Flow fields PSY 310 Greg Francis. Lecture 25. Perception

Transcription

1 Flow fields PSY 310 Greg Francis Lecture 25 Structure you never knew was there. Perception We have mostly talked about perception as an observer who acquires information about an environment Object properties Distance Size Color Shape Motion 1

2 Action But most of the time a person does not just passively observe the world Instead a person is actively involved with the world Moving to objects Moving away from objects Getting more information about objects The perceptual process Perception Processing Recognition Action Transduction Stimulus on receptors Attended stimulus Environmental stimulus 2

3 Perception and action To fully understand how perception works, we have to understand how our actions change our perception and provide information about the world Our actions provide a wealth of information about the world that is not available to a passive observer It s complicated But we ve seen some similar issues before Motion parallax Self-motion As you move through the world, the image on your retina changes in a systematic way In principle there is information in the changes that is not present in any snapshot of a scene Not just motion in the environment, but motion of images due to your movement Flow fields 3

4 Often called optic flow fields Flow fields The pattern of motion generated by elements in the world due to movement of the observer Flow field movie Flow fields We are usually interested in the pattern of motion, not the elements themselves Use arrows to indicate direction of motion Size of arrows indicate the speed of motion 4

5 Flow fields We are usually interested in the pattern of motion, not the elements themselves Mark a position with a dot and draw a line to indicate the path the dot would take Length indicates speed Flow fields You get different flow field patterns depending on your motion Moving straight ahead 5

6 Flow fields You get different flow field patterns depending on your motion Turning to the left Flow field Forward motion in a scene like this 6

7 Flow field Would produce a flow field like this Flow field Notice that the motion flow all radiates from the point to which you are moving Focus Of Expansion (FOE) 7

8 Flow field The pattern of the flow field depends on where you look Flow field The pattern of the flow field depends on where you look 8

9 Flow field The pattern of the flow field depends on where you look Using the flow field Looking out the back of a train 9

10 Using the flow field An airplane flying over an airfield Using the flow field Differences between flying over and coming in for a landing Focus of expansion is in different places Flying over Landing 10

11 Using flow fields Consider the flow fields generated by an insect flying Moving forward Hover and rotate Using flow fields Flow fields can easily help guide action Suppose you want to hover in place Same thing as to get rid of the flow field 11

12 Avoiding obstacles Here the flow field indicates that the insect will hit the rock unless it turns Controlling movement Flow field on the left indicates the insect is close to the rock Can turn to avoid risking a collision 12

13 Controlling movement Likewise, the flow field can be used to monitor speed of movement Might want to slow down in a cluttered environment Just keep the flow field constant Conclusions Flow fields contain lots of information Can be applied relatively simply to control movement and identify properties of the world What we haven t discussed is the measuring the flow field is rather a difficult thing to do People (and other animals) do use flow fields, but we also use other aspects of perception to guide behavior Action and perception are closely linked 13

14 Next time More connections between action and perception Action influences perception Perception influences action 14