Objects and scenes part 2 Flashcards
What is another example of bottom up processing?
Gist
What does RBC theory say about perceiving an object?
We build up small details to an overall object
What do experiments on scene perception suggest that indicate we see the gist of a scene?
We can perceive large scale properties first (<250 ms), and then more slowly fill in details (~500 ms) –> see gist first
How do we perceive gist?
Global image features that are holistically and rapidly perceived –> not built up from small bits
What are the 5 global image features we use to perceive gist?
Degree or naturalness
Degree of openness
Degree of roughness
Degree of expansion
Colour
What is degree of naturalness
Undulating contours (irregular) vs straight lines
What is degree of openness
Visible horizon line vs closed-in environment
What is degree of roughness?
Large even areas vs many small elements
What is degree of expansion?
convergence of lines of parallel lines
How do we perceive gist?
We simultaneously process visual scene at multiple spatial scales or frequencies
What do we process at low and high frequencies?
Low frequency = gist –> general trends
High frequencies = detail
What happens when you are shown a hybrid scene in low frequency?
you don’t notice the kitchen in the middle, just the gist
How does the hybrid image experiment work?
Low spatial frequencies –> Marilyn monroe
High spatial frequencies –> Einstein
Combine them
Normally information at low and high spatial frequencies is complementary but in a hybrid image it conflicts
Changing image size or viewing distance shifts the perceived balance
What is top down processing for perception?
Perception is not based purely on the stimulus
It also depends on experience, expectations, goals
Give an example of top down processing?
The numbers 12, 13, 14 and letters A, B, and C
The center symbol is the same but is influenced by context and our prior experience with the context
What do the upside down word examples show?
We reinterpret the same shapes based on context and prior experience
What does the dashed letters in words example show?
Version you saw is from your mind –> top-down
There are multiple possibilities
How does experience influence figure and ground perception? Give an example?
Meaningfulness/familiarity influencing figure/ ground separation –> based on experience
in two images:
1. Black area is more likely to be seen as figure because it looks like a lady
2. Black and white areas equally likely to be seen as figure in second image because it is flipped
Meaningful part is the figure. Not just based on concave/ convex
How does experience influence perceptual organization? Give an example
We have a tendency to perceive faces based on experience
Configuration of rocks looks like a face
How does experience effect object recognition? Give an example
all 4 images have the same blob in the picture but we interpret it differently based on experience
Provide the example that shows experience and scene perception.
First someone is shown the context scene (kitchen) then asked to identify a target object when it is flashed quickly
People show higher accuracy for context appropriate object
Person is better at identifying loaf of bread than a mailbox
Context we have been presented with first alters what we perceive first
What is a theory that explains experience and perception?
Helmholtz’s Theory of Unconscious Inference
What is the principle underlying Helmholtz’s Theory of Unconscious Inference?
Likelihood principle
What is Helmholtz’s Theory of Unconscious Inference?
Likelihood principle: we perceive objects most likely to have caused the pattern of stimuli we receive
Unconscious inference: The application of the likelihood principle is unconscious but based on past experience
What does Bayesian inference tell us?
How our brains incorporate prior experience with current evidence to determine perception/ how we decide which hypothesis is most likely
What is the Bayesian equation?
P(A/B) = P(B/A) P(A)
What is P(A/B)?
Posterior belief –> probability of a snake given I saw something slithering
What is P(B/A)?
Likelihood –> probability of slitering give a snake
What is P(A)?
Prior belief (experience) –> probability of a snake
What stream is involved in the neural basis of object recognition? What direction does it go?
Visual what stream
Rostrally to temporal lobe
What is the fusiform face area (FFA) and where is it located?
Preferentially responds to images of faces
On the fusiform gyrus at the bottom of the temporal lobe
What is the parahippocampal place area (PPA)? Where is it located?
In temporal lobe
Preferentially responds to images of places, houses, and scenes
What is the extrastriate body area (EBA)? Where is it?
Preferentially responds to pictures of bodies and body parts
On temporal ventral pathway but further back
Is MT near the EBA?
Yes
What do people suspect the FFA could be involved in?
Visual expertise
What did the experiment on the FFA do?
Trying to figure out if FFA is involved in visual expertise
Show people faces and greebles (computer generated) then trained them on greebles
What task did they use to train people with greebles?
sequential matching task
had to say same or different after masking the last image
What did the greebles experiment show before and after training?
Before training the FFA only activated to faces
After training the there was similar activation to faces and greebles
What is the evidence that the FFA is a face area?
Face inversion effect
Lesion to FFA area leads to prosopagnosia
Face-selective neurons in FFA
Faces are important for evolution
What is the face inversion effect?
We are particularly sensitive to upright faces
What is prosopagnosia?
deficit in facial percepetion
What is the evidence that the FFA is a visual expertise area?
Greeble activations
Bird-experts show FFA activation for birds
Car-experts show FFA activation for cars
Show experience dependent plasticity for non-face stimuli
Is the FFA a face area or a visual expertise area?
still unknown
What does the the PPA respond to?
Outdoor scenes
Furnished rooms
Empty rooms
Landmarks
What does the PPA not respond to?
Faces
Objects
Groups of objects
What did the study on the PPA area test?
PPA activation after imagining space defining objects and space ambiguous objects
What are space defining objects? examples?
A large oak bed
A dark corduroy couch
An antique rocking horse
What are space ambiguous objects?
Large cardboard box
A small white fan heater
A wicker laundry basket
Large but empty
What did the experiment in the PPA discover?
Imagining space defining objects activated PPA more than imagining space ambiguous objects
Things that take up space activated even through they were objects
What could the PPA represent?
Places and scenes
Contextual relationships –> where house is in neighbourhood
3D space
Navigation –> big things have more effects
