receptors ... our “five senses”

People have distinguished “five senses” in part based on our anatomy and in part based on our behaviour.  Eyes, ears, nose and tongue and skin are both obvious anatomically, and correspond to things that we experience (light, sound, smell, taste and feel) so human cultures refer to these in our various coordinations with each other.  But of course there are other cells that respond to changes in the environment, and there are cells that respond to changes in our physiology that are in turn triggered by changes in the environment. 
We could enumerate more “senses” ... but here I will continue to use vision as a exemplar of how a change in the environment results in an inner change and what we ourselves can then distinguish as “an experience”.

we are not cameras

When I went to school, admittedly a long time ago, I was taught about vision with the camera analogy, which I think many people still hold.  In other words, the lens in our eye focuses an image on the retina, which conveys the upside down information to our brains which then invert it for us.  Lots of experiments have been done with glasses that reverse this image, and people learn fairly quickly (over a few days) to adapt and see the world the right way around and do everything they normally do.  When the glasses are removed, they are quickly able to go back to their normal way of seeing.  But we are not cameras.

molecules and cell dynamics

Any sensation, any trigger from the environment, whether it is radiation, pressure, or molecules encountering the surface of a living being affect a molecular level change.  Light is converted to what we might call “chemical changes” ... but not just any chemical changes (most of these could not be managed in a test tube) but rather molecular cascades that are organized by the biological system into a cascade of rapid changes that progress from cell to cell and thus result in a response that is appropriate for the living being in its current circumstances.  For us, it can result in what we distinguish as experiences and value as “meaningful”.  

The details of these molecular cascades are not relevant here, I am mentioning them now to reiterate the notions of structural determinism, of coherent systemic changes, and most of all, for a sense of appreciation for the incredible beauty of living beings operating as seamlessly as they do!

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blind spot

You have probably encountered this phenomenon before and had it explained.  I’ve reiterated it here as it fits into the story I’m telling.  Close your left eye  and from about a foot away (the distance for this to work will vary with the actual enlargement you have on your computer display) gaze at the blue X.  As you adjust your distance, you will find that the red spot disappears.  This is when its image falls on that place in your retina where the optic nerve leaves the eye; there are no light receptors there. 

What is interesting about the blind spot is that we do not walk around with two holes in our vision, one for each eye.  Our visual field is complete.  For one thing, the two blind spots for our two eyes don’t correspond to the same part of the world, so one eye can fill in where the other leaves off.  But more significant, our brain, or better, our whole nervous system, fills in what is missing.  You don’t experience a blind spot when you look at the world with just one eye!

what can I see? ...

for your interest

1. 1.A video and animation depiction of the progress of a migraine aura.
   

2. 2.An afterimage adds colour -  as far as I can determine through cursory research, this happens in the retina when eye movements (saccade) are minimized as in a intense stare.
   

3. 3.Another fun optical illusion that creates the sensation of motion.  I have not explored the physiology that grounds this.

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a few more bits...

As revealed by my attempts to film the coloured lights, our eyes are not video camera’s either!   What we do so easily is a photographer’s concern - namely deal with high contrast and still experience full colour.  If you want to take a photo of a face, indirect light is much better than full sun. 

Our eyes are also able to adjust to different light conditions.  I like to walk in the dark, giving myself a good 10 minutes to fully dark adapt and then I see surprisingly well, though not in colour.  I get quite annoyed when someone then shines a flashlight at me, as the light adaptation process is quick, and then it takes many minutes to regain my night vision.

What our eyes do, that we avoid with photography, is move.  There is a continuous micro-movement called a “saccade” that keeps changing which retinal cells the image falls on.  If the motor nerves going to the eye are anesthetized, and the head is immobilized we soon “go blind” ... we need the change to see.