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Motion Perception

Demonstrations (Direct Links)

Demonstration 8.1 Motion Detection in the Periphery of the Retina
Demonstration 8.2 Biological Motion
Demonstration 8.3 Perceiving Stroboscopic Motion
Demonstration 8.4 Movement Aftereffects


Before You Start

• For most of the earlier chapters, one might presume a person perceiving a stationary object. Of course, movement is the norm--whether it's the movement of objects around us or our own movement. Thus, in this final vision chapter we examine motion perception to provide a more realistic sense of visual perception.

• As we found in considering other visual phenomena, naive and simplistic explanations abound--but they don't hold water. As we consider various theories of motion perception, the complexities become apparent. For example, how do we perceive an object's motion when we, ourselves, are in motion?

• There are a number of special topics in motion perception that should interest you, including the perception of biological motion. And, as was true for other areas of visual perception, you will be able to explore a number of different illusions of motion. As always, these illusions will help us to understand the perception of real motion.

 


Visual Perception of Real Movement

Detecting Motion

Demonstration 8.1 Motion Detection in the Periphery of the Retina (You can conduct this demonstration on your own, though it may be more effective if you have a friend produce the motion.) Stare at a point directly ahead of you. Hold the forefinger of your right hand directly in front of your eyes. Move it slowly toward your right, keeping the height at eye level, until you can no longer see it. Keep the finger stationary and make sure that you cannot see it at its current location. Then wiggle your finger rapidly. You should be able to see the finger once it is moving. Another approach is to place an object between a lamp and a plain wall, so that it generates a large, faint shadow on the wall. If you look away from the wall, so that the shadow is in your periphery, the shadow will eventually disappear from view. However, if you now move the object, causing the shadow to move, the shadow will again become visible.

Link - Perceiving motion in random dot cinematograms (USD Internet Psychology Laboratory)

Movement of the Observer

Perceiving Biological Motion

Demonstration 8.2 Biological Motion Biological motion is typically studied using point-light displays. Try the links below to experience biological motion for yourself. The Biomotion Lab demonstration allows you to manipulate many aspects of the point-light display, so you may want to try that one first.

Link - Biomotion Lab has provided a nice demonstration of biological motion, with parameters you can vary.
Link - Randolph Blake (Vanderbilt University) provides demonstrations of biological motion from his research.
Link - Bennett Bertenthal (U Chicago, now Dean at Indiana University) has a page with demonstrations and useful information on biological motion.
Link - Thomas Shipley (Temple University) has illustrations of many different point-light displays.


Illusory Movement

Stroboscopic Movement

• Stroboscopic motion arises due to the presentation of a series of still images at a sufficiently rapid rate. If the rate is too fast, no motion is apparent--the two images both appear to be present all the time. If the rate is too slow, no motion is apparent. Instead, the two images simply appear to alternate being present--first one and then the other. Oh, but when the rate is just right, magic happens! In fact, that's the magic of motion pictures.

Demonstration 8.3 Perceiving Stroboscopic Motion Ramachandran and Anstis reported on a number of motion illusions. How would you describe the motion in the three demonstrations below?

1. What appears to happen to the square and the triangle below? Does the triangle appear to move in a particular direction? What about the square?



 

2. What appears to happen to the two dots on the left? How does the top dot appear to move? How does the bottom dot appear to move?


 

3. Notice how the addition of a small change in the display alters the apparent movement of the two dots.


 

Perceiving Motion in Stationary Stimuli

• Autokinesis

• Induced Movement

Link - An example of induced movement.

• Self-Motion Illusion

• Perceiving Motion in a Stationary Image When You Move

• You can experience illusory movement when you move in front of the stationary art of Patrick Hughes and Dick Termes.

• Baingio Pinna and Gavin Brelstaff (2000) produced images that lead to a perception of illusory motion when you move your head toward and away from the screen.

pinnabrelstaff

• Movement Aftereffects

Demonstration 8.4 Movement Aftereffects A stationary object will appear to move after you've looked at a pattern of continuous motion for a period of time. A number of web sites provide demonstrations of a movement aftereffect:

Link - I've linked to Michael Bach's (Freiburg) site often on these pages. It's a wonderful resource. In this case, he's provided a great example of a movement aftereffect.
Link - Mark Newbold has a demonstration of rotating spirals (actually counter-rotating spirals), which allows you to demonstrate motion aftereffects.
Link - Here's another site that provides moving stimuli that will induce movement aftereffects.

• Stationary Images that Appear to Move

Link - Akiyoshi Kitaoka is a professor of psychology who produces stationary stimuli that give the illusion of motion.

Misperceiving Motion Due to Context

• Stuart Anstis (University of California San Diego) has developed a number of demonstrations that illustrate ways in which context can lead one to misperceive motion. One such illusion is the Flying Bluebottle Illusion
Link - Anstis & Casco (2006) Induced movement: The flying bluebottle illusion. Journal of Vision, 6, 1087-1092.
Link - You'll find a funny variant of the Flying Bluebottle illusion, as well as other relevant demonstrations (e.g., Footsteps, Chopsticks) at Anstis's demonstration page• Here's an example of illusory movement...even though it does involve some real motion.

 

Theoretical Explanations for Motion Perception

Corollary Discharge Theory

Direct Perception Approach

Computational Approach


Physiological Basis of Motion Perception

Processing Motion Information Before V1

Processing Motion Information in V1 and Beyond

Link - Melissa Saenz (California Institute of Technology) has a video of brain activity (fMRI) while viewing motion.

Processing Self-Motion Information

 


Test Yourself

1. William Shakespeare wrote, “Things in motion sooner catch the eye than what stirs not.” How is this comment relevant to your visual system? Compare your peripheral vision and vision in your fovea with respect to motion detection.


2. Imagine that an industrial employee has been instructed to report whether a dial on a piece of equipment moves the slightest amount. Describe how uncertainty and the background behind the dial might be important, and mention why apparent movement might be a problem.


3. Summarize the studies on biological motion discussed in the In-Depth section. What kinds of information about motion can we pick up readily, without seeing an entire organism? Obviously, we most often see a complete organism. Why, then, is research on biological motion so important for theories of perception?


4. Suppose you are playing softball and you are up at bat. How would Gibson’s theory explain your perception of motion as the ball is being pitched toward you? Suppose you are pitching and you quickly move your head to determine whether the person on second base is trying to steal third. How might corollary discharge theory account for the stability, despite the motion of images across your retina?


5. Name the kind of apparent movement represented in each of the following situations.
      a. On a dark night, you see a single small light in a neighbor’s house, and you know that the neighbor is on vacation. The light appears to move, and you suspect a burglar.
      b. You’re surfing the web and come across a site at which a set of “lights” appear to go off and on in succession, so that the “light” appears to move across your monitor.
      c. In a planetarium, the star show ends with the stars whirling swiftly about in a clockwise direction for several minutes. Out in the darkened lobby a few seconds later, the room around you seems to be whirling in the opposite direction.
      d. On a dark night, you watch a plane fly over a radio tower. For a brief moment the plane seems to be stationary and the tower light seems to move.


6. Compare the perception of real movement with illusory movement—particularly stroboscopic movement. To answer this question, think about the movement seen on a movie screen as compared to movement in the real world. Why might you think that the same movement perception system gives rise to the perception of both types of movement?


7. We tend to think of some brain areas as specialized for one particular sense (e.g., the visual cortex) or a particular perceptual experience (e.g., motion). Of course, given what we know about brain plasticity, the situation is rarely that clear. That said, there are certainly areas of the brain whose role seems to be to integrate information from various senses (e.g., the superior colliculus and the superior temporal sulcus). Why might some brain areas be more focused and other brain areas be more integrative? [Hint: It may help to contrast the benefits of specialization with the need to perceive the world in a unitary fashion.]


8. Think of a situation involving complex movement perception, such as playing tennis. Players are moving as they track a moving opponent and the ball being returned to them over a stationary net. How would each of the theoretical approaches to movement perception deal with this situation? Which approach do you find best able to deal with the complexities of the situation, and why?


9. Many perceptual phenomena require explanations that are more complicated than you might have anticipated. For example, someone unfamiliar with the topic of motion perception might guess that we simply perceive motion whenever our retinas register a change in an object’s position. Why would that explanation be inadequate? What other explanations would you add?


10. In this chapter, we focused on motion perception and argued that it is a basic process. One argument that a person might make for the importance of motion perception is the extent to which it plays a role in other perceptual processes. Using information in previous chapters, show how motion plays a role in other perceptual processes such as shape and distance perception.


Teaching Materials

Thomson Higher Education has published two very useful CD-ROMs. John Baro (Polyhedron Learning Media) has developed Insight: A Media Lab in Experimental Psychology [see Form and Motion] and Colin Ryan (James Cook University) has developed Exploring Perception [see Module 2].

Link - Brian Rich has a brief page that discusses the various mechanical means of creating apparent motion (thaumatropes, flip books, phenakistoscopes, and zoetropes).

Lafayette Instruments The Illusionator is very effective for teaching about motion aftereffects. Most people use the rotating spiral by having students continuously view it and then stop the motion, producing the perception of motion in the opposite direction. As Jeremy Wolfe pointed out at one EPA conference, it might be even more effective for the instructor to stand facing the class just adjacent to the rotating spiral. If students look at your face after adapting to the rotating spiral, it will appear to explode or implode depending on the rotation of the spiral.

Link - Stephen Macknik article about flicker fusion.

Link - Michael Bach has created a site of visual illusions that contains many motion illusions.

Link - You will find a very extensive set of illusions, including motion illusions, at SandlotScience.

Link - Josh McDermott and Ted Adelson (MIT) have produced a very nice tutorial page regarding motion and form perception.

Link - V. S. Ramachandran (UC San Diego) has provided a number of illustrations of motion effects (e.g., apparent motion).

Link - Yoram Bonneh, Alexander Cooperman, and Dov Sagi (Weizmann Institute of Science) provide a number of different demonstrations involving motion induced blindness.

Link - Terry Bahill's (University of Arizona) site for baseball research discusses various types of motion (motion of ball, etc.).

Link - The Smith-Kettlewell Eye Research Institute maintains a research page that contains relevant links on motion perception.

Link - Rotating grid illusion (O'Reilly)


Recommended Readings

Berthoz, A. (2000). The brain’s sense of movement. Cambridge, MA: Harvard.

Blake, R., Sekuler, R., & Grossman, E. (2004). Motion processing in human visual cortex. In J. H. Kaas & C. E. Collins (Eds.), The primate visual system (pp. 311-344). Boca Raton, FL: CRC.

Bruce, V., Green, P. R., & Georgeson, M. A. (2003). Visual perception: Physiology, psychology and ecology (4th ed.). New York: Psychology Press.

Jansson, G., Bergström, S. S., & Epstein, W. (Eds.) (1994). Perceiving objects and events. Erlbaum.

Knoblich, G., Thornton, I. M., Grosjean, M., & Shiffrar, M. (Eds.) (2006). Human body perception from the inside out. New York: Oxford.