Illusions, Michael – tricks are something whores do for money… or candy.

-after reading this post about the relationship between what your eyes see and how your mind interprets it, your head may collapse and theres nothing in it, and you will ask yourself, where is your mind?  ok ok it had to be done…

much of this post was derived from a really cool article i had to read for a class about image processing in medical devices.  the article is called “The Medawar Lecture 2001 Knowledge for Vision: Vision for Knowledge” and was presented by Richard L. Gregory and published in The Philosophical Transactions of The Royal Society.  it can be found here

one thing that i think is really interesting is how things evolved into existence.  of course most the time we don’t really know how things came from point A to B, but we can make pretty good guesses.  for example, we have a rough idea of how eyes evolved.  first of all, it would be really helpful for an organism to be able to know, for example, if it was in the light or the shade.  probably the first “eye” was just a serious of receptors on the skin of some animal that could sense either light or dark.  of course the skin does a lot of other things, so its not really efficient to have a bunch of sensitive receptors all over, so to increase the space efficiency of the eye, perhaps these receptors began to form shallow pits to increase the surface area without taking up the whole skin layer.  now maybe these little pits collected lots of junk, so some clear surface was made to allow light to pass but to keep junk out.  maybe these surfaces worked better if they were shaped like lenses to focus more light into these pits.  now these pits could become very deep with very small openings – like a camera aperature.  just like you may remember from high school physics or camera aperatures, really small openings and lenses cause the image to get inverted (see picture below).

lens inversion - the image appears upside down after traveling through a lens

lens inversion - the image appears upside down after traveling through a lens

so, all of a sudden, our brain that has become used to seeing things right side up now sees it upside down, but also left is on the right and vice versa.  something needed to be done – either our brain needed to receive an inverted signal from the eyes, or the brain needed to learn to coordinate all of its movements upside down.  it turns out that inverting the image for the brain is pretty easy, it just requires a little cross over of nerves (called the optic chiasm) and doing this is much easier than reversing all the nerves to the muscles etc.

optic chiasm

optic chiasm

interestingly, we can track the evolution of our eye by the distance from the center.  at the very edge of our vision, we can barely see color or shape, but we can see really good with black and white (due to high concentration of rods – dont worry about it) and we can tell movement, but not the specific direction of movement.  in the center of our vision, we can see really well with color and shape and specific movement directions (due to high concentration of cones) but interestingly we have worse night vision in the center of our vision.  it seems that night vision is more “primitive” and the center of our vision has selected away from that trait in favor of better day time vision.

irrefutable proof of evolution

irrefutable proof of evolution

many scientists think that one reason that brains became so developed was due to the quality of images produced by the eye.  while it was nice to know you were very close to something that might be food or might be dangerous, vision wasnt that helpful unless it could help you get a meal or help you get away safely.  thinking on this level involves remembering what danger or food looks like, recognizing it when you see it, understanding what consequences  follow food or danger in the near future and finally planning a course of action.  hence the brain, and hence cognition.  soon to follow in the history of brain adaptation  are complexities like socialization, tool-making etc.

and vision led to other complexities like gurl

and vision led to other complexities like gurl

another cool thing about our eyes – the cones towards the center that give us our color vision come in three types: red green and blue (trichromatic).  some people have genetic defects that do not allow them to see red or green; we call this colorblindness.  a very few people in the world have a genetic trait that gives them four types of cones (tetrachromatic).  normal trichromatic vision allows us to see maybe 10 million colors, but people with tetrachromatic vision can see perhaps 100 million or even a billion different colors.  some scientists say that the difference between having normal vision and this extra color perception is like the difference between a regular TV and an HDTV.  how sweet would that be to have ultra-high definition vision!

they dont make a 10million box yet

they dont make a 10million box yet

another cool eye trick i read about once involved putting glasses on different people that made everything appear upside down.  these people were never allowed to remove the glasses during the course of the experiment and so they would stumble around all day because their brain was really confused.  but after a few weeks they would wake up and everything would seem right side up.  their brain had learned how to see inverted.  if they took the glasses off, everything would look upside down again, however they were able to regain normal vision very quickly – their brain had learned how to adjust to being upside down and right side up.

but of course the image we see with our eyes is not always the image we see in our brain.  over the years we have picked up a few little tricks to help us process things faster, or in other cases make things really confusing.

  • exhibit A: hollow vs convex.   one of those faces is protruding from the surface while the other is molded into the surface, yet it still looks like it sticks out.  our brain has learned to recognize faces, and we know faces stick out, not recess in to the skull, so we “believe” a hollow face is really convex.  similarly, it can be nearly impossible to distinguish the protruding spheres from the recessed spheres.

    hollow face illusion

    hollow face illusion

  • exhibit B: the Ames room.  this one blows my mind.  the room pictured below does not contain one identical twin who is a midget and another who is a cave beast.  instead, the scales of the room have been altered so that they appear normal when viewed at the correct angle, creating an illusion that whatever is inside the room is out of proportion
ames illusion

ames illusion

ames illusion explanation

ames illusion explanation

  • exhibit C: motion illusions. these are not actually moving snakes. i think this one has to do with poor color vision out of the periphery but i dunno?
snake illusion

snake illusion

  • exhibit D: Kanisza Triangle.  When you look at this shape, it seems like there are twos triangle there, but there arent any triangles.  our brain has all of the evidence to believe there should be triangles – the lines necessary to make a triangle match up perfectly in the circles missing a slice as well as the A frames, but assuredly, they are not there.
Kanisza Triangle

Kanisza Triangle

  • and finally exhibit E: Neglect Illusions.  these three images are complete on the left but obviously not on the right, yet we know what each one of those images is supposed to be despite their faults.  our brain is able to put together the visual pieces of an incomplete puzzle.  some people with brain damage to the part of their brain that assembles these pictures would not be able to identify the images on the right even though they are very nearly complete.
Illusion of Neglect

Illusion of Neglect

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