Define perception
experiencing that results from stimulation of senses
What are the properties of perception?
- Perception can change based on added information
- It involves a (often unconscious) process which is similar to reasoning or problem solving
- It also occurs in conjunction with actions- it is more than seeing or hearing, central to our ability to organize the actions that occur as we interact with our environment
What does perception tell us about objects, and stimulus?
- The stimulus on the receptors are ambiguous:
- when u look at a paper, the image cast by the borders of the page on your retina is ambiguous
- the perceptual system is not concerned with determining an object’s image on the retina
- it starts with the image on the retina and
- its job is to determine what obj is ‘out there’ created by the image
- this is related to the inverse projection problem
- Objects can be hidden or blurred:
- people can often identity objects that are obscured -> incomplete/ blurry
- this occurs frequently in the environ
- but people know that part of an obj that is covered will continue to exist
- they are able to use their knowledge of the environ to determine what is present
- Objects look different from different viewpoints:
- this is related to Viewpoint Invariance
Describe the Inverse Projection Problem
- task of determining the object responsible for a particular image on the retina
- as it involves starting with the retinal image
- and then extending rays out from the eye
What is Viewpoint Invariance, and hence Viewpoint dependent theories?
Viewpoint Invariance theories:
- people’s ability to recognize an object
- even when it is seen from different viewpoints
- Biederman : object recog is not affected by observer’s viewpoint
Viewpoint Dependent theories:
- Tar & Bulthoff: changes in viewpoint reduce the speed/ accuracy of obj recog
- Milner & Goodale: brain has both visual processing systems
What is Bottom-up processing and what theory is it related to?
Bottom up processing:
- looking at smth creates an image on the retina
- it starts at the bottom/ beginning of the system
- this is where environmental energy stimulates the receptors
- in this case, perception starts with the senses
It is related to Direct Perception Theories.
- perception comes from stimuli in the environment
- parts are identified and put tgt -> recognition occurs
What is Top-down processing and what theory is it related to?
Top down theory:
- processing that originates in the brain
- starts from the top of the perceptual system
- it involves factors like the person’s knowledge of the environment
- also, expectations that people bring into the perceptual system
It is related to Constructive Perception theories.
- people actively construct perception using info based on expectations
What are the two main conceptions of Object Perception?
- Helmholtz’s theory of unconscious inference
- TOP DOWN THEORY
- some of our perceptions are the result of unconscious assumptions we make abt the environ - Gestalt Principles of organization
- BOTTOM UP THEORY
- our overall experience can be understood by combining basic elements of experience called sensations
- perceptions can be explained by adding up small sensations
What are the concepts involved in Helmholtz’s theory of Unconscious Inference?
- Likelihood principle
- we perceive the obj that is most likely to have caused the pattern of stimuli we have received
- the judgement of what is most likely to occur accord to this
- this happens through unconscious inference - Unconscious Inference
- our perceptions are the result of unconscious assumptions
- or inferences that we make about the environment
Explain Helmholtz’s theory of Unconscious Inference in object perception.
HTOUI:
- some of our perceptions are the result of unconscious assumptions we make about the environment
- his qn was ‘how does the perceptual system decide that his pattern on the retina was created by overlapping rectangles?’
- his answer was based on the Likelihood Principle
- this happens through Unconscious Inference
- HENCE we infer that the pic on the left is a rect covering another rect because of past experiences we have had with them
- IMP: this process of perceiving what is most likely to have caused the pattern on the retina happens
rapidly and unconsciously - these unconscious assumptions are based on the likelihood principle
- which result in perception that seems instantaneous, even tho they r the outcome of a rapid process
What are the concepts involved in Gestalt’s principles of Organization?
Apparent movement- illusion of movement created by stroboscope, as though movement is perceived, nothing is actually moving
- one light flashes on and off at the left side of screen
- there is a period of darkness for a fraction of second
- the second light flashes on and off on the right side
- the resulting perception is a light moving from left to right
- however this actually does not happen even though it seems like it did
HENCE
A. apparent movement cannot be explained by sensations
- as we saw, there is nth in the dark space betw flashing lights
B. the whole is different than the sum of the parts
- the perceptual system creates the perception of movement from stationary images
Explain the Gestalt principles of organization, in object perception.
GPOO:
- perceptions can be explained by adding up small sensations
- intrinsic laws that are built into our syste
- the eg. of Apparent movement can explain how the whole is different than the sum of the parts
- this gave rise to some principles of perceptual org to explain the way elements are grouped together to create larger objects
- Good continuation
- points when connected, result in straight or smoothly curving lines
- these are seen to be belonging together
- lines tend to follow the smoothest path
- objs that are overlapped by other objs are perceived as continuing behind the overlapping obj - Pragnanz/ Principles of simplicity
- the law of pragnanz states that every stimulus pattern is seen in such a way that the resulting structure is simple as possible - Similarity
- similar things appear to be grouped tgt
- eg. columns of red circles vs alternating columns of red and blue circles - Closure
- tendency to see visual items as part of a larger obj - Figure Ground Segregation
- there is a figure and a background
- we are mostly able to see both alternately - Proximity
- how close elements are together
- the strongest proximity relationships are those between overlapping subjects
- but just grouping objects into a single area can also have a strong effect.
- the opposite is also true, by putting space between elements, you can add separation even when their other characteristics are the same.
What are physical regularities and hence the oblique effect?
physical regularities:
- regularly occurring physical properties of the environment
- eg. there are more vertical and horizontal orientations in the environ than obliqued/ angled orientations
- this occurs in human made environments
oblique effect:
- it is therefore no coincidence that people can perceive horizontals and verticals more easily than other orientations
- eg. sand identations -> rounded moulds when pic is flipped -> we interpret light to come from above because that happens on earth
What are Semantic regularities and hence Scene schemas?
Semantic regularities:
- characteristics that are associated with the functions carried out in different types of scenes
- semantics here refer to the meaning of a scene
- this meaning is often related to what happens within a scene
Scene schema:
- our visualisation contains info based on our knowledge of diff kinds of scenes
- and the expectations created by scene schemas, contribute to our ability to perceive objs and scenes
Define Heuristics and hence Algorithms.
Heuristics:
- rule of thumbs
- provide the best guess solutions
- to a prob quickly and correctly
- gestalt laws are heuristics
Algorithms:
- procedure guaranteed to solve a prob
- it takes longer and is slow
- hence it shd produce a definite result
Explain Feature analysis through Geons
3D feature models- are extensions of models to use 3 dimensional features.
Recognition by components theory (RBC)- we perceive objects by perceiving elementary features
Geons:
- are 3D volumes
- there are 36 diff geons proposed and objs are recognized when enough info is avail
- geons can also account for local viewpoints
- local viewpoints: you can identify objs from many diff orientations
What is movement and how is movement related to perception?
Movement- helps us perceive things in our environ more accurately than still images
- Movement helps us perceive objs more accurately
- they reveal aspects of objs that are not apparent from a single viewpoint
- this provides added info - Movement also helps us perceive objs by revealing add info
Describe the What and Where processing streams in the brain.
This involves both brain ablation and neuropsychology.
Ungerlaider and Mishkin
- provided monkeys with 2 tasks
- Obj discrimination prob: shown rect solid and presented with 2 choice task with a target obj (rect) and another stim (tri solid). if monkey pushed target obj it received food
- Landmark discrimination prob: tall cylinder is landmark, and it indicates a food well with food contained in it. need to move the food well close to cylinder.
What/ ventral pathway:
- ablation and part of TL removed
- obj discrim task was difficult for these monkeys
- neural pathway that reaches TL is RESPONSIBLE for determining obj’s identity
- the what pathway: leads from striate cortex to TL
- HENCE IT IS IMP FOR OBJECT PERCEPTION
Where/ dorsal pathway:
- other monkeys had PL removed
- they had difficulty solving landmark prob
- pathway that leads to PL is RESPONSIBLE for determining obj’s location
- the where pathway: leads from striate cortex to PL
- HENCE IT IS IMP FOR SPATIAL PERCEPTION
THIS VISUAL PATHWAY ONLY FOCUSES ON VISUAL REPRE AND DOES NOT EXPLAIN INTERACTION WITH OTHER NON VISUAL PROCESSES
Describe the What and How processing streams in the brain.
Milner and Goodale:
- used neuropsych approach
- 34 yr old woman w damage to TL
- asked to rotate a card in her hand to match diff orientations of a slot ( she could not )
- because she had trouble doing it, it would seem she would have trouble placing the card thru slot
- but when asked to do so, she could
- once she started moving the card towards the slot, she was able to rotate it to match orientation of slot
- she performed poorly in static orientation task, but did well when action was involved
What/ perception pathway:
- based on ventral pathway
- from visual cortex to TL
- LONG LASTING, VIEWPOINT INDEPENDENT REPRESENTATIONS
How/ action pathway:
- based on dorsal pathway
- from visual cortex to PL
- SHORT LASTING, VIEWPOINT DEPENDENT REPRESENTATIONS
THE PERCEPTION ACTION MODEL EXPLAINS VISUAL MOTOR INTERACTIONS.
