Vision Flashcards
Fovea
Cones only At the retina’s periphery, only rods
Parts of the eye (front to back)
Cornea, pupil/iris, lens, retina (fovea, blind spot)
Connection between sensorireceptors and retinal ganglion cells
Rods and cones connect with bipolar neurons Bipolar neurons connect to ganglion cells Ganglion cells group together to form optic nerve
Convergence in the retina
Cones converge less, more likely to have one-to-one connection through bipolar to ganglion cell: greater acuity Rods have higher convergence: better sensitivity to to light but lessened visual acuity
Visual field as it corresponds to retina
Right side of each eye’s visual field forms left half of each eye’s retina; left side of visual field forms on right half of each eye’s retina
Pathway from Visual Field to Cortex
Visual field –> retina –> optic nerve (crossover occurs) –> nasal fibers from left eye go to right hemisphere and nasal fibers from right eye go to left hemisphere, however temporal side fibers do not cross over (all left visual field info ends up in right hemisphere and all right visual field info ends up in left hemisphere) –> LGN (lateral geniculate nucleus of thalamus) –> visual cortex, association areas, & superior colliculus
Hubel and Wiesel found neural basis for…
Feature detection theory: certain cells are maximally sensitive to certain features of stimuli Simple, complex, and hypercomplex
“Simple cells” in visual cortex
give information about orientation and boundaries of a visual object
“Complex cells” in visual cortex
respond to more advanced information about orientation, such as movement
“Hypercomplex cells” in visual cortex
Give information about more abstract concepts, like object shape
Hubel and Wiesel (methodology)
single-cell recording; recording from single nerve fibers Place microeletrode in cortex so sensitive it records activity of single cell
Illumination vs. Brightness
Illumination: physical measurement of amount of light Brightness: subjective experience of light intensity
Adaptation
Adapt to darker environment: dark adaptation Adapt to brighter environment: light adaptation
Rhodopsin
Photochemical/photopigment used by rods; Made of retinal (vitamin A derivative) and opsin (a protein)
Rhodopsin function
When rhodopsin absorbs photon of light, pigment decomposes into retinal and opsin: “bleaching” Dark adaptation is the time is takes for rhodopsin to regenerate after bleaching Vitamin A deficiency –> difficulty seeing in the dark
Simultaneous brightness contrast
A target area of a particular luminance appears brighter when surrounded by a darker stimulus than when surrounded by a lighter stimulus
Lateral inhibition
Adjacent retinal cells inhibit one another causing simultaneous brightness contrast. If a cell is excited, neighboring cells are inhibited. Creates contrast; sharpen and highlights the borders between dark and light areas
Wavelength of light
Color perception. Humans: 400 to 800 nm
Subtractive color mixture
Occurs when we mix pigments. (Ex. Blue + yellow = green)
Additive color mixing
Has to do with lights. Primary colors with additive mixing are red, blue, and green.
Young-Hemholtz theory
Trichromatic theory. Suggests that the retina contains three different types of cones which are differentially sensitive to different colors: red, green, blue. Combine stimulation of these receptors produces all color. Young demonstrated that by mixing the three primary lights, all other colors of the spectrum can be produced
Ewald Hering & Opponent-Process Theory of Color
Criticized the trichromatic theory of color vision; held that yellow must be one of the primary colors, and yellow was a basic color along with red, blue, and green. Organized in opposing hair cells: red would excite a red-green cell and green would inhibit the red-green cell. (Hence, you can’t see reddish-green). Also included an opposing parent to code brightness (something like black-white).
Modern research in color processing
Supports Helmholtz’s theory. Are indeed three types of cones, each one maximally sensitive to a different primary color. However, cells in LGN of thalamus may apply a system similar to the opponent-process theory
Afterimages
This concept led Hering to his theory. The visual perception that appears after prolonged or intense exposure to a stimulus.
George Berkeley, 1709
Listed various cues for depth perception
Interposition (overlap)
Refers to the cue for death perception when one object covers or overlaps another object. We see object A as being in front.
Relative size
Can judge distance by comparing the size of images you perceive with what you know about their actual size
Linear perspective
Refers to the convergence of parallel lines in the distance.
Cues for depth perception
Interposition, relative size, linear perspective, texture gradients, motion parallax, binocular disparity (only binocular cue, all others were monocular)
Texture gradients (J. J. Gibson)
Changes in texture gradient can indicate surfaces receding in depth (as distance increases) or may indicate a corner. For example: hardwood getting narrower as it gets further away (horizontally; different from linear perspective) or the way tile pattern changes, indicating a corner.
Motion parallax
Phenomenon where… When in motion (as in a car/train), when fixated on an object halfway between you and the horizon, objects closer to you and your fixation point appear to move the same direction you do. The perceived speed at which these objects appear to move also varies depending on how close the object is to your fixation point.
Kinetic depth effect
Specific type of motion parallax. Object is moving rather than the observer. The motion of that object gives us cues about the relative depth of the parts of the object.
Binocular disparity
Also called stereopsis. Cue depending on the fact that the distance between the eyes provides us with two slightly disparate views of the world.
Binocular parallax
The degree of disparity in the retinal images of the eyes due to the slight differences in the horizontal position of each eye
Perceptual objects
Use perception of form cue including consideration of figure and ground
Gestalt laws explaining organization of visual information
Proximity, similarity, good continuation, closure, prägnanz
Law of proximity
Elements close together tend to be perceived as a unit
Law of similarity
Objects that are similar tend to be grouped together
Law of good continuation
Elements that appear to follow in the same direction tend to be grouped together (ex. Break down overlay of two lines as their most simple versions)
Subjective contours
Perception of contours which are not physically present. Law of closure: when a space is enclosed by a contour, it tends to be perceived as a figure
Law of prägnanz
Encompasses all the other Gestalt laws of organization. States that perceptual organization will always be as regular, simple, and symmetric as possible.
Five ways for light to appear to be moving
Real motion, apparent motion (stroboscopic movement/phi phenomenon), induced motion, autokinetic effect, motion aftereffect (waterfall illusion)
Real motion
Light which is actually moving and appears to be moving
Apparent motion
An illusion that occurs when two dots flashed in different locations on a screen seconds apart are perceived as one moving dot of light
Induced motion
The illusion of movement occurring when everything around the spot of light is moved (when the background moves)
Autokinetic effect
An illusion that occurs when a spot of light appears to move erratically in a dark room simply because there is no frame of reference
Motion aftereffect
Occurs when you first view a moving pattern (such as stripes moving off to the right) and then you view a spot of light, the spot off light will appear to move in the opposite direction
Proximal vs. distal stimuli
Distal: actual object or event out there in the world Proximal: the information our sensory receptors receive about the object
Four constancies of visual perception
Size constancy, shape constancy, lightness constancy, color constancy
Wolfgang Kohler
Introduced theory of isomorphism: suggests there is a one-to-one correspondence between the object in the perceptual field and the pattern of stimulation in the brain. Addresses how figure-ground configurations are represented in the brain. Has not fared well empirically.
Two types of psychological processing in visual system (directional)
Bottom-up processing: refers to object perception that responds directly to visual input (data-driven processing) Top-down processing: refers to object perception guided by conceptual processes such as memories and expectations that allow the brain to recognize the whole object and then the components (conceptually driven processing) Modern theories of object recognition assume both.
Size constancy
When an object appears to remain the same in size despite the fact that it’s image on the retina has changed in size (perceive the change in retinal size as distance)
Emmert’s law
Relates size constancy and apparent distance Led to size-distance invariance principle, which states size constancy depends on apparent distance
Ames room
Fools observer into believing person A & B appear to be at same distance so observer perceives equally sized people as different sizes because of lacking information on distance (difference in visual angles is not attributed to distance but size)
Moon illusion
Moon on the horizon appears larger than moon at its zenith (despite the fact that both moons are the same size, in actuality and on the retina) One explanation is distance cues like buildings causes moon on horizon to appear bigger
Shape constancy
Retinal shape does not necessarily match perceived shape (example an open door) We use information like depth cues to perceptually resolve the shape
Lightness constancy
Refers to the fact that, despite changes in the amount of I light falling on an object (illumination), the apparent lightness of the object remains unchanged. Occurs because levels of illumination are the same for both the object and the background
Color constancy
Tendency for the perceived color of an object to remain constant despite changes in the spectrum of light falling on it.
Visual perception research in infants
Preferential looking (measure time spent looking at two stimuli; difference in time infers that the infant can discriminate between the two stimuli) Habituation (when new stimulus is presented, if the infant can discriminate between the old and new, he/she will orient toward it)
Infant visuals
Can follow object/light with their eyes when it’s placed in the center of their visual field. Can perceive color, simple figures, sharp contrast, and can see in dim light.
Visual cliff
Glass on table creates “visual cliff”; developed by Gibson and Walk As young as 6 months, infant will not cross the cliff, indicating their ability to perceive depth
