The Educational Implications of Visual Persistence


People vary in their ability to read text. There may be many contributing causes for this variation. Here we are focusing on one possible cause - interpersonal variations in 'visual persistence'.

Visual persistence is an interesting feature of our perceptual system.

  If we are exposed briefly to an isolated visual image (a letter of the alphabet for example), the image of the letter persists in our visual system for a period of around 40 - 250 milliseconds after the stimulus is removed from view. If presented with a rapid sequence of images (such as when reading or tracking movement) a backlog can build up resulting in multiple images persisting simultaneously. The brain resolves this conflict by paying more attention to some of the conflicting images and ignoring or delaying the perception or others. This phenomenon is called masking and can result in a range of perceptual distortions - letters appearing to move about or change position, reversals, parts of words or letters missing, etc.

  We have found that all our dyslexic students have a visual persistence near the high end of this natural range, and we are interested to see how visual persistence correlates to self-assessed reading ability in a range of different professions. We are currently conducting an on-line experiment to test the correlations between visual persistence, reading abilty and choice of occupation.


Initial results from this ongoing survey suggest that the natural variation in the speed at which people can comfortably read letters, numbers, and words, is greater than we had expected, and the correlation with self-assessed reading ability is even more significant than we had anticipated. We need more data, so you are invited to take the test (we recommend you take the test anyway as it will help you understand the rest of this item) and fill in and submit the survey form, if you are so inclined.

(The test is written in javascript and php, and runs within your browser, so it poses no threat to your system.)

Implications for education
Those of you who can read comfortable at 40 ms may be a bit surprised to hear that many of us limp along at 360 ms. And those of you who struggle at 360 ms or higher will find it hard to believe that there are plenty of people who can read at 40 ms. So it is beginning to look as if people who happen to have a longer than average visual persistence also have greater than average difficulties reading text.
  The human brain did not evolve to read text. Long visual persistence presumably had evolutionary advantages in the world before text, and it may still have those advantages, but in a text orientated world it clearly has some very specific disadvantages. It may be, that the current design of our education system is accidentally amplifying those disadvantages.

  Education is a text intensive profession, which makes it rather unattractive to those of us who have longer than average visual persistence. The profession actively and passively filters out slow readers, and is therefore staffed from a biased filtrate, by people with shorter visual persistence, who happen therefore to be quicker with text, and who have no personal experience or understanding of how inaccessible the text based elements of their pedagogy is for the others.

  The ability to read text is not directly related to intelligence. There are plenty of 'smart and capable' people who find reading difficult, there are plenty of 'not so smart' people who can read easily, and there are many shades in between.


The people who direct education policy say they understand this but they continue to design education systems which rely heavily on text as the primary medium for conveying crucial information. The operational assumption seems to be that the ability to process text is very closely linked with intelligence and is a good measure of the kind of intelligence they value.

  Unfortunately this assumption is rather self-fulfilling. A difficulty with text is very likely to lead to poor performance - in a text based education system - and can easily lead on to a host of other related problems .


So despite 30 years of 'equality' driven adjustments to our education system, (I am writing about the UK here,) this slight natural variation in ability to process text is still being amplified and exaggerated, possibly more than before, and is producing highly discriminatory outcomes.

What a waste an unintentional, unnecessary and easily avoidable act of discrimination with a huge social cost.

The English Language has a particularlty complex (many-to-many) grapheme to phoneme relationships. Letters and letter combinations often make more than one sound, and a sound is often made by more than one letter or letter combination. A human neural network is quite capable of passively detecting these letter sound associations - IF - the association patterns are presented close together in time. If a child has a long visual persistence, which is disturbing the perception of the graphemes, this reduced the natural ability of the brain to detect the associations. Equally, a child who has a difficulty detecting the subtle sounds in speach may have difficulty detecting the letter sound associations.

In either situation it is a good idea to present the young brain with well structured list of words which group together plenty of familiar examples of each grapheme phoneme pattern. There is no need to consciouly explicitly draw attention to the complexity of the many-to-many grapheme phoneme relationship. The brain can passively implicitly learn and use these associations. If the child notices the inconsistency, congratulate them for their excellent pattern matching skills. If you know enough to explain the inconsistencies in terms of the Latin, Greek, French, German, Scandinavian, etc, influences on the language, most kids in my experience will love this. The richer the better.