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.
- Carry on wearing them and get called ‘stupid’ because they still find reading slow, difficult and possibly painful.
- 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.
- 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 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.