Defining Vision II
This section continues from the previous discussions of visual anatomy and signal acquisition skills and abilities. First, we will look at Visual Signal Processing (Visual Information Processing, or simply Visual Perception) and see how once a signal is captured, it undergoes ‘parallel streamed’ processing in cortical and subcortical areas of the brain. These sub-elements of perceptual processing can be described hypothetically using the constructs of psychometrics and cognitive psychology. Also, there are notes on sensory attention and its role in classroom performance and vision.
It’s important to note that what is written here is only a very simplified version of an old standard typically taught in schools of Optometry, Ophthalmology, and increasingly in the realm of Occupational Therapy. This model is primarily derived through iterations of muli-axial tests of general intelligence, refined through the lens of behavioural Optometry, namely through the evolving Test of Visual Perceptual Skills (TVPS General Search).
Testing is testing, nothing more. What we see in test results does not mirror neural processes, it only provides a score comparisons on specific tasking. While test results may help to procure funding, they should never be interpreted as any direct probe of neural functioning. Testing like the TVPS series is akin to scoring clients on how well they solve cross-word puzzles – they are not only test of behaviour, but of context, previous experience, quality of sleep, nutrition and so forth. Re-testing nearly always provides improved results, suggesting intervening therapy is efficacious, but the reality is that we can make no such conclusion.
Still, testing what is referred to as ‘visual perceptual’ skills does provide some value in that it can expose where clients struggle. Bear in mind that different test paradigms will present visual perception in different ways, in the end, it is practically impossible to define Visual Information Processing (VIP) aka Visual Perception aka Visual Signal Processing (VSP, my own preferred usage) – clearly perception includes the eyes, but does not always start there, and clearly the signal runs through multiple direct and indirect pathways in the brain. We are an intensely visual being and so VIP/VP/VSP are broadly integrated in our beings, even if we cannot precisely define what the specific sub-elements are, we can appreciate that these elements dovetail with one another to create the amalgamated experience we call vision.
Visual Signal Processing – Making Sense of What Is Seen
Once the visual system has acquired the desired visual signal (Visual Signal Acquisition, VSA, like a word on the page, for example), the brain’s visual processing takes over to interpret what is seen into meaningful content. The process of taking input from the eyes and making sense of it before it is sent forward to more advanced and integrated processing is called Visual Signal Processing (VSP, sometimes called visual information processing (VIP), or more simply, visual perception). For example, once a word on a page is targeted and the image is reproduced on the retina in the eye, the brain, starting at the retina, begins to refine the image, applying rules to it in a predictable way to make sense of it. Once that signal (target, word, etc.) is defined visually in the brain’s visual processing areas, it is then available to trigger other processes like memory to recognize the word, and the anticipation of what should come next, which relies upon other brain areas. VSP, then, is the visual processing software that helps reproduce visual signals in the brain so that they become useful to other processes, like facial recognition, body movement, reading, and many others.
It is important to note that input from the peripheral retina in the eyes, that is, peripheral vision and information regarding spatial awareness, is required to assist in the next step of visual signal acquisition (VSA) by providing information required to calculate the next movement of the eyes. In this way, VSA and VSP are in a constant ‘dance’ with one another with the visual system alternating quickly and rapidly between states of central and peripheral awareness. For this reason, learning and reading therapy can and should strive to bolster both VSA and VSP, but also the ability to move mentally between central and peripheral awareness. The elements of VSP can all be trained therapeutically, like VSA skills.
What follows is a rudimentary description of some core visual signal processing (perceptual) elements based on the TVPS-III paradigm. It should be noted that different tests of visual perception will use different referents, some much more complex and detailed than what is provided here.
- Visual Discrimination – The ability to distinguish differences in dominant features between objects, such as position, shape, form, and color. In school, fine visual discrimination is especially relevant early when learning to distinguish letters and graphemes.
- Visual Memory – The ability to recognize one stimulus item after a very brief interval.
- Spatial Relationships – The ability to discriminate between relative positioning of objects, and the spatial relationships between objects and oneself, such as figure reversals or rotations.
- Form Constancy – The ability to recognize a visual signal (target) even when it is positioned or represented somewhat differently. When an apple appears to be an apple, even if it is turned upside down, or a letter ‘A’ is still an ‘A’ in a different font, or font size.
- Sequential Memory – The ability to recall visual signals (such as letters and words, or other symbols or objects) in a specific order.
- Figure-Ground – Figure-ground is the ability to distinguish items of interest from a noisy background, like specific words on a pages full of text, or ‘Waldo’ in a crowd.)
- Visual Closure – The ability to mentally complete a partially completed signal, such as when only a part of a face is visible in a photo, or when only a part of a word or letter is visible.
Some authors include ‘visualization’ and define it as the ability to actively formulate and manipulate visual imagery in the absence of the actual stimulus of the physical signal. This behaviour, and other complex behaviours like reading almost certainly rely on similar neurological underpinnings for the mental recreation and anticipation of the visual signals we encounter. Advanced readers, for example, will not so much look at words as scan text, searching for recognizable patterns in small collections of words. This sort of advanced skill requires that the underlying neuropsychological building blocks, such as listed above, be fully functional and robust.
Sensory Attention
In addition to the very fine sensory abilities we are endowed with, we have a strong ability to alternate between being generally aware, like being in a state of ‘stand-by’, and a state of extreme mental and sensory focus. Vision, balance, body sense (touch, limb position), and hearing all can be ‘tuned’ this way. That is, each is capable of specific and general awareness that may be referred to in other terms, including central (or focal) and peripheral awareness. This is especially so in the case of vision, hearing, and touch. These dual modes of awareness, and the ability to switch between manual control and automatic, extends to our senses generally, but also to our general state of awareness or ‘consciousness’ on a more global level. We also have the capacity to modulate, or ‘change the volume of’ some parts of our sensory awareness by paying particular attention to another sense or combination of senses, or by physically blocking the sense through covering the eyes or ears, physical activity, or, finally, by anaesthetic or other chemical modulator of brain chemistry.
People can learn to modulate sensory input through training in self-awareness and self-discipline, such as yoga and simple meditative techniques, but our default behaviour is to respond to, that is ‘pay attention to’, novel (new) stimuli. So, even in deep meditation, an exploding water heater in the room next door will grab our attention and we have no choice in the matter – what we do after that fact is our choice, but the point is that there is an ‘override’ in place that is there to protect us, but this override system is important in the classroom. As a further example, if our senses take our attention away from the task put in front of us in the classroom, like someone tapping you on the shoulder, we will need to address that distraction before we can get down to work.
Our senses, then, are available for our conscious use given nothing else is distracting us. Furthermore, all we need to do to ‘use’ them is simply to pay attention to them – and we can choose between either the central or peripheral elements of each sense, in any sensory combination we choose. Keep in mind that as we pay attention to one sense, we by necessity must pay a little less attention to something else. So, an acrobat is much more aware of her peripheral vision which guides body movement and is not so concerned with her focal (central) vision, but must pay special attention to her central hearing in order to filter out her acrobatic partner’s voice hidden in the background noise of the crowd. In the classroom, a child’s senses must be especially well tuned to visual and auditory stimuli and these senses must be ‘effortless’ to use so the child can attend to the higher-level tasks of reading, writing, and mathematics. Many visual impediments, for example, require the child actually pay attention to vision because it takes physical and mental effort to ‘work’ the eyes and visual processes. The effort (that is, energy) required to overcome even mild or moderate visual impediments to learning (VILs) necessarily takes energy away from other mental processes that should be fully engaged for learning. In more severe cases, the child struggles against vision so intensely that it becomes fully distracting and even leads to emotional outbursts and ‘mysterious’ medical concerns.
Introduction to LVT Quick Reference
