V1,V2,V3,V4 & V5

(See Appendix I: Cortical Areas).

Vectograph

A photograph consisting of varing degrees of polarization based on photographic content. Typically used to make stereoscopic photographs or slides that are viewed with special polarized glasses.

Velocity Field

A vector representation of the velocity of image motion of many small regions of a time-varying image

Ventral Pathway

One of two theorized systems of visual information processing. Information though to progress toward the temporal cortex V1-> V2 -> V4 -> IT. Functions for analysis of object qualities such as pattern shapes, size and colors.
(See also Dorsal Pathway).

Vernier Acuity

The ability to judege whether two line segments are collinear.

Vieth-Muller Circle

When the foveal centers are pointed at an object, the range for which images of all other objects fall on corresponding points of zero horizontal disparity. This differs from the perceived range of zero disparity, the Horopter.

Viewer Centered Coordinate System

The projection of an objects shape on the retina depends on the vantage point of the viewer.
(See also Object Centered Coordinate System).

Visual Angle

A measurement of the area of the retina in degrees subtended by a stimulus. Roughly speaking the width of one's thumb at arm's length is approximately 2 degrees.

Visual Cliff

Apparatus consisting of a raised platform which divides two surfaces with optical texture (i.e. checkerboard pattern) covered with glass sheets. One is at a similar level to the platform, one is at a lower level. The optical information of the lower level produced the perception of a steep drop. Young animals of all species which guide themselves primarily by vision avoid venturing onto the glass covering the deep side.

Visual Interferometry

(LeGrand 1935)

Technique which allows the use of fine spacial patterns at much higher contrast than would be possible using ordinary optical techniques (because of optical blurring due to diffraction under ordinary conditions.) Uses a beam splitter to create an interference pattern.

Visual Phosphene

The visual perception resulting from non-photopic stimulation such as electrical stimulation of the cortex or pressing on the eyeball. Brinkdley & Lewin 1968) and Bak et al (1990) have shown that stimulation of the cortex produces visual pherceptions.

Vitreomacular Traction Syndrome

A traction-induced visual deficit in which partial posterior vitreous detachment is present in combination with persistent macular adherence.

Vitreous Humor

Liquid filling the eye cavity.