The Neuroscience of Illusions and Dictionaries

Scientific American is running a pair of stories about what words and illusions can tell us about the brain. Mark Changizi of the Rensselaer Polytechnic Institute is interviewed about his research into the relationship between the mechanisms of the brain and the evolution of language. The second article contains a slide-show of various illusions and why the brain interprets them as it does.

Comments

Link to the meat

[SheeEttin]

Link to the one-page/print version of the dictionary article and the meat of the illusion article
Also, a summary of the illusion article: The brain uses context, rather than absolute sampling.

So can somebody explain?

[quokkapox]

Why do LED clocks jiggle up and down when I'm eating crunchy things?

Re:So can somebody explain?

[Dachannien]

The LEDs aren't actually illuminated all the time. They are actually flashing very fast - faster than your brain can discern. When you eat crunchy foods, it vibrates your head (and therefore, your retinas) at a frequency sufficient to allow some of the LED flashes to appear above or below the other flashes.

Re:So can somebody explain?

[Eighty7]

Hang on, do you weigh less than a duck.

Re:So can somebody explain?

[Trogre]

I can discern Pulse-Width Modulated LEDs without eating :) By rapidly oscillating my eyes I can tell you in a second which light sources in a room are PWM. Car brake lights, dashboard lights, billboard signs, power LEDs - it's surprising how much equipment is now PWMd. That unfortunately includes other POV-based technologies like DLP. I see the rainbow effect in every single-chip implementation that I've ever come across.

Binocular vision and elephants

[Red Flayer]

For the evolution of forward-facing eyes, I am arguing that it is for a kind of x-ray vision. It actually allows us to see through stuff--like when you hold up a finger vertically and you see through it instead of beyond it. For animals that are large and living in forested environments, there should be selection pressure for forward-facing eyes, because you can actually see more of your environment.

That makes a lot of sense, and is very interesting to me since I recall learning that predators have forward facing eyes so they can better detect movement of prey (binocular vision) while prey animals have outward facing eyes so they can better be aware of threats (greater field of vision).

I had always wondered why elephants had forward-facing eyes, since they are not predators... and this helps explain it. I had always supposed that it was because they were social animals, and communication ability and multiple individuals scanning for threats was better than one individual with a larger field of view. This makes even more sense if the scanning in a smaller area is more effective due to the binocular vision associated with forward-facing eyes.

Rods and cones

[Dachannien]

In the first FA, Changizi states his hypothesis that primates evolved color vision in order to detect changes in emotional state indicated by things like blushing/flushing of the face. I find this a bit problematic, primarily because it doesn't explain why our vision evolved to respond to three different wavelength ranges of light (red, green, and blue). It would make more sense to have only evolved cones responsive to red light, or perhaps red and one other color, if that were the only reason.

It seems to me that a more reasonable hypothesis is that trichromatic color vision co-evolved along with the colorings of fruits that primates would find nutritious. Emotional cues seem like a more subtle issue - as well as a mostly-solved problem - that would have taken advantage of color vision that was already partially or fully evolved.

More/Better Optical Illusions

[martyb]

The second article contains a slide-show of various illusions [CC] [GC] and why the brain interprets them as it does.

Maybe I missed something, but I found the second article to be a let-down.

(Warning for epileptics: if visual stimuli can set off a seizure for you, you should probably stay away from the following links. I am not susceptible, but I found the second link to be visually overwhelming at first.)

IMHO, more interesting galleries of examples can be found at Wikipedia's Optical Illusions page and at Michael Bach's 78 Optical Illusions & Visual Phenomena page.

Re:Brightness and Color Illusions

[hansraj]

As always wikipedia is your friend. The reason for this illusion is summarized in the following line:

When interpreted as a 3-dimensional scene, our visual system immediately estimates a lighting vector and uses this to judge the property of the material. So, in effect the brain sees something that looks like a 3D image and imagines that there is a source of light somewhere. If you look at the picture again, you would notice that the perceived color difference of the two squares appear distinctly with a mental image of a shadow of the cylinder on the chequered platform. The brain imagines a light source on the upper left side of the picture. Why exactly there? Probably because the cylinder seems to have a lighter shade in that direction and darker on the opposite side, making it seem as if there is a light source in that direction.

Fascinating really!

Serious conceptual flaws

[Estanislao Mart�nez]

Quoting from the slide show link:

It's a fact of neuroscience that everything we experience is actually a figment of our imagination. Although our sensations feel accurate and truthful, they do not necessarily reproduce the physical reality of the outside world. Although our sensations feel accurate and truthful, they do not necessarily reproduce the physical reality of the outside world.

The whole philosophy of perception that this quote embodies is fundamentally wrong. As an example of this, take a look at the first so-called "illusion" in the slideshow: the Edward Adelson checkerboard-and-shadon example. This is called an "illusion" on the basis that our eyesight "misleads us" by telling us that a light square in the shadow is lighter than a dark one in the light, whereas they are, supposedly, "the same color." By "the same color," what they seem to mean is that the stimulus, i.e., the rays of light reflected or emitted from the squares that hit our retina, have the same spectrum and intensity.

What they're missing is that the point of vision, and perception in general, isn't to give us information about the rays of light that hit the retina. What vision does is give us information about the objects in our environment, which reflect or emit rays of light. The reason we see the two squares as having different colors, despite the fact that our retinas are getting the exact same pointwise stimulus from them, is because the visual system, using contextual information about light and shadow across the whole scene, can figure out that the surface spectral reflectivity of the two squares must be different. Square B looks lighter than square A because the visual system judges, correctly, that it must reflect more light. Or put alternatively: the visual system figures out that if the two squares were in the same light, the point stimulus from the reflected light rays would be different.

This is accurately reproducing an aspect of the physical reality of the outside world; vision is accurately reproducing the spectral reflectivity of surfaces in our environment, at the apparent expense of failing to reproduce the spectral distribution of the rays of light that hit our retina. But of course, the answer to that one is that the rays of light aren't the object of visual perception, they're just the means.

Seeing the squares as different colors is not an illusion. There is only one visual illusion in that example, and they don't remark on it: the illusion of seeing, in a flat surface, a 3D scene with light and shadow. The judgement that the two squares have different colors follows from that, because in the real-world scene the image depicts, those squares would in fact be surfaces with different colors when seen under the same light.

Re:Serious conceptual flaws

[Estanislao Mart�nez]

According to physics of relativity, "insideness vs outsideness" is an illusion of consciousness.

I don't think physicists have very much to tell us about psychology or philosophy. What they think is not completely irrelevant, but it is not imbued with the authority you pretend it should.

Reality is a continuous field. i.e. If we were in a simulation you wouldn't know it. There is no object "out there" per se, all your mind is doing is discretizing a continuous surface of data that you percieve or have access to into chunked-objects that don't really exist. i.e. a tree is not seperate from the earth, which ultimately is not seperate from space, which is ultimately not seperate from the sun, all of these things are continuously connected in ways we don't fully understand.

Your problem is that your claim to know this is self-defeating. In order to "know" all this, you have to rely on your knowledge of a real world that you inhabit and interact with, with everyday objects at everyday scales.

A more philosophical way of putting it: there are two main, related problems with what you're saying here:

1. You're giving metaphysical status to the theories of contemporary physics. The "real" world is whatever physics says the world is; therefore, everything that physics leaves out (like everyday experience) must be "illusory."
2. You're granting metaphysics priority over epistemology. You want us to accept that physics gives us true knowledge of what is "real" and what is "illusory." However, the knowledge that physics offers us is the result of the interactions of people in an everyday world making predictions about what they will experience when they manipulate that everyday world in sophisticated ways. Knowledge of physical theories presupposes participation in the everyday world; therefore physical theories cannot tell us what is "real" and what is "illusory" in the metaphysical sense. You can only rescue that line of thought by assuming that knowledge itself is illusory (which I wouldn't be surprised if you do).

Needless to say, I don't think physics gives us a metaphysics, and I don't think metaphysical problems have a priority over epistemological ones.

This is why...

[jd]

...strong AI cannot come from the processing of real data. That is not how minds work. Minds exist in a self-contained virtual reality that are periodically updated with real-world sensory data. This is why autism can impact the flow of that data and its connectedness without impacting the underlying mind. They're simply not associated in that way.