CVI or Cerebral Visual Impairment, is the leading cause of pediatric visual impairment in developed countries. Consequently, it is essential for today’s teachers to have a solid understanding of how and why injuries to the brain cause vision issues. The journey starts by discovering how the brain processis input from the eyes to turn it into what we see and understand about the visual world.
There are two higher-order visual pathways responsible for processing visual information in different ways. Both are located in the visual cortex at the back of the brain. The Ventral Stream is referred to as the “what” pathway because it is what allows us to know what things we see are. The Dorsal Stream pathway is called the “where” pathway because it is how we understand the location of what we see in space. Damage to the components of either of these pathways results in interruption to the processes they carry out.
Ventral Stream Dysfunction Results in Difficulty With
- Constrast sensitivity
- Limited awareness of visual attributes
- Understanding form of objects
- Building up a library of known images (Deficits in visual memory)
- Depth perception
- Object recognition
- Face recognition
- Utilizing landmarks to navigate (route-finding)
Dorsal Stream Dysfunction Results in Difficulty With
- Perceiving motion
- Tracking movement
- Spatial orientation
- Moving through space accurately
- Visually guided reach and step
- Avoiding obstacles when moving
- Discriminating between similar objects
- Discriminating between objects in a group
- Seeing more than one object when placed close together
- Perceiving object position accurately
- Understanding object position in relation to other objects
These two processes (what and where) are not separate but integrated with one another. To successfully function visually, these processes must work together. Here is an example. If you are trying to pick up a bottle of water sitting on a desk, you must not only be able to recognize that the thing you see is a water bottle rather than a tape dispenser, but you must also know where the bottle is located in space so you can connect your hand with it in the right place. Your visual system must tell you both what it sees and where that target is positioned in space and in relation to everything else you see.