The reason you are seeing this test, rather than smelling it, tasting it, or hearing it, is because your visual receptors are being stimulated and the information is being sent along the optic nerve to the occipital lobe in your brain. this process is called

The brain code or the neural code, which is sometimes also referred as the mind code is a interpretation of the neural activity taking place in our body. It refers to the interpretation of the activity in the brain (cerebral cortex) as data structure. It represents the mental activity as a step by step data flow in the different structures from the point of generation of the impulses to the actual sensation.  

In this case, the neural coding of the optical signals is given, hence, it is a type of brain code or neural code.