Perception Chapter 6

Positivism

• A philosophical position that argues that we only have the information of our senses to go off of.

Realism

In philosophy, the argument that there is a real, external world that one can sense

Probability Summation

The increased detection probability based on the statistical advantage of having two detectors instead of just one

Monocular

Referring to one eye

Binocular

Referring to two eyes

Binocular Summation

The combination of signals from both eyes in ways that makes performance better than when relying on just one eye

Binocular Disparity 

Difference in retinal images between the two eyes

Stereopsis

Ability to use binocular vision for depth perception

Monocular Depth Cue

A depth cue that is available even when just using one eye

Binocular Depth Cue

A depth cue that only is available when using information from both eyes

Pictorial Depth Cue

A cue to distance or depth used by artists to depict 3D depth in 2D objects

Occlusion

A cue relative to depth order in which one object obstructs part of another object from view

Nonmetrical Depth Cue

A depth cue that provides information about the depth order (relative depth)  of a given image, but not about depth magnitude (ex. Ones’ nose being in front of their face)

Metrical Depth Cue 

A depth cue that provides quantitative information about distance in the third dimension

Projective Geometry

• Describes the transformations that occur when a three-dimensional image/scene is projected onto a 2D surface

Texture Gradiant

A depth cue based on how items of the same size form smaller images when they are further away, and how when an array of images change in size smoothly across an image, they will appear to form a tilted surface

Relative Height

• A depth cue based on how images at different distances from the observer on a ground plane will form images at different heights in the retinal image of the observer, even if they are at the same height in reality. 

Familiar Size

Depth cue based on knowledge of typical sizes of objects, such as humans and their hands

Relative Metrical Depth Cue

Depth Cue that can specify if one object is farther away from another without providing information about the absolute distance between them

Absolute Metrical Cue

A depth cue that provides quantifiable information about distance in the third dimension (ex. Nose sticking out 4 cm from the face).

Haze/Aerial Perspective 

A depth cue based on the fact that light is scattered by the atmosphere, and that more light is scattered when we look through the atmosphere, and as such more distant objects will appear fainter and are subject to more scatter, and have less depth to them.

Linear Perspective 

• A depth cue based on the fact that lines that are parallel in the third dimension will appear to converge when projected onto a 2D image

Vanishing Point

The point on an image where parallel lines converge

Anamorphic Projection/Anamorphosis

Uses the rules of linear perspective to distort a 2D image to the point of only looking “correct” when viewed from a certain angle or from a mirror that counters distortion

Triangulation

• In vision, the triangle formed by the two eyes and the point on which they fixate in the 3D world. 

Motion Parallax

• A type of triangulation cue based on head movement where the geometrical information from one eye at two different positions and times  is similar to the information from two eyes in different positions in the head at the same time

Optic Flow

• Pattern of apparent visual motion of objects in a visual scene produced by the relative motion between the observer and the scene 

Accommodation

Process where the lens gets fatter as its gaze gets directed towards closer objects

Convergence

Ability of eyes to turn inward

Divergence

• Ability of eyes to turn outward

Vergence Angle

• Angle formed by lines from each eye at the current object of fixation 

• Larger angle implies a closer object, and vice versa 

Absolute Disparity 

• Difference in angular distance of images of an object from the foveas of the two eyes

Relative Disparity

Difference in angular disparities of two objects

Corresponding Retinal Points

• 2 monocular images of an object in the world are said to be on corresponding points of the points are the same distance from the fovea in both eyes. 

Veith-Muller Circle

Imaginary circle/horopter that runs through the two tines and where the object of attention is fixated. Two objects who fall on this horopter have zero binocular disparity

Horopter

Location of objects whose images lie on corresponding points, where zero disparity occurs

Diplopia

• Double vision. If visible in both eyes, stimuli falling off of zero disparity in the horopter, or in front of or behind the horopter (panum’s fusional area) will appear diplopical

Penum’s Fusional Area

• The region of space, in front of and behind a horopter, where binocular single vision is possible 

Crossed Disparity 

A depth cue where an object is closer than your point of focus on a horopter. The term “crossed” references how images located in front of the horopter appear to be displaced to the left when viewed from the right eye, and displaced from the right when viewed through the left eye

Uncrossed Disparity

Sign of disparity created by objects behind a horopter. Images are “uncrossed” in that images appear to be displaced to the right from the right eye, and to the left from the left eye

Stereoscope 

A device used to simultaneously present one image to one eye and another image to the other

Free Fusion

• Crossing or diverging eyes to view a stereogram (a 2D image that creates the illusion of a 3D image) without a stereoscope

Stereoblindness

Inability to use binocular disparity for depth perception

Random Dot stereogram

• A stereogram made of a large number of randomly placed dots, and that contains no monocular cues to depth perception. 

Cyclopean

• Stimuli that are defined by binocular disparity alone

Uniqueness Constraint

The observation that a feature in the world is represented exactly once in each retinal image

Continuity Constraint 

• Observation that, except at the edges of objects, neighboring points in the world lie at similar distances from the viewer 

Correspondence Problem 

When using binocular vision, the problem of figuring out which bit of a given image being viewed through the left eye should match which bit in the right eye.

Bayesian Approach

Prior knowledge and current knowledge of a stimuli influences our perception and estimates of the probability of a current event.

Binocular

• Competition between the two eyes for control of visual perception, is evident when two different stimuli are presented to the two eyes

Stereoacuity

A measure of the smallest binocular disparity that can generate a sense of depth

Dichoptic

Referring to the presentation of two different stimuli, with one presented to each eye

Critical Period 

A period of time where an organism is particularly susceptible to change. In the context of visual development, it is a period early in development when normal binocular visual stimulation is required for normal cortical development

Strabismus 

• A condition where the two eyes are misaligned to a point where a single object in space is imaged on the fovea of one eye and a non-foveal area of the other. The two eyes do not point to the same spot in the world. 

Esotropia 

When one eye is pointed too far inward 

Exotropia

When one eye is pointed too far outward

Tilt Aftereffect

Perceptual Illusion of tilt, usually caused by adaptation to a pattern

Suppression

Inhibition of an unwanted image, often used to eliminate diplopia