PSYO 1021 Lecture Notes - Lecture 5: Binocular Disparity, Parallax, Moon Illusion
27 Jun 2018
School
Department
Course
Professor
Vision: perceiving visual stimuli
So far, we have followed visual info from light entering the eye to impulses sent to the thalamus
then to the visual cortex, where cell fire to very specific stimulus. How do we move from there to
perceiving objects?
Processes work together to help us recognize objects:
- Motion
- Depth
- Size
- Grouping
- Color perception - seen in the previous lecture
Perceiving motion
Factors that contribute to motion perception:
- Background against which an object moves
Complex background makes it look like its moving quicker than normal background
Ex: dear running with background of tree vs plain sky background
Background objects provide reference that help us note the position change
- Size of object
Smaller objects appear to move faster then bigger object when all else is equal
Ex: smaller rabbit in a clear plain looks faster than deer
Prehistorical times hunting sees when things are moving
Human designed to perceive change more than constant stimulus – sensory adaptation
Apparent motion
Illusion that fools us to interpret an object as moving when it’s not
Reason: brain interpret images that move across the retina as movement
Ex: light that turns on and off in a line looks like it’s a moving line
Real movement neurons
Neurons specialized in detecting real movement (not fake movement)
Respond only when the image itself moves, not the eye moves
They fire when the image moves and don’t when you press your eye
Ex: If you push your eyeball
Brain is not interpreting environment as an earthquake
Akinetopisa – “motion blindness”
Affected have trouble perceiving movement- perceive images well
Affects people differently – some people can’t see fast movement, other any movement
World looks like changing photographs
Can be dangerous
Look up - YouTube
find more resources at oneclass.com
find more resources at oneclass.com
Depth perception
Ability to discriminate what is near what is far even is the retina’s image is 2D
2 processes allow for depth perception:
Binocular depth
Relies on input from both eyes
2 binocular depth clues:
- Binocular disparity
The eyes are separated by space, each image provides a different viewpoint:
= is the difference in image from each eye
Play a key role in perceiving depth
The brain integrates 2 different 2D images into one 3D
Ex: putting finger in front of you and closing each eye= looks like it’s moving
Further away it moves less
- Convergence
Concept that when objects are closer, your eyes are closer together
Brain uses this information to determine the distance of the object
More effective for images that are close to us (3m – rely on other for further)
Ex: cross-eyed when looking at your nose
Monocular depth
Only requires the input from one eye
People with one eye can still perceive some amount of depth
2 monocular cues in 2D images:
- Motion parallax*** video
Similar to binocular disparity
Closer an object is to the eye, more it appears to move from the background
Ex: This can be demonstrated by closing one eye and holding your finger in front of your face
while moving your head from side to side
- Monocular depth cues
Can be used to assess 3D in 2D representations (images and photographs)
Most common ones
1. Linear perspective
Parallel lines become closer together in distance
2. Texture gradient
More details/texture in objects that are close
3. Relative image size
Same size objects will be smaller in distance
find more resources at oneclass.com
find more resources at oneclass.com
When we know they are the same size, know the size difference is due to distance
4. Atmospheric perspective
Looking across a vast outdoor space, particles in the air (pollution, vapor) scatter light so
things appear hazy in the distance
5. Interposition
Partial blocking of objects farther away by the closer away objects
6. Light and shading
Light hits the closest objects and make them appear brighter
Casts object that are further away into a shadow
Visual pathway
Left visual field and right visual field take in different amount of information
2 eyes see something different, and both fields too \= binocular disparity
Integrate into brain to allow us to see depth
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
So far, we have followed visual info from light entering the eye to impulses sent to the thalamus then to the visual cortex, where cell fire to very specific stimulus. Processes work together to help us recognize objects: Color perception - seen in the previous lecture. Complex background makes it look like its moving quicker than normal background. Ex: dear running with background of tree vs plain sky background. Background objects provide reference that help us note the position change. Smaller objects appear to move faster then bigger object when all else is equal. Ex: smaller rabbit in a clear plain looks faster than deer. Prehistorical times hunting sees when things are moving. Human designed to perceive change more than constant stimulus sensory adaptation. Illusion that fools us to interpret an object as moving when it"s not. Reason: brain interpret images that move across the retina as movement.
