Perception and Action

118 Motion

Learning Objectives

Know the importance of motion in scene segmentation.

Be able to define the aperture problem and optic flow.

Know that visual area MT/MST are sensitive to motion coherence and MST is responsive to optic flow.

Scene segmentation is best put as breaking down the scene you are looking at to see the different parts of it. The importance motion has in scene segmentation includes motion parallax as a depth cue, motion for breaking camouflage, and motion for grabbing attention. Motion helps us pick out things in a scene that otherwise would blend in if it were still; similarly, someone sitting across a room full of people would probably blend in with everyone else in the room, but if they were the only ones waving at you, they would stand out.


Fig.12.1.1. Take a look at these cells. You’ll notice the ones that blink and move stand out in the crowd. (Credit: Jarod Davis. Provided by: University of Minnesota. License: CC-BY-4.0)

The aperture problem refers to when the direction of motion of straight lines is ambiguous because you can’t see the ends or corners; in other words if something (the aperture) is in the way of what we are viewing, it can distort the movement we are seeing by making it appear to be stagnant.


Fig. 12.1.2. Aperture Problem. Notice that if you watch the block through the larger square, it seems as though the block is not moving, since its lines go with the block’s direction of motion. But the smaller square shows obvious motion, as its lines do not follow the direction of the block’s motion. (Credit: Jarod Davis. Provided by: University of Minnesota. License: CC-BY 4.0)

Visual area MT responds to local motion which is closest to us. MST likes optic flow, which is motion that’s coordinated across the entire scene and has a heading, or a point of convergence much like a car driving towards the¬†horizon and looking increasingly smaller as it goes. Check out this cool site with moving examples of optic flow!


Cheryl Olman PSY 3031 Detailed Outline
Provided by: University of Minnesota
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License of original source: CC Attribution 4.0
Adapted by:  Megan Hulke



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Introduction to Sensation and Perception by Students of PSY 3031 and Edited by Dr. Cheryl Olman is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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