As partly distinct from the rest of the brain, the optic system seems to be a relatively clearly perceived entity. Far from simple in functioning, its outlines can be categorized into the eye and its structure, the cells of the retina, the optic nerve pathways and the brain areas which the optic nerves lead to. Many structures can already be explained in remarkable detail, however, the current challenge lies in explaining the way images form from the signals initiated by the retinal cells.
Most of the axons from the optic tract innervate the lateral geniculate nucleus (LGN) of the dorsal thalamus, where the information is passed onward to cortical areas of the occipital, temporal and parietal lobes. Around two dozen cortical areas have been identified to be part of visual information processing, many of which functions are still largely unclear. However, it seems different parts manage different aspects of the processing. E.g. from the two large-scale cortical streams involved, the dorsal stream appears to analyse visual motion and visual control of action, while the ventral stream is thought to be involved in building a perception of the visual world and recognition of objects.
For me, the most devouring question lies in how in the world are the initial electrical signals transformed into a subjective experience of seeing? Where in the brain does the image of the visual field reside?
Apparently, the current hypothesis of perception is that certain groups of neurons, receptive fields, are activated according to different objects of the physical world (e.g. the face of my clamorous nocturnal neighbor which occasionally resembles a punching bag). Yet, this approach opens up more questions than it answers: concepts of objects are also utilized in the act of thinking. How do thoughts utilize the concepts built by the visual system? How do initial concepts form? Which was first: the concept or the visual? Where do thoughts come from and who does the thinking? How did this text come into being, and is it understood by anyone?