A Paradoxical Sight

Almost everyone has heard of the saying "seeing is believing." My question to you is, do you believe you are aware of everything you see? Well, up until a few months ago (even though I study science and understand there are some strange complex things that occur in our brain we are not aware of), I would claim this is very much true.

What changed my belief of this was a lecture on the visual pathway and processing structures in the brain. To summarize what I have learnt without going into too much detail. Visual perception occurs when a light hits the back of your retina and stimulates the rods and cones to send a nerve impulse (an electrical stimuli similar to your power cables) to your brain. A specific area in the back of the brain called the primary visual area (V1) is one of the important structures that allows you to perceive what you see. Now the important thing is, V1 has been described by neuroscientists as necessary but not sufficient for 'conscious' awareness of visual stimuli. The other side of the story are specific extrastriate areas required to communicate with the V1 area for awareness of visual phenomenons like motion, color, and shape.

So what does all of this have to do with awareness? The thing I find remarkable about neuroscience is that they can only study certain aspects of brain function when and if there is someone with a lesion to specific structures. This means they're in the business of proving the saying "you don't know what you've got until it's gone."

Now one of the more interesting things that has been studied in the past 10 years has been blindsight. In 1996, Weiskrantz et al., did experiments on a patient with a lesion to the primary visual cortex (his name was D.B.) who, when prompted to do so, was able to identify visual figures and follow targets with his fingers while reporting to do so in the absence of visual consciousness. Remember I said before that V1 is necessary for conscious awareness of what you see? How is it possible then that someone with damage to V1 can be aware of something they cannot possibly see? The experiments found that D.B. was able to discriminate between two possible stimuli such as an X vs. an O or horizontal lines vs. vertical lines with an above chance performance. In later studies, it was described by D.B. as having "a strong feeling of something being there" despite not being aware of it.

So it seems (from a visual perspective in any case) that we are not always 'aware' of everything we see. In the video below, Dr. V. S. Ramachandran attempts to explain this requirement as a necessary feature of everyday life. It is indeed staggering if you stop for a second to consider how many physical phenomenons your brain has to perceive in a short time for you to do something as simple as crossing the road at a traffic light (e.g. the motion of moving cars, the position of your body relative to the car, the colour of the light etc). It is indeed necessary for us to be unaware of a large amount of processing for you to be able to function.

If you still don't believe you are not aware of everything. Well, try this test:

Reference:

Overgaard, M. (2011). Visual experience and blindsight: a methodological review. Experimental Brain Research 209: 473-479.