Perception L8- Depth/size, distance & motion

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What is depth perception?
Percieving a 2D image as a 3D image
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What is the problem of depth perception?
The image reflected onto the retina is 2D-- But we see a 3D image- we do this using cues.
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The power of depth perception:
By transforming a 2D image into a 3D image-this can sometimes trick our brain (do this automaticslly)
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When is the ability to percieve depth developed?
Very early
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Gibson & Walk (1960)
Very well known exp. Using 6 month old toddlers. Glass top on table, half was checkerboard and other half was clear glass with checkboard pattern on bottom- made it appear as though the table dropped. --> babies told to walk towards mothers.
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What did they find?
Babies cried when reached the half way point- they percieved depth
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How do we percieve depth?
Monocular cues/ Binocular cues.
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3 types of monocular cues?
Pictorial cues/ occulmotor cues/ motion-produced cues.
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What are monocular cues?
Need ONE EYE to percieve depth- dont need both eyes.
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MONOCULAR CUES: 7 types of pictorial cue:
interposition, relative size, linear persp, texture gradient, height in the visual field, shading, atmospheric perspective
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MONOCULAR CUES: What is the occulomotor cue?
Accomodation
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MONOCULAR CUES: what are the motion-produced cues?
Moion- produced cues are cues we only use when we are moving/ things are moving around us. 2 types: 1. motion parallax. 2.kinetic depth effect
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BINOCULAR CUES:
Need BOTH eyes. 1. convergence 2.binocular disparity
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MONOCULAR CUES: OUTLINE EACH CUE- Interposition:
When an object overlaps/ includes another: we cannot tell which is closest
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Relative size:
when objects have approx same size- the one that is smaller is seen as being more distant.
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Linear perspective:
Parellel lines will converge with distance- so seem further away- the greater the distance, the greater the convergence
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Texture gradient:
The amount of texture we percieve will decrease with distance- objects further away are less detailed
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Height in visual field:
Object that is high in the visual field is percieved as smaller
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Shading:
we use shadows to percieve depth and distance - Positions fo the shadows determins the perception of objects
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Atmostpheric perspective:
More distant objects are percieved as less clear
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Accommodation:
Property of the visual system- the lens can change its form. If object is distant, lens is more flat/ if object is closer, more curved. Automatic.
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Motion parallax (3D Depth)
Object closure to us seems to move quicker than distant onjects --> eg when in car
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Kinetic depth effect:
Objects in motion reveal their 3D structure: When not moving, doesnt look 3D.
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BINOCULAR CUES: ouline each- Convergence:
When we look at an object that is close to us, the 2 eyes rotate inwards. Further away= dont rotate inwards as much. --> this movement of the eyes gives info on how close/ far an object is.
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Binocular disparity:
the 2 eyes are specially separated so recieve a different image. Brain COMBINES these images to make singular picture. when the 2 images appear very different, this means the object is close to us.
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What is size constancy?
When 2 objects have different size but ARENT percieved as different --> eg car further away looks smaller but we know it isnt. If we remove these cues, this is an illusion.
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Illusions:
When cues are removed- we cannot percieve depth. Example- Ames room
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Cues can produce illusions;
PONZO ILLUSION- 2 horizontal bars. THE MULLER-LYER ILLUSION-one line further away is percieved as larger even when same size.
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PERCEPTION OF MOTION: what are the 4 different functions of motion perception?
1.helps us in percieveing depth. 2.helps us in percieving objects 3.Helps us to attract attention to objects 4.helps with navigation and orientation.
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Motion agnosia- Akinetopsia:
Lesion in V5 (MT)- this processes movement. So may have problems percieveing motion. A deficiency in the ability to see movement in a smooth function. Stationary objects is not impaired.
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2 types of motion:
Real movement and Apparent movement.
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Real movement:
REAL motion when things around us actually move. Image moves in the retina.
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Apparent movement:
When we percieve movement but there actually is none. 5 types.
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Name the 5 types:
stroboscopic movement/ induced movement/ Autokinetic effect/ Motion-after effect/ illusory movement.
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Stroboscopic movement:
When STILL images are presented RAPIDLY in DIFFERENT LOCATIONS
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Induced movement:
Movement is induced by the EDGES
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Autokinetic effect:
In complete darkness, a white dot moves- it is stationary but appears to move
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Motion after effect
(waterfall illusion) visual illusion experienced after viewing a moving stimulus for a time with stationary eyes- and then fixating on a stationary stimulus. The stationary stimulus appears to move in the opposite direction to the original image
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Card 2

Front

What is the problem of depth perception?

Back

The image reflected onto the retina is 2D-- But we see a 3D image- we do this using cues.

Card 3

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The power of depth perception:

Back

Preview of the front of card 3

Card 4

Front

When is the ability to percieve depth developed?

Back

Preview of the front of card 4

Card 5

Front

Gibson & Walk (1960)

Back

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