L Cones

Long wavelength sensitive cones (red). Are most sensitive to a wavelength of approximately 558nm. (See also M Cones and S Cones).

Lateral Geniculate Nucleus

Structure located in the thalamus which is a major recipient of axons from the retina. About 10% of its input is from the retina. It is composed of 6 layers. While input to the LGN from the two eyes is segregated, significant binocular influence can be exerted on the LGN by the cortex.

Parvocellular Layer

4 superficial layers of the LGN. Small neurons, termination sight of midget ganglion cells.

Magnocellular Layer

2 deep layers of the LGN. Large neurons, termination sight of parasol ganglion cells.

Intercalated Zones

Areas of cells falling between the parvocellular and magnocellular layers.

Law of Pragnanz

(See Gestalt Psychologists).

Left Visual Hemifield

The left half of the visual field, projects on the nasal hemiretina of the left eye and on the temporal hemiretina of he right eye.

(See Lateral Geniculate Nucleus).

Lightness

The perception of reflectance. Related to the perception of an object's surface.

Linespread

The distribution of how the image of a very thin line is blurred on the retina (due to diffraction). Depends on pupil size.

Line Motion Illusion

(See Transformational Apparent Motion).

Linking Hypothesis

(Brindley)

Claim that a particular mapping occurs, or that a particular mapping principle applies between perceptual stages and stages of the visual substrate.

Long-Sightedness

(See Hyperopia).

Lossless Compression

An image compression method which preserves image information perfectly. For example, as nearby pizels in an image are usually similar (highly correlated), one can eliminate this redundency by coding one pixels intensity I(x,y), and subsequenct pixels by their difference (I(x,y+1)-I(x,y)) rather than the values themselves. The new representation has a lower correlation and requires less storage space despite preserving all informatio. The best possible lossless compression is one in which the values are completely decorrelated as correlation (the ability to predict one value from another) is a sign of redundancy. (See also Lossy Compression and Perceptually Lossless Compression).

Lossy Compression

Image processing techniques which save much space but do lose some information about the contens of an image. (See also Lossless Compression and Perceptually Lossless Compression).

Luminance

Amount of light coming off of a surface. Subjectively, the unit of brightness measured in candela per meter squared (cd/m²).