Exam 2 - Sensation and Perception Flashcards
What is the problem with perceptual organization
Stimuli on the retina can be ambiguous and can change from moment to moment based on noise, occlusion, and changes in viewpoint
What is the visual system good at?
Object recognition (of familiar and unfamiliar objects)
Distinguishing between many objects within one category
Viewpoint invariance
Viewpoint invariance
recognizing objects from many different viewpoints
What is perceptual organization
Making sense of patters than are present through assigning boarder ownership, distinguishing figure from ground, and grouping similar regions together
What is Object Recognition
What IS the thing? Matching objects to their representations in stored memory
Shape representation in the brain
The role of gist
What is important about assignment of border ownership
Important in determining what shapes are present
Why is figure-ground organization helpful?
Useful in assigning border ownership
What is figure-ground organization
Figure = “thing”
Surrounded objects are usually seen as figures
Figures are often in the front of ground
Ambiguous Figure- Ground
Switches spontaneously
Lamp/ladies kissing example
Symmetry and figure- Ground organization
Symmetrical items are more likely to be perceived as figures 2
Convexity and figure- Ground organization
Convex items are more likely to be perceived as figure
Meaningfulness and figure- Ground organization
You see the object and figure-ground segregation at the same time
Won and Weisstein study
When the line was tilted toward the figure, just of line was better.
More attention goes to the figure
V2 and visual processing
early on in the processing stream you already have info about scene/background
Very sensitive to detecting difference between stimuli
and there is more activity if the pattern changes
What is perceptual grouping
We naturally group things together whether its conscious or unconscious
Does grouping occur before or after color constancy mechanisms operate
We perceive color AFTER color constancy
What is common fate
things that move together are perceived as belonging together. Neurons sync their firing when activity moves together
What is subjective contours
A misperception of our visual system that sees edge completion in shapes.
qWe see a triangle in three packman shaped circles
How do we do object recognition
Two approaches
1. We have a single representation of every recognizable object, regardless of viewpoint
2. we have viewpoint specific representations of objects
Biederman’s 1985 object recognition theory
Recognition by components (geons). If you can see the geons then you can see the object/know what it is
objects can be ID’d if the geon’s can be ID’d
What is a geon
Geometric ion
Each one is unique from most angles
only 36 needed to make thousands of forms
Geons and vertices
We are good at seeing things when the vertices are present
Geons help make up vertices
What are limitations of geons
Viewpoint invariance
We know the geons of a coffee cup but there are many different kinds of coffee cups so there must be more to object recognition than just geons
What is support for viewpoint specific representations
Objects are recognized more quickly when see from a familiar viewpoint
What region is sensitive to shape orientation
V4. There are neurons that are sensitive to convex and position
What is gist
The general sense. The gist of a scene can be perceived rapidly and can guide object recognition. This is a top down influence
How does gist help guide perception
You are more accurate at responding when the foreground and the background match
What is visual angle
The angle between the rays spanning the object. It’s used to specify the size on the retina
What are spatial frequency channels
Neural mechanisms that are sensitive to only a narrow range of spatial frequencies.
We are most sensitive to intermediate spatial frequencies
What does moving closer do to a low spatial frequency obj
makes it harder to see
What does moving closer do to a high spatial frequency obj
makes it easier to see
What a question that depth perception poses
How do we get 3D info from a 2D retina???
What does retinal size depend on
size of an obj and distance to the obj
What are Monocular cues
All the ways that one eye can help you process
Static Cues
Examples of Static cues
Position Based cues
Size based cues
Lighting based cues
What are the kinds of position based cues
Partial occlusion
Relative height
What are kinds of size based cues
Familiar size
Relative size
Texture gradients
Linear perspective
What are kinds of Lighting Based cues
Atmospheric perspective
Shading
Cast shadows
What are dynamic cues
They require motion
Motion parallax
Optic flow
Deletion and accretion
Examples of binocular cues
Binocular disparity
What is partial occlusion
You can see what thing is closer based on what is blocking what
What is relative height
the closer to the horizon, the father away it is
What is familiar size
We are able to use the retinal image size of a familiar object to gauge our distance from it
We use the separation of headlights to tell us how far away a car is
What is relative size ?
We use the relative size of the retinal image to judge the distance
What is linear perspective
Parallel lines converge with distance
What are texture gradiants
The texture gets smaller and smaller and things get father away
What is atmospheric (aerial) perspective
It gets hazier as you get farther away bc you are looking through more atmosphere
Shape from shading
We assume light comes from above
Cast shadows
Shadows can make us think things are moving in a different direction
What is motion parallax
objects that are closer appear to move faster than objects that are further
Movement to the right causes obj to appear to move to the left with closer objects moving faster
What is optic flow
Like in a car, the yellow line moves really fast bc its close to you whereas the mountain moves slower bc its farther away
Deletion and accretion
strong cues about relative distance
You know what shape is in the front based on what is occluding what
What are oculomotor cues
cues that have origin in the muscles in the eye
accommodation
convergence
What is binocular disparity?
Binocular disparity refers to the difference in image location of an object seen by the left and right eyes, resulting from the eyes’ horizontal separation.
When different images are seen by each eye
What is a horopter
a line or surface containing all those points in space whose images fall on corresponding points of the retinas of the two eyes.
obj NOT on the horopter stimulate disparate points
What do 3D movies have to do with depth perception?
They produce binocular disparity which makes the image pops out
Each eye can only see one image
The correspondence problem
We see depth before form
What is size constancy
We tend to perceive an object to be a fixed size regardless of the distance to the object or the size of it on the retina
How to eliminate depth cues
Darkness
Close one eye
What is the law of visual angle
Judgements of size are based only on visual angle (when depth perception is unavailable)
What is the law of visual angle explain?
Why the moon and the sun are the same shape
What is Emmert’s Law
The perceived size of an object depends on its distance
Kinds of illusions we talked about
Ames room
Moon illusion
Ponzo (railroad tracks) illusion
Muller-Lyer illusion (arrows)
Outside rear view mirror illusion
Where in the visual stream are size and depth combined and processed
V1
When does size constancy fail
When you have misinterpreted depth cues
leads to illusions
The hollow mask illusion
Shape from shading cues. Makes you think the face is popping out. Light comes from below
When you move, cues of familiarity cause the face to move also bc the shape from shading is conflicting with motion parallax and motion parallax is always right
If two depth cues are conflicting, we assume…
That they are both correct. The second depth cue is always motion parallax
Anamorphic projection
Written so it would look normal from far away. This is a failure of shape constancy
What is luminance
luminance = illuminance X reflectance
Its the amount of light reflected by an object
What is the ratio principle
ratio of luminance between and obj and surround elements terminates the obj perceived lightness
