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.