Nasal Hemiretina

That portion of the retina that lies medial to the fovea. (See Temporal Hemiretina and Figure).

Near-Sightedness

(See Myopia).

Necker Cube

A cube with ambiguous perspective. (More on Optical Illusions)

Negative Priming

The increased reaction time (or sometimes error rate) to a stimulus which has recently been ignored in preference to a target in a selection or decision task. (1)

Neon-Color Spreading

A phenomenon in which the color certain stimuli seem to "leak" into surrounding areas. For example using a red cross and an Ehrenstein figure. When the solid red-cross is perceived in isolation it looks normal. When the Ehrenstein figure is viewed in isolation it generates an illusory contour. When the red cross is places in the Ehrenstein figure, the red color flows out of the cross and tends to fill the illusory figure. (More on Optical Illusions)

Neuron Doctrine

(Cajal)

The idea that nerve cells are independent biological units.

Nonclassical Receptive Field

Classical receptive fields are plotted by spots of light or moving stimuli. If a cell responds consistently to that stimulus then the location of that stimulus is said to be within the cells classical receptive field. Activity outside that area can influence a cell's response to the original stimulus. Examples : Motion, Color.

Nucleus of the Optic Tract (NOT)

Receives input from directionally sensitive cells in the retina. Lesions produce deficits in tracking of moving stimuli.

Null Sets

Sets of stimuli which all lead to the same activation of the individual photoreceptor and are thus indiscriminable for that photoreceptor

Nyquist Limit

The highest resolvable frequency that can be unambiguously registered by an array of neural elements. A system that encodes spatial patterns at a seires of uniformly spaced sample points, , can exactly represent sine or cosine gratings of all spacial frequencies up to the Nyquist frequency, where:

(See also Aliasing)