email - February 2015
by Do-While Jones

Birdís Eye View

Mick questioned our statements about depth perception in birds.

In last monthís special issue devoted to the Avian Phylogenetics Project, we talked about the classification of falcons, and whether they should be classified with hawks or parrots.† As part of that discussion we said:

Hawks have eyes set close together, giving them binocular vision, which gives them depth perception. They need depth perception because they are birds of prey, which swoop down on poor defenseless animals and eat them.

Parrots have eyes on the sides of their head, giving them great peripheral vision (so they can see predators coming), but no depth perception.

Mick took issue with that statement.

Hello David

Falcons, buzzards, golden eagles and maybe other raptors have eyes on the sides of their heads.†These eyes are nearer the front of the head than parrots' eyes are. I stood within yards of a wild falcon that was on a dead pheasant. The falcon turned its head to one side, I believe to look at me. I'd say that such a bird has a compromise between both worlds, some depth perception coming where the eyes have a slight overlap.

I haven't tested this, so I won't say I must be right. Neither do I think that golden eagles are more like parrots than owls.


As soon as I read that, I realized that I had fallen into the same trap evolutionists do.† I believed†parrots donít have depth perception†just because my teachers said so, and I didnít question it.† I was taught in school that predators evolved close-set eyes to help them hunt. Their prey evolved widely separated eyes as a defense in the so-called ďevolutionary arms race.Ē

Mickís belief is based on actual observation.

Setting aside the question of whether eye placement evolved accidentally, or was the result of an intentional design, we need to address the question of whether or not our statements about depth perception and peripheral vision are true or not.

Fact Checking

Clearly, parrots must have depth perception.† If they didnít they would not be able to land on a perch.† I have personally seen parrots land on a perch (at trained bird shows), so I know it is true.† It isnít just something my teacher told me a long time ago.† So, our statement last month about parrots not having depth perception is certainly wrong.

To verify eye placement, I turned to my trusty old Field Guide to the Birds of North America (Second Edition 1987). In all of the pictures of owls in that book you can see both of their eyes because the owls are pictured looking right at you.† All the sparrows and finches and doves, et cetera, are shown in profile. The hawks, eagles, and kites, are shown in partial profile.† Their eyes are on the side of its head; but their eyes are closer to its beak, and their eyes do seem to be facing at least partially forward. There appears to be a small region directly in front that is in the fields of view of both eyes.

The Field Guide (published by those militant evolutionists, the National Geographic Society) includes falcons in the same section with hawks, confirming the fact that falcons used to be believed by evolutionists to be very similar to hawks.

Since parrots are primarily South American birds, one might not expect to find any pictures of them in the Field Guide to the Birds of North America; but there were some!† On page 230 the Field Guide said, ďMost of the many parakeets and parrots seen in the wild in North America are escaped cage birds.† We show here the species that have established small populations or are seen as vagrants from Mexico.Ē† (Hereís a news flash for the National Geographic Societyógeographically, Mexico is in North America.† Birds native to Mexico are legal residentsónot vagrants! )† The pictures showed that the budgerigar (the common parakeet) does, in fact, have eyes on the sides of its head.

Depth Perception

Letís ignore what my evolutionary teachers told me about depth perception, and consider what I actually know about depth perception.

My parents had parakeets when I was a child.† Sometimes our birds got out of their cage and flew around inside the house.† I donít remember them ever accidentally crashing into lamps or walls with patterned wall paper; but they did sometimes crash into the picture window or uniformly colored walls.† Crashing into a window is easily explained because glass is basically invisible.

Why could our parakeets apparently not see uniformly colored painted walls; but could see wall papered walls?† I believe it is because there are two ways to perceive depth, neither of which works very well on solid colors.

You are probably familiar with binocular depth perception because thatís how the View-Master stereoscopic viewer 1 works.† Your two eyes are individually shown images of one scene taken from two different angles.† Objects in the distant background are at the same angle from each eye.† Objects in the near foreground are at different angles.† Your brain computes distance based on the difference in angles.† At some point in your life you must have held a finger six inches in front of your face and watched it apparently bounce back and forth as you closed one eye or the other, so you must be familiar with the effect.

A few years ago ďrandom dot stereogramsĒ like this one were a popular fad. 2

Random dot stereogramswere usually published in books, or on calendars.† If you could force your eyes to look past the picture, suddenly a 3-D image would appear.† (Some people found it easy to do.† Other people never could do it.)† It worked because it fooled your brain into perceiving the dots as being at different distances.

If you stare at it the right way, you will see this:

This first type of depth perception, binocular (that is, stereoscopic) depth perception, depends upon two views of the same scene taken from different locations at the same time.† It requires two optical sensors.

There is a second type of depth perception which requires only one optical sensor. It is used in synthetic aperture radars. 3 Parakeets might use this technique for determining the distance to objects.

Hereís the difference between the stereoscopic depth perception used by a View-Master and depth perception in a synthetic aperture radar.† The View-Master uses two cameras in different locations taking a picture of the same scene at the same time.† The synthetic aperture radar uses one sensor to create a picture of a scene, then moves to a different location and creates a second picture of the same scene a short time later.

In both methods, two pictures of the same scene are taken.† The difference is that, in the first method, both pictures are taken at the same time by two cameras in different places.† In the second method, both pictures are taken by the same camera at different times from different places.

Both methods depend upon differences in images.† Two pictures of a uniformly colored wall taken from two different locations (either at the same time, or sequentially) will be identical.† Thatís why our parakeets couldnít tell how far they were from a wall (unless the wall had patterned wallpaper on it).

Evolutionary Implications

So, what does all this have to do with evolution?† Well, an owl clearly uses binocular (stereoscopic) vision because it has two eyes on the front of its flat face, giving it two simultaneous images of what is in front of it.† The owlís brain must have an image-processing algorithm (similar to humansí) that correlates simultaneous images to determine differences in angles, and then computes distance based on angular differences.† Owls (and people) can determine distance while sitting still.

A parakeet can only see a scene with one eye at a time.† Therefore, it has to move to a second location to see the scene with that same eye.† Then, it has to correlate the two images to determine the difference in angles and compute the distance.† But, unlike the owl, in order to do this, the parakeet has to know how far it moved between images.† That means the parakeet has to know how fast it was moving, and how much time elapsed between images.† It must also remember the first image in order to make the comparison.

As an engineer who formerly designed self-guided weapons and proximity fuzes, I am impressed by the image processing in an owlís brain, and even more impressed by the image processing in a parakeetís brain. If eagles and hawks have slightly overlapping fields of view, and use a combination of both methods of depth perception, thatís really amazing!

Learn For Yourself

Hereís an idea for a science fair project to learn about depth perception. It compares stereoscopic depth perception with synthetic aperture depth perception.

In a garage, gymnasium, or other large space, build a three-sided box with a lattice top similar to the one shown in the sketch below using four large plywood boards and whatever external bracing you need to make it stand up safely.

Objects hung from a 4x8 lattice supported by four 4x8 plywood sheets.

For the roof you can use commercially available lattice like the one in the sketch, or just several thin parallel boards, from which you can hang things. (Use invisible fishing line, so the subject cannot tell how far back they are hung by following the string up to the lattice. Be sure the subject canít cheat by looking at shadows on the floor, either.) Paint the two back plywood panels a solid color. When the paint dries, put vertical strips of contrasting colored tape a few inches apart on the two background panels.

Hang four different objects at different distances from the back panel and ask the test subjects to tell you which one is the closest, second closest, third closest, and farthest away. (Donít use identical objects because the closest one will appear to be the largest and spoil the test.) Have the subjects do this at several distances from five feet to very far away. Repeat the process with several people to determine how close the average person has to be to judge the distances correctly. (If you want to be sneaky, make one of the objects a ping pong ball painted like a baseball, to see if the presumed size affects the perceived depth.) The purpose of this test is to see how far away people can accurately determine differences in distance using normal binocular vision. The remaining tests should all be done at this distance.

Do a second series of tests with subjects who have one eye covered. Since they have no stereoscopic depth perception they will sometimes guess correctly, and sometimes not. This is the second control test to measure the average error rate at the distance determined by the first test.

As soon as the subjects have finished the second test, let the subjects move laterally left and right. Allow them to change their answers to see if they can more accurately judge distance using the synthetic aperture method.

In the fourth test, remove all the colored tape and repeat the third test to see if it makes a difference if the back wall is a solid color or has vertical strips on it.

Can people learn to judge distance using just one eye by moving laterally? If so, do they require a patterned background?

Most importantly, will you get a better grade with this project than the kids who just make a baking soda volcano?

Seriously, science is fun! Unfortunately the joy of learning things through experimentation has been replaced by unquestioned acceptance of whatever the teacher says. We hope this science fair project will encourage students to discover the joy of learning things for themselves.

The theory of evolution isnít just unscientificóit is anti-science. Evolutionists encourage students to ignore actual observation and common sense if those observations conflict with the philosophy of someone in authority. If they say hummingbirds evolved from dinosaurs, and dragonflies are closely related to lobsters, they expect you to believe it without question.

Yes, the chemical composition of the DNA molecule was determined scientifically. Real science was used to determine the function of particular genes. But the conclusions about how and why those genes came into existence are not scientific. Those conclusions are nothing more than speculations that change from time to time because they arenít absolute truth.

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2 Magic Eye: A New Way of Looking at the World: 8601200393996: N.E.Thing Enterprises: Books