Vision and the Brain: Part 1

Understanding Cerebral Visual Impairment in Children

Amanda Hall Lueck & Gordon N. Dutton, editors

The children who are the subject of this book have identified brain defects. The name has changed recently from cortical visual impairment to cerebral visual impairment (CVI) recognizing that the problems may exist in areas of the brain other than the cortex. The change also recognizes that these problems are on a continuum. In the past only the most severe problems were recognized. I will share the highlights in a few installments.

Large proportions of children with cerebral palsy, hydrocephalus, and other conditions affecting the brain had visual disabilities that had been masked by and ascribed to their overall disorders.

Dr W at work

Over 40% of the brain is involved in processing and supporting vision, so it is not surprising that damage to the brain commonly impairs vision in a wide range of ways.

It is important to recognize cerebral visual impairment in children with profound visual impairment, but it can also cause difficulties in those with milder manifestations that can impinge considerably on their ability to perform school tasks such as reading and math, as well as compromise independent orientation and mobility, social interaction, and daily living skills.

mobility

Although vision as a sense has typically been associated with the eyes, they comprise only a part of the system that supports and sustains the sense of vision.

The visual brain is a conceptual term referring to the totality of brain elements serving or supporting vision.

In contrast to visual functions (such as visual acuity), functional vision describes how an individual functions using vision and involves evaluation of that person’s visual skills and abilities as applied to the performance of usual tasks of daily life, such as reading. An evaluation of functional vision involves categories that are less precise than measures of visual function, and is often affected by multiple variables at one time.

Visual perception is the act of detecting and recognizing what is seen. Visual cognition is considered an extension of visual perception and involves the capacity to process what is seen, to think about its significance, and to manipulate and use both incoming image data and remembered imagery in the context of creative thought. Visual guidance of movement refers to the mapping of incoming visual information in the mind that is utilized to guide movement of the limbs and body. The conscious visual process of choosing to pay visual attention is an executive function.

 

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Visual dysfunction is applied in this book to disorders of visual perception, visual guidance of movement, and visual attention.

visual guidance

An automatic system exists in our brain that prevents us from bumping into things without our necessarily knowing how we do it. Damage in one part of our brain can result in seemingly paradoxical visual behaviors as some skills are affected and others are not.

The act of recognizing and accurately characterizing the range of visual disorders, and adopting approaches to overcome the resulting difficulties, can be life changing. The person is no longer criticized but is understood and helped.

By observing a child’s daily activities and participating in the collaborative assessment of vision themselves, teachers and family members can better understand how a child functions visually and attempt to see the world “through the child’s eyes”.

Image result for down syndrome baby

 

 

 

Vision and the Brain: part 3

The Role of Attention and Executive Functions in Vision

Sander Zuidhoek

The author is a neuropsychologist in The Netherlands who works with children with cerebral vision impairment. The following is taken from his chapter in Vision in the Brain.

There are essentially two ways in which attention can be allocated to the visual system. The first is “bottom-up” processing which is initiated by the outside world. A pure example of this is reflexively looking at a flash of light. In “top-down” processing, visual targets are consciously chosen. Most visual acts are a combination of the two as the brain tells the eyes what to look for and the eyes tell the brain what they are seeing. Reading is an example of this coordination.

By controlling attentional processes, the executive system allows for the selection, at will, of information from the outside world, as well as the “inside world” of the mind. By controlling attention, the executive system rules the sensory system, our urges, and our motor systems.

The executive processes control our inhibition system and allow an individual to rise above reflexive behavior. They are:

  1. Working memory (from about five months)
  2. Self-regulation of affect, motivation, and arousal (from about five months)
  3. Internalization of speech (verbal working memory, from about three years)
  4. Reconstitution (behavioral analysis and synthesis, from about six years)

The visual modality provides greater and richer information about the outside world than our other sensory modalities. Therefore, our primary attention is often with the visual modality because it is the most appropriate for achieving our goals.

Attention is almost always divided over multiple cognitive processes: at the same time that we are consciously seeing, thoughts are also being formed about what is seen, as well as planning the next step.

  • Processing in the brain’s visual systems depends on attention.
  • Attention is controlled according to prioritizing processes performed by the executive system.
  • These prioritizing processes are driven by the inside world (urges, emotions, and motivations), but take into account possible environmental threats and social factors.
  • The decision about whether or not to pay attention to the visual input, and by how much, is the first role of executive functions in seeing. Image result for Gorilla Icon

Inhibition of eye movement is one of the most basic forms of behavioral inhibition.

While the first attentional processes are of a general nature, employed to choose and switch among sensory modalities, thought processes, and determining to what extent visual information is processed, the next level of attentional processing is specifically visual. The brain needs to select specific visual information from among all the visual information in the visual field. As such, it determines what is perceived from the visual scene. In most normal situations, the abundance of information in the visual field is too much to take in at once. Therefore the information needs to be filtered. The processes involved in attentional selection within the visual field form the first group of higher visual functions: the visual selective attentional functions.

The visual system is tuned to uncover possible relationships between components of the scene. When there are multiple parts of the visual information, the initial size of the attended area is large. Some children have difficulty with this type of processing. Simultanagnosia is described as an inability to see more than a small number of items at a time. In contrast, some children with normal visual acuity have difficulty finding small elements in visually crowded stimuli. They report seeing a blur, or detest looking at crowded visual scenes and may shorten their viewing distance to compensate or look away. Children with central visual crowding typically have difficulty finding information in crowded visual scenes, and have difficulty reading small text. Children who have difficulty integrating focal and diffuse visual attention may be slow to learn a triangle, for example, because they can’t see the individual lines and the whole shape.

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The ability to flexibly increase and decrease the attended area is also a critical function in search tasks, allowing one to zoom out for overview, zoom in to see detail, and be able to identify whether what is being seen matches what is being looked for.

Visual attention is all about limiting the amount of visual information processing.

Components of visual search:

  • Staying visual
  • Not being distracted by objects other than the target of the search
  • Adopting a systematic strategy
  • Moving the eyes and zooming out at will to get an overview
  • Moving attention around without always moving the eyes
  • Zooming in at will
  • Using knowledge of the world to preselect locations where the target may be
  • It is not possible to search without having a visual image of what you are looking for

An important consequence of a visual dysfunction is not being able to form and manipulate images in the mind. This enables us to make things, find things, and not get lost. It is also critical for the development of sight vocabulary and for spelling.

 Image result for corn maze

Image result for Gorilla Icon The Invisible Gorilla: part 1

           The Invisible Gorilla: part 2

           A Causal Link between Visual Spatial Attention and Reading Acquisition

 

Vision and the Brain: part 2

Understanding Cerebral Visual Impairment in Children

The following are more excerpts from the contributors to this volume whose backgrounds vary but they all work with and do research on children with disabilities.

The complexity of how the brain sees is enormous.

We have a meaningful stored image library of everything that we may see, readily available and accessible, so that everything we look at is not only recognized, but its nature and character are implicitly understood. This library needs to be linked to predictive knowledge of the features of the particular image and available for forward planning of our actions.

The electrical signal from the eyes is carried by two enmeshed sets of fibers. The fibers of the big (magnocellular) ganglion cells, particularly those coming from the more peripheral retina (which “see” the peripheral visual field), are largely responsible for detecting and analyzing moving images, while those for the smaller (parvocellular) ganglion cells, mainly from the central retina, are largely responsible for analyzing detail. The identity of an object and its location and size (which are required for the visual guidance to pick it up) are processed in two separate but interconnected parts of the brain.

The dorsal stream pathways enable us to handle multiple pieces of visual information. If the dorsal stream is dysfunctional, it can be difficult to track moving objects because the dorsal stream tells the eyes, via the frontal lobes, where to look next. This can cause reading problems.

How often have you heard the expression, “Look where you’re going!”? The fact is, we do not look where we are going. Like all other sighted animals, we move through the visual world without giving it a thought, by using our subconscious visual systems. Most people, when they first learn how to drive a car, find steering difficult until they look into the distance, at which point it becomes much easier. Although we check the view ahead to choose where we are going, we use our peripheral vision in a subconscious way to drive a car, move through a crowd, or walk over uneven ground. Progressive improvement in driving skill shows that certain aspects of our subconscious visual system can be trained.

balbeamkids

Attention is both subconscious and conscious. Background, subconscious visual attention prevents us from bumping into things by simultaneously dealing with the salient items of the moving visual scene through parallel processing of the relevant information. Elements that are sufficiently different, due to their movement, bright color, or contrast, are drawn to our conscious attention because they “pop out”. In contrast, the conscious visual attention that we use to recognize faces and words, for example, is slower, because it functions sequentially, focusing on one thing at a time. Attention competes with sound, smell, discomfort, pain, and the child’s thoughts and imagination.

Vision enables children to actively, and often without pause, take in a massive amount of information about events, objects, and people in their surroundings.

A key milestone in early cognitive and motor development that supports the development of object permanence is the formation of mental images, which is an important step in giving meaning to the world.

An important factor that deserves consideration when embarking on rehabilitation programs for individuals with visual impairments is motivation. Motivation is a critical component of all the major theories of learning.

Baby on Rug

The results of using certain computer games to treat amblyopia are important because they suggest the feasibility of a binocular approach to the treatment of childhood amblyopia and indicate that visual training has the potential to be successful even after the sensitive period of visual development.stereogram_dragons_big