Bandwidth

The ratio of the spatial frequencies at which half the maximum contrast sensitivity is obtained.

Barber Pole Illusion

(Wallach 1935)

The direction of motion of a diagonal grating pattern drifting behind a rectangular aperture depends upon the elongation of the aperture. The prevailing explanation is that the perceived direction of motion results from the integration of motion signals from grating terminators at the edges of the aperture. As a vertically elongated aperture has larger number of terminators with vertical trajectories, vertical motion prevails. (More on Optical Illusions)

Benussi Ring Illusion

(See Koffka-Benussi Ring Illusion)

Binding Problem

If color, form, and motion are processed in separate areas of the brain, how/where is this information reassembled to create a single unified percept? (e.g. a purple box moving to the left).

Binocular Disparity

The difference in position of two retinal images of an object that do not fall on exactly corresponding retinal positions.
(See Figure).

Binocular Vision

Vision performed with two eyes/sensors whose outputs are often used to extract relative stereoscopic depth.

Binocular Field

A receptive field which responds to a cells optimal stimulus if it is presented to either eye

Binocular Overlap

The segment of the optic array sampled by both eyes.

Binocular Rivalry

Occurs when the two eyes are presented with different stimuli. Instead of seeing a summation of the two images, our perception switches from one image to the other.

Binocular Zone

The central region of the visual field from which light enter both eyes. (See also Monocular Zone).

Binoptic Stimulation

When the same image is presented to each eye. (See also Dichoptic Stimulation and Monoptic Stimulation).

Bioluminescence

The emission of light by organisms

Bipolar Cell

Key interneurons in the retina. Antagonistic center-surround receptive field organization. Makes excitatory connections to ganglion cells.

Bleaching

Photoreceptors, most notably rods, can be driven to saturation by bright visual stimuli and become insensitive to light changes in this region, then they are said to be 'bleached'.

Blind Spot

The location where optic nerve fibers leave the retina. This area has no photoreceptors and therefore no visual input. The cortex appears to fill-in this missing information so we are not conscious of the blind spot.

Blindsight

A phenomenon reported in individuals suffering from cortical blindness (i.e. damage to the primary visual cortex resulting in blindness). Individuals with blindsight report that they are unable to see, yet under forced choice conditions are able to indicate the presence and location of visually presented objects.

Block Artifacts

Visual artifacts created when an image compressed with an algorithm using block coding is reconstructed. (See also Block Coding).

Block Coding

Any image processing technique which begins by subdividing the image into blocks. (See also Block Artifacts).

Blobs

(See Appendix I: Cortical Areas, V1).

Bregman-Kanizsa Display

A display which suggests that the presence of visible occluders permits amodal completion which aid figure-ground segmentation and object recognition.

Border Contrast

A localized contrast effect which is limited to the border immediately adjecent to the contrast discontinuity. (As opposed to Area Contrast).

Brightness Constancy

The perceived brightness of real objects in a natural environment is largely independent of changes in the overall illumination.

Broadband Channel

(See Magnocellular Pathway).

Broadband Stimulus

A visual stimulus that can be considered to be the sum of a large number of sine-wave components.

Brow-Sulzer Effect

An enhancement of brightness/darkness perception is found in the time domain. Stimuli of short duration evoke stronger sensations than stimuli of long duration.