Laboratory for Motion Perception

Because these demonstrations of motion involve the computer monitor, you should realize that they all involve illusory motion. That is, unlike the motion of real objects in the world, these demonstrations involve little lights being turned off and on in a systematic fashion. :-) How different, then, are these motion "illusions" from real motion?

1. Biological Motion

Johansson is the person who did most of the early work on biological motion. Note how little information is needed in Mather's demonstration (click on Biological Motion on the left) for you to determine the nature of the motion. And note how the nature of the "object" is almost impossible to determine when the dots are not in motion. Now play with the sliders on the Bio Motion Lab walker to see if the changes to the point-light display yield the expected differences in the perception of the walker.

2. Apparent Motion (Phi Phenomenon)

First, examine a few different demonstrations of phi movement: Phi1, Phi2, and Phi3. The last demonstration should strike you as quite interesting. What path did the dot seem to take? Next, note that not all durations are optimal for phi movement (No Phi).

Given your experiences, play with an adjustable display to try to create the smoothest phi movement that you can. What seemed to be the critical factors to producing good phi movement?

3.Context Effects in Motion Perception

The Barber Pole Effect is quite interesting. You can experience the illusion at a couple of sites. Try out the Trieste version of the Barber Pole Effect (and the IllusionWorks version). On your worksheet describe the experience of the illusion and then provide a brief account of the source of the illusion. How do the various apertures affect your experience?

Next, check out the Chopstick Illusion. Do you think that the effect is produced by the same factors that produce the Barber Pole effect? Why?

Apertures and motion can produce some wacky effects. Check out the Sliding Effect. How might this effect be related to these other effects? Do you think you would get the sliding effect with all aperture shapes?

Note that the receptive field creates its own aperture problem, which can make veridical motion perception difficult. (And, yes, the lines on the left figure are moving left to right!)

Another example of context effects in motion perception is the Bluebottle Fly Illusion (Anstis).

4. Implicit Figure Motion

Mather has done research on the motion of illusory contour figures, which he calls implicit figures. You can view a demonstration of this effect (choose Implicit Figure Motion from the left list). Does the motion appear to be clockwise or counterclockwise? Look carefully at the stimulus and you'll see that it is ambiguous regarding the direction of motion. Why do you think that you perceive the direction of motion that you do? Can you see the reason that this display is problematic for theories of motion perception? There's nothing really moving! :-)

Do you think that this perceptual experience is related at all to the breathing square? Why or why not? How are the effects similar?

5. Ambiguous Motion

For the three demonstrations below (from Ramachandran & Anstis), record your experience of motion and discuss the implications of your experience.

For the spinning figure or the rotating wheel, do you see the direction of rotation change as you watch the figure?

6. Motion Aftereffects

As you saw demonstrated in class, you can perceive motion when no motion is occurring as an adaptation to motion in a particular direction. Take a look at the complex motion aftereffects you get when there are multiple types of motion present in the display. Then look at an object (e.g., your palm) to see the aftereffects of the motion. Can you see how the notion of opponent processes is present in this demonstration as it is in the negative color afterimages?

7. Illusory Motion from Stationary Figures
a. First, look at some of the art of Kitaoka, who is a psychologist and an artist. His Rotating Snakes (on the first page) is an excellent example of illusory motion from a static figure. What might cause the apparent motion?

b. The Pinna-Brelstaff Illusion is another illustration of motion in a stationary figure, but it requires that you move closer to and farther from the screen. Thus, there is some motion involved!

8. Wheel Motion

Suppose that you placed a light at the center of a wheel and one somewhere on the rim. Could you tell that you were looking at a moving wheel? Check out the demonstration. (I know, black and white are reversed from the way I described the situation, but you get the idea.) OK, now suppose that you turned off the light at the center of the wheel. Wouldn't you think that you could still tell it was a wheel in motion? Hmmm. Then check out this demonstration. What's going on here? You can play with various factors that affect your perception of this cyclical motion.

9. Color and Motion Together

a. Color Spread and Motion. We saw examples of color spreading earlier in the lab. Now, let's look at color spreading and motion together. Is that neat or what? You're now seeing a moving colored object when there is no real motion, nor is there a colored object. What factors seem to have an impact on this effect? To explore some possibilities, use the adjustable demonstration.

b. Disappearing Dots. Try this demonstration. Do the yellow dots disappear quickly? Why do you think you experience this effect?

c. Out of step? Try this demonstration. When the background is absent (no context), you have one perception. When the background is present (context), you have a different perception. Why do you think you experience this effect? Can you relate it to context effects in shape perception?

d. Moving negative color afterimage? Can you come up with an explanation for this demonstration (from Jeremy Hinton)? (And, no, there is not a green dot moving along!)