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169 Cards in this Set

  • Front
  • Back
Color vision
the ability to see difference between lights of different wavelengths
Visible spectrum
the portion of the electromagnetic spectrum in the range of 400 to 700 nm
-within the range, people with normal vision perceive differences in wavelength as differences in color
Spectral Power Distribution (SPD)
the intensity (power) of a light at each wavelength in the visible spectrum
Heterochromatic Light
light that consists of more than one wavelength
Monochromatic Light
light that consists of only one wavelength
Achromatic Light
light containing wavelengths from across the visible spectrum with no really dominant wavelengths, perceived as more or less colorless (or white light)
Spectral Reflectance
the proportion of light that a surface reflects at each wavelength
Hue
the quality usually referred to as color that is blue green yellow red and so on, the perceptual characteristic most closely associated with the wavelength of light
Saturation
the vividness or purity or richness of a hue
Color Circle
a 2D depiction in which:
-hue varies around the circumference
-saturation varies along any radius
Color solid
a 3D depiction in which:
-hue varies around the circumference
-saturation varies along any radius
-brightness varies vertically
Subtractive Color Mixture
a mixture of different colored substances called subtractive, because the light reflected from the mixture has certain wavelengths subtracted (absorbed) by each substance in the mixture
additive color mixture
a mixture of different colored lights called additive because the perceived color of the mixture is the result of adding together all of the wavelengths in all the lights of a mixture
Complimentary Colors
pairs of colors that when combined in equal prportion, are perceived as a shade of gray
Primary colors
any 3 colors that can be combined in different proportions to produce a range of other colors
Color Perception
two step process
1) Trichromatic color representation
2) Opponent color representation
Trichromatic color representation
light evokes different responses from 3 different types of cone photoreceptors in the retina
Opponent color representation
the responses from the cones are combined and processed by a subset of retinal ganglion cells and by color selective neurons in the brain
Metamers
any 2 stimuli that are physically different but are perceived as identical
EX) using the test patch and comparison patch examples
Spectral Sensitivity Function
the probability that a cones photo pigment will absorb a photon of light of any given wavelength
Principle of Univariance
with regard to cones, the principle that absorption of a photon of light results in the same response regardless of the wavelength of the light
Hue cancellation
an experimental technique in which the person cancels out any perception of a particular color in a test light by adding light of the complimentary color
first physiological evidence for opponency
Single cones in the retina were found to that responded in opposite ways to wavelengths from different parts of the visible spectrum (began in 1950s)
Physiological Evidence for Opponency
Photopigment Bleaching
Chromatic Adaptation
Color constancy
Lightness constancy
Monochromacy
Rod monochromacy
Cone monochromacy
Dichromacy
Protanopia
Deuteranopia
Tritanopia
Ishihara color vision test
Achromatopsia
Pixels
Photopigment Bleaching
a photopigment molecules loss of ability to absorb light for a period after undergoing photoisomerization
Chromatic Adaptation
a kind of photopigment bleaching that results from exposure to relatively intense light consisting of a narrow range of wavelengths
Color constancy
the tendency to see a surface as having the same color under illumination by lights with very different spectral power distributions
Lightness constancy
the tendency to see a surface as having the same lightness under illumination by very different amounts of light
Monochromacy
a condition in which a person has only rods, or has only rods and one type of cone
-in either case, the person is totally color blind perceiving everything in shades of gray
Rod monochromacy
a condition in which a person has rods only , no cones
Cone monochromacy
a condition in which a person has rods only and ONE type of cone
Dichromacy
a condition in which a person has only 2 types of cones, instead of the normal 3. (limited form of color vision but cannot discriminate as many colors as a person with all 3)
Protanopia
a condition in which a person has M cones and S Cones but lacks L cones
Deuteranopia
a condition in which a person has L cones and S cones but lacks M cones
Tritanopia
a condition in which a person has L cones and M cones but lacks S cones
Ishihara color vision test
a test using configurations of multicolored disks with embedded symbols, the symbols can be seen by people with normal color vision by not by people with particular color vision deficiencies
Achromatopsia
loss of color vision caused by brain damage
Pixels
picture elements in the display screen of a color monitor, a pixel consists of 3 subelements, each designed to emit the light of one of 3 primary colors red, green, or blue
Oculomotor Depth Cues
Provide information about the depth based on feedback from the Oculomotor muscles controlling the shape of the lens and the position of the eyes
A) Accommodation
B) Convergence
Accommodation
(Oculomotor Depth Cues)
The shape of the lens adjusts to focus an image sharply on the retina
-Focusing on something far (more than a few feet away): Need a relatively flat lens... ciliary muscles relax
-Focusing on something close: Need a more rounded lens... ciliary muscles contract
-Only serves as a depth cue for objects up to about 2 meters away
Convergence
(Oculomotor Depth Cue)
The eyes cross or uncross to fixate on an object.
-Distant objects: uncrossed, almost parallel
-Close objects: crossed (when a distant object comes closer, eyes cross)
-Only serves as a depth cue for objects up to about 10 meters away
Monocular Depth Static Cues
Cues that provide information about depth on the basis of:
A) the position of objects in the retinal image
B) the size of the retinal image
C) the effects of lighting in the retinal image
Position in the Retinal Image
(Monocular Depth Static Cue)
-Partial Occlusion (or interposition)
-Relative Height
Partial Occlusion (or interposition)
(Monocular Depth Static Cue- Position in the Retinal Image)
In scenes where one object partially hides (occludes) another object, the occlusion indicates that the former is closer than the latter
-The assumption is that the objects in a scene and their arrangement with respect to each other and the observer are as simple and natural as possible
Relative Height
(Monocular Depth Static Cue- Position in the Retinal Image)
The relative height of the objects in the retinal image with respect to the horizon, or with respect to eye level if there is no visible horizon, provides information about the objects' relative distance from the observer
-The power of this depth cue is indicated by the fact that relative height in the retinal image affects depth perception even in scenes where there is no visible floor or ceiling
Size in the Retinal Image
(Monocular Depth Static Cue)
-Size Distance Relation (visual angle, size perspective)
-Familiar Size
-Relative Size (Texture gradients, linear perspective)
Size Distance Relation
(Monocular Depth Static Cue- Size in the Retinal Image)
The farther away an object is from the observer, the smaller is its retinal image
A) Visual Angle
B) Size Perspective
Visual Angle
(Monocular Depth Static Cue- Size in the Retinal Image: Size Distance Relation)
A size distance measurement of the retinal image size of an object- The angle subtended (occupied) by the object in the visual field.
-The size of the retinal image decreases in the same proportion as the distance to the object increases
Size Perspective
(Monocular Depth Static Cue- Size in the Retinal Image: Size Distance Relation)
A depth cue in scenes in which the size distance relation is apparent
-The regular decrease in the retinal image size of objects as their distance from the observer increases
Familiar Size
(Monocular Depth Static Cue- Size in the Retinal Image)
Knowing the retinal image size of a familiar object at a familiar distance lets use its retinal image size to gauge its distance
-Ex: If you're familiar with the relative sizes of a golf ball (small), a baseball (bigger), and a basketball (even bigger), then in a situation where all three produce retinal images of the same size, you know that the golf ball is closer than the baseball and that the baseball is closer than the basketball
Relative Size
(Monocular Depth Static Cue- Size in the Retinal Image)
Under the assumption that two ore more objects are about the same size, the relative size of their retinal images can be used to judge their relative distances
-Ex: If the racers were aliens of unknown size riding alien bikes on an alien track on another planet, and if we assumed that all the aliens were approximately equal in size, w would still know which rider was twice as far away as the leader
A) Texture Gradients
B) Linear Perspective
Texture Gradients
(Monocular Depth Static Cue- Size in the Retinal Image: Relative Size)
If surface variations or repeated elements of a surface are fairly regular in size and spacing, the retinal image size of these equal size feature decreases as their distance increases
Linear Perspective
(Monocular Depth Static Cue- Size in the Retinal Image: Relative Size)
Parallel lines appear to converge as they recede in depth
-A fixed distance projects a smaller and smaller retinal image as it recedes from the observer
-Ex: Train Tracks
Lighting in the Retinal Image
(Monocular Depth Static Cue)
-Atmospheric Perspective
-Shading
-Cast Shadows
Atmospheric Perspective
(Monocular Depth Static Cue- Lighting in the Retinal Image)
The farther away an object is, the more air the light must pass through to reach us and the more that the light can be scattered, with the result that distant objects appear less distinct than nearby objects
Shading
(Monocular Depth Static Cue- Lighting in the Retinal Image)
-Light falls on curved surfaces in ways that give rise to shading differences, because some parts of the surface are illuminated more directly than others
-Such shading gives us information about the relative depth and orientation of the different parts of the surface
Cast Shadows
(Monocular Depth Static Cue- Lighting in the Retinal Image)
-the farther a shadow moves from the object casting it, the farther the object is from the background.
Monocular Depth Dynamic Cues
A) Movement in the Retinal Image (Motion Parallax, Optic Flow)
B) Deletion
C) Accretion
Movement in the Retinal Image
(Monocular Depth Dynamic Cue)
-As you move through a scene, you see it from a constantly changing viewpoint. The changes in viewpoint result in changes in the positions of the object in the retinal image relative to each other. -These changes provide information about the layout of the objects in the scene, including their relative depths.
A) Motion Parallax
B) Optic Flow
Motion Parallax
(Monocular Depth Dynamic Cue- Movement in the Retinal Image)
-The difference in the speed and direction with which objects appear to move in the retinal image as an observer moves within a scene
-The farther an object is from the fixation point, the farther and faster will be its relative motion across the scene in the retinal image
>Objects closer than the fixation point will move in a direction opposite to the observers direction of motion
>Objects farther than the fixation point will move in the same direction as the observer's direction of motion
Optic Flow
(Monocular Depth Dynamic Cue- Movement in the Retinal Image)
-The relative motions of objects and surfaces in the retinal image as the observer moves forward or backward through a scene
-Critical cue to depth when you're driving
-Every feature in the scene moves outward from the focus of expansion at a rate that depends on how far away it is from you
>The objects and surfaces near the point toward which you are looking (called the focus of expansion) move outward slowly in your retinal image
>Closer objects move away from the focus of expansion much more rapidly
Deletion
(Monocular Depth Dynamic Cue)
The gradual hiding (occlusion) of an object as it passes behind another one
Accretion
(Monocular Depth Dynamic Cue)
The gradual revealing ("de occlusion") of an object as it emerges from behind another one
Binocular Depth Cues
Using both our eyes gives us two views of the world, and our visual system has evolved to process those different views in a way that provides us with an extremely rich source of information about spatial layout, including stereopsis
A) Binocular Disparity
B) Correspondence Problem
C) Stereograms and Anaglyphs
Stereopsis (or stereoscopic depth perception)
The vivid sense of depth arising from the visual system's processing of the different retinal images in the 2 eyes
Binocular Disparity
(Binocular Depth Cue)
A depth cue based on differences in the relative position of the retinal images of objects in the left and right eyes
-Because the horizontal separation between your two eyes means that the line of gaze from your left eye to your finger is quite different form the line of gaze from your right eye to your finger
Ex: Obvious if you hold up a single finger and look at it first with one eye closed and then the other. A lap across the room seems to jump from one side of your finger to the other.

A) Corresponding Points, Noncorresponding Points, and the Horopter
B) Crossed Disparity, Uncrossed Disparity, and Zero Disparity
Corresponding Points
(Binocular Depth Cue- Binocular Disparity)
A point on the left retina and a point on the right retina that would coincide if the two retinas were superimposed
-Ex: the foveas of the two eyes are corresponding points, and two points that are each 4mm to the left of the fovea in each eye are also corresponding points
Noncorresponding Points
(Binocular Depth Cue- Binocular Disparity)
A point on the left retina and a point on the right retina that wouldn't coincide if the two retinas were superimpose
-Ex: the fovea of one eye and a point 4mm to the right of the fovea in the other eye
Horopter
(Binocular Depth Cue- Binocular Disparity)
-An imaginary surface defined by the locations in a scene from which objects would project retinal images at corresponding points
-Whenever an observer fixates an object, a Horopter is established
-Objects that are either closer to the observer or farther from the observer than the Horopter will project retinal images that fall on noncorresponding points, and will be perceived as being either nearer or farther than objects on the horopter
Crossed Disparity
(Binocular Depth Cue- Binocular Disparity)
Produced by an object that is closer than the horopter—you would have to "cross" your eyes to look at it
*Right Left, Left Right Aspect: The observer sees what is to the right of the fixated object with the left eye, and what is left of the fixated object with the right eye
Uncrossed Disparity
(Binocular Depth Cue- Binocular Disparity)
Produced by an object that is farther away than the horopter—you would have to "uncross" your eyes to look at it
*Left Left, Right Right Aspect: The observer sees what is to the left of the fixated object with the left eye, and what is right of the fixated object with the right eye
Zero Disparity
(Binocular Depth Cue- Binocular Disparity)
The retinal image of an object falls at corresponding points in the two eyes (the object that lies on the horopter)
Correspondence Problem
(Binocular Depth Cue)
The problem of determining which features in the retinal image in one eye correspond to which features in the retinal image in the other eye
-Solved with the Random Dot Stereogram (RDS) experiment
Correspondence Problem: Hypothesis A
Object recognition precedes correspondence matching!!
-The visual system surveys the left and right retinal images and separately performs 2D object recognition on them
-The visual system in effect "labels" each feature of each retinal image as belonging to an object in the scene
-A labeled representation of the entire object could be built up in each retinal image, and the visual system could then assess the binocular disparity for each part of the object
Correspondence Problem: Hypothesis B
Correspondence matching precedes object recognition!!
-The visual system matches parts of the retinal images based on very simple properties, such as color or edge orientation, before proceeding to object recognition (without assigning object labels)
Stereoscope
(Binocular Depth Cue)
Two photos are simultaneously taken of the same scene with two camera lenses separated horizontally by the 6cm interocular distance
-One photo is then shown only to the left eye and the other only to the right eye, simulating the slightly different views one would experience if actually viewing the scene
-The resulting binocular disparity produces a vivid perception of depth
Stereograms
(Binocular Depth Cue)
Two depictions of a scene that differ in the same way as an observer's two retinal images of that scene would differ.
-An observer who simultaneously views one image with one eye and the other image with the other eye (as in a stereoscope) will see a combined image in depth
-Resulting binocular disparity produces a vivid perception of depth
Anaglyph
(Binocular Depth Cue)
A stereogram in which the two photographs taken from adjacent camera positions are printed in contrasting colors and then superimposed
-An observer who views an anaglyph with special glasses, in which one lens filters out one of the colors and the other lens filters out the other color, will see a single image in depth
Random Dot Stereograms (RDS)
(Binocular Depth Cue)
A stereogram in which both images consist of a grid of randomly arranged black and white dots, identical except for the displacement of a portion in one image relative to the other
-An observer who views a RDS in a stereoscope or as an anaglyph will see a single image with the displaced portion in depth
*** The crucial experiment to help determine how the human visual system solves the correspondence problem, to help answer the question of whether object recognition occurs before or after matching parts of the retinal image
How RDS addresses the question of whether correspondence matching precedes or follows object recognition
1. Correspondence matching is necessary for the perception of binocular disparity
2. If object recognition necessarily precedes correspondence matching, an RDS wouldn't produce a sense of depth, because an RDS doesn't contain any objects; it's just a random array of square dots or tiny scribbles, none of which can be separately labeled in either of the two images
3. But RDSs do produce a sense of depth. Therefore, the correspondence matching must PRECEDE object recognition.
How the brain actually solves the correspondence problem
The brain makes two simple and quite reasonable assumptions about the world when matching features in the left and right retinal images (whether they're dots or scribbles in an RDS or features of objects in a real scene):
1. Each feature in one retinal image will match one and only one feature in the other retinal image
2. Visual scenes tend to consist of smooth and continuous surfaces with relatively few abrupt changes in depth
Neural Basis of Stereopsis
Binocular Cells
Binocular Cells
-Neurons that respond best to the stimulation of their receptive fields in both eyes simultaneously
-Provide a means by which the visual system can measure binocular disparity
-Different binocular cells are tuned to different disparities—crossed, uncrossed, or zero—and a cell tuned to crossed or uncrossed disparity will be tuned to a specific magnitude of disparity
Binocular Cells are found in...
1) Areas V1, V2, and V3
2) In the dorsal pathway ("where"/ "how"), including the motion selective area MT and the intraparietal sulcus (where they provide the precise depth information needed to guide reaching and grasping)
3) In the ventral pathway ("what"), including area V4 and the inferotemporal cortex (where they provide depth information needed to support object shape perception)
Integrating Depth Cues
-No single depth cue dominates in all situations, and no single cue is necessary in all situations. Partial occlusion may come closest to being always dominant

-The more depth cues that are present in a scene, the greater is the likelihood that we'll perceive the scene in depth and the greater is the accuracy and consistency of depth perception

-Depth cues differ in the kinds of information they provide, and we use these differences to construct a more accurate view of the layout of a scene than would be possible using just one or a few of the available cues.
(For example, partial occlusion provides good information about which object is in front of which other object, but it doesn't tell us anything about how far apart objects are. But if you're moving, you can use motion parallax to judge how far apart in depth the objects are. These cues complement one another; together, they help us build a more accurate representation of the scene)

-
-Depth perception based on multiple cues is a rapid, automatic process that occurs without conscious thought. The visual system employs unconscious inference to make a "best guess" about the lay out of a scene based on the current retinal images
Depth and Perceptual Constancy
A) Size Constancy and Size Distance Invariance
B) Shape Constancy and Shape Slant Invariance
Size Constancy
A type of perceptual constancy—the tendency to perceive an object's size as constant despite changes in the size of the object's retinal image due to the object's changing distance from the observer
Size Distance Invariance
The relation between perceived size and perceived distance—the perceived size of an object depends on its perceived distance, and vice versa
-Emmert's Law
Emmert's Law
Size distance invariance of retinal afterimages—the perceived size of an afterimage is proportional to the distance of the surface on which it's "projected"
Shape Constancy
A type of perceptual constancy—the tendency to perceive an object's shape as constant despite changes in the shape of the object's retinal image due to the object's changing orientation
Shape Slant Invariance
The relation between perceived shape and perceived slant—the perceived shape of an object depends on its perceived slant, and vise versa
Illusions of Depth, Size, and Shape
-Ponzo Illusion
-Ames Room
-Moon Illusion
-Tabletop Illusion
Ponzo Illusion
Page 216 figure 6.32
(a) the two taxies are the same size, but the top one appears larger. This happens because we see the taxis in relation to the railroad tracks, which appear to recede in depth based on the cue of linear perspective and supported by other cues in the photo—texture gradient of the stones in the track bed, familiar size of tracks, relative height in the image, and so forth.
(b) the illusion is much less strong (but still present) because only the cue of linear perspective remains.
Ames Room
Page 217 figure 6.33
(a) This shows the actual shape of the Ames room. Except for the rectangular wall containing the viewing peephole, all the surfaces of an Ames room are trapezoidal, but they all appear rectangular to a person looking through the peephole. Thus, the left and right corners of the wall opposite to the peephole appear to be equidistant from the observer, and the wall appears to be perpendicular to the line of sight.
(b) In this photo taken through the peephole, the girl on the right looks twice as tall as the girl on the left, but they are exactly the same height. The Ames room creates an illusory perception of depth.
Moon Illusion
Page 218 Figure 6.34
-The actual distance from an observer to the moon, and therefore, the size of the retinal image projected by the moon are constant whether the moon is near the horizon or directly overhead
-But if you perceive the image as being at the height of the clouds (as indicated by the apparent path of the moon), then it's apparently more distant when its near the horizon. As a result, the size distance relation leads us to perceive the moon near the horizon as larger
Tabletop Illusion
Page 219 Figure 6.35
-The two table tops in this figure are exactly the same shape and size. Thus, their retinal images are the same shape and size too. But because of the perceived slants, we perceive them as very different.
Awareness
Active thinking about or concentration on some source of stimulation
Attention
The selection of some source of sensory stimulation for increased cognitive processing
Divided Attention
The task of actively paying attention to more than one task at a time, and it is both important and common in every day life.
Focused Attention
The state of concentrating on one stimulus to the exclusion of all others. The purpose of focused attention is to actively focus on one thing without being distracted by other stimuli
Selective Attention
Attention to some things and not others. Regardless of whether attention is divided or focused, it is always selective attention
Selective Attention and the Limits of Awareness
-Dichotic Listening
-Inattentional Blindness
-Change Blindness
-Gist Awareness
Dichotic Listening
Listening to one message in the left ear and a different message in the right ear
Experiment Demonstrating Dichotic Listening
-A person listens through headphones to two different messages, attending to one while ignoring the other; attention is ensured by having the person repeat (shadow) the attended message
-Generally, people are able to recall little or nothing about what they heard in the unattended message
*These experiments show that low level sensory changes in the ignored ear (a change from a low pitched voice to a high pitched voice) are noticed, but changes related to meaning aren't
Inattentional Blindness
Failure to perceive a fully visible but unattended visual object
Experiment Demonstrating Inattentional Blindness
-Participants were required to judge whether the vertical or horizontal arm of a large, briefly flashed object was longer. After each critical trial, participants were asked whether they'd noticed the critical stimulus
-Typically, 60% - 80% of participants showed no awareness from the critical stimulus, because their attention was directed to the large cross
*These experiments show that even when you're looking directly at something, you're quite likely not going to see it if you're paying attention somewhere else
Change Blindness
Inability to quickly detect changes in complex scenes
Experiment Demonstrating Change Blindness
-Two scenes are shown in rapid alternation separated by a brief blank interval. Observers have to say what is different between the two scenes.
-Even when you can see both scenes at once, it may take you a while to see the single big difference
Gist Awareness
We typically have a background awareness of the gist of a scene; this general sense of what the scene is "about" is the awareness that comes at a glance, as when we first enter a room
Experiment Demonstrating Gist Awareness
Rapid Serial Visual Presentation (RSVP)
Rapid Serial Visual Presentation (RSVP)
-An experimental procedure for Gist Awareness which participants must note whether a particular type of scene occurs in a series of photographs presented at very high rate (3 to 10 photos per second)
-People can detect scenes in response to such questions with an accuracy well above chance, suggesting that the gist of a scene can be extracted within a fraction of a second
*These experiments show that a brief exposure to a scene allows us to get its gist but doesn't give us any significant enduring perception of specific elements in the scene. For that, we have to direct our attention to the specific elements themselves
Attention to Locations
-Not only can attention be directed to different spatial locations, enhancing awareness of and other cognitive responses to stimuli that appear in those locations, but also that attention affects the responses of neurons with receptive fields in attended locations
-In effect, attention selects which of many competing stimuli will be represented for further cognitive operations
-Filter Theory of Attention
-Attentional Cuing
Filter Theory of Attention
The theory that all sensory information is registered as physical signals but that only the signals selected for access to a "limited capacity system" are interpreted for meaning, while the unselected signals are filtered out and the information in them is lost
-The mechanism that performs the selection is attention, which serves as a filter
-The limited capacity system supports awareness and the storage of information in memory
Attentional Cuing
-Providing a cue (e.g., an arrow or tone) about the location and timing of an upcoming stimulus
-To examine how the spatial location of a person's attention affects the speed with which the person can become aware of something and respond to it
-Affects neural responses in V4
Attentional Cuing Experiment
Figure 8.5
-A monkey looks continuously at a fixation point while attending to one of two stimuli in the receptive field of a V4 neuron whose activity is being recorded

-Even though both stimuli are present in the receptive field...
>The neuron responds strongly when attention is directed to the EFFECTIVE STIMULUS (a red vertical bar, which evokes a strong response when presented alone)
>The neuron responds weakly when attention is directed to the INEFFECTIVE STIMULUS (a blue horizontal bar, which evokes a weak response when presented alone)
Attention to Features
-Psychophysical experiments have shown that our ability to detect a very faint sound is enhanced if we know beforehand what pitch the sound will have and direct our attention toward listening for a sound that will pitch
- The distinction between rapid, efficient feature search and slow, inefficient conjunction search provides good evidence that binding features together requires attention to the spatial locations of those features, to make sure that the features are in the same location and belong to the same object
A) Visual Search
B) Feature Search
C) Conjunction Search
Visual Search
Searching for a specific target in a scene containing one, a few, or many objects
Feature Search
Searching a display for an item that differs in just one feature from all other items in the display
-The response time is fast regardless of the number of items in the display
-The observer can detect the unique feature by attending to the entire visual scene—the target "pops out"
Conjunction Search
Searching a display for an item that differs from all other items in the display by having a particular combination of two or more features
-Much more difficult that feature search
-The response time increases as the number of items increases
-Requires the observer to direct attention to one item at a time, sequentially, to determine whether each item contains the required conjunction of features
Attention to Features Experiment
Figure 8.9
-The average brain activity in area MT in increased after attention shifted to the moving dots, and decreased after attention shifted to the stationary dots
-Given that both the moving white dots and the stationary black dots were always present ant scattered through the display, the changes in brain activity were likely due to the shift in attention to particular features (motion or rest) and not to shifts in the spatial location of attention
Distributed Representation
A representation that is distributed across multiple regions of the brain
-Ex: When you look at a moving read square, neurons in both MT and V4 become active and produce a distributed representation of that object
-This is fine for scenes containing a single object—the visual system "knows" that the signals coming from the many different active regions must all relate to the features of that lone object
-However, most scenes contain many object, each with its own combination of features... (The Binding Problem)
The Binding Problem
The problem faced by the visual system of perceiving which visual features belong to the same object
-So how does the visual system know which features go with which objects?
-Consider a visual brain that has an orientation selective region and a color selective region.
-In the orientation selective region, some neurons respond strongly to vertical objects (of any color) in their receptive field and not at all to horizontal objects, while other neurons do the opposite.
-Similarly, in the color selective region, some neurons respond strongly to green and not to red (of any orientation), while others do the opposite
Feature Integration Theory (FT)
The theory that the brain solves the binding problem by selectively attending to one object and ignoring any others
-When attention is directed to an object, neurons with an RF at the attended object's location respond to that object's features only and not to he features of ignored objects
-Thus, there is no ambiguity—the neural responses are all related to the features of a single object at that location, the object being attended to
-Because FIT is based on the idea that conjunction search requires directing attention to one at a time, it predicts the linear increase in response times
Competition for Neural Representation
-The object with features that match the neuron's preferences drives the neuron to produce a strong response, while objects with features that don't match the neuron's preferences evoke only a weak response
-The competition must be resolved otherwise, the neuron's response will be some sort of average or compromise that doesn't correspond to the features of any of the competing objects
-The higher we go in the visual hierarchy, the more intense this competition becomes, because neurons in higher visual areas have larger receptive fields with more objects or object features within them
-Biased Competition Theory
Biased Competition Theory
The theory that the brain resolves the competition for neural representation by selectively attending to one object and representing the features of just that object
-Attention biases the competition so that only the features of the attended object are represented, as if only the attended object were present
Attentional Control
How the brain control attention—that is, how the brain directs attention to locations and features that are of interest to the person—is explained by two forms: top down and bottom up
Top Down Attentional Control
Deliberately/ purposefully paying attention to something in order to get information needed to achieve goals
(AKA Voluntary Attentional Control)
Bottom Up Attentional Control
The involuntary, unavoidable capture of attention by a salient perceptual stimulus
(AKA Stimulus Driven Attentional Control)
-Sudden changes in the environment are often accompanied by salient perceptual stimuli and might well require a rapid response (ex- to avoid an approaching predator)... Perceptual Reflex
Perceptual Reflex
The kind of rapid, automatic response in Bottom Up Attentional Control that bypasses the relatively slow mechanisms for deliberately directing attention via top down control
-Sudden changes in the environment are often accompanied by salient perceptual stimuli and might well require a rapid response (ex- to avoid an approaching predator)
Sources of Attentional Control in the Brain
Where do the signals that control attention come from?
-Studies using fMRI have shown that the human Posterior Parietal Cortex (PPC) and Frontal Eye Field (FEF) are important sources of Attentional Control.
-In one study, people were instructed to attend the left or right side of a display in preparation for detecting a briefly flashed target.
-Activity increased on the contralateral side of the brain in both the PPC and the FEF, well before the target appeared.
-This is the brain activity that you'd expect if the regions were sources of Attentional Control signals.
PPC and Unilateral Visual Neglect
-A condition in which a person has difficulty attending to stimuli in one half of the visual field (almost always the left half), as a result of damage to the contralateral Posterior Parietal Cortex (PPC)
-Failure of awareness- These patients don't respond to people sitting in their left visual field, they leave the food on the left side of their plate, and if they're asked to draw something from memory, they'll often omit elements from the left side
-They are not blind on the left; it is possible to get them to see sufficiently salient visual stimulus there.
*This suggests that attention, not vision, is the issue, and therefore, the PPC region of the brain is important for the control of attention
FEF and Covert Attention
-FEF: Involves in the control of eye movements
-Covert Attention: Attention can be deployed to an object or location in peripheral vision, without moving the eyes or head
-Single neuron recordings of the FEF neurons show a significant modulation in firing rates associated with the spatial location of covert attention independent of any eye movements
The Easy Problem
Explaining how color vision works, how we know one object is farther away than another, how we are able to shift our focus of attention, etc.
-Involves Third Person Data: Objectively observable data that can be investigated using standard scientific methods
-We can either refer to more or less well understood structures and functions of the brain or at least see how to approach the problem scientifically.
The Hard Problem
(philosopher David Chalmers)
How can the activities of physical things—the neurons in our brain—produce conscious, subjective experiences like the awareness of objects?
-Involves First Person Data: Subjective experiences that cannot be observed by others and that have been difficult, if not impossible, to address scientifically
Neural Correlates of Consciousness (NCCs)
-Chalmers claims that scientific progress on The Hard Problem is possible, and among the projects he advocates is a search for the NCCs
-Correspondences between neural activity and conscious awareness
-The idea is that if we can find brain activity that is systematically correlated with conscious experience, and if we can also discover what it is about that activity that makes it different from brain activity that is not correlated with consciousness (e.g., a type of neuron, a kind of neurotransmitter, or some other functional or anatomical property), then we will have made progress in addressing the hard problem
2 Approaches to NCCs
1. The first focuses on situations in which visual awareness fluctuates while the visual stimulus and the retinal image do not change
-In this case, brain activity that fluctuate systematically with the fluctuations in awareness are candidates for NCCs

2. The other involves research on people with brain damage who lack aspects of conscious awareness, in order to determine how their brains differ from those of people with normal awareness

-Each of these approaches deliberately addresses just one aspect of the "hard problem," avoiding such issues as the sense of self, the problem of free will, and other aspects of consciousness that are notoriously difficult to decipher
-The idea is the tackle consciousness with minimal reliance on first person data and maximal reliance on third person data, but even so, we must rely to some extent on what people tell us about their contents of their awareness, because we have no way of observing those contents for ourselves
Perceptual Bistability
A phenomenon in which an unchanging visual stimulus leads to repeated alternation between two perceptual experiences
-The retinal image remains constant, but conscious experience changes over time
Ex- When we look at the Necker cube, activity in some parts of the visual system corresponds to the unchanging retinal image, while activity in other parts of the visual system corresponds to the perceptual experience, so that in these areas, the activity changes when perceptual experience flips from one form of the cube to the other
Binocular Rivalry
A phenomenon in which two different images represented to the two eyes result in perceptual bistability
-You don't see a simple blending of the two images, instead the images alternate every few seconds on an irregular basis—that is, they produce perceptual bistability
Blindsight
The ability to point to and sometimes discriminate visual stimuli without any conscious awareness of them

-Residual vision in blindsight (demonstrated by D.B. and T.N.) is based on signals that pass from the retina to the superior colliculus, through the thalamus, and on to the visual cortex
>This pathway apparently cannot support conscious vision, but it provides sufficient visual information to support visually guided action and, in some cases, categorization of emotionally charged objects
Task Switching
A rapid shifting of attention from one task to another and back again
Ex- Multitasking
Multitasking
Multitasking in real life actually involves task switching, and experiments suggest that the very act of switching attention from one task to another significantly increases the time spent on each task
-Multitasking that consists of performing complex task like driving a car while conversing on a cell phone can have serious consequences (Just listening to words over the phone and repeating them back impairs driving performance, but not as much as having to come up with appropriate responses)
Neuron M
will respond selectively to the direction and the speed of motion if the circuit includes a delay in the signals from either neuron 1 or 2
Red Dot Example
A spot of red stimulates the Receptive Field of Neuron 1 and then RF2 and then both neurons send signals to neuron M. Strongly if both Neuron 1 and 2 arrive simultaneously. If there is a circuit that signals from 1 and 2 take equal amounts of time to travel to Neuron M: then neuron 1 reaches M at time 2 and neuron 2 reaches M at time 4.
-**Neuron M in this type of circuit wont provide info about motion.**
-In a circuit in which neuron 1 is delayed then the signals hit M simultaneously but Neuron M strong response indicates that there is MOTION from left to right at a certain speed (in which the red dot travels across the retina)
-neuron M is tuned for speed and direction
direction tuning
whether delay or not
speed tuning
how long the delay is
The Motion Aftereffect (MAE/Waterfall Illusion)
a visual illusion in which a stationary element of the visual scene appears to be moving in a direction opposite to the direction of motion experienced during the immediately preceding time interval.
-EX) staring at a waterfall and then a stationary rock wall afterwards, the wall may appear to be moving slowly upward opposite of the direction of the falling water.
-Motion is represented by the output of an opponent circuit that compares opposite directions of motion
V1 Neurons
-many neurons in Area V1 are tuned to direction and speed of motion, but many neurons do not.
-V1 has small receptive fields, so restricting the areas.
-Individual V1 neurons cannot represent motions of large objects moving over extended distances.
MT neurons respond selectively to motion
-almost all neurons in area MT are tuned for direction of motion (not color or curvature and shape) and receptive fields are huge as well (helping for large scale motions)
-more active looking at motion then stationary object
Activity of MT neurons causes Directionally Selective Motion Perception
-Microstimulation: tiny currents applied to each neuron
-MT neurons cause the perceptual experience of motion because: (Monkey experiment where only MT neurons are stimulated and they responded to the direction of motion)
-Coherence of Motion: a proportion moving in a same direction.
Damage to Area MT
lose all ability to perceive motion visually (but can perceive motion through hearing or touch)
Transcranial magnetic stimulation
a brief magnetic pulse targeted through MT is transmitted throughout, deactivating perception of motion
Aperture problem
the impossibility of determining the actual direction of motion of a stimulus by the response of a single neuron that ‘sees’ the stimulus only through a small aperture and sees only the component of motion in the neurons preferred direction
-Perceiving the motion of objects
-regardless if an object moves straight right and in one direction or down and to the right, the V1 neurons will SEE the same thing (a vertical edge moving to the right across the receptive field) V1 neurons see the world through a small aperture which means they fail at seeing motion of large objects.
-The MT saves the day in the fact that it receives signals from the V1 neurons with RF1 4 and responds according to their PATTERN. This way MT unambiguously indicates if an object is moving.
-MT neurons can combine responses of V1 neurons and or component neurons of MT itself
**Aperture problem occurs because V1 neurons cant unambiguously indicate the direction of motion of a stimulus the problem is solved via MT neurons that combine the information from multiple V1 neurons
Apparent Motion
A visual illusion in which two stimuli separated in time and location are perceived as a single stimulus moving between the two locations
-Movies and TV are examples of this
-Apparent motion plays a role in perceptual grouping by linking the retinal images of objects that appear in different locations at different times
Apparent Motion Quartet
a display where four symmetrically placed stimuli presented at alternating moments in time are perceived as 2 stimuli in apparent motion
-If the dots are closer together vertically than horizontally, perception is very strongly biased toward VERTICAL motion
-If the dots are closer together horizontally than vertically, perception is biased toward HORIZONTAL motion
Figure Ground Organization
motion can enable the visual system to understand a shape without color depth or texture help
-random dot kinematogram
random dot kinematogram
a display in which a grid is filled with tiny randomly placed black and white squared dots and in which the dots in a region of the grid are then moved rigidly together as a group the shape of the region is visible when the dots move but not when they are still.
Point Light walker display
a display in which biological motion is made visible by attaching small lights at critical locations on an organisms body and then shooting a video of the organism in motion in darkness when still they seem random dots but when moving the motion is clear
Eye Movements
-Saccadic
-Smooth Pursuit
-Vergence
Saccadic (saccades) eye movements
brief rapid eye movements that change the focus of the gaze from one location to another
Smooth Pursuit eye movements
movements made to track a moving object or to track a stationary object while the head is moving
Vergence eye movements
occur when the gaze shifts between focusing on objects at different distances
Saccadic Suppression
the visual systems suppression of neural signals from the retina during saccadic eye movements
-when an eye is stationary the retinal image of the moving object moves across the retina (object is moving)
-when the eye is moving to track an object the retinal image of the object is stationary on the retina at the fovea while the retinal image of the stationary object in the scene moves across the retina
Corollary discharge signals (CDS)
a copy of an eye movement command from the superior colliculus to the extra ocular muscles, sent to the brain to inform the visual system about the upcoming eye movements, used to ensure a stable visual experience even during eye movements (intended eye movement)
Perception for Action
-Medial Intraparietal Area (MIP)
-Lateral Intraparietal Area (LIP)
-Anterior Intraparietal Area (AIP)
-Optic Flow and Maintaining and Upright Position
Lateral Intraparietal Area (LIP)
A region of the posterior parietal lobe in monkeys that is involved in the control of eye movements including intended eye movements. an analogous region exists in the human brain
Medial Intraparietal Area (MIP)
A region of the posterior parietal lobe involved in planning reach movements
Anterior Intraparietal Area (AIP)
A region of the posterior parietal lobe thought to be involved in grasping movements
Optic Flow and Maintaining and Upright Position
Optic flow helps determine heading and maintain upright body orientation and produce an illusory perception of self motion
-objects and surfaces in the retinal image move outward from the point in the scene toward which you are moving (focus of expansion), nearby objects the areas in your periphery of optic flow seem to
Upright position example
elevator when the walls move toward a person the optic flow tells then to move and sway backwards keeping the upright position.