Vision and Reading

This report will help you understand some of the complex processes related to vision and its function in the task of reading.
One of the ways to understand how vision problems affect reading ability is to actually simulate a reading problem and let you see how an inefficient visual system can affect your ability to read. The following example simulates how inefficient eye movements can decrease the speed of reading.

As you can see, you must spend a great deal more effort figuring out the words. The spacing has been altered to simulate how some children with vision-related reading problems see. They don't necessary see it exactly as you just did - it was only a simulation. Children with vision-related reading problems require much more processing to understand printed sentences just as you did while reading this example.

Two basic eye movements occur when we read. A fixation or saccade and a pause (fixational pause).

Fixations are rapid eye movements which occur to move the eyes to the next location to input the next group of words into the visual system. A fixational pause is the momentary pause which occurs while the visual systems analyzes the information it is seeing. The above sentence is is grouped into 3 fixational pauses which contain about two words each.
Research over the past 50 years suggests the human visual system is made up of a duality of two subsystems. Scientists and researchers have described this duality with many differing terms describing how human vision functions or is structurally based upon. These terms include:

The Duality of the Visual System
Transient	Sustained
Centering	Identification
Ambient	Focal
Peripheral	Central
Ground	Figure
Global	Specific
Scotopic	Photopic
Superior Colliculus	Cortical
Magnocellular	Parvocellular
Rods	Cones

Fixations are associated with the transient visual system. The transient visual system is active during a fixation. The transient visual system suppresses or turns the sustained visual system off when it is in operation. It is associated with obtaining a quick global analysis of information and has been associated with motion and depth perception.

The sustained visual system concentrates on fine detail and patterns and is active during a fixational pause.

A fixation occurs and then the sustained visual system sees the following image in its "buffer" within the area of the box. The features of the letters are analyzed and decoded.

A fixation occurs next. During this stage, an eraser effect clears the buffer to ready it for the next fixational pause.

and then new information is presented and analyzed and decoded during the next fixational pause.

One theory of vision proposes that a transient visual system defect may prevent the usual erasure from happening. This may produce an accumulation of information being deposited into the buffer and not being "cleaned out" during a fixation when the transient visual system is supposed to be active. A simulation of this problem may look something like this.

This may help describe why some people explain that print may appear scrambled when they attempt to read it.

We do not process letters the same way we process pictures. Pictures seem to be stored in the brain in something like a pictorial form. Letters and words are taken out of their visual form and transformed into an abstract code. This helps explain why we can read many different forms of fonts and handwriting we may have never seen before. Other evidence that letters are not stored in visual form come from research that shows that up to 98% of the visual pathway can be damaged and yet a person can still discriminate patterns.

Letters seem to be sampled on a 30 x 30 grid of Feature Detectors. The fovea which is the most sensitive center of the retina has the greatest concentration of feature detectors. Letters image further from the fovea are sampled by lower concentrations of feature detectors.

Letters away from the fovea are sampled by lower concentrations of feature detectors. Letters however maintain the same spacing so the letters "compete" for attention for analysis by the brain. This competition is called crowding.

Take a look at the chart of letters below. Stare at the central X on each row - do not look away from the X. While staring at the X try to identify the adjacent letters using your peripheral vision. You should identify the first row without any problem. The second row demonstrates crowding as all the letters are too close for easy identification. The third row may be challenging but possibly identifiable. The fourth row is nearly impossible while the fifth row may be identifiable. The letters in this chart compete for lower number of feature detectors but are identifiable if spacing between the letters is increased.

Because of crowding, the brain utilizes a couple of analysis tricks to decode the letters.

In our alphabet, the top half of letters are more unique and identifiable than the bottom half of letters. The brain spends more attention to the top half of letters. Can you identify the letters below?

Not only are letters put into a code but the letter's position and orientation are processed in different brain channels than the channels used to identify the different features in letters for letter identification.

Individual letter identification also involves scan patterns which involves scanning just one part of a letter at a time. The general rule of scan patterns involves scanning:

A salient feature is a feature of a letter that first draws a child's attention. In the case of the small case letter "b", the letter may be broken down and decoded into:

if a salient feature such as the loop draws the child's attention first the code becomes reversed:

This may help explain why b,d, p, and q are some of the most frequently reversed letters.

Some general observations exist about how we write letters. The Grammar of Action rule for right-handed children generalizes the following characteristics about letter construction:

Start at the leftmost point.
Start at the topmost point.
Start with a vertical line.
Given a figure with an apex, start at the top and come down the left oblique.
Draw all horizontal lines left to right.
Draw all horizontal lines left to right.
Draw all vertical lines from top to bottom.
Thread, i.e., draw with a continuous line.

The top of the list in general takes priority over the lower criteria when a conflict occurs. The capital letter N must be drawn with 3 line segments. Left line first going down. Oblique line going down next and then the right line going down. If a lower criteria such as threading is dominant for a child, the tendency not to lift the pencil to construct a new line segment takes priority over the oblique and the top to bottom rule -- resulting in a backwards N.

A person's internal awareness of up and down, left and right is termed laterality.

A person's ability to project direction into space is termed directionality. An example of directionality is your ability to know where North, South, East and West are or your ability to point to another person's right hand as he is facing you. Laterality and Directionality are important developmental milestones which must be mastered in order to read and write efficiently.

If the basic sense of right and left and not well developed, letter reversals can be frequent.

The beginning of words tends to supply the most information for encoding the whole word. Eye fixations tend to land near the beginning of the word so as to more efficiently analyze the most important part.

Knowledge of letter position is critical for good reading skills. In the next page a word will flash for just an instant. Try to write the word down from your memory after it flashes. You will be given two words - one after another.