Monday, August 17, 2020

Sending fire from our eyes

We take it for granted that we see by means of light entering our eyes. The chain of effects begins when a source emanates light energy, which interacts with the surfaces of objects and then travels in all directions, some of it finally entering our eyes and activating our retinal receptors. The signals travel on to our brain, which decodes the information coming from those energized receptors. 

The replicants in Blade Runner seemed to have light emanating from their eyes.
The effect was created with a light shining on a half-silvered mirror set at
45 degrees to the axis of the camera.

People haven't always imagined that vision works that way. Greek writers proposed that we see by means of a kind of fire that is emitted from the eyes toward the object. That idea, known as "emission theory" was bolstered by the reflective retinas of cats and other mammals at night. Other Greek writers doubted that notion. How could we see faraway stars at night? Could it be instead that all objects constantly emit a stream of particles? 

It took centuries to arrive at our modern concept of the eye as a organ receptive to bouncing beams of light. But the story doesn't end there, because vision turns out to be much more active and top-down than we thought. 

The eye is much more than a passive camera. A poet might say that a kind of fire comes from our mind and it meets the light at the front door of our eyes. The stream of data coming from our receptors is really very limited and fragmentary, and our minds have a very active role in fleshing out that trickle of information.

In the 1800s, German physicist Hermann von Helmholtz proposed the idea of "unconscious inference." The idea is that we receive incomplete information and the brain makes unconscious assumptions from this partial data based on previous experience.

As brain scientist Robin Carhart-Harris puts it: "We house internal models constructed by the brain rather than perceiving huge volumes of unfiltered raw information. "So much of our experience of the world is the product of our brain's internal predictive models rather than some kind of receptivity of information coming in." 
Wikipedia on Emissions Theory


Danstovallart said...

I remember reading about these modules and I believe that the human face and outline of the figure are 2 of the most powerful and common modules we have. It accounts for the common pareidolia of seeing faces in many inanimate objects.

Susan Krzywicki said...

Does this also mean that, when confronted with something completely outside our ken, we simply do not recognize it?

How would we start to make sense of something so foreign that we had no model for it?

James Gurney said...

Dan, yes, we even have specialized centers of the brain such as the fusiform gyrus which come into play when we see actual (or imaginary) faces. That's why any face in a picture occupies a region of higher-level interest.

Susan, that's a fascinating point. And I think it's especially true when we're engaged in a task that focuses our perception, such as when we're driving. We only see what we're looking for, and we're blind to something that doesn't fit our expectations. That's why when car drivers hit pedestrians or motorcyclists they say "I didn't see him at all!"

Noo said...

I wish there was a like button, especially for posts like this ;)