Form Perception Flashcards
What did the Gestalt psychologists believe?
With respect to perception, believed that the “whole is greater than the sum of it’s parts”
(Ppl percieve whole stimulus rather than just putting together a collection of its parts)
The Gestalt movement was in response to the Structuralist movement. What did the structuralist movement believe?
That everything could be reduced to its basic elements
Motion is an ______ property of the sequence of _______
Emergent
Pictures
What are the Gestalt principles? (broad translation, don’t list them)
Laws that describe how we organize visual input
We either are born with them, or we acquire them very rapidly
What is the first/most fundamental Gestalt principle?
Figure Ground
- the ability to distinguish an object from its background
What properties of figures and backgrounds help us distinguish the two?
Figures have distinct borders that:
- give it form over the background
- helps it be perceived as being in front of the background
Backgrounds are either formless or made up of multiple forms
What does the Gestalt principle of Proximity state?
Objects that are close together in space tend to belong together
Why will you naturally see regions of high density as one group?
Because of their proximity together (according to the principle of proximity)
XX XXX XXXXXXXX
Which X’s are you more likely to group together according to the principle of proximity?
The Xs that are close together rather than the ones that are farther apart
What does the Gestalt principle of Closure state?
If there are gaps in the contour of a shape, we’ll tend to fill in those gaps and perceive a whole object
If a telephone pole is in front of part of a truck, and blocking some of its contour, what will we see? Why?
According to the principle of Closure, we will see the fill in the parts that are blocked by the telephone pole and end up seeing the whole truck as a whole object rather than parts of an object
What does the Gestalt principle of Similarity state?
That we tend to grp together elements that are physically similar
XOXOXOXO
XOXOXOXO
XOXOXOXO
XOXOXOXO
Why would you see the columns of the same elements (either all Xs or all Os) as belonging together, rather than grouping together a row of XOXO?
Bc we tend to grp together elements that are physically similar (Gestalt principle)
What does the Gestalt principle of Continuity state?
The ability to perceive a simple, continuous form, rather than a combination of awkward forms
According to the principle of continuity, how would we perceive an X?
a) as two crossing lines
b) as two v’s stack on top of each other
a) as two crossing lines
What does the Gestalt principle of Common Fate state?
Things that change in the same way should be grouped together
Why would we perceive school fish moving together, not as a group of elements, but as an object on its own?
Because the tendency to group together things that change/move in the same way is very strong
How does the principle of Common Fate help explain why we can suddenly see a camouflaged animal once it moves?
When it’s still, it’s grouped together with the (nonmoving) background, so we can’t see it
As the animal moves, there are elements within its pattern that are moving in the same direction and at the same time—> these elements allow the contour of the animal’s shape to be seen
What are the first two steps of figure recognition?
1) identifying what aspect of the scene is the figure and what is the background
2) parts of the figure are identified and grouped together into a single object
Object recognition is a combination of two processes. What are these processes (in their respective orders)?
Bottom Up
Top Down
What is Bottom-Up processing?
Features that are present in the stimulus itself guides object recognition
(you recognize what you see by analyzing the individ features and comparing those features to things with similar features that you have in memory)
According to bottom-up processing, how do you recognize a cow as being a cow?
You look at the animal, and then analyze the features (the four legs, the udders, the spots). When you compare it to what you’ve seen before, it matches with the image of a cow that you have in your mind.
What is top-down processing?
Your own beliefs or expectations are the primary influence for det what you’re seeing
Describe a typical priming experiment
Experimenter measures how fast a participant can read a word that is flashed on a screen
If the experimenter tells the participant that the next word is an animal, the participant will recognize it much faster
Priming experiments test which sort of processing?
a) bottom-up
b) top-down
b) top-down
Why can’t you just use top-down processing alone to describe object recognition?
You need some input from the stimulus itself before your expectations about that stimulus can influence your recognition of it
Why can’t you just use bottom-up processing alone to describe object recognition?
Bc it’s not JUST the stimulus that guides object recognition, your expectations also do
What are the theories of object recognition?
Biederman’s Geon
Template
Prototype
What does Biederman’s Geon theory of object recognition suggest?
That we have 36 diff simple geometrical forms (geons) stored in our memory (i.e. cone, sphere, cylinder)
Using these geons, it’s possible to recognize over 150 mill diff objects
What are two problems with the geon theory?
1) Certain stimuli (i.e. faces, crumpled pieces of paper) are diff to det what geon should be used, yet we have no problem recognizing these stimuli
2) Some forms of brain damage lead to very specific deficits (ie. only has difficulty recognizing diff types of fruit). If geons were involved, you would expect deficits in recognizing objects based on shape, not category.
What does the Template theory of object recognition suggest?
That we store many diff (specific) templates in memory and when we come across an object, we compare it to all diff templates in memory
If match found, we name it by activating connections to other language areas in the brain
Why isn’t the Template theory very compelling?
We’d have to store MANY templates to recognize all of the diff objects that we encounter
What does the Prototype theory of object recognition suggest?
That we store the most typical (not specific) example of an object + all of the ones that we are personally familiar with (i.e. ideal dog + all dogs we’re personally familiar with)
Why is the Prototype theory more valued than the Template theory?
It’s much more flexible bc you don’t need an exact match bw the observed object and what is stored in memory
This way, we can easily recognize common objects that we’ve never seen before
Why are we able to recognize objects quickly and efficiently?
Most neural processing of object info is done in parallel
diff brain systems process diff components of visual signal at same time
Which theory of object recognition provides a complete explanation for our ability to recognize objects?
a) Protoype
b) Template
c) Geon
d) none
e) combination of all
d) none
“We retain perceptual constancy despite variation in visual stimuli”
Give an example of this statement
You’d still recognize your dog whether she was sitting on the other side of the playground or by your side (even tho the image on retina is much smaller when looking across playground)
What is perceptual constancy?
Our ability to perceive an object as unchanging even tho the visual image produced by the object is constantly changing
What are the five types of perceptual constancies?
1) Shape
2) Location
3) Size
4) Brightness
5) Colour
What is shape constancy?
The fact that we perceive objects to have a constant shape, even tho actual retinal image changes as the object moves
How does a door display shape constancy?
It’s always perceived as rectangular despite it’s visual change when opening (i.e. an open door doesn’t look rectangular anymore, but we still perceive it as rectangular)
What is location constancy?
Even tho objects are constantly moving around in our retina as we move our eyes/heads, we still perceive them as stationary
How does a driving in a car display location constancy?
We don’t perceive the objects outside to be moving, even those the image is
What is size constancy? Give an example
Tend to see size of objects around us as unchanging despite the size of retinal image varying with distance
ex. when your friend is walking away from you, you don’t perceive him as actually getting smaller
What is brightness constancy? Give an example
Ability to recognize that objects do not change in brightness despite object reflecting more or less light
ex. fav coffee mug is still the same brightness whether it’s outside or inside
What is colour constancy? Give an example
Ability to recognize that objects do not change colour despite diff illumination conditions
ex. still recognize white dog under a red light
How do we account for all of the perceptual constancies? (2 ways)
1) Depends on our knowledge of objects, which provide a top-down influence on how we see the objects
ex. we know that most objects don’t change
2) Cues from the rest of the scene are used as clues to perceiving constancy
How do depth cues help us det that our friend is not shrinking as he walks away from us?
Depth cues indicate the size of an object relative to its distance; other cues in the background indicate that he is normal height
How do colour cues help us det that our white dog is not red under red light?
Everything under the red light has a reddish tint
How do motion cues help us det that the bus is stopped in front of you and not moving towards you?
If bus was moving, everything else in the background would remain stationary while it got larger
Why do perceptual constancies occur?
Bc we know that certain properties of objects do not change (PRIOR KNOWLEDGE) and our perceptual system automatically factors in other CUES in the environ that give us info about the object
Why do visual illusions occur?
Bc our perceptual strategies are used in situations where they don’t belong; arise from ambiguities in perception
What is the Muller-Lyer illusion?
> —< Which line is longer?
okay, doesn’t rlly work on the computer
Give an explanation for Muller-Lyer illusion
Misapplies size constancy + inaccurately det depth
ex. >—< looks like a corner of a wall that receding away from you whereas looks like a corner that is going towards you
Give support for the primary explanation of the Muller-Lyer illusion
Ppl in cultures who live in round huts are less susceptible to the illusion (which relies on right angled walls)
How does the Ames room manipulate distance to trick size constancy?
Looks like a rectangular room but is actually trapezoidal. You’ll guess that two people of equal heights are actually at diff heights if one is on the other side of the room; it will look like they’re diff heights
How does the Ponzo illusion work? (search up the illusion)
Two vertical lines on side are converging—> gives a sense of depth and percieves the top as farther away (which makes it seem longer in the end)
What can visual illusions tell us about the visual system?
- show us how our experiences influence how we perceive events
- show us that perception is an active process, shaped by prior experiences (and not just scene in front of us)
True or false: diff parts of the brain analyze different parts of stimuli simultaneously
False
The brain processes stimuli in one region before passing it on to the next
What is the first step to object recognition?
Magno and Parvo cells in retina transduce the light stimulus into a neural impulse
Where are magno ganglion cells found in the retina?
The periphery of the retina
Where are magno cells used for?
Detecting:
- Changes in brightness
- Motion
- Depth
Where are parvo ganglion cells found in the retina?
Throughout retina
Where are parvo cells used for?
Detecting:
- Colour
- Pattern
- Form
True or false: magno and parvo cells have large receptive fields
False
Small
The cells in the primary visual cortex are called what?Why?
Feature detectors
Bc the cells are very particular about what features will make them fire
What did Hodgkin and Huxely do?
Developed a technique to record the electrical activity for an individ neuron in the squid
How did Hodgkin and Huxley’s experiment help other reserachers?
Paved the way for other reserachers to use this tech to see how individ neurons respond to specific stimuli
What are “bug detectors” in frogs?
Neurons in the frog’s optic nerve that responded only to moving black dots
What did Hubel and Wiesel do?
Extended research on neural activity in the visual cortex
How did Hubel and Wiesel begin their exploration of the visual cortex?
By trying to learn what sort of stimuli the individ cortical cells responded to
How did Hubel and Wiesel perform their experiment on cortical cells?
Put microelectrodes in the cortex of a cat to record the electrical activity of individ neurons as the cat was shown diff types of visual stimuli
In Hubel and Wiesel’s experiment, they weren’t getting much response from the neurons in the cat, until…?
They presented the cat with a slide that had a crack in it
When the line that was projected from that crack went across the cat’s visual field, the neurons fired a lot!
What did Hubel and Wiesel conclude after the cat’s crazy rxn to the cracked screen? (before they modified the experiment)
That neurons must respond to stimuli that are more complex than flashes of light
How did Hubel and Wiesel modify the experiment after their conclusions from the cat and the cracked screen?
They used lines of diff orientations and thickness that moved in diff directions
What were Hubel and Wiesel’s results + conclusions after they modified the experiment?
Results:
- each neuron is very specific about what will make it fire the most
Conclusion
- these cells fire maximally to stimuli of a certain shape, size, position, and movement
- this defines the receptive field for that cell
(and this is how Hubel and Wiesel accidentally discovered feature detector cells)
What do simple cells respond maximally to?
A bar of a certain orientation that is presented to a particular region of the retina
A simple cell responds most to a horizontal bar. What happens if the bar moves to another region of the retina OR if its orientation changes?
The simple cell will be inhibited and fire less than baseline (it’s arranged in an opponent fashion)
What does a complex cell respond maximally to?
A bar of certain orientation + direction of movement
does NOT matter where the bar is in the receptive field
True or false: all complex cells fire at the same rate regardless of where the light is positioned in its receptive field
False
MOST complex cells fire at the same rate
Some do care a little bit (ex. may fire more when it’s positioned at a certain angle; but never inhibited)
What do hypercomplex cells respond maximally to?
A bar of a particular orientation and direction of movement, ending at specific points in the receptive field
(they have a region of inhibition at the end of their receptive fields)
What happens if the stimulus is 3/4 in the “on” region of a hypercomplex cell and 1/4 in the “off” region?
There is a weak response
What happens if the stimulus is 1/2 in the “on” region of a hypercomplex cell and 1/2 in the “off” region? (i.e. when it’s a really long bar)
There is a less than baseline (inhibitory) response
Hypercomplex cells are sensitive to the _____ of the bar
Length
