week 2 Flashcards
perception
taking info that is sensed by sense organs and interpreting it
- sensed by eyes and gives rise to visual perception
eye’s structure
cornea: clear covering
iris: ring of muscles that controls how much light gets in
lens: with cornea, focuses light on back of the eye
retina: photosensitive membrane at back of eye where transduction takes place
* sensing takes place
* center of retina is fovea
* photoreceptor cells (rods and cones)
fovea: point of highest visual acuity
* sharpest color
optic nerve: takes visual info to brain
blind spot: point where optic nerve leaves eye
the eye like a camera
light from object in environment passes through the cornea and iris and is refracted onto the retina at back of eye
- inverse of what people see on outside world
- allows you to adjust the lens to bring into focus what u want to see
myopia: eyeballs are long so you need reflections to be pushed up against retina with glasses
how does light energy get to the brain?
transduction - changing of a physical stimulus into neural energy/electrical signal
transduction takes place in two types of cells
* rods - sensitive to low light but poor acuity
* cones - low sensitivity to light, but high acuity and have different types to respond to different colors of light
—- not evenly distributed
how eyeball functions depends on how the rods and cones are distributed
photoreceptors
have to move eyeballs all the time because photoreceptors need replenishing constantly
constantly move eyes to have new stimulation among photoreceptors to have a clear vision of color
visual pathway
contralateral mapping
* stimulus processed on opposite side of where it was detected
damage on left side of visual cortex = blindness in right eye
blindsight
patients with damage to occipital cortex are blind (no reaction to light)
but vision is not entirely seen
* two pathways observe different aspects of vision
one pathway: from eyeball to visual cortex of brain and you need this cortex to consciously see something
another pathway: from brainstem to higher centers of the brain
* concerned with reflective behavior
* can use to guess direction of movement that u can’t see if visual cortex is damaged
blindsight con’t
when blind people reach for something they guess in the right direction usually bc there are many paths for visual info
blind to visual info on opposite side of occipital trauma
- helps to react to environment more effectively
- shows that our brain processes info that we are not always aware of the end processes
visual perception
ability to interpret visual world makes us think that the way we process the info is easy
what’s involved
* distal stimulus: stimulus out in world
* proximal stimulus: stimulus on the sense organ
for vision: distal stimulus = 3D object in the world and proximal is 2D representation on the retina
2D reflection could be caused by any number of real world situations maybe you have smaller object close up or farther away but will result in the exact same reflection
solution: brain uses info from both eyes (binocular cues) and properties from the proximal stimulus (monocular cues) to make inferences about the relative depth of the distal stimulus
resolving depth
binocular cues: brain uses distance between two objects to interpret
* Convergence
* binocular disparity
monocular cues: the ways that a single eye help you process stuff
* perspective
* interposition
* relative size
* textural gradient
* motion parallax
* aerial perspective
* shading
binocular cues
Two main types:
* convergence: eyes converge and lens accomodates when objects are close (degree of cross-eyedness)
— gives indication of distance
- binocular disparity: slighly different views of the world projected onto each eye
—–fingers
—– each image reflected on retinas at separate angles but interpretation is the images fused so that makes you be able to see depth
monocular cues (7)
many types
* perspective
* shading
* aerial perspective
* relative size
* interposition
* motion parallax
* textural gradient
can get cues from just one eye
using context and knowledge about the world to make inferences about size and distance
perspective
monocular cue
lines converge at a distance
- traintracks
- interpretation of lines bc using knowledge and context about railway to make assumptions about distance
Muller-Lyer illusion - lines converge at a distance
* the way its drawn makes one line look longer than the other
Project Prakash
* operated on congenital blindness bc of cataracts – solution was to take out lenses and with glasses person could see
* found that little visual experience is needed to indicate distance or depth
relative size
monocular cue
* bigger things tend to be closer
interposition
monocular cue
* closer objects obsure distant ones
interposition illusions
monocular cues
* impossible figures (painting of stairs)
motion parallax
objects closer to the viewer move past more quickly than objects farther away
the faster an object seems to go by the closer the object
- drivers use this as a measure of how quickly they’re going
texture gradient
monocular cue
the less detailed the texture to the viewer, the farther away it is
blurring can give the impression of depth
aerial perspective
monocular cue
the farther something is away the more there will be a bluish haze to it
shading
monocular cue
- shading gives us cues about depth and movement
- demo
– motion in depth from shadow
– shadows can make something look like its floating or on the ground
light and shadow
light source is assumed to come from above
- if light comes from underneath it would look like they’re sticking out
object perception
binocular and monocular cues give perception for distance
- object perception needs knowledge about the world
We are good at recognizing imaged and objects…but the image on the retina is limited
** how do we represent the information in the image
** how is this representation matched against a representation in memory
Gestalt Psychology
early approach that looked at how we segregate and group visual information
“the whole world is the sum of its parts”
* premise for theoritcal framework
Gestalt principles (6)
law of perceptual organization
different laws about how you interpret the world
Law of
* proximity
* similarity
* good continuation
* closure
* common fate
* pragnanz
Gestalts laws (5)
Law of proximity
* tend to groups things together the closer they are (has to do with the context of how they are viewed)
Law of similarity
* tend to group together what is most visually similar
Law of good continuation
* how you extract different parts of an object as belonging to that object
* can see that the baby has a full head instead of the bars that are blocking him
law of closure
* illusory contours – when lines of a picture don’t connect but you can interpret what it is
law of common fate
* has to do with motion
* idea that different small sections of a larger object are interpreted as that object as long as they move in the same direction
Law of Pragnanz: Gestalt Principles
interpretation gravitates towards simple explanations
Law of Pragnanz: organization of visual display should be as simple, stable, and as consistent as possible
object perception
bottom-up theories
* template theory
* feature theory
* prototype theory
top-down processes
* context effects
template theory
objects are represented by templates, current image is compared to these
cheque reading machines are an example of a device that uses such template matching
you have a copy of every object you’ve seen in your head
* so when you see the object again, you match it to the memory in your head to interpret what you’re looking at
problem: object has to be same size as template, also same position and orientation
* theory doesn’t allow same image to have different interpretations
* very little room for variability
feature theory
analyzed stimuli as a combination of elemental features
you recognize an object by searching memory for objects with those features
based on findings by Hubel and Weisel showing that we have cortical cells that react to specific features
discovery was by accident
discovery that certain neurons will respond to basic physical features
each neuron feeds into other neurons that collects and combines information until you get the different letter in your head
Pandemonium model
the greater the match between the feature and incoming information, the stronger the signal and the resulting representation is based on which of the features is perceived the strongest
this was the basis for neural net models that they made and are still being used today
evidence for feature theories
Kinney had subjects name briefly presented letters (more mistakes with some letters)
* more confusion with similar letters
faces are better recognized as caricatures than accurate line drawings (Rhodes)
* because caricatures exaggerate features leading to faster recognition
disadvantage of feature theory
hard to say exactly which features we have
doesn’t account for the relative position of those features
* no information in feature theory about what the ordering is
* couldlead to different interpretations of the same stimuli
prototype theories
prototype = the one ideal for a category
perceive object by comparing it to stored prototypes
works at a higher level than feature theory
* takes all representations of the same item and makes into an average which becomes the ideal representation of the object
comparing objects to an average = more room for differences and its less static bc its a prototype and not a template
disadvantage of prototype theories
prototypes are more flexible than features, but also vaguer
criticism is in its definitions
how we store prototypes is vague
bottom-up vs top-down processes
bottom-up processing
* data-driven
* sensory information
* external stimuli
top-down processing
* conceptually driven
* assumptions based on knowledge and experience bc the stimuli might be vague
* world knowledge
* expectations and biases
how do we recognize objects?
- viewer-centered theories (modified template theory)
—> store multiple representations of objects
–> perform transformations of stimuli to match stored representations
more like prototype theory
* everything is stored as a representation that you can use to identify objects later on
* you can transform an experience spatially to match an experience that you had before
Tarr’s multiple view theory
theory on how we recognize objects
there are many representations of a car in your head
even if its a different version, you can change it in your head to match the object
evidence: recognition of novel objects from different view points (Tarr)
– take a snapshot of object and then do a 3D transformation in your head
results of study: showed that multiple views that were learned were stored separately
object perception today
Object recognition requires some form of representation
*top down and bottom up
–> helmholt’s unconscious inference (early 1900s)
–> Bayesian inference (current)
Bayesian theories of object recognition
probability
perceive a stimulus - make a representation of it - use priors which is the probability of distribution
use knowledge, assumptions, and expectation of what you see – combine these with probability distributions to end up with the posterior which is the interpretation of the stimuli
this model allows the system to learn
* because you can use a probability from one experience as a prior for another interpretation
priors get modified by experience
based on assumptions?
what about the real world?
idea that we have a stable representation of the world
but it’s easy to miss stuff
* representations are not as precise as we think
change blindness
change blindness
not noticing when something is happening
* the gorilla
but as soon as you attend to the area with the changing stimulus, you can see it right away
perception
the experiences resulting from stimulation of the senses
basic characteristics of perception
perception changes based on added info
process similar to reasoning or problem solving
perception is automatic and occurs in conjunction with action
creates a picture of our environment
why is it so difficult to design a perceiving machine?
stimulus on the receptors is ambiguous
* inverse projection problem
* ambiguous bc an image on the retina can be created by many different objects
objects can be hidden or blurred
objects look different from different viewpoints
scenes contain high-level information
* moving objects = more complexity
example of top down processing
all blobs are identical but they are perceived as different objects depending on their orientation and the context within which they are seen
hearing words in a sentence
speech segmentation: ability to tell when one word in a conversation ends and the next one begins
* aided by knowing meaning of words
continuous sound signal enters the ears and triggers signals that are sent toward speech areas (bottom-up)
if person understands the language, their knowledge creates the perception of individual words (top down processing)
transitional probabilities: likelihood that one sound will follow another within a word
statistical learning: process of learning about transitional probabilities and about other characteristics of language
* happens too with vision, based on learning about types of things that usually occur in the environment
Helmholtz theory of unconscious inference
realization - image on retina is ambiguous
asked how the perceptual system decides the pattern on the retina
likelihood principle: perceive the object that is most likely to have caused the pattern of stimuli
unconscious inference: perceptions are a result of the unconscious assumptions or inferences we make
gestalt principles of organization
Wundt said our experiences can be understoof by combining basic elements of experience called sensation
Gestalt rejected idea that perception is formed by adding up sensations
gestalt said idea of apparent movement
* an illusion of movement perception that occurs when a stimuli in different locations are flashed one after the other with proper timing
Basic principles of Gestalt psychology
* the whole is different than the sum of its parts
* led Gestalt psychologists to explain how small elements of a scene become perceptually grouped to form larger units
good continuation: when points/lines are seen as being connected
Pragnanz: German “good figure”
* aka principle of simplicity
* every stimulus pattern is seen in such a way that the resulting structure is as simple as possible
principle of similarity
* similar things appear to be grouped together
* grouping can occur based on similarity of size, shape, or orientation
taking regularities of the environment into account
regularities in the environment: regularities like blue sky and green landscapes
physical regularities: regularly occurring properties of the environment
semantic regularities: meanings of words
scene schemas: person’s knowledge about what is likely to be contained in a particular scene
* knowledge of what is usually in an office may cause a person to look towards the desk to see the computer
bayesian inference
Bayes: proposed that our estimate of the probability of an outcome is determined by two things
- the prior probability which is our initial belief about the probability of an outcome
- the likelihood of the outcome
ex: priors in your head that books are rectangular
comparing the four approaches of object perception
the four conceptions of object perception
* Helmholtz unconscious interference
* gestalt laws of organization
* regularities in the environment
* bayesian inference
Helmholtz, regularities, bayesian
* all have in common that we use data about the environment, gathered through our past experiences in perceiving (top down processing)
Gestalt
* idea that principles of organization are built in
* yes perception is affected by experience but he thought that built-in principles can override experience, thereby bottom-up processing
neurons that respond to horizontals and verticals
there are more neurons that respond to horizontals and verticals
theory of natural selection
* good characteristics will survive
experience-dependent plasticity
the shaping of neural responding by experience aka experience dependent plasticity
demonstrated using fMRI
results show the brain’s functioning can be “tuned” to operate best within a specific environment
continued exposure to things that happen regularly can cause neurons to become adapted to respond best to these regularities
movement facilitates perception
adds complexity but also helps us perceive objects more accurately
allows to see different viewpoints
where and what streams
what pathway: involved in initial perception
where pathway: determine location
- perception pathway: from visual cortex to temporal lobe = what pathway
- action pathway: the how pathway
= where pathway
mirror neurons
neurons that respond both when a monkey oberves someone else grasping an object and when monkey itself grapbs object
the neurons responses to watching the experimenter grasp an object is similar to the resopnse that would occur if the monkey were performing the same action
