Processing of Visual Information in Ventral and Dorsal Stream

There is a good agreement between different rehabilitation teams on the list of the ventral and dorsal stream functions that should be assessed. The lists of functions in several questionnaires are also closely similar. At special schools there are in the lists more functions related to reading and math, in the hospitals more ocular motor functions and sensory functions. If both sources of information are combined, a profile of visual functioning can be described 2,3,4. The questionnaires are divided in three main functional areas, vision related functions in the ventral and dorsal stream and in the “mirror neuron system”. The word “stream” depicts flow in one direction. In all these brain functions the flow of the information is in both ways and thus they could better be called networks, inferotemporal and parietal networks. However, for the time being the present names are so widely used that they are preferred also in this document.

Figure 14. The directions of information flow in the ventral stream (VS), dorsal stream (DS), and mirror neuron system (MNS). Other areas of mirror neuron networks are not visible in this picture.

When using the questionnaires we ask ourselves “how does the child/student use vision in this function/activity?” “What other sensory information does he use in this activity?” Since there are many activities that cannot be observed in clinical situations, assessment of visual processing functions is strongly based on the observations of the parents and several people taking care of the child or teaching him.

VENTRAL STREAM FUNCTIONS
Details in pictures, Noticing of errors and missing details
Perception of textures and surface qualities
Recognition of familiar and unfamiliar faces
Facial expressions, Body language
Landmarks, Concrete objects, Pictures of concrete objects,
Abstract pictures of objects of different categories,
Abstract forms (Roman letters, other characters, numbers)
Reading words and lines of text, Optimal reading strategy
Comparison with pictures in memory, ‘Reading’ series of pictures,
Visual problems in copying pictures from blackboard and/or near
Crowding effect, Scanning lines of text

DORSAL STREAM FUNCTIONS
Awareness of surrounding space, directions and distances in space
Perception of near and far space, Body awareness
Orientation in space, Map based, Memorising routes
Motion perception, Figure in motion, Biological motion
Depth perception, Simultaneous perception
Eye-hand coordination, Grasping and throwing objects,
Drawing, free hand, Visual imagination
Copying from near/ from blackboard, motor planning and execution
Spatial concepts in mathematics, Visual attention

In most tasks we use functions of both visual information streams. This is particularly important in reading and mathematics where children may have problems both in the spatial composition of the information as well as recognition of forms and groups of forms. Some children also have specific problems in immediate and short term visual memory of groups of numbers, which leads to the need to say the numbers aloud, even barely audible, in order to be able to copy them. Some children do not notice commas or full stops or small dots above or below the letters, which changes the content of the words and sentences. Increased crowding causes much extra work to teachers to by-and-by find out what is the optimal size and spacing of words and lines and how the text is best presented to meet the child’s needs:

1. as usual text with increased spacing,
2. magnifying to the size that gives best reading speed, with increased spacing if needed
3. presenting texts as single words in the middle of the screen or
4. as vertical rows of words if horizontal saccades are poor but the vertical saccades close to normal.

Mathematical tasks that require perfect 3-dimensional spatial vision should be restricted to testing children who have this special function. When written mathematical tasks are used in examinations we should know, whether we are testing visual functions and concepts more than mathematical reasoning. In some cases the strategies of blind students have been helpful in geometry and in developing the concept of the number line. However, the student must be able to develop spatial concepts based on auditory, tactile, haptic and kinaesthetic information in order to learn like a blind student.