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.
Evidences
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.
