Midterm 2 Flashcards
What is object familiarity?
Visual system must match a mental representation of an object to a representation stored in memory (breaks down information, then complies them into -shapes)
Why can’t we simply match to a template?
Simple translation on the retina fails
What is image clutter?
Objects are recognized when they are seen as part of a jumble of others (rarely seen in isolation)
What is object variety?
Many different types of objects and many different varieties of the same object can be recognized
What are variable views?
Objects can be recognized even when presented from unfamiliar vantage points
What is occulsion?
Some objects partly covering others, but you can still recognize them
What is perceptual organization?
How we recognize what belongs to what
What does perceptual organization involve?
Identifying edges, identifying regions bounded by those edges, determining what object owns the boundaries (figure and ground), grouping similar regions, and handling missing sections by determining what to fill them with
What is perceptual grouping?
Must combine or group together the separate regions based on similarity of properties
What is perceptual inerpolation?
Must “fill in” the parts of the object that cannot be seen
What is perceptual organization?
Dealing with multiple objects, multiple overlapping objects and putting them into a cohesive whole/picture
What is figure-ground organization?
What does the edge belong to
What are the visual system principles used to assign border ownership and organize visual scenes into figure and ground?
Depth, surroundedness, symmetry, convexity, meaningfulness, simplicity
What is depth?
Occurs when one region is perceived to be in front of another
What is a front region?
Owns the border between regions and is perceived as the figure
- other region is perceived as ground
What is surroundedness in figure-ground organization?
If you follow edges around they connect to each other; the completely surrounded gray region tends to be perceived as a figure in front of a black background
What is symmetry in figure-ground organization?
Regions that exhibit symmetry are more likely to be seen as figure than are non-symmetrical regions
What is convexity in figure-ground organization?
Prefer convex objects; regions with convex corders are more likely to be perceived as figure than regions with concave borders
What is meaningfulness in figure-ground organization?
The visual system recognizes the meaningfulness of a shape before assigning border ownership and determining figure-ground organization
What is simplicity in figure-ground organization?
The visual system is strongly biased to interpret any given image in the simplest way it can (simplest is often correct)
What area computes border ownership?
Area V2
What are the Gestalt principles used to group regions?
Proximity, similarity, common motion, symmetry and parallelism and good continuation
What is perceptual interpolation?
Intelligently filling in edged and surfaces that are not visible because they are occluded or blend with the background
What is edge completion?
Perception of a partially hidden edge as complete (one of the operations involved in perceptual interpolation)
What are illusory contours?
Nonexistent but perceptually real edges perceived as a result of edge completion
What is surface completion?
Perception of partially hidden surface as complete; one of the operations involved in perceptual interpolation
What are the 2 different operations within perceptual interpolation?
Edge completion and surface completion
What does the neural basis of perceptual interpolation show?
Neurons in area V2 fill in information outside of its visual field
- there is a reaction even when bar of light does not pass through visual field
What 2 things are important to know about the entire visual system?
Everything is heavily interconnected and hierarchically organized
What does area V4 compute?
Curves also had larger receptive fields and likes cones
How are curved areas represented in area V4?
Smooth curved edge in retinal image –> V1 neurons indicate presence of short straight edges at preferred orientations –> V4 neurons indicates presence of smooth curved edge at preferred orientation
What do we know about visual regions and receptive fields?
The higher brain areas respond to more complex visual stimuli and have larger receptive fields and become increasingly invariant to transformations
What type of curves does V4 have a preference for?
Curves at a specific degree in a certain spot (for example prefers shapes that are pointy (90 degrees) at the very top
What does the Face Inversion Effect/Margaret Thatcher Illusion tell us?
We make errors in recognizing upside-down faces, but not upside-down houses or objects
What does faces are processed holistically mean?
Wouldn’t recognize face parts in isolation (not the same for objects)
What is visual agnosia?
Impairment in object recognition
What is prosopagnosia?
Can’t recognize faces (face-blindness)
What is topographic agnosia?
Person is unable to recognize spatial layouts such as buildings, streets, landscapes, etc. (Scene blindness)
Lesions in what area of the cortex lead to visual form agnosia?
Lateral Occipital Cortex
Lesions in what area of the cortex lead to prosopagnosia?
Fusiform Face Area (FFA)
Lesions in what area of the cortex lead to topographic agnosia?
Parahippocampal Place Area (PPA)
What is invariance?
Visual system may recognize an object as being the same despite changes in retinal image
What is a grandmother cell?
An ultra-selective cell that responds only when you see, for example, your grandmother
Where does the perception of color come from?
Interaction between receptors in the eyes and wavelengths of light reflected from surfaces of objects
What is the visible spectrum?
Portion of the electromagnetic spectrum in the range of about 400 to 700 nm; within this range, people with normal vision perceive differences in wavelength as differences in color
What heterochromatic light?
Mixture of colors (light from a screen)
What is monochromatic light?
A single color (laser light)
What is achromatic light?
No color (white light-equal amount of all colors)
What is Spectral Power Distribution (SPD)?
Intensity (power) of a light at each wavelength in the visible spectrum (SPD of an idealized white light would be a horizontal line)
What is spectral reflectance?
The proportion of light that a surface reflects at each wavelength (amount of light that is reflected back to our eyes from the object’s surface)
What is hue?
What we traditionally would call color (reddishness, greenishness)
What is saturation?
How vivid or pure that color is (how unmixed it is with other colors)
What is brightness?
Luminance (amount of light)
What is the difference between a color circle and a color solid?
Color circle: 2-D depiction in which hue varies around the circumference (hue and saturation)
Color solid: represents 3 dimensions (adds brightness or intensity)
How do we see non-spectral purples?
Blue and red cones are firing but not green ones
What is a subtractive color mixture?
Mixture of different-colored substances (pigments); called subtractive because the light reflected from the mixture has certain wavelengths subtracted (absorbed) by each substance in the mixture
What is an additive color mixture?
Mixture of different-colored lights; called additive because the perceived color of the mixture is the result of adding together all the wavelengths in all the lights in the mixture
What are the primary colors for subtractive color mixing?
Red, yellow. blue
What are the primary colors for additive color mixing?
Red, green, and blue
What are complementary colors?
Colors that when combined yield gray
Color perception in the brain is a two-stage process. What are the 2 main theories that represent this process?
Trichromatic color representation (1st stage)
Opponent color representation (2nd stage)
What are metamers?
Any 2 stimuli that are physically different but are perceived as identical
What is trichromatic color representation?
3 types of color receptors (make up all color), have to compute color and it’s not given
What is the spectral sensitivity function?
The probability that a cone’s photopigment will absorb a photon of light of any given wavelength
What is the principle of univariance?
A single cone can’t disambiguate colors b/c it responds to any wavelength, might respond at it’s peak but would be the same if any light was bright enough
What would happen if you only had 1 type of cone?
You would see gray-scale, other colors look darker than the one the curve peaks at, you could do metameric matching with only brightness
What is retinal densitometry?
Provides direct evidence that people have 3 types of cones (density of individual cones in the retina)
What is evidence for opponent color representation?
Color-sorting tasks, afterimages, and hue cancellation
What is opponent color representation?
The visual system is organized in pairs of opposites
What is hue cancellation?
Experimental technique in which the person cancels out any perception of a particular color in a test by adding light of the complementary color
What did color opponency in RGCs show us?
Evidence for color opponency, compare information from different cones through lateral inhibition
What is lightness constancy?
Relative lightness (or darkness) of an object is perceived as consistent under different intensities of light
What is ratio principle with an anchoring rule?
The region that reflects the most light is perceived as white and the lightness of every other region is perceived in relation to that anchor point
What is color constancy?
Tendency to see a surface as having the same color under illumination by lights of different colors
How does your mind solve color constancy?
By estimating the spectral bias of the illuminant and discounting it (discounting the illuminant)
How does color constancy effect The Dress?
Based on whether the lighting is viewed as warm (blue and black) or cool (white and gold) people see the dress as different colors
What is monochromacy?
Condition in which a person has only rods or had only rods and one type of cone; person is totally-color blind seeing only in gray scale
What is rod monochromacy?
Condition in which a person has rods only with no cones; cannot perceived color, is hypersensitive to light
What is cone monochromacy?
Condition in which a person had rods and only one type of cone; lacks color vision, sees different shades of gray
What is dichromacy?
Condition in which a person has only two types of cones; person has limited form of color vision and cannot discriminate as many colors
What is protanopia?
Person has M-cones (green) and S-cones (blue), but lacks L-cones (red) (most common)
What is deuteranopia?
Person has L-cones (red) and S-cones (blue), but lacks M-cones (green) - hard to distinguish red from green
What is tritanopia?
Person has L-cones (red) and M-cones (green), but lacks S-cones (blue)
What is cortical achromatopsia?
Color blindness from brain damage - usually in area V4
What are the oculomotor depth cues?
Accommodation and Convergence
What are the dynamic depth cues?
Motion parallax, Optic flow, and Deletion and Accretion
What are the position-based depth cues?
Partial occlusion and Relative height
What are the size-based depth cues?
Familiar size, Relative size, Texture gradients, and linear perspective
What are the lighting-based depth cues?
Atmospheric perspective, Shading, and Cast shadows
What is accomodation?
How we change shape of the lens to fine-tune the focus of the image on the retina (short distances)
What is convergence?
Process by which our eyes move together (focus on close objects) or apart (focus on farther objects) - short distances
What are monocular depth cues?
Cues that are based on the retinal image and that provide information about depth even with only one eye open
What are static monocular depth cues?
Cues that provide information on the position, size and lighting of objects in the retinal image (wide range of distances)
What is partial occlusion (interposition)?
A position-based depth cue where one object partially hides (occludes) another; occluded object is further away - common and reliable
What is relative height?
A position-based depth cue where foreground is perceived as lower and background is perceived as higher - flips at horizon
What is size-distance relation?
The farther away an object is from the observer, the smaller is its retinal image
What is familiar size?
Size-based depth cue where knowing the retinal image size of a familiar object at a familiar distance lets humans use its retinal image size to gauge its distance
What is relative size?
Size-based depth cue where 2 or more objects are about the same size, the relative size of their retinal images can be used to judge their relative distance
What is familiar size in the golf ball, baseball, and basketball example?
Where al 3 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
What is relative size in the biker example?
If we assume 2 riders are about the same size we know that the larger one is twice as close as the further (smaller) rider
What is texture gradient?
A size-based depth cue when if surface variations or repeated elements of a surface are fairly regular in size and spacing, the retinal image size of these equal-size features decreases as their distance increases
What is linear perspective?
A size-based depth cue where parallel lines appear to converge as they recede in depth
What is atmospheric perspective?
A lighting-based depth cue where the farther away an object is, the more distant and less distinct it appears compared to nearby objects
What is shading?
A lighting-based depth cue where light falls on curved surfaces to create shading differences (need it to determine a sense of depth and convexity)
Why do we see hollow faces as convex?
We assume that light comes from the sun (convex) and most objects and ALL faces we see are convex so our brain makes assumptions
What is motion parallax?
Motion-based depth cue where we perceive objects that are closer to us as moving faster than objects that are in the distance AND objects closer move in the opposite direction while further objects move in the same direction we move
What is optic flow?
A motion-based depth cue that refers to the relative motions of objects and surfaces in the retina as the observer moves forward or backward through a scene
Things get bigger as you move forward farther = slower
closer = faster
What is deletion?
A motion-based depth cue that refers to the gradual hiding (occlusion) of an object as it passes behind another one
What is accretion?
A motion-based depth cue that refers to the gradual revealing (de-occlusion) of an object as it emerges from behind another one
What is binocular disparity?
Depth cue based on differences in the relative positions of the retinal images of objects in the two eyes (hinges on differences between 2 eyes)
What is a binocular depth cue?
Occurs because two eyes are needed for any of these cues to work
What is stereopsis (or stereoscopic depth perception)?
Vivid sense of depth arising from the visual system’s processing of the different retinal images in the 2 eyes
What are corresponding points?
A point on the left retina and a point on the right retina that would coincide if the two retinas were superimposed (fovea is always corresponding)
What are non-corresponding points?
A point on the left retina and a point on the right retina that wouldn’t coincide if the two retinas were superimposed (most things are non-corresponding)
What is a horopter?
Imaginary circle around you based on what you’re fixating on (corresponding points fall on the horopter)
What are the 3 types of binocular disparity?
Crossed disparity
Uncrossed disparity
Zero disparity - on the horopter
What is crossed disparity?
Cross your eyes, converge/fixate - closer to horopoter
What is uncrossed disparity?
Uncross your eyes to converge/fixate - beyond horopter
What is zero disparity on the horopter?
Has 0 disparity
What effects the type and magnitude of binocular disparity?
Magnitude - depends on distance from horopter
Type - depends on whether eyes are crossed or uncrossed
What is a stereogram?
What we perceive in the world; 2 images, 1 for each eye
What is an anaglyph?
Stereogram in which two photographs taken from adjacent camera positions are printed in contrasting colors and then superimposed - 1 image that requires 3D glasses to filter for each eye
What is the correspondence problem?
Problem of determining which features in the retinal image in one eye correspond to which features in the retinal image in the other eye
How does the visual system solve the correspondence problem?
- Object recognition happens first
- Matches parts of retinal images based on very simple properties (color, edge orientation) before object recognition
What are random dot stereograms (RDS)?
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
What did random dot stereograms (RDS) tell us?
Provide a strong argument that correspondence match must precede object recognition - RDS produce a sense of depth which means that object recognition can’t happen first
How does the brain actually solve the correspondence problem?
Makes 2 simple assumptions about the world
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
What does a binocular cell’s receptive field tell us about disparity?
Cell only likes when there is a specific amount of disparity (V1 cells get input from both eyes and can be tuned to specific types of disparity)
What happens when multiple depth cues are present?
The visual system relies on all information it receives to help determine depth and distance
What type of illusion is forced perspective?
Size-distance illusion
What is size constancy?
If we did not have size constancy we would perceive objects as growing and shrinking as they moved closer and farther away from us instead we know the size of objects stays the same regardless of distance
What is size-distance invariance?
The perceived size of an object depends on its perceived distance, and vice versa
What is emmert’s law?
The perceived size of an afterimage is proportional to the distance of the surface on which it’s “projected”
What is shape 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
What is shape-slant invariance?
The perceived shape of an objects depends on its perceived slant and vice versa
