How the eyes work: We don't see, what is out there. Our inverse problem

Door Chippies gepubliceerd op Monday 27 October 11:28

For my assignment for Visual Perception and the Brain (Duke university on

This course is made by professor Dale Durves...

The essay is made by me.

note. "Dale Purves is Geller Professor of Neurobiology in the Duke Institute for Brain Sciences, with additional appointments in the department of Psychology and Brain Sciences, and the department of Philosophy at Duke University. He earned a B.A. from Yale University in 1960 and an M.D. from Harvard Medical School in 1964." ( Text from the course page,

Inverse problem

Our eyes see objects, light, color, buildings, other people, movement, depth and things that happen in our life. We see our bodies, we see the things we want to reach out for. Like food we find, or buy. We see our children and nurture them. We try to do the things we like. We love to move, to do things, to be busy with things we find on earth. But do we actually see them? 

We register things from outside ourselves. During our life we sense. We feel, we hear, we taste, we touch, we see... All is thought about in our selve. Inside the brain we register our experiences. So isolated as humans are inside with their own brain we attemp to see correctly. But could never know for sure what's really out there. 

We do can measure and follow up on what people regularly see. We understand what people do. What they "see". So it is measurable. 

But seeing is still a thing humans do themselves. The objects we attemp to see we aren't ourselve. We can't check if we truly fully see them. We can not determine if we see all those things outside correctly. 

We simply attemp to understand our outside world and so we can deal with things. But aren't perfectly seeing. As we can not know that. 

Our brains need images to protect ourselves, in evolutionairy point of view. Does it have to be a perfect image? Appearently not, as we still live as a kind. The human kind didnt die out, with these not perfect ways of seeing. Not yet.

Our brains registers what comes inside through our eyes for its own use. To be able to respond to others, and to find food, safe places to sleep and other things we need for our survival. 


To discover and understand what we do see...

We have to check what more it comes down to when we see. What happends when we see? What other aspects are involved?

There is found out in science that when we see we don't just deal with our own eyes, which can not be checked for seeing truth. Also for example: we deal with illuminance, reflection (lightness) and transmittance when we want to see color and light. 

Outside our eyes, lots of things happen that influence images we see in our eyes on the retina. 

Note. The things we want to see, reflect the sunlight and other sources of light to our eyes. Things can seem lighter and darker and change real colours. When we see different colours together they can have effect on eachother and change the real colors we think we see into other colors. Also the atmosphere can change the wavelenghts, and so changes the true colors. 


How do we then see?

We kinda see. When something occurs and tries to be in our lives. We deal with these things. Today, and perhaps easier to understand when we look back in human history, we see simply the brightness of the light that shines, other animals that could attack us, objects that could block our way. Like trees, rocks, rivers and the sea etc in nature. And other humans. 

We live in evolution. And evolution created, for our survival, a set of eyes on human that would help us in nature. We developed through evolution eyes that have a pupil, cornea, a lens and a retina. Which work the same way as a camera works that can take pictures. It creates together an image on the film/ retina. The retina is like a film. 

note. Light and color are different then a total image. Which can have different colors and can have lighter colors. But an image can also be dark. It shows objects. 

Light and color are different kind of rays. Higher frequence or lower frequence of waves that reach our eyes. 

Also there is a difference between lightness and brightness. Something can shine a light. That can be bright. Or something can reflect light and seem lighter or darker, is lightness. 


How we see light, lightness and color?

Photons, are electromagnetic light pieces, with radiant energy.  Holding in a piece electric charge and magnetic monopole. Photons are EMR's, which transfer by wavelenghts. Travels at speed of light, fastest in a vacuum, but will travel no matter the media it travels in. Photons are the smallest part of electromagnetic light. There is a range of frequencies of elctromagnetic radiation. Named the electromagnetic spectrum.


Is a small piece of this wide range of rays in the electromagnetic spectrum. Ultra- violet has higher frequency then blue, yellow or even red. Red has the lowest frequency. Not visible are radio waves with lower frequency then the color red. Nor xrays or cosmic electromagnetic light, which have a higher frequency then the colour ultra- violet. 

Photons reach the surface of the eye, but we don't see the photons. The retina in the eye creates an image. The world doesnt hold that image, the retina does. So images are made by ourselves. 

A camera is alike our eyes and creates images as well. Like us. So images are still not out there. We made an instrument alike our eyes. 

note. How light something is..? Lightness is about how much light is reflecting on a surface. 

So we see color and objects. Ànd how much is reflecting. 


Geometry, depth and movement.

Also give conflicts in our sight. We dont measure with our eyes, but with instruments. Like a yardstick. We do try to measure all around us with simply our sight. Honestly we learn such attemp. And have partially a natural feeling for measurements. But plenty of measurements we try arent just correct. 

Depth is also very difficult to measure with our eyes, as we have 2d eyes. But 2 of them that try to create a 3d sight. Also movement isnt precisely to measure. 


Ways how we then do can succesfully deal with the outside world. 

  • We try to make logical conclusions, inference.
  • We use "trial and error". We simply try and then conclude... And create an idea on such answers in our personel world. Trial and Error. 
  • We can track neurons and see what they do. Which could tell us with effidence what our human body does. Efficient coding. 
  • We can do tests with neurons in the brain and let them fire by using simple stimuli, like a flashlight etc, that creates a reaction to see what happends. It isnt natural a approach, so it doesnt represent the real world but can conclude we see as we respond. Feature detection. 


More about Feature detection, which I propose for this assignment as a way  we can deal with the inverse problem.

There was a cat used in a project by Steven Kuffler, David hubel and Torsten wiesel. (From a book these man made, with the title:"Brain and visual perception. The story of a 25 year collaboration." )The cat was tied down and had to watch a screen with lightbars. Some vertical, some horizontal, and some other angels. To register what the cat could see, their was a divice that registered what happened in the virtual cortex. Neurons in the virtual cortex were attached to the divice. And showed the responses the cat had to the lightbars showed on the screen. The cat mostly responded to vertical light bars. And least to horizontal bars. 

My conclusion. Feature detection is the best system to show us we have visual sight. But also shows we partially see. We dont register all. It's very representive to the fact we see half a world. It's a simple test. 

note. Trial and error shows we try things. Doesnt show truth we see. But that we can sense something unclear. But do find instinctively a way to deal with the world. As we humans as a kind still live and survived with mainly trial and error as a technique. 

Inference, shows humans attemp to see. But doesnt show clearly what we achieve. Do we actually accuratly see, and how correct?

Efficient coding is alike to this cat study. But I find it a difficult technique. Which could lead us to a precize answer on what we see, if we use it alot and try a lot. But feature detection shows what we see in the first place, by trying to get a respons with stimuli. 

I would choose Feature detection and try to find more natural situations and then check the neurons in the visual cortex to see what we really see. 


But we never can completly know what we see,

or could search for that answer as we humans are all alike and stuck in this inverse problem. We are not knowing what all is outside our head. And can not completly see cause of that. Simply cause we are human so excluded of knowing the complete ins and outs of other objects. 

We are inside our body, and restricted because of it. Also in our sight. It will because of that never be completly accurate. 

We arent the sunlight, so we arent completly registering it correctly. We aren't a color, so we can not 100% correctly measure that. We always will be seeing also wrong measurements of any object simply by the atmosphere we live in. 


Perhaps we are within the image. Should we live in it and not attemp to see it completely.

And perhaps thats the true world. Every element holds all atoms. Any ever excisting. so perhaps all that creates color is also a part of us. A tiny part. So we do see, but perhaps simply blend with what there is to see. As all colors can make eachother look different as well. And change what we see. With the reason we are also a tiny part of all. and so we blend. Also the sun can reflect light differently on each surface. Etc. There are many things that are outside of us, that are resonsible of changes in what we attemp to see.  So perhaps we are inside a picture. And shouldnt we try to see the picture but live in it. Fittingly live. Within the image. As thats what we are. Trying to live within all there is. (That we see for the natural use of surviving).

But we do see something,

as the cat shows we do can see a stimuli we put there. But perhaps we can not know all for sure. So we can control control simple stimuli, but we can not know all there is to measure. That goes outside our knowledge. Outside what we could know. We dont know every detail of the world. Like our vision shows when we measure it we can not see everyhting correctly. We do learn more and more. So we can try more and more different stimuli to test animals and humans if they can see these objects and how much correctly, or at least how much they can see them. 



verder lezen.

in dutch.



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