Chapter 8 Overview
Motion Perception
Examine the image at left carefully. What do you see? Most likely, a jumble of randomly oriented lines. Now click and drag your mouse anywhere in the image. A clearly visible airplane should emerge as soon as you start dragging.
What makes the airplane stand out while you are moving it? It is not because the plane is visible in some positions and invisible in others—if you release the mouse, look away for a moment, and then look back, you will most likely find that the plane has melted right back into the jumble of lines again. Therefore, it is the movement of the lines making up the plane that sets them apart from the background. Click here to toggle between three different hidden objects, and see if you can recognize any of them without moving them around first.
Technically, motion is a change in the position of an image over time. As you will learn in this chapter, the human visual system devotes a great deal of resources to motion processing since it is so fundamental to perception. In the activity on Types of Motion you will see that there are a number of distinctly different physical stimuli that we perceive more or less equivalently as objects in motion (see also the essay on Beyond Second-Order Motion). The Motion Detection Circuit activity shows one simple hypothesis about how the visual system processes motion, and the activity on Motion Correspondence illustrates an important problem solved by the visual system—detecting the true direction of moving objects.
The last two activities cover Motion Aftereffects, an interesting illusion that is used extensively by motion researchers, and the important distinction between movements across your retina caused by object motion versus movements across your retina caused by Eye Movements.
Finally, the other essay in this chapter points you to a website with incredible pictures in which you somehow end up Perceiving Motion in Static Images.
Once you have read the chapter in the textbook and done the activities here, use the study aids (Study Questions, Flashcards, and Chapter Summary) to review.