Final Cumulative Flashcards
(157 cards)
1
Q
What is an Environmental (Distal) stimulus
A
An object in the world that creates (leading to) a perception, like a tree.
2
Q
What is Perceptual Process?
What are the 7 steps?
A
A sequence of steps leading from the environment to perception of a stimulus, recognition of the stimulus, and action with regard to the stimulus.
Seven Steps:
1) Stimulus in the Environment
2) Light is reflected and Focused
3) Receptor Processes
4) Neural Processing
5) Perception
6) Recognition
7) Action
3
Q
What is a proximal stimulus?
A
The stimulus on the receptors.
The image formed on the retina from the distal stimulus.
4
Q
Principle of Representation
A
A principle of perception that everything a person perceives is based not on direct contact with stimuli but on representation of stimuli on the receptors and in the person’s nervous system.
5
Q
What is Visual Pigment?
A
A light-sensitive molecule contained in the rod and cone outer segments. The reaction of this molecule to light results in the generation of an electrical response in the receptors.
6
Q
What is transduction?
A
The conversion of light energy into electrical energy by sensory receptors that propagates through other neurons in the retina and then to the brain
- Receptors responsible for the transduction in vision are the rods & cones
7
Q
What are the two components of Visual Pigment? What occurs and where does it occur?
A
1) Opsin - a large protein
2) Retinal - a light-sensitive molecule
Retinal absorbs light–Retinal changes its shape–becomes an isomer of retinal (itself)
- This occurs in the outer segments (pigments reside)
8
Q
What is Neural Processing? (step 4 of perception)
A
Activity in sensory organs causes neural signals that are transmitted to the brain
9
Q
What is the difference between perception and recognition?
A
Perception is becoming aware of a stimulus; recognition is identifying what the stimulus is.
10
Q
What is the absolute threshold?
A
The smallest (minimum) stimulus necessary that can be detected 50% of the time.
11
Q
What is the difference threshold?
A
The smallest CHANGE in a stimulus that produces a noticeable difference. It can be detected 50% of the time.
12
Q
What are the three relationships to study perception? Elaborate each relationship
A
- Relationship A: The stimulus-perception relationship
- Relationship B: The stimulus-physiological relationship
- Relationship C: The physiology- perception relationship
13
Q
What is Bottom-up Processing?
A
- Also called stimulus-based or data-driven processing
Processing based on incoming information from the environment.
14
Q
What is Top-Down Processing
A
- Also known as knowledge-based processing.
Processing based on the perceiver’s prior knowledge.
15
Q
What is Visual Form Agnosia?
A
The inability to recognize objects.
16
Q
What is the wavelength range on the EM Spectrum that is visible to us?
A
400-700 nanometers
17
Q
What is the function of the cornea?
A
Provides 80% of the eye’s focusing power.
18
Q
What is the function of the lens?
A
Adjust shape for object distance; accounts for the other 20%
19
Q
What is Accommodation?
A
Results when ciliary muscles are tightened, which causes the lens to thicken (20% focusing power)
20
Q
What are Spectral Sensitivity Curves?
A
Shows perceptual sensitivity to light of different wavelengths.
21
Q
What is the structure of the retina?
A
The retina is made up of layers of cells.
Rods and cones are found in one layer on the retina.
The final layer of neurons is made up of ganglion cells, which have long axons that project to the brain.
- Rod and Cone Receptors (Face away from the lens towards the back of the eyeball to receive nutrients, oxygen, and replacement molecules for pigments)
- Optic nerve (very long axons that bundle together.)
22
Q
What is the structure of the fovea
A
- The fovea is the central region of the retina that gives rise to highest-acuity vision.
- Fovea is the focal point
-Retinal cells are “pushed aside” at the fovea, making a pit. (0 degrees) - light can get to the photoreceptors (cones) directly
- Only cones found in the fovea
- Blind spot
- Image is focused best on the fovea
23
Q
What do rods detect?
A
Low light levels, useful for night vision.
24
Q
What do cones detect?
A
Color and fine detail in bright light.
25
What is the fovea?
The area of the retina with the highest visual acuity.
26
What is Macular Degeneration?
A clinical condition that cause degeneration of the macula, an area of the retina that includes the fovea and a small surrounding area
Creates a blind region in central vision, so when a person looks directly at something, they lose sight of it.
27
What is Retinitis pigmentosa?
A retinal disease that causes a gradual loss of vision, beginning in the peripheral retina
28
what is myopia or nearsightedness?
Occurs by what two factors?
An inability to see distant objects clearly.
1) Refractive myopia: in which the cornea and/or the lens bends the light too much.
2) Axial myopia: In which the eyeball is too long.
29
What is Hyperopia or Farsightedness?
A condition causing poor vision in which people can see objects that are far away but do not see near objects clearly.
30
What is the signal travel orientation of receptors? (Rods and Cones)
Signals that travel "vertically" :
- Bipolar cells
- Ganglion cells
- Ganglion axons
Signals that travel "horizontally":
- Horizontal Cells
- Amacrine cells
31
Is convergence greater for rods or cones?
Rods!
- Average of 120 rods to one ganglion cells
- Average of 6 cones to one ganglion cell
- Cones in Fovea have ONE to ONE relation to ganglion cells (no convergence)
32
Explain Spatial Summation
What is the trade-off for rods and cones?
By summing over rods, ganglion cells connected to rods can be more sensitive to low level of lights.
Trade off for Rods: They can't tell exactly where the light came from.
Trade off for Cones:
Cones need more light to respond than rods (but less convergence leads to better acuity)
33
What is dark adaptation?
The process by which the eyes become more sensitive to low light over time.
1) cone system adapts at one rate really fast but flattens out bc its not very good in the dark.
2) The rod system continues to adapt; starts to take over (get better) producing your vision.
34
(Infant Visual Acuity) What is the Preferential Looking Technique?
Infants prefer to look at more complex things.
If they prefer one stimulus over another, they must be able to see the difference
35
What is measuring EEG?
- Visual Evoked Potential: electrical activity tied to visual input
If there’s a different response to two stimuli, the brain must detect that difference.
36
What is lateral inhibition?
Is this reduction in firing of neuron caused by increased firing in nearby neurons.
37
What is Mach Bands?
People see an illusion of enhanced lightness and darkness at borders of light and dark areas
38
What is Hermann Grid Illusion? How does it Lateral Inhibition explain it
Receptors responding to white “corridors” send inhibiting signals to receptor at the intersection
Lateral inhibition causes reduced response from receptors at the intersections, which leads to the perception of gray instead of white.
39
What is a receptive field?
The area of the retina that, when stimulated, causes that neuron to change its response. (affects a neuron's firing rate.)
40
What are center-surround receptive fields?
where are they found?
Neurons that respond to light in the center and are inhibited by light in the surround.
- Center-Surround Receptive Fields are found in the retina (ganglion cells) and in the first stop in the brain. (lateral geniculate nucleus (LGN) of the thalamus)
41
Hubel Wiesel discovered what about receptive fields in V1?
Hubel Wiesel discovered that receptive fields in V1 are more complex than center-surround.
- Respond to lines of particular orientations and moving in particular directions
42
What is the Orientation Tuning Curve?
Shows the preferred orientation of response.
43
Given the type of cells, what are their characteristics of receptive field:
1) Optic Nerve Fiber( Ganglion Cell)
2) Lateral Geniculate
3) Simple Cortical
4) Complex Cortical
5) End-Stopped Cortical
1) Center-surround receptive field. Responds best to small spots, but will also respond to other stimuli
2) Center-surround receptive fields very similar to the receptive field of a ganglion cell
3) Excitatory and inhibitory areas arranged side by side. Responds best to bars of a particular orientation
4) Responds best to movement of a correctly orientated bar across the receptive field. Many cells respond best to a particular direction of movement.
5) Responds to corners, angles, or bars of a particular length moving in a particular
44
(Sensory Code)
What is Specificity Coding? Any flaws?
Individual neurons represent specific objects
- Also known as “Grandmother Cell” Coding
Problems with specificity coding:
Possibly too many different stimuli in the world to assign each to a specific neuron
When measured, turns out most neurons respond to a range of stimuli
45
What is Population Coding?
Groups of neurons represent specific objects
Patterns of firing across entire population of neurons represents specific objects
46
What are the dorsal and ventral pathways?
Dorsal is the 'where' pathway (location); ventral is the 'what' pathway (object recognition).
47
What is the Ventral Stream Receptive Fields?
As we move “forward” along bottom of temporal lobe
○ Receptive fields become larger
○ Visual features processed become more complicated
48
What is the Double Dissociation Evidence?
Conducted by Hans-Luka Teubuar on monkeys:
- Lesions in Temporal Lobe (IT) affected the ability to identify shapes ,but can still do landmark discrimination
- Lesions in Parietal Lobe (Dorsal Stream) affected the ability to identify locations but can still identify shapes.
49
How is the cortex organized?
By Modules:
A brain structure that processes information about a specific type of stimulus or does a particular type of analysis
● Modules are parts of larger networks that together fully process a stimulus
50
What is the Fusiform Face Area (FFA) ?
A region on the underside of right hemisphere temporal lobe (fusiform gyrus) also seems dedicated to face perception
51
What is prosopagnosia? (Face Blindness)
The inability to recognize specific faces. Caused by damage in the FFA
52
What is Pareidolia?
Tendency to see a face where there isn't one.
ex. Man on the moon
53
What is flashed face Distortion Effect ?
When faces are flashed very quickly one after another and they're in the periphery area, distortion occurs only occurs for faces.
54
What are four Recognition Modules and their repsondes?
1) Fusiform face area (FFA) responded preferentially to faces
2)Parahippocampal place area (PPA) responds preferentially to spatial layout
3)Extrastriate body area (EBA) responds preferentially to pictures of full bodies and body parts
4)Visual word form area (VWFA) responds preferentially to words over other stimuli or non-word letters
55
What is evidence for Visual Recognition Modules in Humans?
Also come from neuropsychology
○ Look at effects of brain damage on perception
○ Damage to one area (e.g., fusiform gyrus) leads to inability to recognize faces ○ Double dissociation:
■ Damage to fusiform face area leads to difficulty recognizing faces but not words, damage to visual word form areas leads to difficulty recognizing words but not faces
56
What is the retinotopic map?
The spatial organization of the retina preserved in the visual cortex.
- Two points that are close together on the retina project to neurons that are close together in visual cortex
- Two points that are further away from each other on the retina project to neurons that are further away from each other in visual cortex
Retinotopic Map in V1 is a distorted projection.
57
What is cortical magnification?
The fovea is overrepresented in the visual cortex (V1).
- Small central area of visual field, but larger region of V1
- Large peripheral area of visual field, but smaller region of V1
Due to neural convergence, there's less convergence at the center of the retina (fovea)
58
What is Column Organization?
The Cortex is Organized in Columns:
- Cortex (gray matter) is a thin folded (convoluted) sheet of neurons on top of the brain
■ Cortex is about 2-4 mm thick
■ If you measure what the neurons respond to at any given point at the surface of visual cortex, it’s the same all the way down
59
What is Orientation Columns?
Neurons within columns fire maximally (peak of tuning curve to the same orientation of stimuli )
○ Adjacent columns change preference in an orderly fashion
60
What are Location Columns?
The receptive fields for neurons within a column are all at the same (overlapping) location on the retina.
61
What are Hypercolumns?
Location + Orientation
○ About 1 mm across
○ Represents all possible orientation within a given region of retina
62
What is Tiling?
Columns working together to cover the entire visual field
63
The image on the retina is ambiguous!
What are the two general types of ambiguity?
1. Many to One Mapping
● Many (objects) to One (retinal image) Mapping
○ The same retinal image can be generated by an infinite number of environmental stimuli
2. One to Many Mapping
● One (object) to Many (retinal images) Mapping
○ The same environmental stimulus can generate an infinite number of retinal images
64
What is Occlusion?
Objects can be partly hidden by other objects.
(one-to-many)
65
What is viewpoint invariance?
You recognize it as the same object regardless of its orientation.
66
What are Gestalt principles?
What goes with what? Segregation and Grouping (e.g., Proximity, Similarity, Common Fate).
67
What is Figure-Ground?
○ Visual illusions show us the nature of the inferences when they go wrong
○ Illusory contours - contours that appear real but have no physical edge
■ Visual system infers that there must be a whole object in front of the circles
68
What is the difference between objects and scenes?
- A scene is acted within
- An object is acted upon.
69
What is scene gist?
Quickly understanding the overall theme of a scene.
- The scene category
- What the scene is generally about (its meaning)
- The general layout and spatial structure
70
What did Mary Potter (1976) prove ?
Showed that people can recognize scenes just about as fast as they can recognize individual objects picture is only presented for 1/4 second each.
71
What is Global Image Features? (of scenes)
- Degree of Naturalness
- Degree of Openness
-Degree of Roughness
- Degree of Expansion
-Color
These features are holistic (they're across the entire scene) and perceived rapidly.
72
What is the Palmer Experiment?
Demonstrated how seeing context effects can influence object perception.
○ Palmer Experiment:
■ Scene briefly flashed —time—> Then one object briefly flashed
● Results showed that:
○ Targets congruent with the context (a) were identified 80% of the time
○ Targets that were incongruent (B or C) were only identified 40% of the time
● Conclusion: scene context helps perceive object
73
What is Binocular Rivalry?
When 2 completely different images are shown to the 2 eyes, people perceive either one or the other image, and these tend to alternate over time.
- The only thing changing is the perception, not the stimulus.
74
What was the Tong et al. experiment (demonstrated binocular rivalry)
What type of relationship is this study?
Picture of a house shown to one eye and a face to another using filtered glasses (like 3D glasses)
■ fMRI showed an increase in activity in
● Parahippocampal Place Area (PPA) when they perceived the house
● Fusiform Face Area (FFA) when they perceived the face
Physiology-Perception Relationship.
75
What is the reciprocal relationship between perception and attention?
1) Visual Processing: Sends attention to a particular location/region of the visual field/stimuli
2) Attention:
The continuing visual processing, analysis of the object were attending to and gain further info.
76
What is overt attention?
Attention that involves looking directly at the attended object.
77
What is covert attention?
Attention that involves attending independently of looking.
(without moving the eyes)
ex: a basketball hidden pass
78
What is a Scan Path?
Changing/ Moving out attention- The sequence of those movements.
79
What is Fixations?
○ Period of time when the eyes are still
○ Overt attention is directed to a part of the scene
80
What is Saccadic Eye Movements?(Saccades)
Most common form of eye movements.
Very fast movements of the eyes from one location to another
- Moves overt attention from place to place.
81
What is Saccadic Suppression?
We are essentially blind during saccades.
82
What determine where overt attention is directed?
- Bottom-up Image (scene) properties.
- Top-down knowledge
83
What is Visual Salience? (Bottom up control of overt attention)
Areas of visual stimulus (e.g., scene) that attracts attention due to differences in their bottom- up image properties like color, contrast, orientation, motion
Ex. Orientation Salience
84
What is Salience Map?
Highlights salient regions of a scene based on image properties
● Image Salience = different from surrounding area
○ Brightness
○ Color
○ Edge orientation
● Eye movement studies show we tend to attend to (look at) these salient regions
85
What is Cognitive Factors?
(Top-down control of overt attention)
Top-down control of attention based on the perceiver’s knowledge
1. Knowledge about the scene and what it means
2. Knowledge about the task and goals
86
What is a Scene Schema?
A representation of our knowledge about scenes:
■ Knowledge about what is typically found, and where it is typically found, in different types of
scenes
87
What is the Posner Cueing Task? (Posner Paradigm)
■ Key concept is that the arrow directed attention to one side or the other (like a no-look pass)
■ Key Question: Does having attention in the right place (valid trial) rather than the wrong place (invalid trial) make it easier to detect the square?
■ Answer: Yes! Faster to respond following valid than invalid cue
■ We infer operation of covert attention from its behavioral consequences
88
Attention to specific locations is called?
Space-Based attention
89
Attention to specific objects is called?
Object-Based Attention
90
O’Craven et al (1999) – Overlapping houses and faces displayed in fMRI experiment, showed what about neural processes of attention?
■ Not that the stimulus isn’t changing
○ Attending to the face caused enhanced activity in the FFA
○ Attending to the house caused enhanced activity in the PPA
91
What is the Binding Problem?
What is the solution?
Modular systems in perception: features of objects are processed separately in different areas of the brain
Binding:
Process by which perceptual features are combined to create representations of coherent object
Attention bring all modular systems together.
92
What is Feature Integration Theory? The process?
Object
Preattentive Stage ( Features separated)
- Doesn't require attention.
Focused Attention Stage (Feature Combine)
Perception
93
Illusory Conjunctions
Because attention is required for correct binding, lack of attention leads to misperceptions.
94
What is a Inattentional Blindness?
Lack of perception due to lack of attention.
95
What is change blindness?
Failing to notice changes in a visual scene.
96
What is Attentional Capture useful for?
○ Helpful to predators seeking prey
○ Prey will often freeze to hide in plain sight
○ Hunting animals will freeze also so that any movement of the prey attracts attention
○ Change blindness illustrates this–
■ Easy to detect without a blank screen
97
What is "Real" Motion?
Caused by actual physical movement of the entities in the world that are perceived to be moving
98
What is the function of Reichardt detectors?
A neural circuit proposed by Werner Reichardt, in which signals caused by movement of a stimulus across the receptors are processed by a delay unit and an output unit so that signals are generated by movement in one direction but not in the opposite direction.
99
What is Corollary Discharge signal ?
A copy of the motor signal that is sent to the eye muscles to cause movement of the eye. The copy is sent to the hypothetical comparator of corollary discharge theory.
100
Corollary Discharge Theory
The theory that explains motion perception as being determined both by movement of the image on the retina and by signals that indicate movement of the eyes. See also Corollary discharge signal.
101
What is the Aperture Problem?
Motion can’t be detected by small receptive fields alone.
102
What is Akinetopsia?
Motion blindness caused by brain damage.
○ Damage of visual motion pathway, especially the medial temporal V5 area
■ Traumatic injury, Stroke, Alzheimer’s disease
● People perceive that objects are in new locations, but not the change while it’s happening
103
What are function of Area MT (V5)?
● Middle Temporal Cortex (Area MT) (or V5):
○ Specialized for processing the direction and speed of motion
○ Contains many direction-sensitive neurons
○ Input to Medial Superior Temporal Cortex (MST) which processes optic flow
104
Area MT: Neural Processes is often studied with?
Motion Coherence:
Coherence of movement of dot patterns is varied
105
(illusory motion)
What are motion aftereffects?
Reasoning?
Illusions where motion is perceived in the opposite direction after staring at motion.
ex. Waterfall
Caused when direction-sensitive neurons become fatigued
■ Fatigued neurons fire less, so out of balance with neurons spontaneously firing for opposite direction.
106
What is Apparent Motion?
One stationary stimuli are presented in rapid succession in different location.
ex. Picture frames/ movies
More "inferential" bc the visual system has to make guesses and judgements of whats actually happening.
107
What is Implied motion? and its correlation to Top-down influences?
Implied Motion
○ Experiment by Kourtzi and Kanwisher
■ fMRI response was measured in MT to pictures in 4 conditions:
● Implied motion
● No-implied motion (same person)
● At rest
● Houses
■ Results showed area MT was more active in response to pictures of implied motion
108
What are the functions for Color Vision? (color perception)
- Color helps us identify (especially natural) objects ○ Many objects have “diagnostic colors”
-Color vision may provide an evolutionary advantage in foraging for food
- Color facilitates perceptual organization and grouping of elements into objects
○ We see borders (edges) where color changes
○ Helps to find object edges or boundaries
109
What are the wavelength ranges for the given colors:
1. Violet
2. Blue
3.Green
4.Yellow
5.Orange
6. Red
Color perception is related to wavelength: ○ 400 to 450 nm appears violet
○ 450 to 490 nm appears blue
○ 500 to 575 nm appears green
○ 575 to 590 nm appears yellow
○ 590 to 620 nm appears orange
○ 620 to 700 nm appears red
110
Perceived colors are determined by:
(4 influences on color perception)
○ The WAVELENGTHS in the light
○ The INTENSITIES of the wavelengths
■ How much total energy is present
○ The SATURATION of light
■ How much of all the other wavelengths is present
● Broadband (white) light
○ The CONTEXT in which the light appears.
111
Colors of objects are determined (in part) by the wavelengths that are?
Reflected from those objects.
112
What is Subtractive Color Mixture?
○ Objects absorb (remove) certain wavelengths, leaving the remaining wavelengths to be reflected
○ E.g., mixing pigments removes wavelengths
113
What is Additive Color Mixture?
(often used in the lab)
Mixing lights of different wavelengths
○ Surface reflectance remains constant
○ Easier to control precisely
■ E.g., superimposing blue and yellow lights leads to white
114
What is reflectance curves?
Plots of percentage of light reflected for specific wavelengths
115
What are the 3 main processes of Color Vision
1) Trichromacy
2) Opponent Process
3) Context
116
Trichromacy (or) Trichromatic Theory of Color Vision, Proposed by Thomas Young (1802) and Hermann von Helmholtz (1850) is ?
Proposed that three different receptor mechanisms with different wavelength sensitivities are responsible for color vision
Any color from a single pure wavelength can be matched by the right mixture of 3 other independent wavelengths if they were separated along the spectrum
117
What are Metamers?
Two light patches composed of different wavelengths but look identical in color.
118
Cones with 3 pigments absorb and respond maximally to?
○ Short wavelengths (419 nm) (S-cones)
○ Medium wavelengths (531 nm) (M-cones)
○ Long wavelengths (558 nm) (L-cones)
○ But note that there a range around the maximum response
119
What is the Opponent-Process Theory?
○ Proposed by Ewald Hering (1800s) was a competing theory to trichromacy theory
○ Proposed color vision is caused by opposing responses generated by blue vs yellow, and by red vs
green
120
What were the evidences for Opponent Process Theory
Behavioral Evidence 1: color afterimages
Behavioral Evidence 2: Simultaneous color contrast
Behavioral Evidence 3: Color wheel has two opposite quadrants: red vs green and blue versus yellow
Behavioral Evidence 4: (Hurvich & Jameson, 1957):
Common types of color blindness are red/green (most common) and blue/yellow
121
What was Hering's Opponent-Process Proposal
Three mechanisms - red/green, blue/yellow, and white/black
The pairs respond in an opposing fashion, e.g., positively to red and negatively to green
White/Black Opponency
122
Color Vision involves both ?
Trichromacy and Opponent-process mechanisms.
○ Trichromacy explains the responses of the cones in the retina
○ Opponent-Process explains neural response for ganglion cells in the retina and cells in the LGN
123
What is chromatic adaptation? What is its explanation for color constancy?
Exposure to a specific wavelengths reduces sensitivity to those wavelengths due to adaptation of receptors (pigments) and color-responsive neurons.
124
How does Top-Down effects also explain color constancy?
(Unconscious Inference)
1) Learned Knowledge of Lighting
● E.g., Indoor lighting changes colors in predictable ways
2) Learned Knowledge of Typical Colors
● E.g., Grass should look green... if it doesn’t then compensate for both green and other colors
125
What are the function of Depth Cues for the visual system?
○ The visual system uses information (cues) in the stimulus to infer distance
○ The visual system uses a collection of cues to recover the 3D distal stimulus structure from the 2D proximal stimulus
126
What are the three types of cues?
○ Oculomotor Cues
■ Based on muscles associated with the eyes
○ Binocular Cues
■ Cues that require 2 eyes (e.g., stereopsis).
○ Monocular Cues
■ Cues that work with one eye (e.g., perspective, shading).
127
Binocular Depth Cue
What is Stereoscopic Depth Perception?
(Stereopsis/ Stereo Vision)
The perception of depth created by the difference in images from same stimulus on the two retina based on the distance of the stimulus
(cross eye example)
128
What is Overlapping Binocular Visual Fields?
Information about depth that is available due to the fact that we have 2 eyes separated along a plane in space with overlapping (binocular) visual fields
129
What is stereopsis?
Depth perception from combining slightly different images from each eye.
130
Key concepts for Stereoscopic Vision are?
- Corresponding Retinal Points
- Binocular Disparity
- The Horopter
131
What is Corresponding Retinal Points?
■ Points on the two retinas that would overlap if the eyes were in the same location
■ Foveas of the two eyes are corresponding retinal points
132
What is Binocular Disparity?
(often shortened to “disparity”)
The difference in the location of the images on the retinas of the two eyes from the same environmental source.
● Disparity is the reason your finger jumps back and forth when you open each eye.
133
Disparity happens when the images fall on?
non-corresponding retinal points.
Points may have small or large disparity.
134
Images at corresponding retinal points have?
0 disparity
- Same image in same place on the two retinas.
135
What is The Horopter?
■ An imaginary surface (hemisphere) centered on your eyes
136
Horopter surface passes through the point of ____ and contains all _____
1- fixation
2- all corresponding retinal points (all points with 0 disparity)
137
Objects on the horopter...
(3 characteristics)
1) fall on corresponding retinal points
2) are all at the same distance (depth) as the point of fixation
3) produce no (zero) binocular disparity, i.e., fall on the same locations on the two retinas (corresponding retinal points)
138
Objects that are not on the horopter
Fall on non-corresponding retinal points on the two retinas
● Just like your finger that jumped back and forth
139
The greater the angle of disparity
The more different in distance from the horopter
140
Crossed vs uncrossed disparity indicates if object is ?
closer (crossed) or further (uncrossed) from horopter
141
What is binocular depth cells or disparity selective cells?
Neurons respond to binocular disparity throughout the visual pathways of the cortex
142
V1 binocular depth cells draw on _____ in V1 that alternate across orientation columns
Ocular Dominance Columns
Many complex cells in V1 are disparity sensitive
143
What is Disparity Tuning Curve?
V1 binocular depth cells respond best to a particular amount of absolute disparity
■ Response produces a disparity tuning curve
■ Different binocular depth cells produce curves with different peak responses
144
What is Artificial Disparity?
Binocular Disparity can be used to create illusion of 3D depth from 2D images
■ 3D movies and TV
145
Monocular Depth Cues
What are Motion Based Cues
1) Motion Parallax
2) Deletion and accretion
146
What is Motion Parallax?
○ When we move, closer objects appear to move faster than farther objects ○ Related to optic flow for forward motion
○ Also true for side-to-side motion
○ Hold hand up and move head side to side
■ What moves more, hand or distant object?
■ Also works for up/down motion
147
What is Deletion and Accretion ?
Further objects are covered (deletion) or uncovered (accretion) as we move relative to them
○ Objects that become “covered up” inferred to be farther away
148
What are Pictorial Cues Characteristics ?
● Pictorial cues are monocular cues
● Pictorial cues are present in 2D images, including pictures
○ That’s way they are called pictorial cues
● More “top-down” than binocular cues
● Occlusion
● Relative Height
● Relative Size
● Perspective Convergence
● Familiar Size
● Atmospheric
Perspective
● Texture Gradient
● Shadows
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What is Occlusion (AKA Interposition) ?
○ Overlap of one object or surface by another, due to a difference in distance
○ Object that is partially or fully hidden is inferred to be farther away
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What is Relative Height?
○ Objects appear higher or lower in the field of view
○ Objects appearing higher in the field of view are inferred to be farther away
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What is Texture Gradient?
○ Equally spaced elements of equal size appear more closely packed as distance increases
○ So, assume that more densely packed regions are further away
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What is the function of shadows?
1) Indicate distance between objects and surfaces
■ E.g., objects contacting their shadow are on a surface, not contacting are above surface
2) Indicate depth in 3D space
■ E.g., object closer to a distant surface casts a more coherent (smaller, darker, crisper) shadow
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What is Perspective Convergence ( AKA: Linear Perspective)
○ Parallel lines appear to converge as distance increases
○ So, assume lines that appear to be converging are receding in distance
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Size perception on the retina is highly related to both?
How does the perceptual system deal with this?
1) Size
2) Distance
■ It tries to take distance into account when interpreting the retinal image size
■ Size perception is strongly influenced by perceived depth
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What is Ponzo Illusion?
Linear Perspective makes animal on top look further away, and so larger.
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Why does the Ponzo Illusion occur?
Incorrect use of Size-Constancy
The visual system “knows” that an object further away generates a smaller image on the retina than it would if the object were closer
● So the visual system issues that a more distant object must be larger than its retinal image suggests,
● So system compensates and increases perceived size
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What is The Ames Room?
Two people of equal size appear very different in size in this room.
