aerial perspective (or haze)
A depth cue based on the implicit understanding that light is scattered by the atmosphere. More light is scattered when we look through more atmosphere. Thus, more distant objects are subject to more scatter and appear fainter, bluer, and less distinct.
Referring to the presentation of two different stimuli, one to each eye.
random dot stereogram (RDS)
A stereogram made of a large number (often in the thousands) of randomly placed dots containing no monocular cues to depth.
The sign of disparity created by objects in front of the plane of fixation (the horopter).
corresponding retinal points
A geometric concept stating that points on the retina of each eye where the monocular retinal images of a single object are formed are at the same distance from the fovea in each eye.
The technique of converging (crossing) or diverging the eyes in order to view a stereogram without a stereoscope.
A cue to relative depth order in which, for example, one object obstructs the view of part of another object.
The apparent point at which parallel lines receding in depth converge.
As a depth cue, the observation that objects at different distances from the viewer on the ground plane will form images at different heights in the retinal image. Objects farther away will be seen as higher in the image.
In vision, the inhibition of an unwanted image; occurs frequently in persons with strabismus.
A depth cue based on the geometric fact that items of the same size form smaller images when they are farther away. An array of items that change in size smoothly across the image will appear to form a surface tilted in depth.
In stereopsis, the observation that a feature in the world is represented exactly once in each retinal image. This constraint simplifies the correspondence problem.
binocular depth cue
A depth cue that relies on information from both eyes.
An important depth cue that is based on head movement. The geometric information obtained from an eye in two different positions at two different times is similar to the information from two eyes in different positions in the head at the same time.
The ability of the two eyes to turn outward, often used in order to place the two images of a feature in the world on corresponding locations in the two retinal images (typically on the fovea of each eye).
A theoretical observer with complete access to the best available information and the ability to combine different sources of information in the optimal manner.
The ability to use binocular disparity as a cue to depth.
A depth cue based on the fact that lines that are parallel in the three-dimensional world will appear to converge in a two-dimensional image.
For purposes of studying perception of the three-dimensional world, the geometry that describes the transformations that occur when the three-dimensional world is projected onto a two-dimensional surface. For example, parallel lines do not converge in the real world, but they do in the two-dimensional projection of that world.
A philosophical position arguing that there is a real world to sense.
Information about the third dimension (depth) of visual space; may be monocular or binocular.
The location of objects whose images lie on corresponding points. The surface of zero disparity.
monocular depth cue
A depth cue that is available even when the world is viewed with one eye alone.
relative metrical depth cue
A depth cue that could specify, for example, that object A is twice as far away as object B without providing information about the absolute distance to either A or B.
A device for simultaneously presenting one image to one eye and another image to the other eye.
Strabismus in which one eye deviates outward.
The competition between the two eyes for control of visual perception, which is evident when completely different stimuli are presented to the two eyes.
An inability to make use of binocular disparity as a depth cue. This term is typically used to describe individuals with vision in both eyes.
The ability of the two eyes to turn inward, often used in order to place the two images of a feature in the world on corresponding locations in the two retinal images (typically on the fovea of each eye).
The perceptual illusion of tilt, produced by adaptation to a pattern of a given orientation.
The process by which the eye changes its focus (in which the lens gets fatter as gaze is directed toward nearer objects).
A depth cue based on knowledge of the typical size of objects like humans or pennies.
A period of time during development when the organism is particularly susceptible to developmental change.
In binocular vision, the problem of figuring out which bit of the image in the left eye should be matched with which bit in the right eye. The problem is particularly vexing when the images consist of thousands of similar features, like dots in random dot stereograms.
Referring to the geometry of the world, named in honor of the ancient Greek geometer of the third century BCE. Parallel lines remain parallel as they are extended in space, objects maintain the same size and shape as they move around in space, the internal angles of a triangle always add to 180 degrees, and so forth.
With one eye.
absolute metrical depth cue
A depth cue that provides quantifiable information about distance in the third dimension (e.g., his nose sticks out 4 centimeters in front of his face).
metrical depth cue
A depth cue that provides quantitative information about distance in the third dimension.
A way of formalizing the idea that our perception is a combination of the current stimulus and our knowledge about the conditions of the world—what is and is not likely to occur.
Strabismus in which one eye deviates inward.
pictorial depth cue
A cue to distance or depth used by artists to depict three-dimensional depth in two-dimensional pictures.
The location of objects whose images fall on geometrically corresponding points in the two retinas. If life were simple, this circle would be the horopter, but life is not simple.
With two eyes.
The sign of disparity created by objects behind the plane of fixation (the horopter).
Referring to stimuli that are defined by binocular disparity alone.
The combination of signals from each eye in ways that make performance on many tasks better with both eyes than with either eye alone.
A misalignment of the two eyes such that a single object in space is imaged on the fovea of one eye, and on a nonfoveal area of the other (turned) eye.
The differences between the two retinal images of the same scene. Disparity is the basis for stereopsis, a vivid perception of the three-dimensionality of the world that is not available with monocular vision.
anamorphosis (or anamorphic projection)
Use of the rules of linear perspective to create a two-dimensional image so distorted that it looks correct only when viewed from a special angle or with a mirror that counters the distortion.
A measure of the smallest binocular disparity that can generate a sensation of depth.
A philosophical position arguing that all we really have to go on is the evidence of the senses, so the world might be nothing more than an elaborate hallucination.
Panum’s fusional area
The region of space, in front of and behind the horopter, within which binocular single vision is possible.
nonmetrical depth cue
A depth cue that provides information about the depth order (relative depth) but not depth magnitude (e.g., his nose is in front of his face).
Double vision. If visible in both eyes, stimuli falling outside of Panum’s fusional area will appear double.
In stereopsis, the observation that, except at the edges of objects, neighboring points in the world lie at similar distances from the viewer. This is one of several constraints that have been proposed to help solve the correspondence problem.
A comparison of size between items without knowing the absolute size of either one.