Researchers estimate that at least 30% of the cerebral cortex, that is, hundreds of millions of neurons located in probably dozens of integration centres, contribute to the formation of what we actually « see ». Determining how these centres combine the components of our vision (colour, movement, depth, shape, detail) is an exciting and constantly evolving research effort.
The primary visual cortex (also called striated cortex or area V1) is the gateway to the visual cortex for visual information from the lateral geniculate body. This visual area is located on the inner side of the occipital lobe of each hemisphere.
Then, the information is relayed along the tracks for further processing.
- The dorsal path carries them through areas responsible for determining the location of the target object in relation to the observer. Along this path, neural activity encodes the position of the object and its movement. This route leads to the parietal region, which defines action plans relating to the object seen. Indeed, the brain also anticipates where the object will be a fraction of a second later, which ensures the proper synchronization of any action plan related to the object.
To calculate the depth of an object, the brain combines the visual signals sent by both eyes (each eye returns a slightly different vision) and information about how the shape of the image changes with eye movement.
- The ventral pathway transports information from the primary visual cortex to the temporal lobe, where neural activity identifies visions and gives them meaning. Thus, a face is identified and recognized at this level. The information related to the person is then retrieved from the memory.
Data circulating along the ventral and dorsal routes reach the frontal lobe.
DID YOU KNOW THAT ?
There are various sight-related anomalies.
For instance, some people have color blindness, which is an inherited vision disorder. Colour blindness does not perceive certain colours or confuses them. (especially red and green) . Indeed, the two genes that code for the pigments of the L (green) and M (red) cones are aligned one behind the other on the X chromosome. During meiosis, crossing-over can lead to partial recombination of the chromosomes and therefore to a disturbance of coloured vision.