Thursday, 27 February 2014

Is Print Font size in books and examinations,controlling the academic achievement of most people? More evidence from a primary school

Is Print Font size in books and examinations,controlling the academic achievement of most people?
More evidence from a primary school

I have been struggling with how to approach this post. In previous posts I have referred to the issue of font size and the limitations it places on a person’s language/reading performance and development.

The work of my colleagues with dyslexic university students and mine with further education students has given us a clear, simple method of measuring the optimal font size of a person. For the dyslexic undergraduates this surprised us as being a mean optimal font size of 18 after any intervention with ophthalmology.
For the FE students it was again the major easily adjustable factor controlling  their reading performance.
With the Primary school pupils studied last year the outcomes were in many ways quite astounding.
This was a primary school which had an above average intake to start with. I will summarise the outcomes.

For a year 5 class:
The average optimal font needed was   24.6
The average optimal font needed was   24.6

Over two thirds of the pupils needed a font size greater than 18.
Over two thirds of the pupils needed a font size greater than 18

Ok... the word need is crucial hereThese pupils could read fonts that were smaller. But their performance was ( significantly) poorer. So let me make that clear. At smaller ( or larger) fonts than their optimal sizes, they would take longer to read a piece of text and  get more tired/stressed doing so. They would probably be less willing/motivated to undertake extensive reading. 
(Reading development is dependent on the total reading experience; positive feedback from the number of words and the richness/complexity of the experience.)
The word read is also crucial here. 

      This was reading simple, unchallenging text for these pupils.
       This was a measure of the ability of their ‘systems’ ability to collect visual data and convert it into sounds /phonological output. 

The reading speed was not a measure of

  … any intellectual capability;
  … how much they had read before.

So what really was being considered here was what effect the font size of text was controlling the phonological output of the pupils.

Each pupil had a reading speed measured using a default size of 13.
Reading speed was then measured for each pupil at a range of font sizes and the optimal size was recorded.

The graph below is typical of the response of most pupils to changing the font size. What varies of course are the speeds and the fonts.  In this case the difference in performance of optimising the font size was a 31% increase in performance.

At a default of 13, this pupil , with no apparent visual problems was going to be a reluctant reader, not for any sociological, home, economic reason, but simply because it was too slow to be enjoyable, too slow to remember/ understand what they had read, and probably because it was so uncomfortable.  

Or perhaps I should say….

it was, too slow to remember as much as they could have/ understand as much as they could have what they had read, and probably because it was so uncomfortable as a consequence it was  too slow to be as enjoyable as it could be.

This would likely impact on the motivation and attitude to studying of any pupil. The more we enjoy an activity the more likely we are to repeat it.

In the days before computers they would have been condemned to believing they were not very clever, possibly a bit stupid. Even if they knew they were not, they would have been told they were by society. They would have been excluded by the people who could read. Not intentionally, but by ‘default’. With a device such as a’ Kindle’, this pupil and in fact the majority would be able to adjust the font size to what works for them. But they would need assistance to understand what could be.. We all tend to accept our own experience as ‘normal’. We need it to be seen as ‘normal’ that we use a font size that works for us in the same way as we wear shoes that fir our feet!

In my generation and really until the later 1990’s, less than 20 years ago with the Word for Windows and similar programmes, there was no choice.  The people who ran the show were the people who could read effectively using small fonts, and they would see small fonts as ‘normal’.

In a strange way, large fonts were those associated with low intelligence, laziness. In a similar way those who wrote in a ‘large style’ (because they needed to?) were also seen and treated as educational also-runs/failures.  I can remember friends of mine who could not ‘keep between the lines’ in their notebooks and were made to feel stupid by their teachers. It is likely that a person who writes with a larger font also needs to read with a larger font.
In secondary schools, the fonts in books, exams and worksheets were all small; too small for the majority to thrive.  The hierarchical culture of our society has been supported by the acceptance of a relationship between reading small fonts and academic success.  At university level , the texts have even smaller fonts than at school.

In my own early work, using colour background, I accepted these assumptions, unwittingly I had like most researchers been brought up in a world where the font sizes were fixed.  Indeed the development of research and models in dyslexia and reading difficulties developed in these conditions.
Spectacles were about getting sufficient acuity to read the fonts in the books and examinations.  If you still had difficulty then you had a ’visual disability’ or in my school days ‘just not very clever’. What the work I have done tells me is that changing the font sizes and conditions changes the speed at which the text is processed. It also appears to change the speed at which the system is able to discriminate between adjacent letters in a word or adjacent words in a sentence; referred to as ‘crowding’.

The post below is possibly the most important one in the last couple of years. It discusses the most thought provoking day I have had in the study of ‘reading’. It considers the way the visual system is operating during the first few milliseconds of a fixation, when the eye has just started to collect visual data. Have a read and see if you understand what I am trying to explain.

I am wondering whether this font issue will really be taken up by schools and society.  I know that the school which did the study is going to get their SATS printed in larger fonts for its pupils and provide notepads which allow the pupils to use a suitable font.

What about the rest of the world?

As a final point the graph below shows the relationship between what I have called ‘the font stress index’ of each pupil and the proportionate benefit in reading performance they gain from using the correct font size.
The font size index is the difference between the font they optimise on and the default size of 13 point.
The R squared value suggests that  58% of the variation in reading performance in the group could be attributable to the font size thay are having to use.

Thursday, 12 December 2013

Comment on the UK twin study on Genetics and educational outcomes.

I thought it relevant to put directly into my blog the introduction from the twin study concerning educational outcomes and genetics
The PLOS one URL is given below.
The findings of this study will not be a surprise to those studying/involved in the analysis of the biological parameters influencing reading performance. 

Strong Genetic Influence on a UK Nationwide Test of Educational Achievement at the End of Compulsory Education at Age 16

·         Nicholas G. Shakeshaft mail,

·         Maciej Trzaskowski,

·         Andrew McMillan,

·         Kaili Rimfeld,

·         Eva Krapohl,

·         Claire M. A. Haworth,

·         Philip S. Dale,

·         Robert Plomin

Children differ in their success in learning what is taught at school – skills such as reading and mathematics, and knowledge such as scientific theories and historical facts. To what extent are these individual differences in educational achievement due to nurture or nature? As academic skills and knowledge are taught at school but are seldom explicitly or systematically taught outside of school, it would be reasonable to assume that differences between students in how much they learn are due to differences in how well the educational system teaches these skills and knowledge. From this perspective, it is surprising that quantitative genetic research such as the twin method, which compares identical and fraternal twins, indicates that individual differences in educational achievement are substantially due to genetic differences (heritability) and only modestly due to differences between schools and other environmental differences [1]. For example, we have recently shown in a UK sample of 7,500 pairs of twins assessed longitudinally at ages 7, 9 and 12 that individual differences in literacy and numeracy are significantly and substantially heritable [2]. Across the three ages, the average heritability of literacy and numeracy was 68%, which means that two-thirds of the individual differences (variance) in children's performance on tests of school achievement can be ascribed to genetic differences – i.e., inherited differences in DNA sequence – between them. Remarkably, educational achievement was found to be more heritable than intelligence (68% versus 42%), even though intelligence is not taught directly in schools and is generally viewed as an aptitude of individuals rather than an outcome of schooling.
Although earlier genetic research on school achievement produced a wide range of estimates of heritability, sampling issues may have masked a more consistent pattern. For example, a classic twin study of school achievement found heritabilities of about 40% for English and mathematics in a study of more than 2000 twin pairs [3]. However, heritability estimates in this study are likely to be underestimates due to restriction of range, because the sample was restricted to the highest-achieving high-school twins in the U.S., those who had been nominated by their schools to compete for the National Merit Scholarship Qualifying Test. The wide range of heritability estimates in three other twin studies of general educational achievement is likely to be due to their small sample sizes, which were underpowered to provide reliable point estimates of heritability: Petrill et al., 2010 (314 pairs) [4]; Thompson, Detterman, & Plomin, 1991 (278 pairs) [5]; Wainwright, Wright, Luciano, Geffen, & Martin, 2005 (390 pairs) [6].
In addition to the UK study mentioned above which showed high heritability (68%) for literacy and numeracy (Kovas et al., in press; 7,500 pairs) [2], a study of twins in Australia, the US and Scandinavia has reported high heritability (77%) for reading at age 8 (Byrne et al., 2009; 615 pairs) [7] and in the US at age 10 (Olson et al., 2011; 489 pairs) [8]. Similarly high heritability (62%) has been reported for science performance in 9-year old twins (Haworth et al., 2008; 2602 pairs) [9]. A Dutch study of 12-year-old twins reported a heritability of 60% for a national test of educational achievement (Bartels et al., 2002; 691 pairs) [10]. Another study of general educational achievement in 12-year-old twins in the Netherlands (1,178 pairs) and in the UK (3,102 pairs) did not have zygosity information (Calvin et al., 2012) [11]. However, these studies estimated identical and fraternal twin resemblance from the proportion of same-sex and opposite-sex twins, and this procedure yielded heritability estimates of about 60% in the Dutch sample and 65% in the UK sample.
The purpose of the present study was to investigate the extent to which the remarkably high heritabilities for educational achievement in the UK persist to the end of compulsory education. Unlike many countries such as the US, the UK has a nationwide examination for educational achievement, called the General Certificate of Secondary Education (GCSE), which most pupils complete at the end of compulsory education, typically at age 16. The GCSE provides a valuable test of the hypothesis of strong genetic influence on educational achievement because the GCSE is administered nationwide under standardised conditions. Furthermore, the GCSE is important for individuals, for society, and for government because it is used to make decisions about further education.

On the basis of the evidence from earlier school years – most specifically, in our research on educational achievement in the UK at ages 7, 9 and 12 – we tested the hypothesis that the high heritability of educational achievement persists to the end of compulsory education, as assessed by the GCSE at age 16. Additional support for this hypothesis comes from a recent report extending the analysis of the UK dataset described above [11] to total GCSE scores at age 16 [12]. As in the previous report for this dataset, zygosity information was not available, but estimating identical and fraternal resemblance from the proportion of same-sex and opposite-sex twins suggested substantial genetic influence on GCSE scores [12]. Although heritability was not reported because of the absence of zygosity information, the imputed correlations for identical and fraternal twins suggest a heritability of about 60%. However, a definitive estimate of the heritability of educational achievement can only be made on the basis of evidence from twins with known zygosity, which was achieved by the present study.

Tuesday, 3 December 2013

Report on the outcomes of a consultation looking at visual intervention with a student identified as being Dyspraxic and dyslexic.

 Report on the outcomes of a consultation looking at visual intervention with a student identified as being Dyspraxic and dyslexic.

This particular post is I believe of considerable importance; it is a detailed analysis / deconstruction of the response of one individual to changes in the presentation of text on a computer screen. This could have been any adult but the graphs would have different peaks. About half of the students show a negative response to red reduction rather than a positive response.  Other posts will supply more general background to the ideas. The comments on visual span are highly relevant to the emerging research that was reported at the Oxford event.

The student was referred as part of her Disabled Student’s allowance.

The student was diagnosed as Dyslexic/Dyspraxic.

The consultation was to ascertain visually associated intervention to ameliorate her difficulties with text.

  1. Background
  2.  Focussing issues, Optical correction
  3.  Font size, image size, reading distance orthoptic/convergence issues.
  4. Reading speed and stamina
  5. Crowding.
  6. Visual span
  7. Screen  luminosity and colour, 
  8. Memory issues
  9. Summary of interventions
  10. Comparisons of eye movements  in default and optimal conditions.

Background information.

The student  was first diagnosed with ophthalmic problems at the age of 7 years.  Since then there has been a progressive change in her prescription which is to be expected.

She has correction for myopia (short sight) and for astigmatisms in both eyes. The correction for her left eye is greater than for her right eye.

She has been told that her left eye is suppressed (there is difficulty processing visual information with data from her left eye. If she covers her right eye the image is less clear than if she covers her left eye.

When reading for extended periods she often…
  1. Covers her left eye
  2. Turns her head sideways (turning towards the right).
  3. If using a computer, increases the size of the text using the ‘zoom’ facilities on the computer.
  4. Becomes very tired giving her very short work periods and needing longer and longer rest/recovery times. These work periods are only a few minutes.
  5. Becomes increasingly, easily distracted.
  6. Experiences upper body and neck discomfort.

The consultation concentrated on identifying these issues quantitatively and identifying strategies to reduce/remove these barriers to studying.

Outcomes of the Consultation.
Focussing issues, Optical correction
         Using her glasses, which she uses continuously, the correction for her right              eye appears to leave distance vision still too difficult.

This implies that the correction is too weak for distance vision. A bifocal correction might be a solution.

The astigmatism correction appears to be correct for both eyes.

The vision from her left eye is still compromised at far and near as would be expected with monocular visual suppression.

This asymmetry in visual performance would give rise to distance judging problems at far and near. This would give ‘clumsiness’ characteristics at far and near which would mimic dyspraxia.

There is visual data being collected by the left eye which would assist in distance judging but ‘at near’, when reading or writing. 

There is evidence from the eyetracking data that the  left eye data is further suppressed leading to increased suppression of the left eye and increased and fluctuating fixation disparity between the two eyes.  This is reduced by the head turning but not prevented.

The head turning  would also give rise to upper body and neck discomfort as small movements would occur as a reflex in trying to overcome the diplopia.

She experiences diplopia (double vision effects) when reading or viewing near objects. The diplopia is greater if the object is nearer. The further away the object is the less the diplopia.

Using the larger fonts the distance from the text increases, reduces this effect.

(Diplopia occurs when the two eyes are focussed (fixated) at points too far apart (fixation disparity) so that the visual system is unable to compute a single perception (image). In all people there is some disparity  and this is part of efficient vision. But if it is too great then the visual system is incapable of the computation of a single image.  This is referred to as ‘insufficent fusional reserves.. and is associated with the idea of ‘convergence insufficiency’.

If the system can intermittently ‘fuse the data’ or the disparity keeps varying and data from one eye is not continually suppressed then the person gets a perception of unstable or wobbling text or the whole visual scene appears to wobble… Oscillopsia. To reduce this effect some people keep ‘wobbling their heads subconsciously which can give rise to nausea and neck/upper body/back aches.


Reading speed

Changing the font size affects her reading speed as shown in the graph below. This will be in response to a combination of the following effects.
  1. Changing reading distance.
  2. Changing  crowding effects(ability of the system to compute the edges of the letters)
  4. Changing the distance for the eyes to travel between words./ changing the demand on the eye muscles.

The first two of these will affect the number of letters which she can ‘see’( perceive) in each fixation, her visual span. Recent research has shown this to the controlling factor in reading speed for many people.

( please remember the reading speed is a measure of phonological output as a response to changing visual input)

Using the bigger font size increases the image size on her retina, this would reduce crowding effects and allow the processing of more letters at once (parallel processing). Too big a letter size will move the target fpor the next saccade too far into the peripheral retina ( away from the fovea) reducing the accuracy of the saccade, slowing the reading down.

On default (font 12) the visual span is averaging 1.60 letters. A person with no difficulties will be processing 10+ letters per fixation
When using her optimal conditions.   There were initially 3.3 characters per fixation .  This is more than a 100% improvement.
In the last line, however, the number of fixations was 14 for 79 characters That is 5.6 letters per fixation.

 There is a continual gain in the size of the visual span as she reads with optimal conditions and this is reflected in the improving reading rate the more she reads, as in the graph below taken from the eyetracking data.

We can compare this to changing reading rate when reading in default conditions in the graph below..

Combining the two graphs makes the difference in reading performance very clear.

These reading performance graphs reflect the changing visual span as the reading period changes.  Visual span can be considered as controlling reading performance rather than controlled by reading performance. As the visual system gets ‘stressed’ the visual span decreases to the point where the process becomes to difficult to make use of the process. This is likely to be a component of her reading stamina problem.

Memory issues

If a person has a short visual span, then the number of bits of visual data needed to ‘read’ a sentence will be much greater than for someone with the ‘normal visual span’ .To read and comprehend a sentence would make a much greater demand for working memory  from the ‘central executive’( Alan Baddeley’s model) leaving reduced resources  for comparison of the concepts intrinsic in the sentence with the concepts in long term memory. Other /additional memory strategies would be needed. Study time would need to be greater.
By increasing the visual span, memory difficulties, when reading should be ameliorated.

The decreasing reading speed in default reading conditions and associated limited reading stamina consequence, would further limit her total read/study time.

Reading speed, screen pixel luminosity

Overall screen brightness.

There is a relationship for The student  between overall screen brightness and reading performance.  This can be seen in the graph above.
The total amount of light entering her eyes is controlled by her pupil dilation. This reflex is designed to optimise the rate at which the photons are captured by the pigment molecules in the cone cells of her retinas; but it is controlled by ambient lighting intensity. There may be a difference between the optimal intensity landing on her fovea ( centre of focus of the images on the retina) and the peripheral retina. We do not know. In her case when font size has been optimised this is now limiting her reading performance.
158/255 is the brightness used for the rest of the testing..

Changing the green pixel brightness

As the green pixels are dimmed then the rate at which the green pigment in the green cone cells gets bleached is reduced.  This will lead to a change in nerve impulse generation. Possibly to an increase in crowding effects and reduced visual span for The student .


Changing the red pixel brightness

This is completely different to the effect of changing the green component. Although in a way we are really still changing the ratio of red : green stimulation.This ratio is the basis of the colour vision /colour recognition process which must ultimately be based on changing the impulses per second delivering information to the visual cortex and hence the mediator in object edge detection..visual processing.

This graph shows clearly the mathematical relationship between the ratio of green to red pixel brightness and the reading performance of The student .
All the red:green optimisation to this point has been undertaken with the blue value set at 158 as determined by the initial screen brightness study.

Changing the blue pixel brightness.

The cone cells containing the blue sensitive pigment are not found in the centre of the fovea.  There is a response to changing the blue pixel brightness but often very little and there appears to be a change with use of the background on screen for reading.

 There is good research evidence that the amount of blue light affects the magnocellular system particularly ( see research by John Stein al.). The red/green ratio is likely to be more associated with the ‘parvocellular system’, the edge detection system; the system which collects the data to identify the ‘object being looked at’/receiving attention.

The graph below shows the effect on one aspect of reading performance (scanning).  However, in terms of visual clarity when using an overlay or reading The student , preferred not to have the blue reduced. As such a cyan overlay closely mimicking the optimal red green ratio was provided for her to use with printed material.  Looking at the graph about reducing the red, it must be remembered that if the cyan filter removed too much red then this ‘same colour’ would  start to limit her reading performance, similarly if the cyan did not remove enough red then there would only be a partial benefit to her.  The computer screen setting will provide the optimal red/ green.
On her computer screen she has the option of using a low blue   ( green looking!) screen or the optimal red:green screen ( grey/Cyan).

In two months time a second consultation will determine changes in her visual system’s need and then precisely coloured prescription glasses mimicking her optimal screen settings can  be provided as an alternative to overlays or screen colour management.

The student  needs the following interventions to optimise /maximise her reading performance.

  1.  Printed material where possible printed at font 21.
  2. Where possible all documents to be provided electronically to enable optimal reading conditions.
  3. To be able to make use of her cyan overlay whenever appropriate.
  4. In lectures meetings, to be able to sit to the  left of the main centre of visual attention to minimise distractibility.
  5. At the next consultation the possible provision of optimally tinted prescription glasses .

Comparison of eye movements using default conditions and optimal conditions.

With default conditions the distance between the two graphs keeps changing. Whereas with the optimal conditions it stays more consistent.
If we look at the more detailed graphs, shorter time periods the difference between the two conditions is clearer.

Graph showing the detail of saccades and fixations by both eyes using optimal conditions for a 2 second period for comparison with a 2 second period using default conditions.

The graph shows that both eyes are in general working together.  If this is compared with the eye movements when reading on default it is easily seen that the left eye is hardly saccading.

Thursday, 28 November 2013

Comments on an article from Harvard about e-readers and dyslexia. A visual component acknowledged in the USA!

I have been thinking a great deal about the ‘research’ that has come out of Harvard recently.
The abstract I reprint below.  This research has been published on PLOS ONE, a peer reviewed, open access journal.
The original, article makes very interesting reading especially in the context of the USA  where to even imply the possibility of a visual component in dyslexia can bring down the ‘wrath of the IDA’ !
After re-reading the original article, which I commend everyone to read, the conclusions seem a bit guarded. I have highlighted components of the abstract which I feel need much more consideration.
E-readers are fast rivalling print as a dominant method for reading. Because they offer accessibility options that are impossible in print, they are potentially beneficial for those with impairments, such as dyslexia. Yet, little is known about how the use of these devices influences reading in those who struggle. Here, we observe reading comprehension and speed in 103 high school students with dyslexia. Reading on paper was compared with reading on a small handheld e-reader device, formatted to display few words per line. We found that use of the device significantly improved speed and comprehension, when compared with traditional presentations on paper for specific subsets of these individuals: Those who struggled most with phoneme decoding or efficient sight word reading read more rapidly using the device, and those with limited VA Spans gained in comprehension. Prior eye tracking studies demonstrated that short lines facilitate reading in dyslexia, suggesting that it is the use of short lines (and not the device per se) that leads to the observed benefits. We propose that these findings may be understood as a consequence of visual attention deficits, in some with dyslexia, that make it difficult to allocate attention to uncrowded text near fixation, as the gaze advances during reading. Short lines ameliorate this by guiding attention to the uncrowded span.

In the actual paper, they state that they were comparing reading performance on a font 14 in the print with font 42 on the e reader.

In the actual paper, they state that they were comparing reading performance on a font 14  in the print with font 42 on the e reader.

Now don’t get me wrong, but perhaps they should have looked at other font sizes on paper?  They did say that the e reader allows accessibility options so really they were not really looking at e readers, but at font size. If you read other postings in this blog, this would not surprise you at all.  The graph on optimal font size for an individual shows the critical importance of font size.

Each individual appears to have an optimal font size. For most students in the UK which myself or my colleagues have seen it is far greater than font 14, the default used on the printed task.

The ‘pretty ‘graph above shows how the optimal font size varies in a population of dyslexic students.  The modal size is font 17. About half the students need a font greater than this. Very few though benefit from a size greater than 24.  This data is collected from students who have full optometric correction. The range of font optimal font sizes will reflect issues such as...
  1. Crowding effects associated with cone cell size.
  2. Diffraction issues associated with corneal problems
  3. Other low vision issues not correctible by optometrists.

In other postings there are graphs showing the effects on reading performance of
  1. Changing the background brightness to the text for individuals
  2. Changing the relative brightness of the red, green and blue pixels.

These effects will be affected by the individual’s working cone pigment densities, how quickly the epithelial cells they are plugged into can re-activate the pigment molecules after they are bleached, as they read as well as the ability of the individual’s iris to dilate and constrict to optimise the rate at which the pigments in general are being bleached.  I could even ‘hypothesize’ that changing the relative stimulation of the red and green cells, which is the basis of foveal edge detection, will change the rate of data transfer about those edges to the visual cortex.  I challenge anyone to explain it differently!
As such for each individual there would be a specific ratio which sends the most data per millisecond and this would provide the best provision of data for phonological processing, and ‘gaze’ management.

But I am not a Harvard researcher. So I will have to wait until they catch up.

Tuesday, 12 November 2013

Eye movements for a student with nystagmus reading compared with a fluent reader.

It has been said that Nystagmus is one of the most common forms of visual disability experienced by Schoolchildren. The same would then of course be true of all age groups, since it does not ‘ go away’.

What I have done in this blog is to try to explain and demonstrate how a ‘nystagmus’ actually affects the biology of reading. I have been privileged in my work with undergraduates in the UK; working with and assisting many adults who despite their nystagmus have made it into Higher education. With each one I have had the opportunity to work with them for several hours in my work with OmniRead and before that TintaVision.

I have been able to work with them to reduce the barriers to studying which their disability creates.

All this work is done objectively, using a binocular eyetracker which allows me to compare the actual dynamics of their eye movements as they read to those students with no reading difficulties.

Together we then calculate the conditions which will maximise their reading performance, by careful  adjustment of the parameters  which control the visual system’s ability to collect and transmit visual data as they read.  All the optimisation work is done using the controlled reading environment of a computer screen using the protocols and software developed by OmniRead and before by TintaVision.

Each person needs their own specific conditions to read the most effectively.  When they use these conditions then the way their eyes collect visual data mimics much more closely the way the most fluent readers do so.

Enjoy this posting . Please post comments or ask any questions that will help you further . There are other postings in the blog which put this work into context.
The graph below shows the eye movements of a Higher education student in the UK reading from a computer screen. This is for a period of 14 seconds.
The data was collected using an infra red eye tracker measuring horizontal eye movement at 300Hz. 

A student with a nystagmus ….

1. Collects and transmits a very small amount of visual data per second compared with a fluent reader.

 2. Almost certainly need to use more computational resources making greater demands on their central executive for visual processing than a fluent reader.

3. Collects reducing amounts of visual data per second as the reading time extends.There is a serious stamina problem.

4. Using optimised reading conditions increases the amount of visual data collected and transmitted per second and can improve the quality of the data, thereby probably reducing the demand for resources from the central executive with the major benefits ensuing from this.

5. A person with a nystagmus has difficulty maintaining a fixation.

A fixation is when the eye stops to collect the visual data allowing edge detection. The computation of the data into lines /edges can be converted into visual images matched against visual images retained in long term memory and enable reading.  This is not really ‘ like photography’ as taught in schools but  more like the way the digital data  from a roadside camera can be used to identify a car number plate. Or the way data is used in object recognition in airport baggage security systems.

The best way of seeing  what is going on is to compare the eye movement of a person with a nystagmus with the eye movement of a fluent reader using a binocular eyetracker.

The graph above shows the eye movements of a typical fluent reader. If we look at the graph as sets of stairs, the flat parts of the steps are when the eyes effectively stop moving for a while ,the fixations, to collect visual data to do the actual ‘reading’. The vertical lines are when the eye moves extremely quickly to position the eyes to take the next picture.  These fast movements are called saccades.

The longer vertical lines are the saccades back to the beginning of the next line of text.

There are 9 to 10  fixations during this 2 seconds. I have marked the fixations in green.
During this 2 seconds of reading, the system is not collecting and transmitting visual data for around 10 milliseconds per fixation, during the rapid movements.  

That  is  for around 100 milliseconds  5% of the time.
This pattern of eye movement is really a modified ‘nystagmus’. 

The nystagmus eye movement pattern  can be considered as a ‘primitive eye  visual search mechanism from before a mechanism developed to allow more extended time to collect and analyse visual data in a more detailed way.  This is partly possible by the development of the types of muscle fibres found in the muscles which control the eye movement. I need to write a posting on that !

Let’s now look again at what happens when a person, with a nystagmus is reading. Look at the graphs below.

What you can see is the eyes moving from left to  right ( the wobbly lines moving gradually up the graph) and after 10 seconds a sudden move back to the left of the page.

The left  eye appears to be continually ‘wobbling’. The right  eye sometimes wobbles, sometimes it does not.  After 11 seconds both eyes start to wobble with a much greater amplitude.

During the 10th second the left eye looks like it is reading moving along the line while the right eye wobbles.  There are 5 wobbles during this 10th second.  What is important is that the reading pattern by the system does ‘change’ over time; sometimes the ‘wobble’ is more obvious, sometimes not.

The duration of the ‘slow stages ( data collection and transmission times) is not consistent. Sometimes the left eye and sometimes the right eye appears to be collecting /sending the most data.

The graph below shows the eye movements after 3 seconds of reading. During these two seconds the right eye ‘wobbles’ 7 times. The left eye appears to wobble about 5 times while the right eye appears to go through an extended fixation.


If we compare this to what happens after 11 seconds when the system goes into a more obvious ‘wobble’/nystagmus; in this 2 seconds there are 6 ‘wobbles’.

Most people when reading take three or four pictures per second, so that is effectively the same as the number of ‘wobbles our  student was experiencing.

If we look at the amount of time being spent actually collecting and sending visual data to the ‘brain’, you can see quite clearly that the left and right eye are able to send different amounts of data and that the   two eyes although acting ‘sort of together’ are to some extent out of step, or phase, with each other.
In the first few seconds of reading by the student with the nystagmus….
the ‘green’ (data transmission) time is far less than the 95%  of time for the fluent reader

1. The fast movements are slower than for the fluent reader.

 2. The ‘slow’ stages are very unstable and actually hardly stop at all, so that the ‘computing of  steady images will be more demanding on the  central executive  leaving fewer resources to  make sense of the ideas in the text.

(Please note though that for even for a fluent reader, when you look really carefully at the eyes during fixations, the eyes do not actually stop. There have to be small movements continuously or they stop collecting and sending data; but these are very small movements.)

The graph of the reading after 11 seconds, shows that the ‘slow movement (visual data collection and transmission time) is becoming more restricted.  Increasing the demand on the visual processing system.

 Now consider what happens in terms of vision during the nystagmus eye movements.

There is no data transmission from retina to ‘the brain’ while the eyes are travelling rapidly,during the saccades.  The transmission only takes place during the moments when the eye is ‘stationary’( the fixations) OR during the slow phases of the nystagmus eye movement, as the eye changes direction.
In the graphs for the student with nystagmus above the slowest phases the eye effectively stops. Often it seems to ‘stall’ as if it is being ‘held back’ as if there is a feedback inhibiting the ‘fast movement’ or saccade.

There is a mechanism for ‘fixing’ but the feedback seems very weak and variable.

The following graphs were made using data when the student was reading using optimised conditions.

The first graph shows all the data collected by the binocular eyetracker with a period of about 2 seconds before they saw the text. This shows the ‘typical eye movement of a person with a nystagmus. There is then a period of around 12 seconds of reading ,when the eye movements are much more organised, starting to look much more like those of a fluent reader.  This reading period is followed by 3 seconds when the text has been removed from the computer screen. The eye movements revert to the typical nystagmus ‘style’.

Using the optimised conditions the visual data collection and transmission time ( green  sections) is a far greater proportion of the time.  There are now quite clear ( although still unstable) fixations.  The fast movement phases are ‘faster’ and a much smaller proportion of the reading time.

The student starts to enjoy reading.