Sensory Illusions

[xSilverPhinx]

Sensory systems are a wonderful thing, as is the brain that integrates experiences and creates expectations. But they can be tricked...

Some of you might have seen the Checker shadow illusion or some variation before. To jog the memories of those who have, and to show those who haven't, here it is:

Even if you know beforehand that blocks A and B are the same colour, you still can't help seeing them as grey (A) and shaded white (B).



Don't believe your eyes? Try blocking the connecting rectangle between squares with a piece of paper or even your finger, and you will see the blocks change colour again!

But visual illusions are well known. Ever heard of an auditory illusion?

Listen to this, called the Shepard tone:

Don't believe your ears? Set the video to a loop and hear what happens.

(This effect is used in movie scores to create an sense of uneasy forboding. Does it induce some anxiety in you?)

Remember I mentioned the brain also integrates experiences? Check out the McGurk Effect:

Being a primarily visual animal, we will most likely favour sight over hearing.

[jumbojak]

I wonder how the McGurk effect plays out with deaf lip readers vs the blind. Varying degrees of blindness too. That's fascinating.

[xSilverPhinx]

What about this famous dress? What colour do you perceive it to be? Blue lined with black under a yellow-tinted illumination or white lined with gold under a blue-tinted illumination?

[xSilverPhinx]

I wonder how the McGurk effect plays out with deaf lip readers vs the blind. Varying degrees of blindness too. That's fascinating.

I wonder too how it plays out with varying degrees of blindness, but since it's an illusion that involves two senses -- sight and hearing -- I'm assuming if you remove one sensory modality it won't work at all. Deaf lip readers will only see what the lips are saying and blind people will only hear the word 'ba'.

Try it out, turn off the audio and read his lips in both instances. Then turn the audio on but don't look at the video. Your results will differ. 

[xSilverPhinx]

[hermes2015]

There was a movement in the 60's called Op Art that exploited other optical effects like perceived movement. One of the leaders was Bridget Riley, who always wore black.



Others were Vasarely and the Israeli artist Yaacov Agam, whom I met once.

[Icarus]

Other brain and or color perception foolery is the principle of Pointellism.  Seurat, Van Gogh and others used the method for color influence. Place some tiny dots of one color close to dots of another color and our eyes perceive the dots as a blend that makes a  different color. 

All sorts of applications are in every day use, not the east of which is the color we see on our screen.  Fine magazine color photos are composed of dots at the rate of perhaps 240 dots per inch. a square inch then might contain more than 57 thousand dots.  Ordinary newsprint color photos are of lesser dot frequency, commonly 60 to 90 dots per inch.

There are only four colors used in such printed matter.  It is, among the users, referred to as CYMK which translated implies Cyan, Yellow, Magenta, and black. With those four components we can create the illusion of any conceivable color or nuance thereof.  Place a bunch of dots of the red hue near  or mixed within the equal number of yellow dots and we have a shade of orange.  The shade of orange can be manipulated by using more or fewer dots of either color.  Same with blue and yellow dots  to make green and so on.

Placing the dots accurately spaced between colors is a matter of  considerable importance. If the dots overlap or are twisted slightly  in some part of the picture there will seem to appear some wavy lines called Moire.  Gotta get the dots in the right positions relative to one another. That means that printing presses must be capable of positioning the colored dots with a high degree of precision.

Use a magnifying glass to inspect some printed photos to see the actual dots. 

[xSilverPhinx]

[Tank]

Just goes to show that vision resides mostly in the brain and that the brain ain't perfect.

[Tank]

  If visual perception is mostly a brain function and brain function deteriorates with age does visual perception deteriorate with age?

[Bad Penny II]

If visual perception is mostly a brain function and brain function deteriorates with age does visual perception deteriorate with age?

If the eye breaks down with age and they often do, the brain is going to have hard time perceiving anything useful.

Maybe not directly relevant buy anyway:

Alzheimer's disease can be spotted Alzheimer's disease can be spotted through simple eye test," reports the Daily Telegraph.

A new study has found that people with Alzheimer's had fewer blood vessels and less blood flow in the retina (back of their eye).

[Tank]

If visual perception is mostly a brain function and brain function deteriorates with age does visual perception deteriorate with age?

If the eye breaks down with age and they often do, the brain is going to have hard time perceiving anything useful.

Maybe not directly relevant buy anyway:

Alzheimer's disease can be spotted Alzheimer's disease can be spotted through simple eye test," reports the Daily Telegraph.

A new study has found that people with Alzheimer's had fewer blood vessels and less blood flow in the retina (back of their eye).

Interesting. However a though occurs. Are the lack of blood vessels caused by the Alzheimer's or does a poor general blood vessel structure cause the Alzheimer's?

[xSilverPhinx]

Just goes to show that vision resides mostly in the brain and that the brain ain't perfect.

It's not perfect but it does what it evolved to do very well, which is why so many of these illusions work. 

[xSilverPhinx]

If visual perception is mostly a brain function and brain function deteriorates with age does visual perception deteriorate with age?

That's an excellent question

...

I'll get back to you on that one.

[billy rubin]

i have lost most of my sense of smell with age.

one evening i was cutting the head off a dead deer my wife and i came across on a walk, and started wrinkling up her nose.

why are you making faces?

that dead deer stinks.

i couldnt smell anything.

i cant smell the sulfur compounds in gearbox oil, or cinnamon.  i can still smell skunks, but theyre not the same as they used to be. apparently i the sensory loss is uneven.