exercises or the use of tinted lenses.

The fact these skills undergo such a long development period (up until 16 to 17 years of age) demonstrates significant plasticity.

The following slides will consider some of the evidence…

Eye Tracking Training

There are studies in recent literature to support that saccadic eye movements can be trained. Dyckman & McDowell (2005), Kveraga (2002), Solan et al (2001)

Fischer & Hartnegg (2000), shows that voluntary saccades (the type used for reading) can be trained in dyslexics by over 10 times their normal rate of maturation so that they are no longer significantly different from those of non-dyslexics. Training non-reading saccades (ie. reflex saccades) for the same time period of time however does not improve voluntary saccades (anti-saccades).

Eye Tracking Training

Furthermore, training eye movements reduces the number of errors observed in reading (green bars) compared to a control group that received reading intervention alone (red bars). Training typically took 10 minutes a day over a 3 to 8 week period. Fischer & Hartnegg (2008)

Saccade training has also been shown to significantly improve reading fluency for elementary school students in a randomized crossover trial. Training was done in school for 20 minutes a day (3 days a week) for 6 weeks. Leong et al (2014)

Fixation Training

Patching one eye while reading can improve fixation by reducing binocular instability (eye wobble) in younger children resulting in significant improvements in reading compared to placebo controls or other types of remedial methods.Stein, Richardson & Fowler (2000)

A reduction in binocular instability with monocular occlusion has also been reported by Fischer and Hartnegg (2008) as shown in the graph below.

Visual Count Training

Visual counting and subitizing can be trained. Groffman 2008 This can lead to improvements in basic arithmetic (on DEMAT) as shown in

the graph below, Fischer, Kongeter & Hartnegg (2008). Group 1 has 3 weeks of training (green) and then waits but continues to

improve (blue). Group 2 waits with no improvement (red) and is then trained showing

significant improvements in basic arithmetic (yellow).

Visual Span Training

Studies show that the visual span can be trained with subsequent improvements in reading speed of around 40 to 60%. Legge et al (2007), Kwon et al (2007), Chung et al (2004)

Training the visual span in dyslexia can also result in faster reading speed (confirmed with fMRI scan). Valdois et al (2013), Geiger et al (1994)

Visual Spatial Training

As reading appears to be dependent upon the development of visual spatial coding it is not unreasonable to expect that visual spatial training (that draws on similar spatial coding patterns required for reading) should translate into better reading skills.

Studies that use sinusoidal gratings (where the student has to respond in which direction the grating moves), have been shown to improve reading outcomes for students with dyslexia compared to age matched controls. The treatment was given twice a week for 15 minutes over a 16 week period. This demonstrates that targeting the visuospatial system with regular training can help remediate learning problems. Lawton (2004), Lawton (2007), Lawton (2011)

Another approach that is used routinely in optometric vision training uses symbol charts (eg. arrows and pdpq’s) and links them to kinesthetic awareness.

This method differs from earlier methods of perceptual training described in the literature (eg. identifying shapes, labelling body parts, matching the start and ends of words etc) as it uses developmental principles of daily repetition in combination with progressively increasing the task difficulty.

This approach appears promising however there is currently a need for more studies. Mandani (2009), Fredericks (2006), Pienaar (2011)

Side: Auditory Discrimination Training

Multiple studies show that auditory skills can be trained. Schaffler, Sonntag, Hartnegg, Fischer (2004), Gaab et al, (2007), Murphy & Schocat (2011).

Schaffler, Sonntag, Hartnegg, Fischer (2004)

Side: Auditory Discrimination Training

Studies are mixed when it comes to showing that auditory training can help with reading (converting graphemes to phonemes). Temple et al (2003), Gaab et al (2007), Hook (2001), Strong et al (2010)

Auditory training however may be more helpful for assisting with spelling as shown by the green bars below compared with the wait group and placebo controls. Schaffler, Sonntag, Hartnegg, Fischer (2004)

Tinted Lens Therapy

Research done by Professor Stein and colleagues at Oxford University show that tinted lenses (blue and yellow) can improve reading in selected students with dyslexia by around 2 months/month compared to placebos (grey). Normal progress is considered to be 1 month/month with most dyslexics falling below this. Ray, Fowler, Stein (2005), Hall, Ray, Harries, Stein (2013),

Other controlled studies show a positive effect of tinted overlays on reading for selected students. Noble et al (2004)

Visual Model of Reading

Evidence such as this has led to the Visual Model of reading. This is summarized in the book Visual Aspects of Dyslexia by Stein & Kapoula. It does not necessarily replace the Phonological Model since BOTH may be

true. Furthermore, students with learning difficulties still require educational

assistance!

This view is supported by the American Optometry Association who claim that “unresolved visual deficits can impair the ability to respond fully to educational instruction. Management may require optical correction, vision therapy, or a combination of both.”

“Dyslexia affects about 10% of all children and is a potent cause of loss of self-confidence, personal and family misery, and waste of potential. Although the dominant view is that it is caused specifically by linguistic/phonological weakness, recent research within the field of neuroscience has shown that it is associated with visual processing problems as well. These discoveries have led to a resurgence in visual methods of treatment, which have shown promising results.”

Visual Model of Reading

Independent research from the University of Padua in Italy claims that not only does developmental dyslexia have a visual perceptual basis but that we should consider perceptual training for students with dyslexia as well as for young at risk students. Gori & Facoetti (2013)

“Our aim is to review the literature supporting a possible role of perceptual learning (PL) in helping to solve the puzzle called DD (Developmental Dyslexia). PL is defined as improvement of perceptual skills with practice. Based on the previous literature showing how PL is able to selectively change visual abilities, we here propose to use PL to improve the impaired visual functions characterizing DD and, in particular, the visual deficits that could be developmentally related to an early magnocellular-dorsal pathway and selective attention dysfunction. The crucial visual attention deficits that are causally linked to DD could be, indeed, strongly reduced by training the magnocellular-dorsal pathway with the PL, and learning to read for children with DD would not be anymore such a difficult task. This new remediation approach – not involving any phonological or orthographic training – could be also used to develop new prevention programs for pre-reading children at DD risk”.

Other Visual Factors

Visual factors such as refractive error (eg. long-sight or hyperopia over +1.00DS) and vergence facility (binocular co-ordination) whilst not considered to be a basis for dyslexia, are significantly related to reading (see graph below) and so should not be overlooked. Quaid & Simpson (2003)

All students with a significant learning problem should have a thorough optometric assessment before starting vision training.

Objection - 1

Havn’t we disproved the perceptual theory or shown that perceptual factors only play a minor role? Vellutino et al (2004), Ramus (2002)

There are numerous studies to suggest that vision is not a factor in reading problems or dyslexia and one can use these to support an argument against the role of vision. In the end, one must critically examine each of the studies to see if their conclusions hold.

In the 80’s it was believed that erratic eye movements observed in dyslexia were due to poor reading skills. The methods used to study eye movements however were not adequate to draw such conclusions. Using current scientific methods it can be shown that a problem exists with eye movement control in dyslexia independently of language.

Another reason for finding a lack of significance can be due to “ceiling effects” (eg. when the test is not sensitive enough to discriminate between two groups) This was argued by Fletcher & Satz (1979) when we moved away from the perceptual model.

A study may also show no significant difference because of the way a group is selected for testing. Eg. giving all dyslexic students tinted lenses.

Finally, a study may show no difference because of the manner in which a treatment is applied. An example might be the Perceptual Motor Programme (PMP) used in many NZ schools. A study by Klomp (2012) found no effect on learning outcomes for young primary school children. The study was done in just 10 weeks and targets a gross level of perceptual motor development. In order to show a significant improvement in academic learning however would require that the perceptual motor development be improved to a level necessary to support academic skills.

Objection - 2

The position statement by the American Academy of Ophthalmology (2014) claims that “children with dyslexia or related learning disabilities have the same visual function and ocular health as children without such conditions” .

The evidence clearly shows however that students with dyslexia or related learning disabilities do NOT have the same visual function as those without such conditions! Eden (1995), Kulp,Schmidt (1996), Kulp (1999), Maples (2003), Valdois (2004), Goldstand (2005), Solan (2007), Shin (2009), Bosse (2009), Chen (2011), Franceshini (2012), Pienaar (2013)

They also argue that since children with dyslexia like to play computer games (a highly visual task) that vision cannot be a factor.

This is not supported by any evidence. The eye movements used for computer games are NOT the same as those used for reading books. Also, the nature of the visual tasks found in gaming are quite different from reading text.

They claim there is inadequate scientific evidence to support visual interventions. In fact there is quite a lot of evidence to support visual interventions as shown by

this review but there are not many randomized placebo controlled trials (studies providing the highest level of evidence). This does not mean that visual interventions are not “evidence based” however as most medical treatments also fail to meet this standard. The basis for speech therapy, occupational therapy and rehabilitative medicine is that the brain is plastic and can be trained. The evidence showing that vision can be trained is at least as good. If this is accepted in other fields, one must accept the possibility that vision can also be trained.

Objection - 3

A study by Olulade et al (2013) was widely promoted in the media claiming to rule out vision as a factor in dyslexia.

The study showed that visual motion activity measured using fMRI brain scans to be less in dyslexic students compared with non-dyslexic students of the same age.

However when dyslexics were compared with younger non-dyslexic students of the same reading age then the visual activity was about the same.

Furthermore, when dyslexics are given reading intervention visual activity increased suggesting that any failure in vision was due to inadequate reading exposure.

These findings taken together are used to support the Phonological Model. This finding argues the point that the visual activity is normal relative to reading

age and that reduced visual activity is therefore a function of low reading exposure.

Another explanation however is that the reduced reading age of dyslexics is a function of their poor visual development! The lower the visual activity the lower the reading age. This being the case we would expect that improving visual development would improve the reading age by removing visual barriers to reading.

The fact that reading practice improves visual activity is not too surprising since there may be a level of “reciprocal effect” in much the same way there is with phonological processing and reading practice.

Conclusions

There exists a large body of evidence to show that visual skills are related to reading ability and that visual problems are linked with dyslexia.

Much of the evidence points towards a problem with the development of visual skills supported by the Magnocellular Pathway, however general optometric findings should also be considered for individual students.

Although more studies exist to show a phonological link (due to the higher level of attention it has received) there are limitations to the Phonological Model.

The evidence that visual skills can be improved with training is substantial. More placebo controlled studies showing the efficacy of visual treatments

for dyslexia are needed but this does not negate the many controlled studies and clinical reports currently available or preclude it as an evidence-based intervention.

Without intervention the gap in visual skills will often persist despite maturation.

The view that vision problems do not contribute to the symptoms observed in dyslexia or general learning disabilities seems very unlikely.

Given the currently available evidence a more balanced approach may be to use visual (and auditory) interventions to complement traditional therapies.

END

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