Ebbinghaus Illusion

Although the two central circles are the same size the one surrounded by smaller circles usually appears larger than the one surrounded by large circles. (More on Optical Illusions)

Eccentricity

Angular distance of a point on the retina from the center of the fovea

Ecological Approach

(Gibson)

Emphasizes the information which may be available in extended spatial and temporal pattern in the optic array to guide the actions of animals and people and to specify events of importance or interest as opposed to considering information just present in the retinal image

Edge Integration

Describes a model of lightness perception in which a region's lightness is computed by integrating over the contrast edges in an image. (See The Retinex algorithm)

Efferent

Heading away. A system's efferent signals are those exiting to elsewhere. (As opposed to Afferent)

Ehrenstein Illusion

(Ehrenstein 1941)

A series of radial lines create an illusory circle that appears to be brighter than the background. (More on Optical Illusions)

Eigengrau

German word for 'intrinsic gray'. When both entire retinal images are stabilized, the observer does not perceive black but a non-descript gray fog.

Emmert's Law

(Emmert 1881)

A monocular after-image is located on any surface to which a subject fixates while the after -image is present.x The perceived size of the after-image increases as the perceived distance of the surface increase. Shows that monocular cues may be insufficient to estimate an object's length.

Emmert's Law

Emmetropia

An eye whose image is focused on the retina, rather than in front of behind it. (As opposed to Hyperopia and Myopia).

Empiricism, British

Rejects the notion that ideas were implanted in the mind at birth. Instead all complex ideas are built up for the sense organs. Ultimately all knowledge is achieved by associating simple sensations.

End-Inhibition

A property of some cells in the visual cortex which respond strongly to either an edge, a bar or a slit which ends within the receptive field.

End-Stopped Cell

An orientation selective cell which is also sensitive to the end of a line or edge, responding to short but not long lines or edge stimuli.

Epicapsular Stars

Remnants left on the eye of the hyaloid canal, from development in the womb.

Epipolar Line

For a given point in space, this is the line on which the point will fall in the opposite eye. This line is tilted out of the horizontal unless the eyes are fixated on a very distant object.

Episcotister

Equidistance Tendency

Equiluminant Stimuli

Visual stimuli that vary only in color but not in luminance. Stereopsis and motion perception disappear at equiluminance indicating the presence of separate processing channels for color, motion and stereopsis.

Equivalence Classes

(See Null Sets).

Extrastriate Cortex

Region of primate cerebral cortex anterior to striate cortex. (See also
Appendix I: Cortical Areas).

Extrinsic Terminators

(See Terminators)

Eyespot

A concentrated patch of photoreceptor cells on the skin present in some species.