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Perception of animation-- sidebar to lecture notes, April 10, 2000 -- |
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Visual change over time, i.e., animation, is something that our perception system is well tuned to. Some basic facts about the perception of animation are presented and illustrated below. |
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Expressive |
Animation is generally good for expressing things like causal relationships and structural transformations.
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Click in the scene above to start. Slightly surprising, perhaps, that the target ball turned into two balls. Did it clone or were there two of them in the same place? Note that there is no question about what happened: the left ball hit (one or two) balls on the right, causing them to move. But in reality, there are no balls, no collisions, no causing. The right balls move because I have scripted them to start moving in frame 25. They would move even if I took the left ball out of the movie. The point is that we interpret animation much like we look at motion in the real world, where objects are solid and gravity works.
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Click in the scene above to start. The transformation from one structure to another is a perfect theme for animation. In this simple example, it is a dead movie, but it could just as well be combined with interactive features to create a more malleable material. At what point does the new structure emerge in your eyes? |
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Easy to perceive |
Our skills in perceiving and interpreting motion are significant, in particular when it comes to motion that has biological origin.
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Click in the scene above to start. Click and hold to stop temporarily. Notice how little synchronized motion is necessary to make some of the balls stand out. Stop the motion and notice how they disappear among the rest again.
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Click in the scene above to start. Could any of you see what the picture was before starting the animation? Could any of you not see what it was after animation? Our perception system is remarkably good at interpreting motion with biological origin, even when the data is scarce.
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Click in the scene above to start. What happened in this little movie? Now, what words did you use to talk (or think) about what happened? Words reflecting human intentions, goals, emotions? Nothing strange about that; we understand much of the animate world in our own terms. |
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Requires perceptual continuity |
Perception of animation requires perceptual continuity, which means that the user/viewer can maintain some sort of relation between what just happened and what happens right now. Typical recommendations to ensure perceptual continuity include: The above list is from Wickens, and strikes me as a little too strict. Representations need not be consequent, as long as they make sense and contribute to the story over time. It is not always necessary to provide overview maps; sometimes it is pleasant to let the big picture emerge gradually. We should not rule out the magical possibilities of animation in interaction design. Let us make sure that the magic has perceptual continuity in the same way stage magic has. A skilled illusionist performs physically impossible feats in perfect perceptual continuity. A bit like the possible roles of a computer in a well-designed information environment.
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