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VISUAL ATTENTION IN CHILDREN WITH CORTICAL VISUAL IMPAIRMENT

Presenter
Stacey Cohen-Maitre, Ph.D.
Childrens Hospital/Los Angeles
323-669-2350
818-349-5678

One type of developmental, bilateral disruption in visual function is known as cortical visual impairment (CVI). CVI is caused by a disease or event that affects the areas of the brain corresponding to the geniculate and extrageniculate pathways. This results in abnormalities associated with the optic radiations and/or the visual cortex (Good, Jan, DeSa, Barkovich, Groenveld & Hoyt, 1994). The neuroanatomy of these particular regions is extremely important in understanding the residual vision, as well as the potential for recovery of vision typically seen in children with CVI (Good et al., 1994).

According to Groenveld (1990), CVI has been incorrectly perceived as "nothing more than a fancy term for brain damage" (p. 13) even though the majority of brain-damaged children are not visually impaired. Moreover, CVI is often referred to as cortical blindness. However, these two conditions are not one and the same (Birch & Bane, 1991; Good et al., 1994; Whiting, Jan, Wong, Flodmark, Farrel, McCormick, 1985). Given this, it is extremely important to describe and characterize CVI from other conditions, such as cortical blindness (Good et al., 1994; Whiting et al., 1985).

Cortical blindness is defined as bilateral loss of vision, with normal pupillary responses and normal ocular examination with no other abnormalities (Good et al., 1994; Marquis, 1934). However, abnormalities as seen in children with CVI, associated with the optic radiations and/or visual cortex do not always lead to a complete abolishment of visual functioning. Since children with this kind of visual cortex injury do show some residual vision, the term "cortical visual impairment" (CVI) is preferred when referring to such patients (Good et al., 1994). Thus, on a continuum of neurologically-based vision, with cortical blindness at one end and normal vision at the other, CVI could be essentially everything in between, albeit in a range from mild to severe.

There are several causes of cortical visual impairment. The most common cause of CVI in children is perinatal hypoxia-ischemia (damage to the brain due to a diminished supply of oxygen and temporary deficiency of blood) (Brodsky, 1996; Flodmark, Jan & Wong, 1990; Reitan & Wolfson, 1992). This has a high incidence of occurrence since the posterior visual pathways and the visual cortex are quite vulnerable to damage during the perinatal period (Good et al., 1994). Other causes of CVI include; trauma, epilepsy, infections, drugs or poisons, and neurologic diseases (Brodsky et al., 1996; Good et al., 1994).

Varying levels and functions of attention and arousal of the child, characteristics of the environment and stimuli, visual crowding and lighting conditions are known to play significant roles in the behavioral manifestations of this impairment (Porro, Dekker, Nieuwenhuizen, Wittebol-Post, Schenk-Rootlieb & Treffers, 1998). For example, it has been widely observed that children with CVI are especially responsive to brightly colored objects, particularly ones that are red and yellow (Baker-Nobles & Rutherford, 1995; Jan & Wong, 1988; Jan & Wong, 1991) in comparison to objects with sharp black and white contrasts (Good et al., 1994) and are able to identify colors much more readily than shapes (Jan. Groenveld & Syknanda, 1987). Good et al. (1994) suggests (because color perception is represented bilaterally and diffusely in the hemispheres of the visual cortex), that color perception is spared because it is typically unablated by the kinds of brain damage that causes CVI.

The perceived (or intact) perception of motion is also another characteristic feature of many children with CVI. According to Jan, Groenveld, Sykanda and Hoyt (1987), parents reported that their children saw moving objects better than stationary ones and that they often saw better when traveling in a car. This residual ability to detect the movement of stimuli may indicate that the temporal crescent (the peripheral portion of the temporal field) and/or the extrageniculostriate visual pathways are preserved (Brodsky et al., 1996).

Methods for maximizing the residual vision of these children have generally relied on enriching or enhancing the visual environment (Good et al, 1994). For example, Baker-Nobles and Rutherford (1995) suggest that the simplification of the visual environment, uses of color and common or familiar objects, integration of tactile and visual inputs, and computer technology are important for enhancing the residual vision in children with CVI. Moreover, they stress the importance of individualizing interventions and the monitoring of visual responses in children with CVI, since they are more often than not, subject to variability from child to child, moment to moment, activity to activity and internal factors such as arousal level.

A major concern shared by many healthcare specialists, parents and educators is how to promote residual vision and in turn, optimize visual learning in children with CVI (Baker-Nobles & Rutherford, 1995; Merrill & Kewman, 1987). Until this recent research, there has been a paucity of scientific literature that adequately addresses this concern. Nonetheless, there are many state and community agencies that are currently providing vision instruction and educational consultation services, including computerized technology, to those working with, as well as directly to these children, with limited scientific foundation on which to base these interventions. Unfortunately, little has been known as to whether these interventions or educational strategies were appropriate and effective. Given this, more information was needed to help children with CVI maximize their residual vision and utilize their particular visual strengths to function better at home, school and within the community.

The purpose of my research was to determine whether certain basic features of the visual world such as, color and motion, which have been previously clinically observed, increase visual attentiveness in children with CVI. Additionally, whether conjunctions of color and motion, as opposed to either one presented individually, increases visual attentiveness in these children. Finally, whether there are particular colors of the color spectrum that these children are more visually responsive or attentive to than others.

The results of my research, which encompassed seven experiments through the use of a computerized Forced Preferential Looking (FPL) procedure with eleven children with both CVI and cerebral palsy indicated that they prefer color over gray, moving over nonmoving stimuli, color over moving stimuli, and color/movement conjunctions over color or movement alone. No preferences for specific colors or background colors were found among these children.

These results suggest that basic color and motion perception appear to be preserved in children with CVI and may serve as the foundation for their residual vision. It has been observed that children with CVI behave like sighted children in familiar environments and blind children in unfamiliar environments. In such cases, it may be that children with CVI use color and motion perception to make sense of familiar environments. However, the residual vision in children with CVI may be somewhat misleading as it may give others the impression that they see more (i.e. visual details, human faces, etc.) than they actually do. For example, their use of color and motion perception allows them to have what has been called "inferential perception", in that they use color and motion feature attributes in their environment to infer the identity of objects and an understanding of their visual space. For example, a child with CVI may think, as it were, "that thing is red and my mom is moving it towards my mouth so, it must be my cup". Or, "we took this turn here and moved this far down the road and then made a turn here by the big yellow thing so, we must be going home". Given this, as important as it is to think of children with CVI as not blind, it is equally and perhaps more important to understand and appreciate their reliance on basic color and motion perception for "what" and "where" recognition and how it can help them function across visual environments.

The results of this study are consistent with some of the anecdotal information in the literature. Physicians, therapists and parents describe children with CVI as having strong visual preferences for colorful and moving objects (Baker-Nobles & Rutherford, 1995; Blind Babies Registry, 1995; Good et al., 1994; Jan, Goenveld, Sykanda and Hoyt, 1987; Jan and Wong, 1988; Jan & Wong, 1991). Conversely, the present study also challenges some of the anecdotal reports by Good et al. (1994) and others who describe children with CVI as having stronger visual preferences for red and yellow than for other colors.

My research findings also indicate a lack of any specific color preferences. In addition, there are no previous reports in the literature that describe children with CVI as having strong visual preferences for movement over color. The findings in the present study indicate children with CVI demonstrate more visual attentiveness for moving over color stimuli. This is important since much of the anecdotal literature emphasizes preferences for color. Moreover, the results suggest that children with CVI initially prefer color over moving stimuli. This may be due to the functional differences between the parvocellular and magnocellular pathways in terms of how they differentially handle fast and slow speeds. Specifically, the magnocellular stream responds better to fast motions as compared to the parvocellular stream which responds better to slow motions.

Given that the parvocellular stream is more sensitive to color and slow moving stimuli, it was able to process the nonmoving, color stimuli more readily than the magnocellular stream. Thus, at the neurological level, this may explain the participants' initial attention to the color stimuli in spite of their additional and repeated attention to the moving stimuli.

The current literature is silent regarding the question of preferences for color stimuli presented on black backgrounds versus black stimuli presented on color backgrounds.

Nevertheless, interventions promoting the residual vision in children with CVI have already been marketed that assume an answer to the question. For example, the emphasis on red and yellow colored objects in the visual environment which was suggested by Good et al. (1994) and others, may deprive a child with CVI opportunities for object recognition by cluttering his or her environment with too many objects consisting of the same or within a similar range of colors. Future research on color combinations and size of patterns would be beneficial to provide further clarification regarding specific color and/or specific background preferences as well as, to support the varied ways in which colorful objects can be used in interventions including computer software to promote residual vision in children with CVI.

There are several important implications based on the findings of this study. Although children with CVI have significant visual deficits, they do have residual vision, hence the term CVI and not cortical blindness. The results of my research suggest that children with CVI appear to have basic color and motion perception. For example, the participants in this study appear to be trichromatic as they looked at blue as much as the other colors. Thus, we can assume that children with CVI have color vision which is, at the minimum, functionally commensurate with a three to four-month-old child, the point in development when trichromatic vision typically appears. Additionally, the results of the study imply that the two main anatomical visual pathways, the geniculate ("what") and tectopulvinar ("where") systems, are not completely ablated by the insult that causes CVI. Since color is diffusely and bilaterally represented in various layers of cortical tissues (areas V1 and V4) (Corbetta et al., 1990) damage to the geniculate pathways does not completely ablate color vision. Given this, it is not surprising that children with CVI demonstrate basic color perception.

The results of my research suggest that cortical area V5, which is important for motion perception, may often be largely intact in children with CVI. The area may receive input from the geniculate striate pathway or it may be that children with CVI detect motion much like people with a phenomena known as "blindsight". Blindsight relies on a subcortical extrageniculostriate visual system and refers to the unconscious residual visual ability detected within a visual field defect corresponding to a lesion in the striate cortex (Weiskrantz, 1986).

Color and motion are very important featural attributes of the environment for children with CVI and it may be helpful to utilize color and movement whenever possible to assist them in recognizing and finding items within their environments.

Wolfe's (1994) model of visual attention, Guided Search 2.0, postulates that attention selects one area at a time within a "master map" of locations, retrieving the features linked to corresponding locations in a number of independent feature maps. Thus, attention binds various features into objects (Treisman & Glade, 1980; Treisman & Sato, 1990). Given that children with CVI possess relative strengths in color and motion perception, Wolfe's theory can be used to understand how children with CVI rely on color and motion to recognize objects and locations. For example, a child with CVI may think as it were, "I am eating and this blue thing next to that big red thing must be my cup. So, I think I'll pick it up and drink". Although their attentional structures may be more simple than those of children with normal sight, being based primarily on color and motion, these structures allow for the allocation of attention and in turn, the binding of information into recognizable objects and locations. In Wolfe's (1994) approach, color and motion and their conjunctions can facilitate preattentive processes in both stimulus-driven or bottom-up processing and user-driven or top-down processing. According to Wolfe (1994), bottom-up activation can index how unusual an item is in it's present context. For example, by using color to code objects, such as a red cup in the context of mealtime where there is no other red object, a more efficient search would be possible. Bottom-up activation would be able to code the red cup based on differences with other items in the neighboring area. In contrast, top-down or user-driven activation guides attention to a desired item when the featural properties of that item are not unusual (Wolfe, 1994). Given this, a child who has already been familiar with the color-coded items (i.e. cup, spoon, plate, placemat, etc) used during mealtime might generate a "top-down" request for his or her red cup. So, by searching the table, the child would look for something red, knowing in advance, that it would likely be his or her cup.

There are also several important implications for treatment considerations based on the results from my research. Color and motion attributes of the environment should be utilized whenever possible in the child's everyday, therapeutic and educational environments. For example, it may be beneficial to consistently use a yellow plate, a red cup, a blue fork and so on during mealtime. This way, it would allow a child with CVI to more efficiently identify objects in the visual environment. It may also make reaching for that object much easier as each object is likely to elicit a different motor plan. By recognizing the object that a child is reaching for, he or she may be able to coordinate his or her body movements more efficiently. This suggestion is in consideration that the neurological event that causes CVI is also known to cause cerebral palsy.

Another implication is the use of color, not only for object recognition but to simulate depth perception. For example, the placement of a red object in front of a blue background may create the illusion of depth more efficiently than a blue object in front of a purple background. In turn, this may help to more efficiently identify an object as well as, enhance the child's understanding of his or her visual space. This information should also be particularly helpful to software designers in designing educational and recreational programs.

Color and motion can also be used to promote specific cognitive concepts. For example, one could spin the apple on the lazy Susan very fast or slow to teach the concept of speed. Or, one could put the child on a moving device, such as the child's wheelchair and push it fast or slow. Color can be used to teach the concept of large and small. For example, a red apple could be used to demonstrate the concept of small when compared to a red automobile, which could be used to demonstrate the concept of large. Moreover, physicians, occupational, physical and speech and language therapists, psychologists, and teachers would benefit from recognizing the impact of color and motion in their assessment, evaluation and treatment of children with CVI. For example, to elicit as much motivation and competence as possible when evaluating these children, it would be beneficial for professionals to modify their assessment and therapy materials by using large, colorful and moving objects as well as, by moving the children whenever possible in order to get an accurate estimate of their optimal functioning.

The use of color in assisting a child with CVI understand his or her visual environment should be done cautiously. For example, it would be important for parents and professionals to avoid cluttering their home and work environments with too many colorful objects. This would possibly make it difficult for a child with CVI to identify objects and/or understand visual spaces within their environment. In addition, the storing of colorful and/or moving objects in consistent areas may allow the child to obtain familiarity with the environment and in turn, help him or her function more like a sighted child by leading the person and/or orienting to the object or area of interest.

In summary, my research was the first empirical study to demonstrate the importance of color, motion and their conjunctions in increasing visual attentiveness in children with CVI. This results of this study were consistent with some but not all of the anecdotal reports published in the literature. Interventions which utilize colorful and/or moving objects in educational, therapeutic, vision training and home environments are likely to help children with CVI increase their motivation to use their residual vision and in turn, promote their efficiency in visual learning. Additionally, the results of this study may be helpful to software designers in creating more stimulating and appropriate computerized programs for children with CVI.

References

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Wolfe, J. M. (1994). Guided search 2.0: A revised model of visual search. Psychonomic Bulletin & Review, 1, (2), 202-238.


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