Tuesday, 19 February 2013

Effective reading performance,dyslexia and lessons from AMD.

Effective reading performance, dyslexia and lessons from AMD.

What is controlling the reading performance in adults? Crowding? Visual attention span?

Ok so what really controls how well an adult can read?

‘Reading well’ is an interesting idea.
 Is it….
·         How fast a person can read?

·         How long a person can read for?

·         How well they understand what they have read?

·         How well they enjoy what they read?

Research on reading performance it is often reduced down to  the number of words which can be read correctly per minute. But many people can read faster than people who understand the ideas in the reading better than them. So the idea of intelligence gets drafted in. But the meaning of the word ‘intelligence’ is not really fixed so we have discussions and research using lots of imprecise words.

I want to use an idea of ‘effective reading performance’.(ERF) I want this ERF to somehow be independent of the level of education , culture or language sophistication of the person.

ERF needs to be a measure of how fast a person can read a set of instructions to correctly undertake a simple task.  So the ERF will involve the effective interpretation of text to as quickly as possible .

So what will control how fast and accurately the reading will take place?  There appears to be strong evidence that in adults their ‘reading speed’ is no longer dependent on phonological processing unlike when they were young. 

Visual attention span (VAS) 
Visual attention span (VAS) is a measure of the number of letters which can be processed / identified at the same time as each other when a person looks at a string of letters, a word

In young children there appears to be evidence building up that visual attention span (VAS) may have a controlling effect on the development of their phonological understanding, rather than the other way round, which has been argued in the past.
Perceptual span  (PS).

This is the number of letters you can see without moving your eyes when looking at a string of letters
This is not quite the same as VAS when looking at a string of letters.  You could describe it as how many VAS you can process in one fixation.

Crowding effects

The way the presence of letters and proximity of letters nearby, affect the speed and correct of recognition of a letter.


1.   That how large the letters are in words can affect how easily the letters in words are identified
2.   That how easily the letters in words are identified can be affect ed by how close they are to each other. .
3.   The proximity of lines of text above and below the one being read can affect how easily the line being read is identified.
4.   The proximity of words to each other (the gap between words) can affect how easily the word will be identified.
5.   The  spatial regularity (pattern nature) of the words  around the word affects how easily the word will be identified. (pattern related visual stress.. PRVS)
·         .
·         .
These are just five variables that are fixed in printed text. Evidence suggests that what each person (the distances/proximities/size) needs to maximise their reading speed is personal to them.  The phenomenon being referred to here is crowding.

Here the word ‘easily’ is being used to mean how many milliseconds to identify the word. A measure of speed of processing or perhaps a measure of how little ‘computing power’ or memory us needed.

So let’s think about the way crowding and VAS and PS may interact when reading.

When using a binocular eyetracker to study the way an adult’s eye move when they are reading certain things become obvious.

1.    An accomplished reader needs fewer stops/fixations/photographs to get through a sentence than a ‘poor reader’.

2.    An accomplished reader processes more characters/letters per stop/fixation/photograph than an accomplished reader.

3.    An accomplished reader takes a shorter time to process each letter/character than a poor reader.

4.    Everyone’s eyes appear to stop/fixate/photograph around 4 times a second.

So what we need to do is to find out if it is possible increase the speed of processing of the letters.

 Either as more letters processed at a time (VAS) or/and fewer milliseconds to process each group (VAS) of letters so that more letters can be processed in each fixation. An increased perceptual span (PS)

The VAS will control how big a word is (number of letters) which can be parallel processed. VAS will then influence the ability to recognise and blend the phonemes within a word. Giving rise to a sense of fluency and then intonation.

 If VAS is very restricted then the person is unlikely to achieve a fluency of delivery when reading aloud or in their ‘inner voice’ when reading silently.
If the VAS is processed very quickly then it may be possible to hold in memory (Increased PS) the phonemic components of a word and still blend them hence achieving a higher level of fluency/intonation.

The time needed to process each group of letters (The VAS) is appears to be  associated with automaticity. The greater the reading experience the lower the amount of spatial (edge) detail needed to identify the letter string.

Crowding affects VAS and probably PS.  This is particularly obvious in people with age related macular degeneration (AMD). Loss of function in the centre of the retina, the fovea and macular, creates an increasing need to use the parafovea and peripheral retina to process text. The cells and and organisation of the connectivity between cells get larger away from the fovea.

 As such the crowding effect on the VAS gets bigger and bigger, reducing the VAS AND increasing the time needed to process the VAS reducing the PS.  These difficulties lead to a gradual but persistent reduction in reading speed/performance with the person taking on some of the characteristics of a person with ‘developmental dyslexia’.

Raising the font size which is a common response ends up counterproductive, since that will itself constrain the VAS and the PS ( perceptual span) ultimately needing a fixation per letter. The person reverts to a reading style reminiscent of the beginner reader in terms of the eye movement management demand,

Those working with colour, with adults know that the phonological components of the reading performance of their clients increases in a step like way., without any training. The use of a binocular eyetracker can show the increased number of characters processed per fixation and hence per second.

The issues to be addressed are these.
Does the colour (chromaticity) affect….
1.            The VAS?

2.            The crowding which controls the VAS?

3.            The time taken to process each VAS?

4.       The perceptual span as a consequence of affecting the VAS and the time to process the VAS?

If we can investigate / answer these issues we will be starting to make sense of the mechanisms.

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