Vision for Doing
Assessing Functional Vision of Learners who are Multiply Disabled
Chapter 7 Assessing Vision for Doing
Section 11 Responses to Approaching Object
Aims of section 11
In this section we are going to take a degree of poetic licence. The diagram indicates an object moving on a certain path, and within a fairly restricted distance from the learner. Despite this restriction, we intend in this section to discuss opportunities for the learner to perceive objects and events, which are at distances outwith this range. We will, however, develop some of these points in Section 15 (Responses to Size).
How to use section 11
Turn to the diagram. For your observations of the learner you will be using that part of the diagram which is above the dotted line. The diagram consists of three slanted 'squares' plus a drawing of a person's head. The three sizes of 'squares' represent how a square might look to a person as it moves to approach his face. Although the drawings look like three different sized squares, it is actually the same square drawn at different distances from the person. The arrowed line below this indicates the starting distance (1 metre) and the end distance.
You need not use a square, instead use any object which is well contrasted. Sometimes even your own hand may serve the same purpose (though it may not be well enough contrasted). Try to move the object at a speed fast enough to appear to be on a collision course. But not so fast that it causes a large movement of air. For a response from the person may then be a reaction to that air movement on the face.
Below the dotted line there is a little table. On it record the results of your observations. This is where to record the learner's responses to the object's approach. The kind of response to look out for is an eye blink, or his head moving back, or hands coming up to the midline - or any combination of these. You will see that there are two rows on the table. The top row (hit path) is for recording responses to the object approaching right up to the person's face. The second row (miss path) is to record results when the object starts off at the same spot, but moves off to the side past the person's face. Instead of the approaching object coming straight on, it veers at a slight angle.
Transferring results to Section 18
Now you have to decide what the results of your observations mean for the Summary Chart in Section 18. In that Summary Chart, you will find that in the row for Section 11 there is only space to tick Aware, Attend and Localise. The other two boxes are shaded. This is because any general response to an approaching object cannot tell us more than that there is an ability to Localise.
As before, if he makes a very specific response (eg; naming the object approaching), this would mean he could Recognise through vision. Additional information will be needed if you are to tell that the learner is doing more than Localising. If you have that kind of extra information by all means tick boxes in the filled areas as appropriate.
No response to approaching objects?
If the learner Never shows any visual response to any of the items in this section, try again on subsequent occasions with different objects and in different lighting conditions (that is in other Settings). You should at least try Section 12, 13, 14 and, if he can walk or guide a wheelchair, Section 17. If these too result in Never you should refer back to the curriculum suggestions in Sections 9 and 10.
Or score localise only if
The learner Consistently distinguishes a 'hit path' versus a 'miss path'. That is when the object comes on a path which will miss the learner, he notices the new path of movement. (To score Consistently he does not have to respond on every single presentation, just enough for you feel comfortable that the response is consistent.) Then move on to Section 12. It is unlikely that the suggestions for curriculum development contained in this section will be of much interest.
Or score attend if:
You have ¡ Consistent responses only to the 'hit path'. He does not notice the different path of movement made by the object on a miss path. In this case go to the Summary Chart, find the row for Section 11, and tick in the box for Attend. Then move on to Section 12. You will probably want to return to the suggestions for curriculum development given later in the present Section.
Or Score aware if:
The learner shows no Consistent responses, but some are tick Occasionally. If so, tick Aware in the Summary Chart Section 18). Then move on to Section 12. In this case, too, you may want to return and use the curriculum suggestions given in this Section.
Where to go now?
Having noted the results of your observations and transferred these to the Summary Chart, you are then ready to make a choice. The choice you make will depend on the results you obtained.
You can skip the remainder of this section and proceed directly to Section 12, dealing with assessment of visual fields. By doing this you will continue your assessment of the use of Vision.
Postpone further assessment and read the remainder of this section. In it we suggest activities for curriculum development.
To have an interest in this subject you will have found from the completed Summary Chart that the learner is only Aware through vision. Similarly the learner's use of 'the Other Senses' will be functioning at the level of Awareness. Those most interested in this part of Section 11 will be working with people who have very severe difficulties in learning about the world.
It might seem a little odd to consider a positive response to an object approaching as being restricted to Awareness of the world. Surely, you may ask, such a response would indicate an understanding of distance? To understand why a learner may respond in this way, but may still only be Aware rather than Iocalising or recognising objects, we need to think of what purpose might be served by this response to an approaching object.
Response to threat
A clue to its purpose is suggested when we realise that a great many of the animals in the world show a similar response. Cats, frogs, goats and many other animals all show this response. Not only that, but the animals with which this response has been studied do so from a very early age. Evolution seems to have conferred on human beings and other animals a useful means of avoiding threats from other predators.
The fact that the response occurs in very young animals also suggests that the response is inbuilt at birth. Both of these conclusions, while tentative as the evidence is not certain, suggest that response to approaching objects is a very basic response. That being the case it might well be only one way of gaining information about distance, one that is somewhat rudimentary and available to those who are less cognitively able.
How it works
The information that comes to the eye when an object approaches is of an expansion on the retina (the 'camera film' at the back of the eye - see Figure 7.8.1). At half the distance the object appears twice as big on the retina. This is known as an optic expansion pattern. While everything else remains the same size, the approaching object appears to increase in size.
Is it useful?
We have already pointed out that this response is so useful that it has probably evolved to become inbuilt into the genes of higher animals (including humans). It is also useful to learners who are multiply disabled. For just as objects in the world can move while the learner stays still, so too can the learner move while the world stays still. That movement may depend on other people pushing a wheelchair, or a self-controlled wheelchair (see Section 17 for a more detailed discussion of this topic), or independent mobility may be possible.
This allows you to be creative in designing surroundings through which the learner will pass. By carrying out the other sections, you can then use results obtained in these sections to discover the kind of visual information the learner is able to use. Is it only reflected light? Do certain contrasts work better than others? What about size? What about the position of objects in relation to the learner?
Using other senses
A useful way to proceed to help awareness of an object's approach is to call into play the other senses. For example, use a squeaky toy, a scented object; a balloon with the air being expelled; a human face approaching while blowing, whistling, singing or talking.
You will be interested in this topic if you found that the learner responded to items of Chapter 7 at this level. It is also possible that the learner responded differently when the object was on a hit path versus a miss path,
Hit path = Consistently ticked
Miss path = Never ticked
You may have found a similar level of attending when you carried out Section 10.
Using other senses
Where the learner responds differently to an object approaching to touch the face (hit path), as opposed to one which is on a miss path, this offers good evidence for the learner seeing some differences in direction as well as in depth. This is dealt with in greater detail in Section 15.
As in the other sections you will be most interested in this topic if you have already carried out the items of Chapter 7 and found that the learner responded at this stage. You will want to ensure that, for the purposes of curriculum development, you refer also to these other sections.
Under this topic heading we propose to subsume most of our suggestions on how the learner perceives distance. We do this because it was our experience that staff usually thought of an object moving in depth as part of an understanding of how the learner perceived distance. (A reasonable enough assumption).
Reaching and grasping
For those who are physically able to reach with some degree of accuracy, the act of reaching itself indicates that the learner is able to Iocalise objects in space. What about where reaching goes wrong?
This is a bit like the old good news / bad news joke1. Swiping is good news in that it demonstrates that the learner is trying to contact objects "out there". But it is also bad news. Swiping can prove highly destructive. Not only is it destructive to favourite ornaments. It discourages active exploration that is meaningful in constructing an understanding of objects.
Failure in coordinating eye with hand movements may result in objects being swiped at rather than vision being used to guide the hand to an object. Because we do not wish to see the learner fail, we may often unknowingly encourage this kind of response. We do so by placing objects in positions to which a swipe will be accidentally successful, contacting the object. It is important to try to establish visually guided reaching rather than swiping, which although visually elicited is not guided by vision. One possibility is for the object to produce a sound when placed in a new position.
The source of poorly directed reaching in a child with a visual impairment can often be traced back to the period of infancy. At this time sounding mobiles are occasionally placed around the child's bed but beyond the extent of the child's reach. Two things happen. First because reaching will result in failure, it tends to diminish in both frequency and accuracy. Second, swiping becomes the action most likely to result in contact with the object - on those occasions where it does happen to be within reach. A vicious circle is set up.
People frequently try to alleviate this by using a variety of widely available mobile arrangements. The problem with a mobile is that a child with this level of sight is unlikely to produce either an accurate reach or a precise grasp. Naturally for the child with additional physical disabilities, the errors are compounded. It can be helpful to set up a stabile rather than mobile arrangement. Try to avoid using the universally available plastic materials, which tend to look good but feel monotonous.
The stabile can be constructed using a variety of materials. The range of materials is vast and can be tailored to the level of vision ascertained using this book. One stabile could use mostly highly reflective surfaces such as wine bags, tinsel, or unbreakable Christmas tree baubles. Which can be cut to size and fixed in position.
Some activity centre type toys are more appropriate than others. Those which have variations in colours and plastic may offer little that is of interest.
How do we judge distance?
Traditional understanding as to how we perceive distance is not entirely accurate. If binocular vision (two eyes working together to perceive distance) is absent, other visual information can specify distance. An understanding of these 'cues for distance' helps to show how these same stimuli might be employed to aid the learner with visual defect to obtain more information as to the distance of objects and events in her surroundings. First we need to give a little more detail on the more traditional understanding of how we perceive distance.
As the name implies, this depends upon the eyes working together. There are two elements comprising binocular parallax. One is the angle of convergence, the other binocular disparity. Convergence angle changes with the distance between the person and the object being looked at (decreasing as the object gets further away). Binocular disparity is a feature of having two eyes, each side by side. This means that an object not being fixated is projected onto points which do not correspond in the two eyes.
Without going into too much detail, we may question whether this should be regarded as the primary means specifying distance. We need only reflect on the fact that the distance between our eyes must change from birth the first few years of life to understand that this the case. If it were primary, then absolute distance would have to be specified from birth. As the distance between the two eyes changes in this early period, binocular disparity (and therefore binocular parallax) cannot be the primary means of specifying distance.
Other stimuli specify distance. Optic expansion, which we have already met, is unaffected by changes in growth during a child's development. It is therefore much more likely to be a primary indicator of distance. It is also more likely to be available to a learner with even severe visual disability. When we move toward an object, its image on our retina expands (as we saw earlier). The amount of this expansion may, in some situations, inform us of the distance of the object. For instance, ball rolling and catching are useful games to utilise the depth cue of optic expansion. This too does not require access to information being provided by two eyes. Punch bags may be covered with suitably contrasted materials and swung from a variety of directions at different speeds. (Be gentle!) Prior to use of precise information on time to contact, this is the kind of information used for mobility.
Motion parallax describes the changes in the image on the retina which occur when we move our head to the sides. Although independent of the distance between the eyes, and therefore constant throughout a child's development, it is unlikely that motion parallax gives absolute information as to distance. One would need to have some other way of indicating the distance of a point of fixation.
How do babies do it?
Experiments with infants suggest that the visual system dodges this conundrum of absolute calibration of distance. It does so by being able to detect the association between hand and object. One then sees why there may be great problems where both visual and physical abilities are impaired. It becomes much more difficult to judge one against the other. Hence the reason for the suggestion, given in Section 10, of accentuating the existence of the hand using reflective tape.
What to do
We can conclude that there are not one but several ways of gauging distance (as we will see from Section 15, there are in fact other cues for distance). Any or all of the following may be used as techniques for aiding intervention.
- Lateral head movements can be demonstrated to the child passively, while using objects that are reflective or highly contrasted.
- Attention may be drawn to changes in depth by varying the contrasts of two surfaces.
- Compensatory head postures are often useful to a child in improving depth perception.
- Where there is some colour perception this can be associated to provide other conceptual discrimination. For example a large object can be of one colour. A half-sized object of a different colour can be presented at half the distance. A child could have fun saying "Zoom "to show that he/she is detecting the nearer half- sized object.
Using prism lenses
With learners who have additional physical disability it is often difficult to determine a cause for poor reaching in depth. It could be due to visual problems in perceiving depth, or it could be due to the physical difficulties experienced in reaching for objects, or it could be a combination of both. To test for this, one possibility is to compare reaching to an object which has a transparent surface, such as a clear ball containing a small toy. Observe whether the hand reaching out is shaped to that of the transparent surface before contact. The best time to do this is on the first occasion the transparent object is presented to the learner. Otherwise hand shaping may have been learned on the previous presentations.
There are other more refined techniques such as having the learner wear distorting prism lenses for a very short time, and observe whether reaching in depth is affected (see Figure 7.11.1). As a long term strategy this is not recommended. Use on one or two occasions can however be of benefit, helping to determine the presence of visually guided reaching.
Figure 7.11.1 Prism displacing apparent position
You will be interested in following up this part of Section 11 if the responses to approaching objects showed some consistency. As well as this the Summary Chart will have indicated the learner to be functioning at the "level" of Recognising.
Use of contrast and lighting
You will be interested in following up this part of Section 11 if responses to approaching objects were Consistent. Also the Summary Chart will have indicated the learner to be at the "level" of Understanding.
To the more major cues specifying distance that we outlined above, might be added the so-called 'painter's cues'. These include linear perspective, in which separation of lines decreases with increasing distance (like railway tracks going into the horizon); interposition or occlusion (one object covering another) gives information on object distance as does a differences in height between objects. For the child with visual disability, you may have to introduce these cues in the form of games, rather than simply expecting the learner to be able to understand their significance. One of these "painter's cues" are depicted in Figure 7.11.2.
Figure 7.11.2. Painter's cue showing density gradient
Some learners may benefit from the introduction of eye pointing to objects. Especially those who have severe forms of physical disability, as well as those who have language delay, and those who have a mental handicap, may be able to demonstrate communicative intent through eye pointing. Unfortunately, the label of visual disability may, in the minds of some, preclude this avenue from being explored. As we have seen in many instances throughout this book, this view may be no more than a self-fulfilling prophecy. The criterion to go by is this. Would eye-pointing have been considered as a route for communication, had it not been known that the learner was visually disabled? If the answer is yes, and the learner has a degree of vision which encompasses the range of objects which could be pointed to with the eyes, it may be worthwhile attempting eye pointing.
Eye pointing is an early form of communication. It is a clear demonstration of a move towards active use of vision. As such it should not be in itself. In the presence of visual disability, additional effort will be required to improve the learner's facility in eye pointing.
The information given earlier on optimum conditions of lighting, improving contrast between foreground and background, securing good positioning, are all relevant. Augment these by using an object size and distance from the learner that are comfortable rather than at the limits of the learner's visual abilities. To these essentially visual enhancements should be added the rather obvious notion that the best way to obtain eye pointing is to use objects and events which are known to be motivating for that learner (in answer to the question "What does the learner like?").