Early Processing of Visual Information

It is possible to learn about problems in the early processing of visual information at the V1-V2 level where line directions and lengths, colours, movement speed and direction are coded. There are game-like tests (LEA Rectangles Game) designed to detect difficulties in using visual information in tasks that require awareness of length of lines and objects. In testing with the rectangles we use observations on higher visual functions, thus we must be aware of the possibility that there may be simultaneous problems also in the function of other cortical areas than V1 and V2 affecting a child’s functioning.

A.	B.	C.

Figure 9. A. The student is asked to grasp the grey rectangles and place them on the black rectangles of the same size. The first part of the task measures the exactness of (eye)vision-hand-coordination, a parietal visual function (dorsal stream). B. The second part is a purely visual comparison of the length of the rectangles, an inferotemporal visual function (ventral stream). C. Children with restricted hand movements can be tested only for the purely visual part of the test. They use gaze pointing or pointing with nose.

A.	B.	C.

Figure 10. Awareness of directions of lines can be assessed using the LEA Mailbox Game where the card is given to the child in the opposite direction of the slot in the “Mailbox”. A. If the child is not aware of directions, the child does not turn the card, and it hits the Mailbox in the original direction even if the child can rotate her wrist (a weak function in many vision impaired children). B. Children with limited wrist movements should be tested holding the Mailbox horizontally. C. Children at early developmental levels need to experience the slot tactily and with the hand movements, drop the card several times through the slot with the tester and show that they can rotate their wrist before the card can be given in the opposite direction for testing.

Awareness of directions of lines is often difficult also to typically developing children in kindergarten and the first grade. They may have never thought what “same direction” means and it needs to be explained before testing.

Some children perceive the directions of the lines better if they can move their finger along the lines, thus receiving the information via kinaesthetic and proprioceptive information. A set of pairs of angles of different sizesmakes an additional easy play situation to experience how easy or difficult it is to perceive line directions and the size of angles. Often we need to use several kinds of narrow objects placing them I I I I, / / / /, \ \ \ \, ≡ before the concept “same direction” is clear enough to allow further testing.

A.	B.

Figure 11.A. Direction of lines is such a central concept in tasks at school that it is worth exploring with several tests. The test with one metal rod fixed on a piece of cardboard or wood and another that can be rotated to bring it in the same direction as the fixed one is a good training and testing tool. If the child has good hand movements he can move the rotating rod himself, otherwise the tester moves it while asking the child whether it needs to be moved more or is it in the same direction as the other rod. B. Direction of lines is more difficult to perceive when lines are parts of complex line structures. One of the most difficult tasks is to tell whether two angles are of the same size. One side of the angle is glued on a piece of cardboard or wood and the other can be turned to the same position as the movable line of the model angle.

At this early visual processing level, information from both eyes is fused if the child has developed binocularity during early visual development. A student may have good fusion and even stereopsis and yet have major problems in the higher visual functions.

Figure 12. Fusion of images can be tested in children with communication difficulties with the Worth 4-dot test or its paediatric modification Berens Three Character Test (Gulden Ophthalmics, Elins Park, PA).

School children with severe cerebral palsy can have normal or near normal visual acuity and stereopsis although they may have great difficulties in awareness of space and orientation in space (parietal functions) and difficulties in several recognition functions.

Also the ability to detach figures and objects from their background depends on good encoding and early processing. Problems in figure-ground perception are more common than usually diagnosed. There are hundreds of thousands of students using teaching materials and communication cards that they do not see correctly, do not recognise as easily as the designer of the picture or cannot read the text printed on a picture because it cannot be detached, “lifted loose” from the picture. This very common problem should be considered in creating teaching and communication materials because this early processing function does not seem to improve in most children.

In the primary visual cortex, form, colour, orientation of lines and motion, are separated from each other. They are brought together in the higher functions and thus we do see colour on the object and not next to its form. After long standing blindness, restoration of sight through surgery may lead to strange perceptual phenomena like seeing the colour floating above the object.

Figure 13. This picture is from the film "Learning to see" (reference 124 in the CV). Professor Scholler describes his vision after odontokeratoprosthesis (clear plastic lens placed in the cornea): "For the first weeks [after the operation] I saw the colour separate from the object itself, floating above it."

The role of immediate and short time memory functions in the early visual processing at the V1-V2 level may be understood better when there is more information available from the transcranial magnetic stimulation experiments5 and other on-going investigations on early processing of visual information. Since we recognize faces and objects instantly, the comparison with the template in the memory storage must be available at the same time as the image is processed as a picture. Memory functions are not the only “newly found” functions that are present in the V1-V2 level. Haptic space and auditory information are also recordable there but the visual information is the information we are usually most strongly aware of.