The what pathway, or ventral pathway, is responsible for recognizing objects, and attributing a value to them. Damage to this pathway can lead to visual agnosia, where objects can no longer be recognized from visual information.
The what pathway is associated with recognizing objects and representing shapes. From this area there are connections to areas responsible for long-term memory and emotions.
As you progress further down this pathway, the receptive fields of the neurons become larger. A receptive field is the area of the retina (the back of the eye) that you must stimulate for the cell to be active. In V1, the receptive fields are very small, meaning that the neurons respond to very small pieces of the visual field. In V4, the receptive fields are already a lot larger. As a result, the neurons respond to a much larger portion of the visual field. So, in this way the neurons can respond to an object as a whole, rather than just lines.
This pathway goes from the occipital lobe to the temporal lobe and is therefore also called the ventral pathway (at the bottom of the brain). It contains the areas V1, V2, V3, and V4. This pathway is involved in recognizing objects. From here it goes to the bottom (inferior side) of the temporal lobe, where there are many areas involved in recognizing objects and categories.
The areas in the ventral pathway are sensitive to various factors not related to vision. You can think about attention and working memory. In this way, the pathway is responsible for recognizing objects, but also in judging how interesting or important these objects are.
Damage to this pathway can lead to visual agnosia. This condition makes it difficult to recognize objects based on visual information. Thus, people with visual agnosia can walk down the street without causing accidents but distinguishing a strawberry from a grape in a store is a lot more difficult.
Author: Myrthe Princen (translated by Melanie Smekal)