The visual system is hierarchically organised into different areas. The lower visual areas see small parts of the visual field, and they are sensitive to very simple features, such as edges and their orientation. Higher up the hierarchy, the visual areas start encoding more abstract representations of the world, expanding their visual field to respond to stimuli such as objects and faces.  

Oxidative stress is a direct consequence of an excess in the body of so-called “free radicals” – reactive, unstable molecules that contain oxygen. Free radicals are normal metabolic by-products and also help to relay signals in the body. In turn, oxidative stress (an overload of these molecules) can be caused by lifestyle, environmental and biological factors such as smoking, high alcohol consumption, poor diet, stress, pollution, radiation, industrial chemicals, and chronic inflammation.