47 terms

Sensation and Perception Ch 8

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Accommodation (depth cue)
A depth cue based on muscular sensations that occur when the eye accommodates to bring objects at different distances into focus. This cue provides information about the distances of nearby objects.
Accretion
A cue that provides information about the relative depth of two surfaces. Occurs when the farther object is uncovered by the nearer object due to sideways movement of an observer relative to the objects. See also Deletion.
Ames room
A distorted room, first built by Adelbert Ames, which creates an erroneous perception of the sizes of people in the room. The room is constructed so that two people at the far wall of the room appear to stand at the same distance from an observer. In actuality, one of the people is much farther away than the other.
Angle of disparity
The visual angle between the images of an object on the two retinas. When images of an object fall on corresponding points, the angle of disparity is zero. When images fall on noncorresponding points, the angle of disparity indicates the degree of noncorrespondence.
Angular size-contrast theory
An explanation of the moon illusion that states that the perceived size of the moon is determined by the sizes of the objects that surround it. According to this idea, the moon appears small when it is surrounded by large objects, such as the expanse of the sky when the moon is overhead.
Apparent-distance theory
An explanation of the moon illusion that is based on the idea that the horizon moon, which is viewed across the filled space of the terrain, should appear farther away than the zenith moon, which is viewed through the empty space of the sky. This theory states that because the horizon and zenith moons have the same visual angle, the farther appearing horizon moon should appear larger.
Atmospheric perspective
A depth cue. Objects that are farther away look more blurred and bluer than objects that are closer because we must look through more air and particles to see them.
Binocular depth cell
A neuron in the visual cortex that responds best to stimuli that fall on points separated by a specific degree of disparity on the two retinas. Also called Disparity-selective cell.
Binocular disparity
Occurs when the retinal images of an object fall on disparate points on the two retinas.
Conflicting cues theory
A theory of visual illusions proposed by R. H. Day, which states that our perception of line length depends on an integration of the actual line length and the overall figure length.
Convergence (depth cue)
See Perspective convergence.
Correspondence problem
The visual system's matching of points on one image with similar points on the other image in order to determine binocular disparity.
Corresponding retinal points
The points on each retina that would overlap if one retina were slid on top of the other. Receptors at corresponding points send their signals to the same location in the brain.
Crossed disparity
Binocular disparity in which objects are located in front of the horopter.
Cue approach to depth perception
The approach to explaining depth perception that identifies information in the retinal image, and also information provided by aiming and focusing the eyes on an object that is correlated with depth in the scene. Some of the depth cues that have been identified are overlap, relative height, relative size, atmospheric perspective, convergence, and accommodation.
Deletion
A cue that provides information about the relative depth of the two surfaces. Deletion occurs when a farther object is covered by a nearer object due to sideways movement of an observer relative to the objects. See also Accretion.
Disparate points
See Noncorresponding points.
Disparity detectors
Neurons that respond best to stimuli that fall on retinal points separated by a specific angle of disparity. Also called binocular depth cells.
Disparity-selective cell
See Binocular depth cell.
Emmert's law
A law stating that the size of an afterimage depends on the distance of the surface against which the afterimage is viewed. The farther away the surface, the larger the afterimage appears.
Familiar size
A depth cue. Our knowledge of an object's actual size sometimes influences our perception of an object's distance.
Horopter
An imaginary surface that passes through the point of fixation. Images caused by a visual stimulus on this surface fall on corresponding points on the two retinas.
Microstimulation
A procedure in which a small electrode is inserted into the cortex and an electrical current is passed through the electrode that activates the neurons near the electrode. This procedure has been used to determine how activating specific groups of neurons affects perception.
Misapplied size constancy scaling
A principle, proposed by Richard Gregory, that when mechanisms that help maintain size constancy in the three-dimensional world are applied to two-dimensional pictures, an illusion of size sometimes results.
Monocular cue
Depth cue, such as overlap, relative size, relative height, familiar size, linear perspective, movement parallax, and accommodation, that works when we use only one eye.
Moon illusion
An illusion in which the moon appears to be larger when it is on or near the horizon than when it is high in the sky.
Movement parallax
A depth cue based on the fact that as an observer moves, nearby objects appear to move rapidly whereas far objects appear to move slowly.
Müller-Lyer illusion
An illusion consisting of two lines of equal length that appear to be different lengths because of the addition of "fins" to the ends of the lines.
Noncorresponding (disparate) points
Two points, one on each retina, that would not overlap if the retinas were slid onto each other.
Occlusion
Depth cue in which one object hides or partially hides another object from view, causing the hidden object to be perceived as being farther away.
Oculomotor cue
Depth cue that depends on our ability to sense the position of our eyes and the tension in our eye muscles. Accommodation and convergence are oculomotor cues.
Perspective convergence
The perception that parallel lines in the distance converge as distance increases.
Pictorial cue
Depth cue, such as overlap, relative height, and relative size, that can be depicted in pictures.
Ponzo illusion
An illusion of size in which two objects of equal size that are positioned between two converging lines appear to be different in size. Also called the railroad track illusion.
Random-dot stereogram
A pair of stereoscopic images made up of random dots. When one section of this pattern is shifted slightly in one direction, the resulting disparity causes the shifted section to appear above or below the rest of the pattern when the patterns are viewed in a stereoscope.
Relative height
A depth cue. Objects that have bases below the horizon appear to be farther away when they are higher in the field of view. Objects that have bases above the horizon appear to be farther away when they are lower in the field of view.
Relative size
A cue for depth perception. When two objects are of equal size, the one that is farther away will take up less of the field of view.
Size constancy
Occurs when the size of an object is perceived to remain the same even when it is viewed from different distances.
Size-distance scaling
A hypothesized mechanism that helps maintain size constancy by taking an object's perceived distance into account. According to this mechanism, an object's perceived size, S, is determined by multiplying the size of the retinal image, R, times the object's perceived distance, D.
Stereopsis
The impression of depth that results from binocular disparity—the difference in the position of images of the same object on the retinas of the two eyes.
Stereoscope
A device that presents pictures to the left and the right eyes so that the binocular disparity a person would experience when viewing an actual scene is duplicated. The result is a convincing illusion of depth.
Texture gradient
The visual pattern formed by a regularly textured surface that extends away from the observer. This pattern provides information for distance because the elements in a texture gradient appear smaller as distance from the observer increases.
Uncrossed disparity
Binocular disparity that occurs when objects are located beyond the horopter.
Ventriloquism effect
See Visual capture.
Veridical perception
Perception that matches the actual physical situation. An example of veridical perception would be perceiving a line to be vertical when it is vertical. Examples of nonveridical perception are provided by illusions, in which what is perceived does not match the physical stimulus.
Visual angle
The angle of an object relative to an observer's eyes. This angle can be determined by extending two lines from the eye—one to one end of an object and the other to the other end of the object. Because an object's visual angle is always determined relative to an observer, its visual angle changes as the distance between the object and the observer changes.
Visual capture
When sound is heard coming from its seen location, even though it is actually originating somewhere else. Also called the ventriloquism effect.
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