Reading performance and visual processing: What appears to happen in the first 50ms of you seeing a word?
Recently I took part in a pilot study looking at crowding and ‘colour’. Further study will start again this summer.
I learnt a great deal from this initial study.
It required the ‘subject’ to look at a computer screen and then a letter T would appear.
The T would be upright, upside down, laying to its right or laying to its left; as below.
The letter was displayed for 50ms and then had to decide which way round it was.
What I did not expect was that I would ‘see’ or ‘perceive’ four or five letters from that 50ms. As below.
During the 50ms, of course my eye was moving relative to the screen, as a result of muscle tremor in the eye muscles, neck muscles and back muscles. I had seen this movement in the eyetracking, but not appreciated its importance.
My visual system was recording positions that I was conscious of, as an overlapping image about every 10ms.
So if we consider say a couple of words next to each other. The visual data my brain was trying to cope with would be similar to that below.
The two words are actually
The gap between the words is obviously important to stop the words over lapping allowing the system to identify it as two separate words...
Another experience was this. In setting up the experiment, before I was aware of this effect, we had to decide on how many milliseconds the letter T would appear on the screen for. At longer exposures I was NOT aware of several images. I perceived a clear letter T.
There were four of us in the pilot and it looked like each person took longer for the brain to compute a clear steady image.
What has this got to do with the theories about the origin of developmental dyslexia?
This was very much a visual experience which would limit the phonological output.
It concerns the way in which the spatial information and timing information about the image are computed by the brain.
That is there are several competing images, collected in sequence during a fixation, the relative position of which are a consequence of small movements on the retina of the eye. These relative movements will be caused by slight changes in muscle tone controlled by or as a result of signals from the cerebellum.
The cerebellum is closely linked to the magnocellular system and this phenomenon can easily be linked to motion processing efficiency. Ideas developed by such as John Stein and Al Galaburda
When the background settings were changed, the clarity/ singularity of the image appeared to change.
The nearby presence (and closeness) of other letters (crowding) changed that perception of ‘singularity’.
This fits closely into Facoetti’s ideas on visual crowding and reading and Valdois’ ideas on visual attention span.
It also fits some of the ideas associated with the Meares-Irlen syndrome.
More work needs to be done.