1. How Far Away Is It? Depth Perception

2. Depth Perception
The ability to see objects in three dimensions although the images that strike the retina are two-dimensional, allows us to judge distance
How do we see a 3-D world using only the 2-D retinal images?
We are able to see in 3-D because the visual system can utilize depth cues that appear in the retinal images

3. Gibson & Walk’s Visual Cliff
A laboratory device for testing depth perception in infants and young animals
Infants that have been crawling for about a month are reluctant to crawl past the “edge” of the visual cliff
Other animals had similar results.
Suggests that depth perception, to some extend, is inborn but needs experience of crawling

4. Click on link above to view the visual cliff experiment

5. Depth Perception: Monocular Depth Cues

6. Monocular Cues Depth cues that require the use of only one eye
Monocular depth cues include:
relative size
relative motion
interposition
relative height
texture gradient
relative clarity
linear perspective.

7. Monocular Depth Cues – Relative Size
Using the perceived size of a familiar object to determine depth
The larger the object appears, the closer the object is to the viewer
The smaller the object appears, the farther away it is to the viewer.

8. Monocular Depth Cues – Relative Motion (Motional Parallax)
A person who is moving can determine depth by focusing on a distant object.
As we move, objects that are actually stable may appear to move
Objects further away than the object of focus will appear to move slowly in the same direction as the subject is moving.
Objects closer than the object of focus will appear to move quickly in the opposite direction.

9. Relative Motion
In this example, the passenger is moving past a stable world. If she fixes her gaze on the bridge, objects behind it will appear to move forward. The farther away the object is, the more slowly it will appear to move. Objects in front of the fixation point appear to move backward.

10. Monocular Depth Cues – Interposition
Method of determining depth by noting that closer objects partially obstruct/block the more distant objects
Also called “overlap”

11. Monocular Depth Cues – Relative Height
Method of determining depth by noting that distant objects appear higher in your field of vision than do closer objects
This reversed above the horizon where higher objects seem closer.
You know that the trees and houses are farther away than the lake because they are higher up in the drawing than the lake is.

12. Monocular Depth Cues – Texture Gradient
Method of determining depth by noting that distant objects have a smoother texture than nearby objects
Individual flowers are visible in the foreground, but in the distance they look like a smooth carpet.

13. Monocular Depth Cues – Relative Clarity (Aerial Perspective)
Method of determining depth by noting that distant objects are less clear than nearby objects
Tends to work outdoors because light from distant objects passes through more atmosphere, we perceive hazy objects as farther away than sharp, clear objects
The distant mountains look blue & hazy because of dust & moisture in the atmosphere.

14. Monocular Depth Cues– Linear Perspective
Method of determining depth by noting that parallel lines appear to converge in the distance
The lines appears to eventually merge on the horizon.
The sides of the road seem to converge in the distance.

15. Monocular Depth Cues– Light and Shadow
Nearby objects reflect more light into our eyes.
Given two identical objects, the dimmer one seems farther away.
Brain assumes that light comes from above.
Watch as the picture flips upside down.

16. Can you apply these principles to a painting?
On a piece of paper explain the following:
Relative Size
Interposition
Relative Height
Texture Gradient
Relative Clarity/Aerial Perspective
Linear Perspective
Light & Shadow

17. Explain how those terms are being used in this picture.

18. Accomodation
Accommodation is also used by the brain to estimate distance.
Brain takes into account how the muscles in your eye affect your lens - thickens (for nearby objects) or flattens (for far away objects).
However, we rely on pictorial cues more than this.

19. Depth Perception: Binocular Depth Cues

20. Binocular Cues Depth cues that require the use of both eyes
There are two types: Retinal Disparity & Convergence

21. Retinal Disparity
A binocular depth cue resulting from slightly different images produced by the separation of the retinas in the left and right eye
Because our eyes are about 2 ½ inches apart, the retina receives slightly different images of the world.
The greater the difference between the two images, the closer the object is to the viewer.
The more alike the two images, the further away the object is perceived.
Is most effective when the item is quite close to the person
Example: hold a pencil just in front of your nose and close one eye, then the other. The pencil should move showing the disparity. Now focus on something far away and do the same. What happens?

22. Some People’s Eyes are Further Apart than 2 ½ inches

23. Binocular Depth Cues: Finger Sausage
Hold your two index fingers about 5 inches in front of your eyes, with their tips half an inch apart. Now look beyond them and note the weird result. Move your fingers out farther and the retinal disparity—and the finger sausage—will shrink.

24. Autostereogram
Another way to create the illusion of depth through binocular stereopsis is with an Autostereogram
An autostereogram is formed by superimposing two repeating patterns
The two patterns are slightly offset, and when viewed properly, this offset is seen as a binocular disparity

25. Autostereogram
To see the 3-D image, first view the picture closely. Focus your eyes as if you are looking at some far off distant object (look through the picture). Try relaxing your eyes so they swing outward. Without changing your focus, slowly move away from the picture. The image will begin to to come into focus. Do you see a Face? If you have trouble, it just means your eyes are difficult to trick, they want to focus at the proper depth!
Hockenbury powerpoint (Schulman)
This image should be viewed by crossing the eyes until the two target circles at the top are seen as three. What you will see is a checkerboard pattern.

26. Convergence
A binocular depth cue related to the tension in the eye muscles when the eyes track inward to focus on objects close to the viewer
The brain notes the angle of the convergence and then computes the distance of what you are focusing at.
The more tension in the eye muscle, the closer the object is
Works best at close distances

27. Depth Illusions
Sometimes our perception of depth can be tricked.

28. Julian Beever’s Sidewalk Chalk Art
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29. Julian Beever’s Sidewalk Chalk Art
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