Midterm Flashcards
1
Q
What’s the difference between the physical world and the psychological dimension
A
- Physical world = environment that’s outside of us
- Psychological dimension = how we experience things that are outside of us/our minds
2
Q
Why can’t we see/perceive the different electromagnetic waves?
A
- Because we don’t have any receptors for them
- Except for the visual spectrum because we have receptors for these (why we can see and perceive them)
3
Q
What kind of mechanism are receptors compared to?
A
A lock and key mechanism
4
Q
What’s perception?
A
- Whatever your brain makes of the activation of receptors by external stimuli
- OR the experiences that result from stimulation of the senses
- How we experience the world through our senses
- Identified with complex processes that involve higher-order mechanisms such as interpretation and memory that involve activity in the brain
- Ex: identifying the food you’re eating and remembering the last time you had it
5
Q
What’s sensation?
A
- Detection of stimulus
- Often identified as involving simple “elementary” processes that occur right at the beginning of a sensory system
- Ex: when light reaches the eye, sound waves enter the ear, or food touches the tongue
6
Q
Give an example of the easy VS hard problem of consciousness
A
- Easy problem: figuring out how the detection of colour occurs
- Hard problem: how is that processing of stimuli suddenly turned into the perception of a colour? Neuroscientists don’t know how to answer this
7
Q
TRUE OR FALSE: Different organisms have different perceptual capabilities
A
TRUE: Different organisms have different perceptual capabilities -> due to having different receptors
8
Q
How many steps inside a person’s brain describe the process of perception?
A
7 steps, plus “knowledge”
9
Q
What are the steps of the perceptual process?
A
- Stimulus in the environment
- Stimulus hits the receptors (light is reflected and focused)
- Receptor processes
- Neural processing
- Perception
- Recognition
- Action
+ “Knowledge” inside the person’s brain
10
Q
What’s transduction?
A
- Crucial for perception
- In the senses, refers to the transformation of environmental energy to electrical energy
11
Q
Why does transduction occur with light energy?
A
The brain doesn’t understand light energy, so it’s transferred into electrical energy which is understood by the brain (electrical-chemical energy)
12
Q
What steps of the perceptual process correspond to knowledge?
A
- Perception
- Recognition
13
Q
Describe distal stimulus
A
- Actual image
- The stimulus “out there” in the external environment
- “Distant”
14
Q
Describe proximal stimulus
A
- The representation of the distal stimulus on the receptors
- Stimulus is “in proximity” to the receptors
- Patterns of wavelengths reflected on retina are the proximal stimulus
15
Q
What’s environmental stimuli?
A
All objects in the environment that are available to the observer
16
Q
What’s the principle of transformation?
A
When the stimuli and responses created by stimuli are transformed, or changed, between the environmental stimuli (distal stimuli) and perception
17
Q
What’s neural processing?
A
- Changes that occur as signals are transmitted through the maze of neurons
- Involves interactions between the electrical signals travelling in networks of neurons
- Operations that transform electrical signals within a network of neurons or that transform the response of individual neurons
18
Q
What forms the optic nerve?
A
Retinal ganglion cells
19
Q
What are sensory receptors?
A
- Cells specialized to respond to environmental energy, with each sensory system’s receptors specialized to respond to a specific type of energy
- Sort of like a bridge between the external sensory world and your internal (neural) representation of that world
20
Q
What does transduction do with environmental energy?
A
It changes environmental energy to nerve impulses
21
Q
What do rod and cone receptors do with light energy?
A
They transform it into electrical energy and influence what we perceive
22
Q
What do visual pigments do?
A
React to light
23
Q
TRUE OR FALSE: the primary visual cortex is the only part of the brain that processes visual information
A
FALSE: The Primary visual cortex is not the only part of the brain that processes visual information -> visual info also goes to the temporal and parietal lobes
- Blindsight happens to people who have damage to their visual cortex
- If they can’t perceive the light, how can they know where the dots are moving or that there are obstacles?
- Because visual info doesn’t only go in the visual cortex but in other brain areas too (leads to processing visual information in an unconscious manner)
24
Q
Where does recognition take place in the brain?
A
In the temporal lobe
25
What part of the brain corresponds with "Vision for action"?
Parietal lobe
26
Electrical signals are transformed into what?
Conscious experience
27
Describe the perceptron
- An electronic computer
- "Perceiving machine"
- Expected to be the 1st non-living mechanism able to perceive, recognize & identify its surroundings without human training or control
- The 1st Perceptron could teach itself to distinguish between basic images -> but couldn't do complex tasks
- Rosenblatt claimed that this computer could "learn to recognize similarities or identities between patterns of optical, electrical, or tonal information, in a manner which may be closely analogous to the perceptual processes of a biological brain
28
What do many consider to be a key precursor to modern artificial intelligence?
Rosenblatt's Perceptron
29
Why can computers still not perceive as well as humans?
The problem is that computers don't have the huge storehouse of information that humans begin accumulating as soon as they're born
30
Perception starts with _____ and then moves on to the _____
- The detectors (located in the eyes, ears, skin, tongue, nose and mouth)
- The "computer" (the brain)
31
TRUE OR FALSE: the mechanisms responsible for perception are extremely complex
True
32
What are some medical applications that depend on an understanding of perception?
- Devices to restore perception to people who have lost vision or hearing
- Treatments for pain
33
What are some applications of the understanding of perception in the real-world?
- Autonomous vehicles
- Face recognition systems
- Speech recognition systems
- Highway signs
34
Everything we see, hear, taste, feel, or smell, is the result of what?
The activity in our nervous system and our knowledge gained from past experience
35
Perception depends on what?
The properties of the sensory receptors
36
What's the difference between sensation and perception?
Sensation involves detecting elementary properties of a stimulus and perception involves the higher brain functions involved in interpreting events and objects
37
What's the perceptual process?
A sequence of steps leading from the environment to perception of a stimulus, recognition of the stimulus and action with regard to the stimulus
38
What's the difference between distal stimulus and proximal stimulus?
Information about the stimulus in the environment (distal stimulus) hits the receptors, resulting in the proximal stimulus
39
What are receptor processes?
They include transduction and the shaping of perception by the properties of the receptors
40
What's the retinotopic map?
- Map of the retina on the cortex
- This organized spatial map means that two points that are close together on an object and on the retina will activate neurons that are close together in the brain
41
Why is the spatial representation of the visual scene on the cortex considered distorted?
Because there's more space in the cortex being allotted to images located near the fovea than to images located in the peripheral retina
42
What's cortical magnification?
- Occurs when a disproportionately large area on the cortex is activated by stimulation of a small area on the receptor surface
- Ex: the relatively large area of visual cortex that is activated by stimulation of the fovea.
- Although the fovea accounts for only 0.01% of the retina’s area, signals from the fovea account for 8-10% of the retinotopic map on the cortex
43
What's the cortical magnification factor?
The size of the cortical magnification effect
44
How has cortical magnification been determined in the human cortex using brain imaging?
- Robert Dougherty and coworkers (2003) had participants in the fMRI scanner look at stimuli
- The participant looked directly at the center of the screen, so the dot at the center fell on the fovea
- During the experiment, stimulus light was presented in two places: (1) near the center, which illuminated a small area near the fovea; and (2) farther from the center, which illuminated an area in the peripheral retina
- This illustrated cortical magnification because stimulation of the small area near the fovea activated a greater area on the cortex than stimulation of the larger area in the periphery
45
What's the purpose of cortical magnification in the visual system?
- The extra cortical space allotted to letters and words at which the person is looking provides the extra neural processing needed to accomplish tasks such as reading that require high visual acuity
- Also, when you look at a scene, information about the part of the scene you are looking at takes up a larger space on your visual cortex than an area of equal size that is off to the side
- That more space on the cortex translates into better detailed vision rather than larger size which is an example of the fact that what we perceive doesn’t exactly match the “picture” in the brain
46
Who carried out a series of experiments in which they recorded from neurons they encountered as they lowered electrodes into the visual cortex?
Hubel and Wiesel
47
What did Hubel and Wiesel find when they inserted an electrode perpendicular to the surface of a cat’s cortex?
- They found that every neuron they encountered had its receptive field at about the same location on the retina
- Also that these neurons all preferred stimuli with the same orientation
48
What did Hubel and Wiesel conclude about location columns in the striate cortex?
They concluded that the striate cortex is organized into location columns that are perpendicular to the surface of the cortex, so that all of the neurons within a location column have their receptive fields at the same location on the retina (they overlap)
49
What are location columns?
A column in the visual cortex that contains neurons with the same receptive field locations on the retina
50
What did Hubel and Wiesel conclude about the cortex and orientation columns?
They concluded that the cortex is also organized into orientation columns, with each column containing cells that respond best to a particular orientation
51
What are orientation columns?
A column in the visual cortex that contains neurons with the same orientation preference
52
What did Hubel and Wiesel conclude when they moved an electrode through the cortex obliquely, so that the electrode cut across orientation columns?
- They found that the neurons’ preferred orientations changed in an orderly fashion, so a column of cells that respond best to 90 degrees is right next to the column of cells that respond best to 85 degrees
- They also found that as they moved their electrode 1 mm across the cortex, their electrode passed through orientation columns that represented the entire range of orientations
53
What's the size of one location column?
- 1mm
- Meaning that one location column is large enough to contain orientation columns that cover all possible orientations
54
What's a hypercolumn?
- A location column that a receives information about all possible orientations that fall within a small area of the retina
- Any oriented edge or line that falls within the location column’s area on the retina will be able to be represented by some of the neurons in this location column
- It's therefore well suited for processing information from a small area in the visual field
55
TRUE OR FALSE: The cortical representation of a stimulus does not have to resemble the stimulus
TRUE: The cortical representation of a stimulus does not have to resemble the stimulus; it just has to contain information that represents the stimulus
56
What's tiling?
- The adjacent (and often overlapping) location columns working together to cover the entire visual field (similar to covering a floor with tiles)
57
What's the extrastriate cortex?
- Collective term for visual areas in the occipital lobe and beyond known as V2, V3, V4, and V5
- Referred to as the extrastriate cortex, since they are outside of the striate cortex
58
What happens as we move from V1 to higher-level extrastriate areas?
- The receptive field sizes gradually increase
- The representation of the visual scene builds as we move up this hierarchy of extrastriate cortex areas, adding more and more aspects of the visual scene such as corners, colors, motion, and even entire shapes and objects
59
What happens when the visual signal leaves the occipital lobe?
It continues through different “streams” or pathways that serve different functions
60
What did Leslie Ungerleider and Mortimer Mishkin find with their research on visual pathways?
They presented evidence for two streams serving different functions that transmit information from the striate and extrastriate cortex to other areas of the brain
61
What technique did Ungerleider and Mishkin (1982) use to better understand the functional organization of the visual system?
Ablation (aka lesioning)
62
What's ablation?
- Destruction or removal of an area of the brain (or of tissue in the nervous system)
- This is usually done in experiments on animals to determine the function of a particular area
- AKA lesioning
63
Describe the method of brain ablation (lesioning)
- The goal of a brain ablation experiment is to determine the function of a particular area of the brain
- First, an animal’s ability to carry out a specific task is determined by behavioral testing
- Once the animal’s performance on a task has been measured, a particular area of the brain is ablated (removed or destroyed), either by surgery or by injecting a chemical that destroys tissue near the place where it is injected
- After ablation, the monkey is retested to determine how performance has been affected by the ablation
64
Why are brain lesioning experiments usually conducted on monkeys?
Because of the similarity of their visual system to that of humans and because monkeys can be trained in ways that enable researchers to determine perceptual capacities such as acuity, color vision, depth perception, and object perception
65
In their experiments on visual pathways, what two behavioural tasks did Ungerleider and Mishkin present monkeys with?
1. Object discrimination problem
2. Landmark discrimination problem
66
Describe the object discrimination problem in Ungerleider and Mishkin's experiment with monkeys
- A monkey was shown one object, such as a rectangular solid, and was then presented with a two-choice task which included the “target” object (the rectangular solid) and another stimulus, such as the triangular solid
- If the monkey was able to discriminate between the two objects and thus push aside the target object, it received the food reward that was hidden in a well under the object
- When part of the temporal lobe was removed in some monkeys, behavioral testing after lesioning (ablation) showed that the object discrimination problem was very difficult for these monkeys
67
Describe the landmark discrimination problem in Ungerleider and Mishkin's experiment with monkeys
- The monkey’s task was to remove the cover of the food well that was closest to the “landmark”—in this case, a tall cylinder
- When monkeys had their parietal lobes removed, they had difficulty solving the landmark discrimination problem
68
What did Ungerleider and Mishkin call the pathway leading from the striate cortex to the temporal lobe?
- The "what" or ventral pathway
- Since their results indicate that the pathway that reaches the temporal lobe is responsible for determining an object’s identity
69
What did Ungerleider and Mishkin call the pathway leading from the striate cortex to the parietal lobe?
- The "where" or dorsal pathway
- Since their results indicate that the pathway that leads to the parietal lobe is responsible for determining an object’s location
70
What's the ventral pathway?
- Pathway that conducts signals from the striate cortex to the temporal lobe
- Also called the "what" pathway because it is involved in recognizing objects
71
What's the temporal pathway?
- Pathway that conducts signals from the striate cortex to the parietal lobe
- Has also been called the where, the how, or the action pathway by different investigators
72
What did researchers discover about the relationship between the dorsal and ventral streams and the retina and LGN?
- Using the techniques of both recording from neurons and ablation, they found that properties of the ventral and dorsal streams are established by two different types of ganglion cells in the retina, which transmit signals to different layers of the LGN
- The cortical ventral and dorsal streams can actually be traced back to the retina and LGN
73
In what direction do signals flow along the dorsal and ventral visual pathways?
- Signals flow not only “up” the pathway from the occipital lobe toward the parietal and temporal lobes but “back” as well
- AKA feedback
- The “backward” flow of information provides information from higher centers that can influence the signals flowing into the system
74
TRUE OR FALSE: the dorsal and ventral pathways are completely separate from each other
FALSE: the pathways are not totally separated but have connections between them
- In our everyday behavior we need to both identify and locate objects, and we routinely coordinate these two activities every time we identify something and notice where it is
- Thus, there are two distinct pathways, but some information is shared between them
75
What did Milner and Goodale propose about the dorsal stream?
- They proposed that the dorsal stream is for taking action, such as picking up an object
- Taking this action would involve knowing the location of the object, consistent with the idea of where, but it goes beyond where to involve a physical interaction with the object
- Thus, reaching to pick up a pen involves information about the pen’s location plus information about how a person should move his or her hand toward the pen
- According to this idea, the dorsal stream provides information about how to direct action with regard to a stimulus
76
Where is evidence supporting the idea that the dorsal stream is involved in how to direct action provided?
- It's provided by the discovery of neurons in the parietal cortex that respond when a monkey looks at an object and when it reaches toward the object
- The most dramatic evidence supporting the idea of a dorsal "how" or action stream comes from neuropsychology
77
What's neuropsychology?
The study of the behavioral effects of brain damage in humans
78
One of the basic principles of neuropsychology is that we can understand the effects of brain damage by determining what?
Double dissociations
79
What's an example of double dissociations?
- The monkey with damage to the temporal lobe was unable to discriminate objects (function A) but had the ability to solve the landmark problem (function B). The monkey with damage to the parietal lobe was unable to solve the landmark problem (function B) but was able to discriminate objects (function A)
- The fact that object discrimination and the landmark task can be disrupted separately and in opposite ways means that these two functions operate independently of one another
80
Describe patient D.F.
- A 34-year-old woman who suffered damage to her ventral pathway from carbon monoxide poisoning caused by a gas leak in her home
- One result of her brain damage was that D.F. was not able to match the orientation of a card held in her hand to different orientations of a slot
- But when D.F. was asked to “mail” the card through the slot, she could do it! Even though D.F. could not turn the card to visually match the slot’s orientation, once she started moving the card toward the slot, she was able to rotate it to match the orientation of the slot
- These results for D.F. are part of a double dissociation because there are other patients whose symptoms are the opposite of D.F.’s
81
What method did Milner and Goodale use to study patient D.F?
They used the method of determining double dissociations
82
What did Milner and Goodale conclude from their observations of patient D.F.?
- D.F. performed poorly in the static orientation-matching task but did well as soon as action was involved
- Thus, Milner and Goodale interpreted D.F.’s behavior as showing that there is one mechanism for judging orientation and another for coordinating vision and action
- They hence suggested that the ventral pathway should still be called the what pathway, but that a better description of the dorsal pathway would be the how pathway, or the action pathway, because it determines how a person carries out an action
83
What do psychophysical experiments that measure how people perceive and react to visual illusions demonstrate?
They have demonstrated the dissociation between perception and action that was evident for D.F.
84
In our normal daily behavior, why aren’t we aware of the two visual processing streams?
Because they work together seamlessly as we perceive objects and take actions toward them
85
Describe Tzvi Ganel and coworkers' experiment designed to demonstrate a separation of perception and action in non-brain-damaged participants
- Used a visual illusion task where line 1 was longer than line 2 but in the illusion line 2 appears longer
- They presented participants with two tasks:
1) a length estimation task in which they were asked to indicate how they perceived the lines’ length by spreading their thumb and index finger
2) a grasping task in which they were asked to reach toward the lines and grasp each line by its ends
- Sensors on the participants’ fingers measured the separation between the fingers as the participants grasped the lines
- These tasks were chosen because they depend on different processing streams: the length estimation task involves the ventral or what stream & the grasping task involves the dorsal or where/how stream
86
What were the results of Tzvi Ganel and coworkers' experiment designed to demonstrate a separation of perception and action in non-brain-damaged participants with the use of a visual illusion
- The results of this experiment indicate that in the length estimation task, participants judged line 1 (the longer line) as looking shorter than line 2, but in the grasping task, they separated their fingers farther apart for line 1 to match its longer length
- Thus, the illusion works for perception (the length estimation task), but not for action (the grasping task)
- These results support the idea that perception and action are served by different mechanisms
87
What's the inferotemporal (IT) cortex?
- An area of the brain outside Area V1 (the striate cortex), involved in object perception and facial recognition
- Located in the temporal lobe
- Neurons in the IT cortex have the largest receptive fields—large enough to encompass whole objects in one’s visual field
88
What do IT neurons respond to?
They respond to more complex objects that occupy a larger portion of the visual field
89
Describe Charles Gross and coworkers' experiments on neurons in area IT
- They recorded from single neurons in the monkey’s IT cortex
- In these experiments, Gross’ research team presented a variety of stimuli to anesthetized monkeys
- Using the projection screen procedure, they presented lines, squares, and circles, some stimuli were light, and some dark
- A few days into one of their experiments, they found a neuron that refused to respond to any of the standard stimuli like oriented lines or circles or squares
- Nothing worked, until one of the experimenters pointed at something in the room, casting a shadow of his hand on the screen, which caused a burst of firing
- The experimenters then began testing the neuron to see what kinds of stimuli caused it to respond
- They used a variety of stimuli, including cutouts of a monkey’s hand
90
Describe the results of Charles Gross and coworkers' experiments on neurons in area IT
- After a great deal of testing, they determined that this neuron responded to a handlike shape with fingers pointing up
- After expanding the types of stimuli presented, they also found some neurons that responded best to faces
- Finding neurons that responded to real-life, complex objects like hands and faces was a revolutionary result
- Gross’s results were largely ignored when they were published in 1969 and 1972
- Finally, in the 1980s, other experimenters began recording from neurons in the IT cortex of the monkey that responded to faces and other complex objects
- In 1995, Edmund Rolls and Martin Tovee found many neurons in the IT cortex in monkeys that responded best to faces, further confirming Gross’s initial findings that IT neurons respond to specific types of complex stimuli
91
Describe Doris Tsao and coworkers's research on the "face area"
- They presented 96 images of faces, bodies, fruits, gadgets, hands, and scrambled patterns to two monkeys while recording from cortical neurons inside this “face area.”
- They classified neurons as “face selective” if they responded at least twice as strongly to faces as to non-faces
- Using this criterion, they found that 97% of the cells were face selective
92
What did Charles Gross discover?
He discovered inferotemporal neuron specificity
93
Where are face selective neurons grouped together in the brain?
In the inferotemporal cortex
94
What's the hippocampus?
Subcortical structure in the brain that is associated with forming and storing memories
95
Some of the signals leaving the IT cortex reach what kind of structures in the medial temporal lobe (MTL)?
- The parahippocampal cortex, the entorhinal cortex, and the hippocampus
- These MTL structures are extremely important for memory
96
Describe the case of H.M.
- The classic demonstration of the importance of the hippocampus
- He had his hippocampus on both sides of his brain removed in an attempt to eliminate epileptic seizures that had not responded to other treatments
- The operation eliminated H.M.’s seizures, but it also eliminated his ability to store experiences in his memory
- Thus, when H.M. experienced something, such as a visit from his doctor, he was unable to remember the experience, so the next time the doctor appeared, H.M. had no memory of having seen him
- H.M.’s unfortunate situation occurred because in 1953, the surgeons didn't realize that the hippocampus is crucial for the formation of long-term memories
97
Describe the experiment by Hagan Gelbard-Sagiv and coworkers on epileptic patients
- These researchers had epilepsy patients view a series of 5- to 10-second video clips a number of times while recording from neurons in the MTL
- The clips showed famous people, landmarks, and nonfamous people and animals engaged in various actions
- As the person was viewing the clips, some neurons responded better to certain clips
- Ex: a neuron in one of the patients responded best to a clip from The Simpsons TV program
- First the patient remembered “something about New York,” then “the Hollywood sign” -> the neuron responds weakly or not at all to those two memories
- However, remembering The Simpsons causes a large response, which continues as the person continues remembering the episode (indicated by the laughter)
- Results such as this support the idea that the neurons in the MTL that respond to perceiving specific objects or events may also be involved in remembering these objects and events
98
TRUE OR FALSE: the visual system is flexible
TRUE: the visual system is flexible and neurons can change depending on changing conditions
99
TRUE OR FALSE: the response to stimulation within the receptive field can't be affected by what’s happening outside the receptive field
FALSE: the response to stimulation within the receptive field CAN be affected by what’s happening outside the receptive field
100
What's contextual modulation?
Change in response to a stimulus presented within a neuron’s receptive field caused by stimulation outside of the receptive field
101
The large response that occurs when the 3 lines are presented together may be related to an example of what kind of perceptual phenomenon?
Perceptual organization
102
Do the steps in the perceptual process always unfold in a one-follows-the-other order?
- No
- The perceptual process is a cycle
- Perception and recognition could happen at the same time or even in reverse order and when perception or recognition leads to action, that action could change perception and recognition
103
What's the principle of representation?
- Another principle of perception
- States that everything a person perceives is based not on direct contact with stimuli but on representations of stimuli that are formed on the receptors and the resulting activity in the person's nervous system
104
What's the retina?
A thick network of nerve cells which contains the receptors for vision
105
What do visual receptors respond to?
Light
106
When sensory receptors receive information from the environment, they do what 2 things?
1. They transform environmental energy into electrical energy
2. They shape perception by the way they respond to different properties of the stimuli
107
Electrical signals travel through a vast interconnected network of neurons that do what?
1. Transmit signals from the receptors to the brain and then within the brain
2. Change (or process) these signals as they're transmitted
108
The electrical signals created through transduction are often sent where?
To a sense's primary receiving area in the cerebral cortex of the brain
109
What's the cerebral cortex?
A layer of the brain that contains the machinery for creating perceptions, as well as other functions, such as language, memory, emotions and thinking
110
What are the 4 lobes of the brain?
- Occipital lobe
- Frontal lobe
- Parietal lobe
- Temporal lobe
111
Describe the frontal lobe
- Receives signals from all of the senses and it plays an important role in perceptions that involve the coordination of information received through 2 or more senses
- Also serves functions such as language, thought, memory and motor functioning
112
What are optogenetics?
- Genetic cloning techniques used to implant light-sensitive molecules into neurons
- This makes it possible to activate the neurons by illuminating them with light
113
What's recognition?
The ability to place an object in a category that gives it meaning
114
What's visual object agnosia?
The inability to recognize objects
115
What's action?
Motor activities in response to the stimulus
116
What did Milner and Goodale propose the major goal of visual processing was early in the evolution of animals?
They proposed that it wasn't to create a conscious perception of the environment but to help the animal control navigation, catch prey, avoid obstacles, & detect predators (all crucial functions for the animal's survival)
117
What's evidence that perception is a continuously changing process (dynamic process)?
The fact that perception often leads to action
118
What's knowledge?
- Any information that the perceiver brings to a situation, such as prior experience or expectations
- Can be from years ago or just recently acquired
119
What does the rat-man demonstration highlight?
- It shows how recently acquired knowledge can influence perception
- It illustrates an effect of top-down processing on perception
120
What's macular degeneration?
- A clinical condition which is most common in older people that causes degeneration of the macula, an area of the retina that includes the cone-rich fovea and a small area that surrounds it
- This creates a blind region in central vision, so when a person looks directly at something, they lose sight of it
121
What's object recognition?
Detecting the objects in the image and then matching those objects to existing, stored representations of what those objects are
122
What have computer vision systems been designed to do?
- Engage in object recognition -> generate descriptions of a scene based on the objects that it detected in the image
- to learn how to recognize objects and determine not a description of a scene, but rather, the precise locations of objects in that scene. Computers can do this by placing boxes around the recognized objects
123
What do computer vision systems often struggle with?
Identifying objects under degraded conditions—like when an image is blurry—or in uncommon or unexpected situations
124
What information does a self-driving car's computer system use?
1. the layout of the course, which has been programmed into the computer
2. forms and motions in the environment, which are detected by sensors mounted on the car
125
Why Is It So Difficult to Design a Perceiving Machine?
- The Stimulus on the Receptors Is Ambiguous
- Objects Can Be Hidden or Blurred
- Objects Look Different From Different Viewpoints
126
When you look at a page of a book, the image cast by the borders of the page on your retina is what?
- Ambiguous
- the flat 2D image created by the book on the retina can be created by an infinite number of objects, among them the tilted trapezoid and the large rectangle
- The image of the book on the retina is the same image on the retina as the tilted trapezoid and the large rectangle
127
Is the perceptual system only concerned with determining an object’s image on the retina?
No, 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 the object “out there” that created the image
128
What's the inverse projection problem?
- The idea that a particular image on the retina could have been caused by an infinite number of different objects
- Meaning that the retinal image does not unambiguously specify a stimulus
- The visual system solves the inverse projection problem and determines which object out of all the possible objects is responsible for a particular image on the retina
129
What is the task of determining the object responsible for a particular image on the retina called?
The inverse projection problem, because it involves starting with the retinal image and extending rays out from the eye
130
What are examples of artists taking advantage of the inverse projection problem?
- They have taken advantage of the fact that two-dimensional projections, like the image on the retina, can be created by many different objects, to create interesting “art constructions.”
- Ex: “Bonjour Madamoiselle” art piece by Shigeo Fukuda, in which a spotlight shining on a stack of bottles and glassware casts a two-dimensional shadow on the wall that looks like a silhouette of a woman with an umbrella. This shadow is a two-dimensional projection of the stack of bottles that occurs when the light casting the shadow is placed in just the right location
Ex: An environmental sculpture by Thomas Macaulay, which when viewed from the exact right vantage point, the stones appear to be arranged in a circle but moving to another viewpoint reveals that the rocks aren’t arranged in a circle after all
- This demonstrates how images projected onto a surface don't always accurately depict what is out there in the environment
131
How does the problem of hidden objects occur and how is it solved?
- The problem of hidden objects occurs anytime one object obscures—or “occludes”—part of another object
- This occurs frequently in the environment, but people easily understand that the part of an object that is covered continues to exist, and they are able to use their knowledge of the environment to determine what is likely to be present
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What's viewpoint invariance?
- The condition in which object properties don’t change when viewed from different angles
- Responsible for our ability to recognize objects when viewed from different angles
- The images of objects are continually changing, depending on the angle from which they are viewed, but humans recognize they are part of the same object
- A task that's difficult for computers
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What do the difficulties facing any perceiving machine illustrate?
That the process of perception is more complex than it seems
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What's perceptual organization?
- The process by which elements in a person’s visual field become perceptually grouped and segregated to create a perception
- During this process, incoming stimulation is organized into coherent units such as objects
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What are the 2 components of perceptual organization?
- Grouping
- Segregation
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What's grouping?
In perceptual organization, the process by which visual events are “put together” into coherent units or objects
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TRUE OR FALSE: The process of grouping works in conjunction with segregation
TRUE
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What's segregation?
The process of separating one area or object from another
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What are Gestalt psychologists?
- An approach to psychology that developed as a reaction to structuralism
- The Gestalt approach proposes principles of perceptual organization and figure–ground segregation and states that “the whole is different than the sum of its parts.”
- Wanted to know how configurations are formed from smaller elements
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Describe structuralism
- Proposed by Wilhelm Wundt, who established the first laboratory of scientific psychology
- Approach to psychology, prominent in the late 19th and early 20th centuries, that postulated that perceptions result from the summation of many elementary sensations
- The structuralists saw sensations as analogous to the atoms of chemistry. Just as atoms combine to create complex molecular structures, sensations combine to create complex perceptions
- The Gestalt approach to perception was, in part, a reaction to structuralism
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How did the gestalt approach differ from the structuralist approach and what was Wertheimer's influence in this?
- The Gestalt psychologists rejected the idea that perceptions were formed only by “adding up” sensations
- This was influenced by psychologist Max Wertheimer who from buying a stroboscope made an observation that involved a phenomenon called apparent movement
- The stroboscope, which is a mechanical device that creates an illusion of movement by rapidly alternating two slightly different pictures, caused Wertheimer to wonder how the structuralist’s idea that experience is created by sensations could explain the illusion of movement (apparent movement) he observed
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What's apparent movement?
- An illusion of movement that occurs when two objects separated in space are presented rapidly, one after another, separated by a brief time interval
- Physically there are two images flashing separated by a period of darkness
- But we don’t see the darkness because our perceptual system adds something during the period of darkness—the perception of an image moving through the space between the flashing lights
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What are the three components that create apparent movement?
- In this case, using flashing lights
1. One light flashes
2. There's a period of darkness, lasting a fraction of a second
3. The second image flashes
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What are modern examples of apparent movement?
Electronic signs, which display moving advertisements or news headlines and movies
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What 2 conclusions did Wertheimer draw from the phenomenon of apparent movement?
1. Apparent movement can’t be explained by sensations alone, because there's nothing in the dark space between the flashing lights
2. The whole is different than the sum of its parts, because the perceptual system creates the perception of movement where there actually is none (this became one of the basic principles of Gestalt psychology)
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The idea that the whole is different than the sum of its parts led the Gestalt psychologists to do what?
To propose a number of principles of perceptual organization to explain the way elements are grouped together to create larger objects
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What are illusory contours?
- One of the gestalt principles of perceptual organization
- Contour that is perceived even though it is not present in the physical stimulus
- Ex: 3 Pac Men form the illusory edges of a triangle -> have created the perception of a triangle
- Sensations can’t explain illusory contours, because there aren’t any sensations along the contours
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What are the principles of perceptual organization?
- Principles that describe how elements in a scene become grouped together
- Many of these principles were originally proposed by the Gestalt psychologists, but new principles have also been proposed by recent researchers
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What are the starting points for the principles of perceptual organization?
Things that usually occur in the environment
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What's the principle of good continuation?
- Points that, when connected, result in straight or smoothly curving lines (no sharp turns) are seen as belonging together, and the lines tend to be seen in such a way as to follow the smoothest path
- Objects that are partially covered by other objects are seen as continuing behind the covering object
- Ex: Rope on the floor or tangled earphones
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What's the principle of prägnanz/principle of good figure/principle of simplicity?
- Every stimulus pattern is seen in such a way that the resulting structure is as simple as possible
- Ex: The Olympic symbol -> we see this display as five circles and not as a larger number of more complicated shapes
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What's the principle of similarity?
- Similar things appear to be grouped together
- This law causes circles of the same color to be grouped together
- Grouping can also occur because of similarity of shape, size, or orientation
- Grouping also occurs for auditory stimuli -> ex. notes that have similar pitches and that follow each other closely in time can become perceptually grouped to form a melody
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What's the principle of proximity/nearness?
Things that are near each other appear to be grouped together
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What's the principle of common fate?
- Things that are moving in the same direction appear to be grouped together
- Ex: when you see a flock of hundreds of birds all flying together, you tend to see the flock as a unit; if some of the birds start flying in another direction, this creates a new unit
- Common fate can work even if the objects in a group are dissimilar -> the key to common fate is that a group of objects is moving in the same direction
- Common fate can also apply to changes in illumination when elements of our visual field that become lighter or darker simultaneously are perceived as being grouped into a unit
- Ex: if you’re at a rock concert and some of the stage lights are flickering on and off at the same time, you might perceive them as one group
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What are the principles of perceptual organization that were proposed by the Gestalt psychologists in the early 1900s?
- principle of good continuation
- principle of prägnanz/principle of good figure/principle of simplicity
- principle of similarity
- principle of proximity/nearness
- principle of common fate
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What's the principle of uniform connectedness?
A connected region of the same visual properties, such as lightness, color, texture, or motion, is perceived as a single unit
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What are the principles of perceptual organization that were proposed by modern perceptual psychologists?
- Principle of common region
- Principle of uniform connectedness
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List all of Gestalt's principles of perceptual organization
- principle of good continuation
- principle of prägnanz/principle of good figure/principle of simplicity
- principle of similarity
- principle of proximity/nearness
- principle of common fate
- principle of common region
- principle of uniform connectedness
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What's the principle of common region?
- Elements that are within the same region of space appear to be grouped together
- Ex: even though the circles inside the ovals are farther apart than the circles that are next to each other in neighboring ovals, we see the circles inside the ovals as belonging together
- This occurs because each oval is seen as a separate region of space
- In this example, common region overpowers proximity
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What's the function of the Gestalt principles?
They predict what we will perceive, based on what usually happens in the environment
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What's a common approach to studying perceptual segregation?
To consider the problem of figure–ground segregation
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What's figure-ground segregation?
- The perceptual separation of an object from its background
- When we see a separate object, it is usually seen as a figure that stands out from its background, which is called the ground
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What's a reversible figure-ground?
- A figure–ground pattern that perceptually reverses as it is viewed, so that the figure becomes the ground and the ground becomes the figure
- The best-known reversible figure–ground pattern is Rubin’s vase–face pattern
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What's recognition by components (RBC) theory?
- Theory proposed by Irving Biederman in the 1980s that states that objects are comprised of individual geometric components called geons, and we recognize objects based on the arrangement of those geons
- This theory accounts for viewpoint invariance -> even if a mug was viewed from the side rather than from the front, it is still comprised of the same geons, so it is still recognized as a mug
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What are geons?
- Individual geometric components that comprise objects
- Geons are three-dimensional shapes, like pyramids, cubes, and cylinders
- Biederman proposed that there are 36 different geons from which most objects we encounter can be assembled and recognized
- Geons are the building blocks of objects and the same geons can be arranged in different ways to form different objects
- Recognizable objects can be formed by combining just 2 or 3 geons
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What are some of the many aspects of object perception that the RBC theory could not explain?
- It doesn’t account for grouping or organization like the Gestalt principles do, and some objects simply can’t be represented by assemblies of geons (like clouds in the sky that typically don’t have geometric components)
- It also doesn’t allow for distinguishing between objects within a given category, such as two different types of coffee mugs or species of birds that might be composed of the same basic shapes
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What's a scene?
A view of a real-world environment that contains (a) background elements and (b) multiple objects that are organized in a meaningful way relative to each other and the background
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What are some of the properties of the figure and ground?
- The figure is more “thinglike” and more memorable than the ground
- The figure is seen as being in front of the ground
- Near the borders it shares with the figure, the ground is seen as unformed material, without a specific shape, and seems to extend behind the figure
- The border separating the figure from the ground appears to belong to the figure (border ownership)
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What's border ownership?
When two areas share a border, as occurs in figure–ground displays, the border is usually perceived as belonging to the figure
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What are figural cues?
Visual cue that determines how an image is segregated into figure and ground
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What's the difference between the gestalt principles of perceptual organization and the gestalt figural cues?
While the principles of organization determine how elements of an image are grouped together, figural cues determine how an image is segregated into figure and ground
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List the Gestalt figural cues
- Areas lower in the field of view are more likely to be perceived as figure (in our normal experience, the “figure” is much more likely to be below the horizon)
- Figures are more likely to be perceived on the convex side of borders (borders that bulge outward)
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What were the results of Mary Peterson and Elizabeth Salvagio's (2008) study on the convexity of figure borders?
- The result, in agreement with the Gestalt proposal, was that convex regions were perceived as figure 89% of the time
- Their results indicated that segregation is determined not by just what is happening at a single border but by what is happening in the wider scene
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How did Gestalt psychologists interpret perception and the influence of past experiences on perception?
- They believed that although perception can be affected by experience, built-in principles can override experience
- Ex: The W & M figure. The uprights, which are created by the principle of good continuation, are the dominant perception and override the effects of past experience with Ws or Ms
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What was the Gestalt proposal of one of the first things that occurs in the perceptual process?
- That one of the first things that occurs in the perceptual process is the segregation of figure from ground
- They contended that the figure must stand out from the ground before it can be recognized -> the figure has to be separated from the ground before we can assign a meaning to the figure
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Describe Bradley Gibson and Mary Peterson's (1994) experiment that argued against the Gestalt proposal that one of the first things that occurs in the perceptual process is the segregation of figure from ground
- They did an experiment that argued against this idea by showing that figure–ground formation can be affected by the meaningfulness of a stimulus
- They demonstrated this by presenting a display that can be perceived in two ways:
1. a standing woman
2. a less meaningful shape
- When they presented stimuli such as this for a fraction of a second and asked observers which region seemed to be the figure, they found that observers were more likely to say that the meaningful part of the display (the woman, in this example) was the figure
- When they turned the display upside down so that it was more difficult to recognize the black area as a woman, participants were less likely to see that area as being the figure
- The fact that meaningfulness can influence the assignment of an area as figure means that the process of recognition must be occurring either before or at the same time as the figure is being separated from the ground
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What's one way of distinguishing between objects and scenes?
- Objects are compact and are acted upon, whereas scenes are extended in space and are acted within
- Ex: if we are walking down the street and mail a letter, we would be acting upon the mailbox (an object) and acting within the street (the scene)
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What's the gist of a scene?
- General description of a scene
- People can identify most scenes after viewing them for only a fraction of a second, as when they flip rapidly from one TV channel to another
- It takes longer to identify the details within the scene
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What's the paradox of perceiving scenes?
- On one hand, scenes are often large and complex
- However, despite this size and complexity, you can identify important properties of most scenes after viewing them for only a fraction of a second
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Describe Mary Potter's (1976) study on the gist of a scene
- She showed observers a target picture and then asked them to indicate whether they saw that picture as they viewed a sequence of 16 rapidly presented pictures
- Her observers could do this with almost 100% accuracy even when the pictures were flashed for only 250 ms
- Even when the target picture was only specified by a written description, such as “girl clapping,” observers achieved an accuracy of almost 90%
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Describe Li Fei-Fei's study on the gist of a scene
- Presented pictures of scenes for exposures ranging from 27 ms to 500 ms and asked observers to write a description of what they saw (example of the phenomenological report)
- Fei-Fei used a procedure called masking to be sure the observers saw the pictures for exactly the desired duration
- At brief durations, observers saw only light and dark areas of the pictures
- By 67 ms they could identify some large objects (a person, a table)
- When the duration was increased to 500 ms they were able to identify smaller objects and details (the boy, the laptop)
- Ex: for a picture of an ornate 1800s living room, observers were able to identify the picture as a room in a house at 67 ms and to identify details, such as chairs and portraits, at 500 ms
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What did Li Fei-Fei's experiment on the gist of a scene demonstrate?
That the overall gist of the scene is perceived first, followed by perception of details and smaller objects within the scene
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What did Aude Oliva and Antonio Torralba (2001, 2006) propose enables observers to perceive the gist of a scene so rapidly?
They proposed that observers use information called global image features, which can be perceived rapidly and are associated with specific types of scenes
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What are global image features?
- Information that may enable observers to rapidly perceive the gist of a scene
- They're holistic and rapidly perceived -> they're properties of the scene as a whole and don't depend on time-consuming processes such as perceiving small details, recognizing individual objects, or separating one object from another
- They also contain information about a scene’s structure and spatial layout
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List the global image features proposed by Oliva and Torralba
- Degree of naturalness
- Degree of openness
- Degree of roughness
- Degree of expansion
- Color
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Describe Oliva and Torralba's degree of naturalness global image feature
- Natural scenes, such as the ocean and forest have textured zones and undulating contours
- Man-made scenes, such as the street, are dominated by straight lines and horizontals and verticals
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Describe Oliva and Torralba's degree of openness global image feature
- Open scenes, such as the ocean, often have a visible horizon line and contain few objects
- The street scene is also open, although not as much as the ocean scene
- The forest is an example of a scene with a low degree of openness
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Describe Oliva and Torralba's degree of roughness global image feature
- Smooth scenes (low roughness) like the ocean contain fewer small elements
- Scenes with high roughness like the forest contain many small elements and are more complex
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Describe Oliva and Torralba's degree of expansion global image feature
- The convergence of parallel lines, like what you see when you look down railroad tracks that appear to vanish in the distance, or in the street scene indicates a high degree of expansion
- This feature is especially dependent on the observer’s viewpoint
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Describe Oliva and Torralba's color global image feature
Some scenes have characteristic colors, like the ocean scene (blue) and the forest (green and brown)
191
What general property of perception do global image features demonstrate?
That our past experiences in perceiving properties of the environment play a role in determining our perceptions
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Modern perceptual psychologists have introduced the idea that perception is influenced by what 2 types of regularities?
- Physical regularities
- Semantic regularities
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What are physical regularities?
- Regularly occurring physical properties of the environment
- Ex: there are more vertical and horizontal orientations in the environment than oblique (angled) orientations
- This occurs in human-made environments (ex: buildings contain many horizontals and verticals) and also in natural environments (trees and plants are more likely to be vertical or horizontal than slanted)
- Another example: when one object partially covers another one, the contour of the partially covered object “comes out the other side"
- Light-from-above assumption -> our perception of illuminated shapes is influenced by how they are shaded, combined with the brain’s assumption that light is coming from above
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What's the light-from-above assumption?
- The assumption that light usually comes from above, which influences our perception of form in some situations
- Our perception of illuminated shapes is influenced by how they are shaded, combined with the brain’s assumption that light is coming from above
- Light from above and to the left illuminates an indentation, causing a shadow on the left
- The same light illuminating a bump causes a shadow on the right
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What are semantic regularities?
- Characteristics associated with the functions associated with different types of scenes
- These characteristics are learned from experience
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What's a scene schema?
- An observer’s knowledge about what is contained in typical scenes
- An observer’s attention is affected by knowledge of what is usually found in the scene
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Describe the experiment by Stephen Palmer (1975), on scene schemas
- Palmer first presented a context scene of a kitchen counter and then briefly flashed one of many target pictures
- When Palmer asked observers to identify the object in the target picture, they correctly identified an object like the loaf of bread (which is appropriate to the kitchen scene) 80% of the time, but correctly identified the mailbox or the drum (two objects that don’t fit into the scene) only 40% of the time
- Apparently, Palmer’s observers were using their knowledge about kitchens to help them perceive the briefly flashed loaf of bread.
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What's the “Multiple personalities of a blob"?
- What we expect to see in different contexts influences our interpretation of the identity of the “blob” inside the circles of various images
- An effect of semantic regularities
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What's akinetopsia?
- AKA motion blindness
- A condition in which damage to an area of the cortex -involved in motion perception causes blindness to motion (motion is either very difficult or impossible to perceive)
- The most famous and well-studied case of akinetopsia is a 43-year-old woman known as L.M.
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Describe patient L.M.
- Patient with akinetopsia
- Without the ability to perceive motion following a stroke, L.M. was unable to successfully complete activities as simple as pouring a cup of tea
- Ex: as she put it, “the fluid appeared to be frozen, like a glacier,” and without the ability to perceive the tea rising in the cup, she had trouble knowing when to stop pouring
- It was difficult for her to follow dialogue because she couldn’t see the motions of a speaker’s face and mouth, and people suddenly appeared or disappeared because she couldn’t see them approaching or leaving
- Crossing the street presented serious problems because at first a car might seem far away, but then suddenly, without warning, it would appear very near
- Her disability was not just a social inconvenience but enough of a threat to the woman’s well-being that she rarely ventured outside into the world of moving—and sometimes dangerous—objects
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What does motion perception do for us?
Helps with:
- Detecting things
- Perceiving objects
- Perceiving events
- Social perception
- Taking action
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Why is detection so important for motion perception?
- Because of its importance for survival
- We need to detect things that might be dangerous in order to avoid them
- Motion is a very salient aspect of the environment, so it attracts our attention
- Movement perception is extremely important for animals that hunt, because movement reveals prey which, when stationary, may be difficult to see because of camouflage, but which become visible if they move
- Movement serves a similar purpose for the prey, who use movement to detect predators as they approach
- Also consider the problem of trying to find your friend among a sea of faces in the stadium -> looking up at the crowd, you have no idea where to look, but suddenly you see a person waving and recognize that it is your friend
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How does movement help us perceive objects?
- motion of an object can reveal characteristics that might not be obvious from a single, stationary view
- Movement of an observer around an object can have a similar effect
- Our own motion relative to objects is constantly adding to the information we have about those objects, and we receive similar information when objects move relative to us
- Observers perceive shapes more rapidly and accurately when an object is moving
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How does movement serve an organizing function?
- It groups smaller elements into larger units
- Ex: the motion of individual birds becomes perceived as the larger unit of the flock, in which the birds are flying in synchrony with each other
- Ex: when a person or animal moves, movement of individual units—arms, legs, and body—become coordinated with each other to create a special type of movement called biological movement
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What's an event?
- A segment of time at a particular location that is perceived by observers to have a beginning and an ending
- We can segment ongoing behavior into a sequence of events
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What's an event boundary?
- The point in time when one event ends and another begins
- Event boundaries are often associated with changes in the nature of motion
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Describe Jeffrey Zacks and coworkers' experiment on the connection between events and motion perception?
- Measured the connection between events and motion perception by having participants watch films of common activities such as paying bills or washing dishes and asking them to press a button when they believe one unit of meaningful activity ended and another began
- When Zacks compared event boundaries to the actor’s body movements measured with a motion tracking system, he found that event boundaries were more likely to occur when there was a change in the speed or acceleration of the actor’s hands
- From the results of this and other experiments, Zacks concluded that the perception of movement plays an important role in separating activities into meaningful events
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How is movement important for social perception?
- we use movement cues to determine a person’s intentions
- Other experiments have shown that the characteristics of movement can be used to interpret emotions
- The link between motion intention and emotion is so powerful that it can give human characteristics to geometrical objects
- Research has shown that movement can provide social information even when other social cues aren’t available
- Many other studies have shown that movement provides information that facilitates social interactions
209
Describe the experiment by Atesh Koul and coworkers (2019) about interpreting actions by the speed and timing of the movement
- In their experiment, they had participants observe a hand reaching for a bottle, with the intention of either drinking or pouring from it, and were asked to indicate, “pour” or “drink"
- When the experimenter compared motion information such as the velocity and trajectory of the hand, and the nature of the grip, to the participant’s judgments, they found that participants were using this information to decide why the hand was reaching for the cup
210
Describe the experiment by Fritz Heider and Marianne Simmel (1944) on interpreting social interactions from a film of geometrical shapes moving around
- Showed a 2 1/2-minute animated film to participants and asked them to describe what was happening in the movie
- The movie consisted of a “house” and 3 “characters”—a small circle, a small triangle, and a large triangle
- These 3 geometric objects moved around both inside and outside the house, and sometimes interacted with each other
- Although the characters in the film were geometric objects, the participants created stories to explain the objects’ actions, often giving them humanlike characteristics and personalities
- In other studies, researchers have shown how such simple motion displays can evoke interpretations of desire, coaxing, chasing, fighting, mocking, fearfulness, and seduction
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What are point-light markers?
A biological motion stimulus created by placing lights at a number of places on a person’s body and having an observer view the moving-light stimulus that results as the person moves in the dark
212
Describe Laurie Centelles and coworkers' (2013) experiment on point-light markers
- The observers in Centelles’ experiment viewed the stimulus created by two people wearing lights under two conditions:
1. social interaction: the people were interacting in various ways
2. non-social interaction: the people were near each other but were acting independently
- The observers were able to indicate whether the 2 people were interacting with each other or were acting independently
- A group of observers with autism spectrum disorder, which is characterized by having difficulty with real-life social interactions, were not as good as the other observers at telling the difference between the social and non-social conditions
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How is movement perception important for our own movement?
- To navigate ourselves through the environment
Ex: we perceive the stationary scene moving past us as we walk down the sidewalk and we pay attention to other people’s movements to avoid colliding with them
- Movement perception is also crucially involved in sports—both for watching or as you participate yourself
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What are the 3 types of illusory motion?
- Apparent motion
- Induced motion
- Motion aftereffects
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What's induced motion?
- The illusory movement of one stationary object (usually smaller) that is caused by the movement of another object (usually large) that's nearby
- Ex: the moon usually appears stationary in the sky. However, if clouds are moving past the moon on a windy night, the moon may appear to be racing through the clouds
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What's motion aftereffects?
- An illusion that occurs after a person views a moving stimulus and then sees movement in the opposite direction when viewing a stationary stimulus immediately afterward
- Ex: the waterfall illusion
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What's the waterfall illusion?
- Viewing the waterfall makes other objects appear to move in the opposite direction
- If you look at a waterfall for 30 to 60 seconds (be sure it fills up only part of your field of view) and then look off to the side at part of the scene that is stationary, you will see everything you are looking at—rocks, trees, grass—appears to move upward for a few seconds
218
Describe Axel Larsen and coworkers (2006) study on real and apparent motion
- They presented three types of displays to a person in an fMRI scanner:
1. a control condition: in which 2 squares in slightly different positions were flashed simultaneously
2. a real motion display: in which a small square moved back and forth
3. an apparent motion display: in which squares were flashed one after another so that they appeared to move back and forth
Results:
- Each square activates a separate area of the cortex
- Found that the activation associated with apparent motion is similar to the activation for the real motion display
- 2 flashed squares that result in apparent motion activate the area of the brain representing the space between the positions of the flashing squares even though no stimulus is presented there
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Why do researchers study both real and apparent motion together and concentrate on discovering general mechanisms that apply to both?
Because of the similarities between the neural responses to real and apparent motion
220
Why can't motion perception be explained just by the motion of an image across the retina?
Because if person X is walking from left to right and person Y is following their motion with their eyes, person X’s image remains stationary on person Y’s retinas, yet person Y perceives person X as moving
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What would happen if someone was looking straight ahead while someone else passed by their field of vision?
- Because this person doesn’t move their eyes, the image of the person walking by sweeps across their retina
- Explaining motion perception in this case seems straightforward because as the person walking's image moves across the person fixated's retina, it stimulates a series of receptors one after another, and this stimulation signals the person walking’s motion
