"Visual" represents Area 17; Surrounding red cortex is the Occipital Lobe
You’re eyes don’t see; your brain does.
You believe you see because your brain tells you it is such. You feel pain because your brain too tells you such a feeling exists. This can be repeated for all sensations, visions, and perceptions of the world. Don’t believe me? The way scientists and physicians have been able to conjure up such theories is through the misfortunes of others. It is through the deficits of our patients that we begin to unravel in the intricacies of our mind.
You are probably under the false impression that your eyes determine if you believe you see. The eyes may provide you “sight,” but it does NOT provide you vision. Unfortunately for the less science-inclined, I must bored you with a bit of central visual pathways. The basic premise is that your eyes contain Retinal ganlion cells (RGCs) (neurons) that project to the Lateral Geniculate Nucleus (LGN) in your thalamus (this area in your “brain”) to Area 17 (aka Visual Cortex).
Recap:
Eyes –>RGCs –> LGN —> Area 17
Back to the original point. Let us pretend for a moment (and for many unfortunate individuals it is not a matter of pretending) that you had a lesion to Area 17 and Area 17 alone. Would you consider this person blind? By now you are well aware that I never pose simple questions, so I must address it from two perspectives – what the patient believes and what the physician observes.
Patient: The patient believes he/she is blind. We will call this functionally blind (it will be made apparent why this is the case later). There is absolutely nothing you can do to convince the patient otherwise.
Physician: If the physician were to put this patient through a series of tests, he would discover that he/she can still see light through their normally functioning eyes. Big deal, right? Right! These patients were shown random light flashes and were asked to press a button every time one appeared in their visual field (similar to the ones you’ve probably taken part in at an eye exam). What do you think the patient’s response was? “We’re blind you idiot!” (Perhaps, I shouldn’t put that in quotes, but you know they were thinking it). The physicians in their cool calming voice simply told them to play along and push the button whenever it felt right. Well lo and behold, what did they find? The patients perfomed BETTER than chance.
Therefore, they believed they were blind, but in “reality” they had full vision. You can even placeobjects in front of these people and they will unknowingly step out of the way to avoid them. This demonstrates that visions is a cortical construct and that Area 17 is responsible for conscious awareness. Mind boggling, isn’t it?
You didn’t think I was going to leave you on that note? I can’t show you one end of the spectrum and have you believing their isn’t another disorder to counterbalance it. Let us now discuss patients who have a bilateral destruction to their occipital lobe. As you see in the images above, they are (almost) completely responsible for vision. These individuals are in fact blind. Well, what’s so extraordinary abou them? If you were to ask them if they were blind, they would DENY it! These patients believe that they have vision. When put through similar tests as the patients with lestions in Area 17, they actually did at or worse than chance. Clearly, there is a disconnect.
Have I stepped you into a world of unimaginable ambiguity and chaos? Well, if that’s what you perceive, who am I too tell you otherwise?
