PSY 310: Sensory and Perceptual Processes 1

Transcription

1 Prof. Greg Francis PSY 310 Greg Francis Perception We have mostly talked about perception as an observer who acquires information about an environment Object properties Distance Size Color Shape Motion Lecture 25 Structure you never knew was there. The perceptual process Action Perception 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 Recognition Processing Action Transduction Environmental stimulus Stimulus on receptors 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 Attended stimulus 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 But we ve seen some similar issues before Motion parallax 1

2 Prof. Greg Francis Often called optic flow fields The pattern of motion generated by elements in the world due to movement of the observer 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 movie We are usually interested in the pattern of motion, not the elements themselves You get different flow field patterns depending on your motion Moving straight ahead Mark a position with a dot and draw a line to indicate the path the dot would take Length indicates speed You get different flow field patterns depending on your motion Turning to the left Forward motion in a scene like this 2

3 Would produce a flow field like this Notice that the motion flow all radiates from the point to which you are moving Focus Of Expansion (FOE) Looking out the back of a train 3

4 An airplane flying over an airfield Differences between flying over and coming in for a landing Focus of expansion is in different places Flying over Landing Using flow fields Using flow fields Consider the flow fields generated by an insect flying can easily help guide action Suppose you want to hover in place Same thing as to get rid of the flow field Moving forward Hover and rotate Avoiding obstacles Controlling movement Here the flow field indicates that the insect will hit on the left indicates the insect is close to the rock unless it turns the rock Can turn to avoid risking a collision 4

5 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 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 Next time More connections between action and perception Action influences perception Perception influences action 5