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Lecture

Chapter 8: Motion

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Department
Psychology
Course
Psychology 2115A/B
Professor
Christine Tsang
Semester
Winter

Description
Chapter 8 Review: Motion By the end of this section, you should know: - Functions of motion - Two approaches to motion perception - Motion coherence - Corollary discharge theory Motion  Perception is a creation o Our perception of motion is a creation of the nervous system o The fact that we can perceive motion in a static image tells you that it is created and not actually there  Depends on more than just sensation o Depends on more than just what is presented on the retina  Involves interactions between systems o Our own movement gives us clues about the movement of other objects  Perception involves top-down processes o When we think about motion, we are also looking at heuristics about how we think the world ought to work o We impose cognition on what is happening  Not just a simple calculation of how much an image is moving across the retina, it is an interaction of a lot of factors Function of Motion Perception  Understand the environment o Thinks are moving around us and we need to know what is going on around us to successfully navigate o Movement is a critical piece of the world and of understanding how the world works o Women who had a stroke that affected area MT and now has motion agnosia: difficulty in seeing moving objects o Her deficit tells us how important movement is to our everyday lives o Understanding optic flow: objects are moving relative to the observer (in the opposite direction)  Attract attention o Movement ruins camouflage  Information about objects o Our movement around the world tells us about the 3D nature of the objects around us o Provides us key information about how objects work 4 Ways to Create the Perception of Movement 1. Real movement: something actually moving o Moving an object across your field of view 2. Apparent movement: perception of movement even though nothing is actually moving o The inter-stimulus interval between the two images 3. Induced movement: an illusion of movement when one object creates the perception of movement in another object 4. Movement after effect: feeling as though you are still in motion after the actual motion has stopped Real vs. Apparent Motion  Larson et al. fMRI experiment: Same or different neural mechanism? o A participant who was scanned in an fMRI while looking at 3 different displays o Control: 2 dots in 2 different positions in the visual field and presented at the same time o Real movement: 2 dot that movements form one position to another across the screen o Apparent movement: the dots are flashed so that it looks like it moved but didn’t actually o In the control condition, each dot activates separate spaces of the visual cortex o In the real movement condition, there is activation between the two spaces – the movement is represented somewhere between where the two dots are represented o In the apparent motion condition, even though the dot never actually traverses across the screen, the brain area is still active similar to in the real motion condition o The visual cortex is active for both sets of stimuli in the same kind of way for both the real and apparent movement conditions o Indicates that in the apparent motion condition, the motion perceived is the same as the motion perceived in the real movement and is represented by the same neural perception - perceived by the same neural perception, not separate ones for real movement vs. apparent movement o Creates an interesting problem – how does the brain figure out the different parameters of motion detection?  Textbook diagram 1. The object we are observing moves and the observer is stationary 2. The object is moving and the observer isn’t moving but their eyes are moving – movement is tracked so the object's movement is stationary on the retina (observation is same as 1) 3. The room is stationary and the observer is moving through the room – observer is moving, but the world is still o The three examples in terms of optical arrays o Thought there was a local disturbance occurring in 1 – the object is covering/uncovering objects in the environment as it moves o In 2, the object is always moving in the environment but your retina is static – the disturbances tells us that it is the object moving and not the observer o In 3, there are changes in the global optic flow (changes in the optic array itself) – and the observer moves, they are covering/uncovering objects and the environment is moving as well Gibson’s Ecological Approach  Started to think about vision in artificial terms – how is it possible to create a computer that perceives the world in the way that humans do?  Presented an idea of how motion perception may work in computational terms  Information is directly available in the environment for perception – the optic array o Optic array: a theoretical structure that is created by the various surfaces and contours and textures that change as we move through the environment because of our movement o Suggested we gather information about the world via the optic array and we use this optic array to figure out what is going on in the environment with motion as one of
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