University of Edinburgh
 

Teamwork with children with cerebral palsy and
visual impairment: Towards a common language

Presented in November 2000

Reproduced by kind permission of Dr G N Dutton (Oct 2000)

Impaired Vision due to Brain Damage: designing educational strategies

Paper given by Dr G N Dutton at Castle Eringerfeld, Geseke, Germany, on 24 September 2000: Low Vision in Early Intervention.

Introduction

  • Brain damage is now the commonest cause of visual impairment in the developed world.
  • Damage to the eyes and visual pathways degrades the 'picture' presented to the brain.
  • Damage to the visual brain can also interfere with how the 'picture' is processed and understood.
  • Damage to eye movement control centres can cause blurring of the moving image and can interfere with reading.
  • Damage to the focusing control centre blurs the picture which is seen.
  • Effective communication is essential for successful education.
  • Educational information needs to be easily seen and understood. It therefore needs to be presented in a way which is well within the limitations of the damaged visual system.
  • The way the visual system works and the ways it can be damaged needs to be understood by everyone teaching visually impaired children.
  • A system which allows the VI teacher to determine the nature and degree of all the limitations of the damaged visual system needs to be developed.
  • A programme of development of educational/curricular material so that it is well within the child's ability to see, recognise, understand and learn from it needs to be set up.
  • Resources are currently being wasted by presenting information in such a way that it cannot be easily learned from. A structured approach which matches the presentation of educational material to the visual abilities of the child is likely to have major resource implications.

This paper summarises the main ways in which the visual system is impaired in children with brain damage and suggests the principles which need to be applied to address the issues outlined above.

Processing of visual information by the brain

There are two visual processing systems which are closely integrated:

1 The brain stem or reflex system

2 The central processing system

1. The brain stem of reflex system is a subconscious system which serves peripheral but not central vision. It allows us to avoid obstacles without (or before) consciously seeing them.

Children with profound cerebral visual impairment may be intact reflex vision. Those who can move are able to navigate slowly without bumping into obstacles.

Food on a spoon coming straight towards the face may not result in the mouth opening but taking the spoon on a curved path around the side of the face may lead to the mouth opening at the right time. Whether this form of vision can be trained needs to be determined.

2. The cerebral processing system can be divided into 3 principal components:

A. The occipital cortex

B. The dorsal stream

C. The ventral system

A. The occipital cortex is at the back of the brain. It processes the incoming information in different 'compartments' . Visual detail, colour and the perception of movement are processed in separate areas which, rarely, can be separately damaged.

B. The dorsal stream comprises the pathways which run from the occipital lobes to 3 main locations:

i) The back of the brain at the top (the posterior prietal area)
This area of the brain handles the complexity of the visual scene. Damage in this area leads to difficulty dealing with complex visual scenes. Young children, with such damage may not be able to find a toy on a patterned carpet. Other problems include fear of going into crowded places such as a busy shopping centre, difficulty in seeing something which has been pointed out in the distance and problems accepting information from a printed page with a lot of information on it.

ii) The part of the brain responsible for movement (the motor cortex)
To pick up an object the action is planned when the arm and hand are moved to the correct location and the hand is pre-configured to match the shape and dimensions of the object.

To do this, we map the visual scene in our minds and pass the co-ordinates of the position of the object to the limb. If the co-ordiantes are degraded the action we take is sometimes accurate and sometimes inaccurate.

It appears from our clinical work that some children with periventricular leukomalacia may be unable to move their feet and legs accurately, but are more accurate with their hands. This may in part be due to impairment of the lower visual field and in part to a disability in matching leg movement to the 3 dimensions of the visual scene. Such children find steps and kerbs difficult and may stop at the boundary of linoleum and carpet to investigate whether there is a step or not.

iii) The part of the brain at the front which is responsible for moving the head and eyes to look quickly into new directions.

Damage to this pathway can lead to eye movement problems ranging from very restricted movement to inaccurate fast eye movemnts. Resultant difficulties range between inability to look in a chosen diretion and disability in locating words on a printed page.

C. The ventral stream primarily takes visual information to the lower part of the cerebral cortex called the temporal lobes. The temporal lobes serve long-term visual memory. The right temporal lobe has a specific function (probably in most people) of recognising peoples' faces and route finding.

Difficulty recognisisng people can be helped by voice recognition and by friends wearing identifiers.

Impaired "route finding" is common. It applies on a large scale when there is a disability finding the way around. On a smaller scale, when there can be disability finding the way about the hme and on a smaller scale again, when there is difficulty finding things which are often 'lost' around the home.

A range of approaches based on language, colour coding and other memory strategies can be considered, and can prove helpful.

The left temporal area is not so specific in its function but in conjunction with the right temporal area it serves. The recognition function in this area includes the recognition of shape and of objects. The naming of colours is probably another left side brain function. Other 'visual' temporal lobe functions include visual memory which is needed for copying what is seen and visual imagination which is required for planning future actions.

Problems with naming colours can be helped by applying appropriate proper names (lemon yellow and sky blue). Problems with copying text can be helped by speaking the words either out loud or silently.

 

Educational approaches

All educational material needs to be presented so that it is well inside the thresholds for rapid, clear and simple perception.

These thresholds can be thought of as follows:

A. Basic thresholds of visual function

B. The threshold for visual complexity (of both foreground and background)

C. Temporal thresholds for presentation of information

D. The proximity threshold for facial expression

E. Specific thresholds matches to the focal brain disorder of the child.

A. Basic thresholds of visual function

These include:

  • Visual acuity
  • Visual field
  • Colour vision
  • Contrast sensitivity

B. The threshold for visual complexity (of both foreground and background)

Methods (urgently) need to be identified which give an objective means of defining complexity thresholds which are then applied to curricular material so that teachers can choose age appropriate enlarged/clear imagery which can easily be appreciated by the child with minimum fatigue.

These methods could comprise specimen educational material which is appropriate for age and which is printed in standard format and in (say) three other progressively less crowded formats.

C. Temporal thresholds for presentation of information

Both the duration of presentation of information and the speed and diretion in which is moves warrant investigation. Specimen educational material (eg; video material) could be devised to match the rate of perception.

D. The proximity threshold for facial expression

Poor vision limits the distance at which facial expressions (and movement of the mouth during speech) can be seen. The distance limit at which facial expression is not recognised needs to be determined.

E. Specific thresholds and strategies matche to the focal brain disorder of the child

The following problems need specific strategies:

  • Impaired recognition of faces often accompanies a disability in recognising the linguistic significance of different facial expressions.
  • Impaired orientation requires approaches for navigation both outside and inside. Organisation of possessions so that everything has its place may be required.
  • Pattern and object recognition needs detailed evaluation to determine the specific deficits.
  • Alexia/dyslexia have many causes which need to be clarified.
  • Inability to name colours can be helped by concept linkage (eg; sky blue, lemon yellow).

Conclusion

Every child with brain damage affecting vision has a different pattern of visual disability.

An educational model of regular assessment of visual function at all levels combined with a planned approach which ensures that all educational material and approaches fall well within the limits of perception will result in many benefits.

Children are likely to progress more quickly and the amount of resources required to bring about such progress is likely to be diminished.

Teamwork