1
Q
The Gestalt Philosophy
A
The whole is other than the sum its parts. Or… The whole has an independent representation in the perceptual system and thus cannot be reduced.
- Analyzing every photograph in a movie will not provide the same experience as watching the movie itself
2
Q
Gestalt Principles
A
Laws that describe how we organize visual input.
* Believed to be innate
- Figure-Ground Segregation: Ability to distinguish an object from its background.
- Proximity: Tendency to group elements that are close together in space.
- Closure: Tendency to fill in gaps in a contour to perceive a whole object.
- Similarity: The tendency to group together elements that are physically similar.
- Continuity: The ability to perceive a simple, continuous form rather than a combination of awkward forms.
- Common Fate: Tendency to group together elements that change in the same way.
3
Q
Figure-Ground Segregation
A
Part of Gestalt’s principles.
- Figures tend to have distinct borders that give it form over background
- Automated process influenced by experiences, biases, heuristics
4
Q
Proximity
A
Part of Gestalt’s Principles.
- Tendency to group elements that are close together in space
- Daisy example: Regions of high density are seen as one group
5
Q
Closure
A
Part of Gestalt’s Principles.
- The tendency to fill in gaps in a contour to perceive a whole object
- Example: Pole covers truck right in the middle… but we are still able to perceive the truck as a whole object by filling in the gaps
6
Q
Similarity
A
Part of Gestalt’s Principles
- The tendency to group together elements that are physically similar
- Example: Grid of alternating x’s and o’s… we see columns of the same elements as belonging together (Rather than xoxo)
7
Q
Continuity
A
Part of Gestalt’s Principles.
- The ability to perceive a simple, continuous form rather than a combination of awkward forms
- “X” is seen as 2 diagonal lines, rather than V and upside down V
8
Q
Common Fate
A
Part of Gestalt’s Principles.
- The tendency to group together elements that change in the same way
- Example: School of fish are moving together in the same direction, hence grouped together!
- Seeing a camouflage animal once it moves (elements of the animals pattern that is moving at the same time)
9
Q
Bottom-Up Processing
A
- Object recognition is guided by the features that are present in the stimulus
- Recognizing what you see by analyzing individual features and comparing it to things w/ similar features in memory
- However, expectations influence our perception…
AKA. Data-driven
10
Q
Top-Down Processing
A
- Object recognition is guided by your own beliefs or expectations
- Recognition can be primed in top-down processing
- Requires input from stimulus to work (in order for expectations about stimulus can influence your recognition of it)
AKA Prediction processing
11
Q
Priming Experiment
A
- Experimenter measures how fast a participant can read aloud a word that is flashed on a screen
- Participant told the next word is a type of animal (establishing an expectation)
- Priming Effect: If subsequent word is an animal, it will be recognized and read much faster than non-animal words
12
Q
Bi-Directional Activation
A
Processing in object recognition occurs in both top-down and bottom-up processing
- Features of object and expectations guide recognition
13
Q
Geon Theory
A
We have 36 different geons stored in our memory that helps us recognize 150 million different objects.
- Geon: Simple geometric form (Cone, sphere, cylinder, etc.)
- Example: Ice cream is just a cone and a sphere
- Processed at a different level of neural signalling, separate from the area of brain damage (comeback to con (2) )
CONS:
(1) Complex stimuli (faces, crumpled piece of paper) are able to be recognized, but geons may be ambigious…
(2) Brian injury can affect recognition for only certain types/category of objects (if geons involved, deficits in recognizing objects based on shape, not category)
(3) Variation in lighting can alter our perception of features
AKA “Recognition-by-components” / RBC
14
Q
Template Theory
A
We compare objects to templates in memory.
- EXACT Match found → familiar object, named by activating connections to language areas in brain
- Match not found → unfamiliar object, new template is stored in memory
- Comparable to exemplar theory (but that theory doesn’t require an exact match like this one!)
CONS:
(1) Too many different stimuli exist to feasibly store in memory (Prototype theory needed!)
15
Q
Prototype Theory
A
We compare objects to our ideal prototype.
- More flexible than template theory as an exact match is not needed
- Easy recognition of common objects and individual objects
CONS: We can categorize unique/specific objects
16
Q
Neural processing of object Information is done in ……………..
A
Parallel.
- Different brain systems process different components of the visual signal simultaneously
17
Q
Perceptual Constancy
5 Types
A
Ability to perceive an object as unchanging even through the visual/retinal image produced by the object is constancy changing
- Retained despite variation in visual stimuli
- Example: You are still able to recognize your dog regardless of distance, light, angle, etc.
- Existing knowledge provides top-down influence on perception (most objects don’t change!)
- Cues are used to perceive constancy in an object
TYPES:
- Shape constancy
- Location constancy
- Size constancy
- Brightness constancy
- Colour constancy
18
Q
Shape Constancy
A
An object is perceived to have a constant shape.
- Despite the shape of its retinal image changing w/ shifts in POV or object position
19
Q
Location Constancy
A
Object is perceived to be stationary despite changing lcoation on our retina due to body movements.
- Example: While driving we don’t perceive the objects outside to be moving
AKA “Position Constancy”
20
Q
Size Constancy
A
An object is percieved to be the same size despite the size of its retinal image varying w/ distance.
- Retinal image gets smaller as object moves away
- We are able to percieve depth… object is just getting farther away
21
Q
Brightness Constancy
A
An object is perceived to be the same brightness despite reflecting more or less light onto our retina.
- Depends on ambient lighting condition
- Objects have the same brightness whether in high or low illumination
22
Q
Colour Constancy
A
An object is perceived to have a constant colour despite different illumination conditions.
- Able to recognize different colours of light shining on object
23
Q
Cues in Visual System
A
- Used as clues to perceive constancy in an object
- Edges, contours, textures, luminance, colour
Example:
- Depth cues indicate the size of an object relative to its distance (preventing you from seeing the object shrinking in size as distance increases)
- Colour cues indicate the influence of light on an object’s colour (Many objects under a coloured light will change colour, not just target object)
24
Q
Perception of Overlapping Objects (Development)
A
3 month olds in percieving overlapping objects
- Arises from ambiguities in perception
- Helps examine perceptional strategies can be manipulated
- Perceptual constancies can be overcome by removing relevant contextual info
25
Muller-Lyer Illusion
>---<
<--->
* Misapplies size constancy and misterprets depth
* Angled lines that are perceived as closer → shorter
* Perceived as further → longer
* Cultures without exposure to right angles are less susceptible to this illusion
26
The Ames Room
* Trapezoidal room where one side is closer to you than the other, making individuals seem drastically different in height
* Manipulates distance to trick size constancy
27
Ponzo Illusion
/---\
/ --- \
* Manipulates depth cues (convergence) to trick size constancy
* Top is like a point in the distance, further → longer
* closer → shorter
28
Ganglion Cells in Object Recognition
* Axon of cells exit via optic nerve → LGN → Primary Visual Cortex
29
Feature Detectors
* Cells in the primary visual cortex that detect features
* Simple, complex, hypercomplex cells
* FIre maximally in response to different stimuli
30
Hodgkin & Huxley's Squid Experiment
* Electrical activity of nerve cells recorded in squid **giant axon**
* 1.5 mm in diameter (compared to 0.5mm)
* Enhances responding of water jet propulsion system in the quid
Inspired other researchers to investigate how individual neurons respond to specific stimuli:
* "Bug detectors": Cells in frogs that only responded to moving black dots
31
Visual cortex neuron firing can be affected by stimulus:
* Location
* Orientation
* Direction of movement
32
Hubel & Wiesel's Feature Detector Cells
* Goal was to learn what type of stimuli the individual cortical cells responded to
METHOD:
* Microelectrodes placed in the cortex of a cat to record electrical activity of indv. neurons
* Cat was shown different types of visual stimuli (flashing lights, etc.) → not much response
* Cat present slide w/ crack in it that moved across visual field → lots of neuronal response!
* Lines of varying thickness, angles, orientations were presented
* Neurons fire maximally at a stimuli of a specific shape, size, position, movement
33
Simple Cells
Feature cells that respond maximally to a bar of a certain orientation in a particular region of the retina
* Receptive field is organized in an opponent fashion
* No stimulus → Baseline
* Bar w/ specific orientation allowing it pass through ON region → Strong excitatory response
* Bar w/ unpreferred orientation making it pass through OFF region → Strong inhibitory response
34
Complex Cell
Feature cell that responds maximally to a bar of a certain orientation, regardless of location. Some also respond maximally to a specific direction of movement.
* Indifferent to the position of light on its receptive field
* Continues to fire if bar is moving within receptive field
* There COULD be a direction of movement causing maximal cell firing
* No stimulus → Baseline
* Bar w/ specific orientation allowing and direction of movement regardless of where it is on receptive field → Strong excitatory response
* Bar w/ unpreferred orientation or direction of movement → Strong inhibitory response
35
Hypercomplex Cells
Feature cells that respond maximally to a bar of a particular orientation and direction of movement, ending at specific points within the receptive field.
* Receptive fields have a region of inhibition at the end
* No stimulus → Baseline
* Bar w/ specific orientation, direction of movement, allowing it pass through ON region → Strong excitatory response
* Bar w/ unpreferred orientation making it pass through OFF region → Strong inhibitory response
36
Topographic Organization in Visual Cortex
* Layout of visual scene preserved in visual cortex
* Neighbouring areas on visual field processed in neighbouring areas on brain
* Not exact → Largest amt of cortex devoted to processing info from fovea
* Allows for parallel processing
37
Why have simple and complex cells if hypercomplex cells are more specific?
* Conservation of energy... cases where only simple and complex are needed to process some stimuli
* Allows brain to optimally balance the function of each
38
Visual Association Cortex / Extrastriate Cortex in Visual Integration
* Surrounds V1
* Multiple subregions that each recieves different info from V1 about visual scene
Information segragated into two streams
* Dorsal: Where objects are located and how they are moving (V1 → Parietal)
* Ventral: What the object is, form and colour (V1 → Temporal)
39
Temporal Cortex in Responding to Stimuli
* Arranged in vertical columns orientated perpendicularly the orientation of the cortex
* Heavy duty "WHAT" processing... very specific and complex stimuli
* Each cortical column → 6 layers of neurons (corresponds to complex stimuli from same category)
* Each successive layer responds to slightly different features within category
* Objects are represented by activity patterns, rather than specific neurons
40
Can infants perceive visual stimuli the same way we do?
| and why?
No. Even if they have the right machinery, they do not perceive patterns, objects, and faces like adults do.
* This is due to poor visual acuity limiting their ability to perceive whole forms!
* Infants prefer to look at complex patterns (that they can perceive!*) over plain stimuli
| *checkerboard grid example
41
When do infants begin focusing on whole forms?
| Describe the experiment that confirmed this fact.
After two months.
EXPERIMENT: Eye tracking, where is visual attention focused?
* 2 week old shown triangle... they look only at one corner
* 12 week old shown triangle... they looko at the entire shape
Hence, newborns are only attracted to certain features of a stimulus (angles, edges, ...) & whole form perception is **learned** in the first 2 months.
42
When do infants begin perceiving partial forms as whole forms?
| Describe the experiment that confirmed this fact.
3 months.
* Infants observe objects more holistically guided by Gestalt principles
EXPERIMENT: Habituation!
* Repeatedly present whole form stimulus (square) to infant until habituated
* Presented w/ new stimulus:
* 4 circle square (less interest/time as it's like the square)
* 4 circle circle (more interest/time)
Hence, 3 month olds are guided by Gestalt principle of closure and can perceive whole objects instead of isolated parts.
43
3 month olds in percieving overlapping objects
Can identify separate objects if objects move independently of one another.
44
3 month olds in percieving overlapping objects
Begin to use cues like colour and texture to distinguish objects.
* Even if neither are moving!
45
When do infants develop perceptual constancy?
4 months.
* Brightness, colour, shape
* Teddy bear experiment demonstrated that 4 month olds understand that an object that is farther away should produce a smaller retinal image (**size constancy**)
46
Preference to Face Stimuli
| Experiment?
* Innate preferences allowing infants to oreint towards PEOPLE, forming necessary social bond
EXPERIMENT: Infants shown many stimuli... but prefer looking at faces
* By 2 months, infants prefer to look at attractive over unattractive faces + preferring mothers face
* By 5 months, they detect different emotional expressions
COUNTEREXPERIMENT: Infants may have no preference for faces over equally complex stimuli...
(1)Infants were shown three faces: one w/ arranged features, disarranged features, control
* Infants preferred to look at the first two the same amount
(2) Infants shown to focus gaze on outer contours of the face
| overall our early experiment with faces develops our preference for them
47
Kitten Visual Deprivation
STRIPED:
* Kitten 1 was raised in a cylinder w/ only vertical stripes.... failed to develop feature detectors for horizontal stripes
DARK:
* 1 month old kittens kept in dark for 3-4 days experience visual degeneration
* 1 month old kittens kept in dark for an entire week suffer severe and permanent visual degeneration
* **visual degeneration** occurs because brain starts using cells for vision for other functinos
48
Do humans have a sensitive period in human visual development?
| How did we do experiments on ts
Yes, some form of early visual input is needed.
* Experiments w/ kids that had **cataracts** (cloudy lens) and were corrected at different ages
* Infants experienced INCREASE in visual impairment the LATER they had cataracts removed (less visual exposure)
* **Sleeper Effects:** Deficits are not revealed until individual is further developed
49
Cataracts
* Lens becomes cloudy, only allowing diffused light to reach retina
* Results in a complete loss of ability to perceive objects, patterns, or details
50
Damage to Regions in V1 Results In...
* Loss of vision in specific visual fields
* You are still able to recognize objects
51
Visual Agnosia
* Damage to Extrastriate/Visual Association Cortex
* You would be able to SEE all the objects in the scene
* Difficulty in object recognition
52
Object Agnosia
* The inability to perceive objects
Could be specific objects!
* E.g: Can't recognized different tools but can recognize fruits
* Many are able to read as well (recognizing letters different from recognizing objects
53
Prosopagnosia
* The inability to recognize faces
* Pattern recognition disorder
* Damage to the **right fusiform gyrus**
* Can recognize categories but not specific objects (can rec dog, but not their own dog)
* Not related to memory loss or impaired vision
* Must rely on other cues (voice, smell, walk, etc.)
* Even familiar faces, and own face in mirror
54
Law of Pragnanz
We have a bias to organize things into the simplest organization.
* Pyramid of triangles vs. triangle, triangle, triangle, ...
55
Carpentered World Hypothesis
Our experience of living in a world of human made objects (buildings, furniture, etc.) with right angles drive the Muller-Lyer illusion
* Individual from more rural areas (less experience w/ buildings) are less susceptible to the illusion
56
Pareidolia
| Facial Pareidolia
Interpret vague stimulus as something familiar to observe....
**Facial Pareidolia:** Seeing faces when a face isn't present due to patterns
57
Two Strategies for Processing Faces
| Corresponding evidence
Configural Processing: Processing faces as a whole (holistic)
* Flashed face distortion effect
* Inversion effect
* Tatcher illusion
Featural Processing: Processing each feature individually
58
Flashed Face Distortion Effect
Comparative distortion based on last appearing face in periphery
59
Inversion Effect
We are slower at processing inverted faces as we are used to eyes being above the nose, nose being above the mouth, etc.
60
Thatcher Illusion
Mouth and eyes inverted when face is upside down
* We are not accurate at processing it
* Looks creepy only when its rightside up
61
The Hollow Face Illusion
* 2 hypotheses: H1, faces are convex ; H2, faces are concave
* Experience tells us H1 >>> H2
* Seeing all the features of the hollow face… it is seen as convex (popping out) due to prior experience
62
Microexpressions
* Lying people show microexpressions of fear and disgust
* Concealed emotions that are shown on the face for a short amount of time
Psych 1XX3
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