Sunday, 30 December 2012

Visual attention span a major factor in reading speed?

For a few years now there has been almost an orthodox view that reading difficulties, such as Dyslexia are a consequence of what is referred to as a Phonological  processing difficulty.

That there is a visual component has been sort of accepted but ignored by many researchers.

Work by Sylviane Valdois and others has strongly reignited the discussion finally demonstrating that it is possible to test out the role of visual processing independent of phonological contribution.

2014 promises to be a fascinating year in the dyslexia story. Watch this space!

Tuesday, 18 December 2012

slow reading and dyslexia

Slow reading and dyslexia

This is comment on the effects of optimising a computer screen, on a student at what is arguably the top university in the world, diagnosed as dyslexic

The graphs show her eyes struggling with reading on a white, default background and allow comparison with her eyes reading on a computer screen adjusted to her measured needs.

On the white background her eyes showed many sudden moves reminiscent of what is called a nystagmus and her left eye regularly  ‘gives up trying to  fix on the words ‘ to take pictures’.

The two graphs on default show her reading after 15 seconds and after 28 seconds. The visual performance gradually deteriorates.

Using the optimally set screen the eye movements are regular and symmetrical.

On all three graphs the scales are the same.

When we look at the number of fixations (pictures) needed to get through the text, and the reading speed the difference is very stark.
On a default screen

100 words in 111 fixations                                0.9 words per fixation
207 wpm
On her optimised screen

 102 words in 72 fixations                                 1.42 words per fixation.
360 wpm

Effect on working memory?
This student was experiencing increasing fatigue in her reading, when on a white background. More ‘bits of visual data’ were needed to read a sentence and it was taking longer to read this would have made greater demand on her central executive, limiting he ‘working memory’ which in dyslexia assessments is commonly considered to be less the non dyslexic peers.

Ok so how much benefit?

In terms of what matters to the student, more effective reading/ studying
This represents a 74% improvement in speed (reduction in working memory demand?).
The comfort effect is almost impossible to measure.  The stamina effect is very difficult to measure.
She had glasses made to match the colour settings of her optimised computer screen

What did her tutors say?

She is a good mathematician who was struggling but once she got her glasses made exceptional progress. From bottom she became comfortably mid-group!

This was only about the visual target. The opticians had already done their job.

Is this important?  

There was no teaching involved. No phonics. no learning just fitting the task to her eyes. 

If you have difficulties walking, a walking stick can help you walk faster, more confidently and for longer.  

BUT.. the walking stick does not solve your, repair, cure what was causing the slow painful walking. 

If you are assisting someones walking you would make sure that their shoes fit first and give them a walking stick if it helps!

Friday, 14 December 2012

Story of John, a dyslexic young adult

I make no apologies for the technical nature of this blog. John wanted this written down for others to read. It is not his name but in a way it could be the story of thousands of people in this and other countries.
It will continue to be re-enacted across the world until this issue is dealt with logically and effectively.

John did not recognize that he had ‘visual stress’ issues but volunteered for a 1: 1 session to enable him to read more effectively.
He had actually been diagnosed as dyslexic when in Primary school. At secondary school there was a breakdown in his relationships with teachers.  By mid day his reading capability had virtually collapsed.
 He did not wear glasses but had been to an optician when he was 11 years old at the beginning of secondary school, because he was experiencing headaches by the end of the school day.
He was told by the optician that he had good eyesight, in fact exceptional, and was not prescribed glasses.

John had to turn his head sideways to prevent his left eye aching when he read.  Similarly he needed to turn his head slightly sideways when looking at you. 

In class he needed to sit on a particular side of the class to be able to concentrate.  He would regularly be admonished for reasons he did not understand, indeed for actually concentrating because the teachers misinterpreted his behaviour.

At 13 he had left with his parents for Spain, where he no longer attended school.
A quick Visual assessment of John

A rudimentary check on John’s vision identified the following issues.
1.    His left eye was short sighted with a far point (loss of focus) at around 70 cms.

2.   The left eye demonstrated significant astigmatism.

3.   His right eye appeared to have no refractive issues but he had been told that it was ‘lazy’, suppressed.

We do not know what the effect of correct glasses prescription may have had on John’s education.
Too often I hear similar stories from dyslexic undergraduates.
Eye tracking data
A 120 Hz binocular eyetracker was used to assess his visual management during reading

The two graphs above show that the right eye (upper graph) is suppressed and not really’ travelling along the lines of text, the saccades and fixations virtually indistinguishable. 

The graph at the end of this blog report shows that the saccades (rapid moves /straight lines on the graph) are not really happening for the right eye! 

By  the third line the right eye is no longer really moving along the line at all This seems to be influencing the left eye a there appears to be a need to turn his head.

The fixations by the left eye show signs of ‘stress with forward and backward drift ‘during picture taking. The graph at the end of this blog shows that clearly.
Baseline reading scores
Using silent reading as a measure of reading performance

It took 25 seconds to read the text which consisted of.102 words 224 words per second.

Reading text used with academically successful age equivalents the rate was 91 words per minute aloud…Long words more complex syntax,

Rapid automatic naming
149 words per minute

There was no evidence of a need for a larger or smaller font. Actually his optimum font appeared to be 12.

Screen background optimisation

Using his optimal background his silent reading speed doubled to around 440 words per minute.

Reading complex text aloud his reading speed increased to 182 words per minute for text which was with familiar vocabulary.

With complex text using advanced vocabulary and syntax his reading speed, aloud increased to 134 wpm from 91 wpm on a white background. Thus is a nearly 50% improvement in performance.

The graph below shows his eye movements when using his optimum settings.

Both eyes are now moving in a similar but not identical pattern.
The above graph was obtained after an initial use of his optimal background gave the following data.

The top graph, his right eye was gradually turning out and there was consistently a great deal of head movement associated with reading.  This test was followed by a series of reads using only his right eye with the optimal conditions.  This has been used in the past with other students and appears to trigger a change in eye movement management enabling better coordination.

Details of eye movement data.

Using optimal conditions the saccades and fixations are more like those of a fluent reader.
In addition the fixations are taking shorter amounts of time. The average time needed is 285 milliseconds. Using default conditions the time needed was 400 milliseconds.

There were also 41 fixations for 99 words 2.41 words per fixation, whereas on default there were for 100 words, there were 85 fixations or 1.17 words per fixation.

  In other words the system was typically processing twice as many words per fixation.  This is possibly the most important factor influencing the improved fluency heard when someone is reading using optimal conditions.

Friday, 7 December 2012

Questions from A dyslexia specialist

Questions from A dyslexia specialist

What are the symptoms of

A. Imbalance in the field of vision overlap…

1.   The person experiences steady ‘double vision’ when looking at something with both eyes, then it is referred to as diplopia.
2.   The two images move across each other or the whole visual scene appears to be moving rhythmically it is referred to as oscillopsia

  It sounds like this could be described as an orthoptic issue. (eye muscle problem) but on its own that is a bit of a cop out...

If it does not occur when viewing pictures/diagrams but only when reading then it is likely be a task caused issue.  The two images are both having attention given to them but the brain cannot compute them into a single image. Essentially the centre of attention of each eye is too far apart for the system to combine the data. 

 If only when reading then it suggests that prisms (an orthoptic response) might be the answer.

Quite a lot of people find that the double images stop and start, if that happens then it is probably because the brain ‘decides to ignore the data from one eye. It suppresses it.  This can be considered to be associated with the idea of a lazy eye, or Amblyopia. This suppression may be a consequence of an uncorrected focussing problem in one eye.  You need to find out if both eyes are the same in terms of focussing?  If they are not then this will need correcting,

This suppression sometimes appears to be intermittent, dependent on visual task.
If the suppression alternates, then I think this is associated with the rhythmical head movements common in some people experiencing reading difficulties. They get the feeling that they have to ‘fight the words’! That in turn can lead to inner ear effects, nausea, a sense of disorientation, referred to by such as the Davis; I do not consider it to be much of a ‘Gift’ though. A certain Harold Levinson used to supply anti-sea sickness tablets to stop this happening!


 Although you may find that with a suitable computer setting the system is able to combine the images.  Are both eyes the same in terms of focussing?

B) Astigmatisms, please?

These are hard to see in terms of symptoms.  Many people have slight astigmatisms. What they do is to make it take longer for the visual system to create/compute a sharp image compared with a non astigmatic eye... An eye may need to refocus during the fixation and collect more data. If both eyes are the same then this just slows thing down. If one eye is worse then, it can lead the visual system suppressing the data from one eye and that eye then turning away from the object of attention. This can impact on separating the field of vision. Likely to happen when reading more than when looking at graphics targets. (This is associated with the iterative horizontal eye movements involved in reading.

Astigmatism is easily checked for.

1.     Find the nearest point that the student can focus on.
2.      Draw a cross (+) about 5cms both ways on a piece of white paper.
3.     Hold it in front of each eye in turn at the near point.
4.     Tell the person to look at where the lines cross.
5.     If either the horizontal or the vertical line appears fuzzy then there is an astigmatism in that eye.

I often find that candidates omit the middle of words when reading and sometimes also when writing. Should I recommend they are checked for the above two?
I think that what is happening is that their field of view is limited to around 2 or 3 letters. And they need to take several pictures to get through each word.  The correct colour and font size should solve that.  I do not think the points above would cause that.

What happens is they subconsciously guess what the rest of the word is based on the visual cues with the guess usually being in the context of the sentence rather than the paragraph!
Writing is associated with Hand eye coordination. If you put a binocular eye tracker on someone, put a cover on the front so that they cannot see what they are writing and then ask them to write down a sentence.  Then the eye tracker will show you that their eyes are moving as if they were reading the words...the visual memory guides the hands! 
If their eye movements are asymmetrical when they read this appears to lead to asymmetrical (messy) writing

Also: is scotopic sensitivity and eye strain the same thing? 

Sort of... SS was termed by Helen Irlen, and is actually incorrect wording really. 

If someone gets a high score on the Visual stress test (online use it freely!) 

They are likely to be identified by Irlen as having SS.  But they could have other optometric issues. I am also unsure (very) of the protocols employed by Irlen

Eye strain is a term with no actual definition. You could call it reading discomfort. Aetiology, origin of the discomfort, is mixed.

sometimes students who benefit from coloured overlays also mention sensitivity to bright light (artificial and/or sunlight) - is that due to eye strain on top of scotopic sensitivity or is it all the same thing and all comes under the heading of scotopic sensitivity?

Sensitivity to bright light can have several origins.

1.   Corneal problems such as Keratoconus.

2.   Delamination of the cornea/waterlogged cornea associated with undiagnosed/untreated glaucoma

3.     Lack of or limited pigmentation in the back of the eye (the sclerotic)   tends to go with easily sunburnt/ginger/blond hair/ freckles

3.   Poor pupil reflex management. The pupil is too large in bright light, it is not closing enough.

5.     Poor rebuild rate of the pigmentation to capture more light after bleaching.

I am becoming increasingly aware of visual weaknesses when assessing candidates and am trying to make the right recommendations for follow ups with opticians and optometrist. It seems incredibly common for someone to say they and their eyes checked recently and all is fine, but then I find it actually isn't.
This is an issue. Not many opticians really look for these problems. They are not always part of their professional qualifications… they need CPD!

Thursday, 6 December 2012

An Icon in the reduction of Barriers My friend David Morris

The Together! 2012 free festival of Disability Arts, Culture and Human Rights continues this week with a two-day low budget film-makers' workshop and a three-day Film Festival at the University of East London. The film festival is supported by Channel 4, and is programmed in association with ADFDaDaFestKynnysKino and the Picture This Film Festival. For full details see

The Film Festival opens at 5pm on Friday evening (7 December) with a tribute to the late David Morris, beginning with his last film Together!,  commissioned by the UK Disabled People’s Council. David Morris was the Mayor of London’s Disability Adviser, in which role he founded the Liberty Festival and led work on External Inclusion for LOCOG until his sudden death in 2010. In the last two years of his life, David also created an extraordinary body of what he described as “filmed poems”, about his lived experience of disability. These were shot by David’s PAs using a domestic camcorder, and edited by David using voice-activated software at his home in Limehouse. 

On Saturday 8 December the Film Festival begins at noon with Oska Bright  on the Road, featuring films by and starring people with learning difficulties from across the world, including animations and dramas. At 2.30pm there are Films from the East, telling unique, moving and powerful stories from ‘Ordinary East Londoners’ and introduced by Eastside Community Heritage and young film-makers from the Barking and Dagenham Ab-Phab group. Then at 4.30pm the festival continues with Animate!, featuring animated films from the UK, Ireland and Canada. On Saturday evening at 6pm we have the UK PREMIERE of Warrior Champions (Brent Renaud, 2010), the multi-award-winning story of four wounded US service personnels’ 12 month-journey as they fight to compete in the 2008 Beijing Games.

On Sunday 9 December the festival restarts at noon with Artists’ Films and Videos, featuring recent films by leading British and international artists, and continues at 1pm with Short Documentaries; a2.30pm with Dance Films; and Short Dramas at 4pm. The festival finishes at 6pm with Jason Becker: Not Dead Yet (Jesse Vile, 87 mins, 2012), introduced by Disability History Month Director Richard Rieser.

Friday, 30 November 2012

Abuse, neglect of a two teenagers with visual needs, or dyslexic?

A couple of days ago, I worked with two teenagers who had dropped out (been dropped out) of the education system but were being pulled back in by a forward looking FE college.

Both young people had simple visual problems which had been overlooked although that is a simplification.

One, the guy, had the following problems. 
  •  One eye being short sighted with an astigmastism,and the other normal.
      • leading to very easy distraction

  • A need to turn his head sideways to look at you without severe discomfort in his left eye.( it turned.)
    • because of the uncorrected focussing problem.

  • Because of this people thinking that he was not looking at them when he was spoken to.
      • The ' Look at me when I am talking to you!'
      • Do not look out of the window boy  
In addition 
  • he needed a large font to read effectively..  font 24.

  • He was light sensitive. Bright lighting was creating reading and visual problems..possibly his pupils were not closing up enough, or it could have been a low level of melanin in the back of his eyes.

  • He needed a specific colour background to read effectively.
Now all of this is correctible. By the time the session was over he was actually reading quite well and comfortably for the first time in his life.

Over 12 years late!
He has been effectively abused by a blinkered education system,  that assumed too much, which labelled him.

Oh by the way he had been labelled as dyslexic.  Did not help him though.

We discussed what he might become now. He must have been wondering how it had taken so long to get to this point.

I was left wondering about the millions of people in the UK who had solvable problems, whose lives had been limited.

Tuesday, 27 November 2012

Over one hundred thousand exam takers in UK in need of glasses.?

Are the children  in British school wearing glasses if they need them?

The graph below shows the result of a small survey of  schools in the UK,actually in all were in England.

This is not claiming to be a scientific survey just the response of parents and teachers to the question.

How many children are in your child's class and how many are wearing glasses and what year are they in? 

The sample sizes vary from year group to year group so see this only as a starting point.  More data is needed to confirm or deny what  looks to be happening.

As would be expected, the % of children wearing glasses goes up gradually from year 1 as more get sent to the optician as difficulties become obvious.
Then from year 8 (second year at the senior school, the % starts to plummet down to the lowest point when they take their examinations!

This  suggests a serious problem.  Either suddenly their visual problems are being magically ‘cured’  or there is a serious problem in our schools which is ignored.  If it really does go down to 5% in year 11, then that means between 20% and 25% of our children taking their examinations are being disabled unnecessarily.

 14% of these are actually known by parents or teachers to be disabled.

So at the lowest estimate at least 72,000   and at most  150,000 of our children taking examinations this year.  Criminal waste.

Monday, 26 November 2012

How do you know if ‘colour will help?’

How do you know if ‘colour will help?’
In the model I have developed, it is not really a ‘colour’ which helps a person. It is the reduction in stimulation of particular cone cell types in the retina; for example the red cones.

Of course you might need a different font size before you notice any difference between them.

The graph above is for a person when their font size had been optimised already and when the screen brightness had already been optimised.
Slight changes in the red pixel brightness had a huge effect on reading performance.

If a cyan filter had been used with a person in inappropriate conditions or the wrong font size I may have not given any benefit.

So to restate.  The reasons a set of coloured filters might not have given benefit can be any one or a combination of the following.

  1. Font size wrong
  2. Ambient lighting wrong
  3. The filters took too much or too little of red, green or blue light out.

As a final point I will consider the blue component of the light.  From our experience, very few people need this reducing compared with say the red or the green.   Most people end up with a sort of ‘mucky cyan’ or a ‘mucky purple’.  What you would call a ‘colour’ something like ‘Rose’ is actually a filter which reduces the amount of green light, and slightly reduces the blue.  A ‘pink’ filter would take out a different amount of green but also a different amount of blue. 

The filter sets used were originally created to test the idea that ‘different colours’ might benefit different people. 

A computer screen is a precise instrument with which to work out/calculate what will work for a person.  It is the best medium to find out what really works.

Friday, 23 November 2012

Why does text blur? One possible reason even with the right glasses

Why does text blur? One possible reason
Text Blurring; Font size and crowding

Many people, who have difficulties when reading, experience perfectly clear text for a few seconds or a few minutes and the letters blur into each other. They then find it hard to see the text. For other people it does not actually appear to all blur but they start to see fewer and fewer letters at once, just the central ones.

When your ‘eyes’ compute the images of letters, one of the difficulties is for the system to identify where one letter ends and the next one begins.  The proximity of one line to its neighbours reduces, or masks’ the ability of the system to compute its existence. This referred to as a ‘crowding effect’. It is a well documented phenomenon of the visual system.

It may well be that this phenomenon is the basis of the blurring effects which large numbers of dyslexic and slow readers experience. 

For each person a minimum distance is needed between the letters to allow the computing of the separate images.
·         To enable the capability to read, to decode, letters and translate into them phonemes.
·         To ultimately blend phonemes and then sound and ultimately spell the word.
This minimum distance is independent of focussing. The minimum distance will vary between people just like their height varies.

So getting this right for a person is absolutely basic. If the letters are too far apart, then this will lead to parts of words or subsequent words being focussed on the retina away from the centre of the fovea to part of the retina where the cone size is much larger and they are at much lower concentrations, increasing the need for more fixations per sentence. This would limit/reduce reading speed. It can also lead to a difficulty in identifying where one word ends and the next begins essential in subconscious control of eye movement.

The first indication of the importance of this letter separation was when Arnold Wilkins announced to me that he ‘had solved dyslexia, you just put the letters further apart!’

This was back in 1998!  It was rather a simplistic statement, but it had great significance.
In Microsoft Word 97, it was easy to increase the character spacing.  Arnold had tried this, I had tried it and a lot of the slower readers did find it easier.

You could argue that a lot of the reason for some fonts being easier to read for some people is really about letter spacing…..The copied lines of text are all in the same font size .

being easier is really about letter spacing…………………..    arial narrow
being easier is really about letter spacing…………………..    Calibri
being easier is really about letter spacing…………………..    Arial
being easier is really about letter spacing…………comic sans
… As well as about the effects of kerning

Unfortunately you cannot do this with a printed book, and it is only some people who find it much easier.
Other variables appear to affect the processing of the edges allowing discrimination between the edges, the ability to separate the letters.  We need to consider possible mechanisms for this.

The data is collected by the eyes oscillating slightly, with cone cells being intermittently stimulated and not being stimulated.   The blurring, fuzzing effects are often only after a few seconds or minutes of reading, suggesting a system with a time/processing component. If the letters are further apart, they do not seem to ‘interfere ‘with each other even after the normal experienced time period.
That could be because the system is not degrading any more or it can keep up.

When the optimal viewing conditions are identified, the subject reports a ‘crisper looking text’ no blurring at default letter spacing.
So what mechanisms might be responsible?
·         The whole process depends on the management of the muscle fibres that create the micro movement which dynamically collects the visual data. Logically   the metrics of this movement must be used in computing the edges,

Of course for the most academically successful usually have very high reading speeds and no reading stamina problems with small fonts. They actually find increasing letter spacing really annoying; slowing them down. There is an unfortunate tendency for high achievers to assume that what is easy for them will also be easy for other people.

 The reality is of course that the majority actually need the increased font sizes and bigger spacing!  The minority are disabling the majority, unintentionally. They do not know any better.

Wednesday, 21 November 2012

Font size and biological diversity (Font size matters)

Font size and biological diversity
(Font size matters)

Font size is an interesting variable. My colleagues and I have been measuring (calculating) which font size is optimal for each student for a couple of years now. This is an essential component of the protocols we have developed and has to be worked out before we consider other factors.

Most people will think of font size in the context of reading glasses; trips to the optician and deciding which of those lines of letters you can read clearly, or in low vision problems, where a person needs a larger font because of degrading eyesight from issues such as macular degeneration, or cataracts.

Another issue is the tendency to associate larger font size with poor academic performance, low intelligence or ageing.  These associations unfortunately leave a negative feeling and resistance towards the use of large size fonts, when they may be needed by people in the main stream population.

The inverse, the attitude to the use of small fonts, is that as we progress through the levels of education, the texts we have to encounter get increasingly smaller. In higher education there is an assumption that intelligent people can read small fonts. The decision makers (academically successful usually) in society tend to find small fonts easy. This use of small fonts, in itself of course as acts a ‘font ceiling’, restricting access to the higher levels of education to those who can cope with the small font sizes. 

Into this set of prejudices and assumptions appears the issue of wearing glasses. Too often, people assume that ‘the correct pair of glasses will enable a person to read small text. For a young person you can extrapolate this to the situation many schoolchildren find themselves in.

·        They go to an optician because of difficulties they experience with their eyes when they are reading,
  • ·        get a pair of glasses,
  • ·        go back into class
  • ·        Find that they still have problems, often still very severe when they try to read.

They then have two choices.

  1.   Carry on wearing them and get called ‘stupid’ because they still find reading slow, difficult and possibly painful.
  2. Stop wearing them, and get told off because ‘if you had your glasses you would be able to read’. The teachers regarding them and often making it quite clear, that they believe the child is ‘lazy’, ‘uncooperative’ not interested in learning and probably a trouble maker.

  3. But a bigger font size might be all they need!

What I will do now is to try and look at the issues of ‘size’ diversity in the human visual system and start the consideration how this diversity could impact on the ‘font size needs’ of the population.

I will ignore, focussing, assuming that an optician has ensured that the physics of focussing has been dealt with. If the person needs glasses they have them (unfortunately this is often not true).

Physical size/dimension variations between people.

The retina.

The light sensitive cells at the back of the eye are arranged in a hexagonal arrangement (like honey comb).  There are two types.
a.     Rod cells... tiny cells used for night vision. Not used in reading.
b.     Cone cells. larger cells used in reading
c.      This picture shows a part of a person’s retina. The red and green cells are the main ones mainly involved in collecting the image when reading. The blue cells have a role, but there are very few of them and probably mainly concerned with getting the image of the word at the fovea.
d.     Notice that the ratio of red to green cells is unequal and they are clumped. This distribution is thought to be controlled by a similar mechanism to that controlling the stripes on a Tiger. Each person is different.

The cone cells at the centre are smaller than those at the edge and packed very closely.

Right at the centre (the fovea) they are extremely small... There are no rod shaped cells here. Actually the cone cells here are so small they are similar in size to the tiny rod cells.

The diameter of the cone cells and ‘proximity’ or tightness of packing is one important variable which controls how ‘coarse’ the image will be.  . The smaller the cone cells and more closely packed, the more detail.

A bit like the number of megapixels in a digital camera;
The more the better.

The fovea itself, with its tiny close packed cone cells, at the centre of the retina, is the reason why the eyes move quickly from object to object in a visual scene.
In the rest of the retina the cone cells are much larger,  and further apart from each other (more numerous rod cells in between them), getting larger towards the edge of the retina.

The data from the each foveal cone cells is treated independently whereas the data from the rest is processed in groups.

1)   So the way they are wired, the size of the groups of cells, together can vary from person to person.

2)   The size of the cone cells in the centre of the fovea can vary from person to person.

3)   The width of the fovea itself (the zone of small cone cells in the middle of the retina.

4)   The size of the cone cells as we move to the edge of the retina.

5)   The ratio of red to green cells varies dramatically from person to person. Some people have many times as many red as green and vice versa.
If we could give a numerical value to each of the five ‘size variables’ above we can see that there is a dramatic range of combinations in design and in a way the number of ‘megapixels in your cameras’...
For example if we consider the width of the Fovea, the central area of small close packed red and green cone cells.

If a person’s fovea is smaller than the average,
 then the smaller fovea will
a.    ‘Process’ fewer letters per fixation.

b.    More pictures will be needed to get through a sentence. Each ‘picture takes about the same time, about a third of a second.

c.    It will take longer to get through the sentence.

d.   Working memory will be compromised.

Beginnings of sentences may well be forgotten by the time the person has taken enough photographs to get to the end.

There is also what you may call a double whammy here. It is thought that if you have developed a smaller fovea then the cone cells in your fovea will be bigger than for those people with a bigger fovea! 

Eye movement during picture taking

An additional complication is that if the eyes are absolutely steady during a fixation then they stop working completely. They have to be constantly wobbling at very low amplitude so that the image is moving across the edges of the cells. It is the switching on and off of the cells which gives rise to the data that is computed by the brain to create the image. It sort of has to scan the image, the words.
This movement is a consequence of

a.   Muscle  contraction in the neck or movement of the object being viewed

b.   Changing contraction /muscle tone in the six muscles which otherwise move the object on to the fovea. The eye muscles have the job of micro movement of the image on the retina.

c.   All this muscle control is being managed by the cerebellum in the brain and feedback from the muscles themselves and feedback from the computation of the image on the retina. (A link to dyspraxia?)

The amplitude and frequency of these micro movements needs to be appropriate to the size of the cells collecting the data.  If there is a problem of muscle tone management in the eye movement muscles this will change this micro movement in terms of amplitude and possibly frequency.
Essentially all of these variables contribute to not whether you can see a word, but to how many milliseconds it will take for your system to collect enough data to identify the icons/ letter/word you are looking at and match that the phonics/sounds associated with it. That time will depend in addition on what patterns have been seen and identified before and how often they have been seen and identified in addition in the context of language, the syntax from the sequence of sounds which will affect the amount of visual data needed to identify each word.

The reading process (visual data collection and computation, in my world) requires an integrated system affected in its functioning by all these variables and most likely more.

If one is compromised, such as the contribution of head/ neck movement musculature, this is almost certain to compromise/ limit the reading process. Many people with whiplash or upper body trauma find their reading performance diminishes.

I could go on much further, but I will stop here. I hope that you can be aware then that there are considerable variations in the ‘sizes’ of the components of the visual system which influence what size of font will work best for you. Most people reading this blog will read best on around a font 12 or smaller, but in the general population it looks like over half of the people need a font greater than 14 to read fluently for long periods. If you need a bigger font copy it onto a word doc.

I think this needs a mind map!  Any offers?

I will develop these explanations further. For example what is called ‘crowding’ in the next blog.