Views On Vision - Vision Is Not Sight

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Vision, and it's most often used inaccurate synonym, 'sight', are very different things, regardless of what the dictionary might have us believe.
It's easier perhaps to define 'sight': The ability to perceive images through passive reception of visual signals from the environment.) Poor eyesight could then be defined as blur, say, while good sight could be said to be 'clear' or 'sharp'.
Vision, on the other hand, is anything but passive. In fact, most of what we 'see' comes after our eyes have done their job. To use another useful analogy, imagine a sports photographer: the camera he carries and uses to capture images would equate to the eye, roughly speaking. The photographer himself, actively scanning, searching, and anticipating events 'looks' for what is of interest and focuses his camera and attention on significant events. While the camera could take pictures on its own, few would be of any interest. It is the active involvement of the photographer, carefully selecting scenes of interests, then implementing his equipment to capture the scene in a meaningful manner that makes the photograph interesting and worthwhile.
Vision relates this way to 'sight' (the film) and the eyes (the camera). Very little of what we perceive is passive, by some estimates 80% of what we 'see' is the act of the mind rather than the simple reception of light signals in the eye. You can, for example, completely ignore most elements in a scene by simply focusing attention on one element. This is demonstrated when reading (only a few words are ever the focus of attention at any one time) or while driving (we commonly only pay attention to a very few elements in our field of view). To a child learning to read, they must learn to focus their attention to the appropriate letters and words, and do this in the proper sequence. This is not a natural born talent.
Vision, as an active process, can be trained and tuned. Like an athlete works with a coach to develop skill and strength, it is quite possible to train visual skills. This all begins by breaking vision down into its simpler components, training them, then building upon these skills to train the ultimate skill: reading.
It is convenient to break vision down into two areas: Activities required to find an image on a page, let's say (signal acquisition) and those that happen after the eyes have done their work, in the brain (signal processing). Both signal acquisition and signal processing happen continuously but it seems as though they take turns, one giving way to the other in a sort of dance. It works something like this (in a child who already knows how to read English):
Let's start with signal acquisition. The brain decides it needs to read a page of words (because it wants to, needs to or because teacher tells it to). It knows to direct the attention of vision to the top left of the page. Numerous parts of the brain coordinate the effort of nerve signals and muscles to direct the eyes towards the first few words. The eyes, head and body coordinate movement so that the eyes are fixated upon the words (multiple nerves and sensory organs are involved with this, including touch and balance). Once the words are in the central field of view, the eyes, working with still other parts of the brain align the image and bring it into focus. When aligned and in focus, the eyes remain fixated upon the words long enough for the brain to capture the image of the words. While fixated this way, the brain is smart enough to calculate the next eye movement using cues from especially the peripheral vision system.
At this point, the captured image can be processed. Visual information processing is complex and involves several sub-components. You might consider the analogy of a symphony orchestra playing a complex piece of music. Various musicians and their instruments add their own sounds and texture, under the direction of the conductor. Likewise in vision (note I did not say 'sight'), image patterns are interpreted by the brain and these are compiled to yield a complete image. Sub-elements of vision include figure-ground discrimination (what is important in a scene versus what is not), closure (finishing an image without having all the details), spatial elements (where is one word in relation to another, which way do the letters face, where should the next set of letter/words be), memory (including memory of sequencing) and others. When the image has been formed (and this takes only milliseconds usually), it can then be used by 'higher-level' brain functions, such as language processing (reading of the words) and semantic processing (what do the words mean to the child). Finally, signal processing hands over control back to signal acquisition, which already has the necessary coordinates to find the next few words in the sentence, and so with a few quick calculations the eyes are repositioned to find the next words in sequence or move to the beginning of the next line.
This sequencing of events happens several times per second in skilled readers and is more or less automatic, with a manual override - that is, you can voluntarily scan the page at your own speed or choose to spend more time looking at some words in particular. Either way, the bulk of the process of reading (and vision in general) occurs in the brain as a deliberate and active process. Visual signal acquisition and processing must be strong and reliable in order to allow reading to occur. If they are deficient, reading may take place but will most often be laboured and delayed; they are pre-requisites to reading and are frequently ignored in assessments of reading ability. In other words, by focusing on the reading problem, we are potentially ignoring the cause.
What is especially interesting is that children with 'reading disabilities' almost ALWAYS show trouble with signal acquisition and signal processing skills. Furthermore, by assessing these skills at a young age, we can predict with some accuracy which children are more likely to end up in remedial reading programs. I contend that by assessing these children early, we can intervene sooner and even make better use of resources by addressing specific needs as opposed to using a one-size-fits-all approach. More specifically, training reading in a child with visual dysfunction is similar to filling a bathtub without plugging the drain - it's possible, but not a great use of resources.
In future articles, I will delve into greater detail about signal acquisition and processing and describe how these can be trained at home AND in the classroom. We will also look at other things that can be done to facilitate reading acquisition.


Dr. Boulet is an optometrist and owner-operator of Diamond Valley Vision Care in Black Diamond (403-933-5552 or info@dvvc.ca.) He is also a former high school teacher and continues to work with children who have trouble learning.