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Color Vision

A. Receptive fields of OFF-center stellate cells in layer 4CP of V1

B. The receptive field of thes OFF simple pyramidal cell is bar shaped and angled at 60u

C. A single orientation column in V1 containing pyramidal cells that respond to dark bars at 60u

FIGURE 12 Receptive field properties of stellate and simple cortical cells. The combined input of several stellate cells with overlapping, circular, center-surround receptive fields (A) establishes a bar-shaped, center-surround receptive field with a preferred orientation in a single

A The Magnocellular or M channel - position and motion detection

Lgn Receptive Field

B. The Parvocellular or P channel - form detection

FIGURE 13 Functional organization of M and P pathways within hypercolumns of the primary visual cortex. The major inputs of most LGN neurons are to layer 4C. The M channel (A) synapses in 4Ca, and the P channel (B) synapses primarily in 4Q6, with a small component (the K channel) projecting directly to the blob regions in layer 2. Thus, color information is processed separately from form.

FIGURE 13 Functional organization of M and P pathways within hypercolumns of the primary visual cortex. The major inputs of most LGN neurons are to layer 4C. The M channel (A) synapses in 4Ca, and the P channel (B) synapses primarily in 4Q6, with a small component (the K channel) projecting directly to the blob regions in layer 2. Thus, color information is processed separately from form.

absorption at approximately 420 nm. Activation of these cones leads to the perception of blue. M cones contain middle-wavelength pigment with a peak absorption at 530 nm and contribute to the perception of green; L cones have long-wavelength pigment with a peak absorbance at pyramidal cell (B). Groups of pyramidal cells with the same preferred orientation are clustered in orientation columns within the visual cortex (C).

A. Left cerebral cortex: lateral view and medial view

A. Left cerebral cortex: lateral view and medial view

movement agnosia prosopagnosi object agnosia movement agnosia prosopagnosi object agnosia color anomia

object agnosia prosopagnosia object agnosia prosopagnosia

B. Right cerebral cortex: medial view and lateral view visual spatial agnosia

B. Right cerebral cortex: medial view and lateral view

Fusiform Gyrus Images

prosopagnosia agnosia of drawings movement agnosia prosopagnosia agnosia of drawings

■ color agnosia visual spatial agnosia movement agnosia

agnosia of drawings prosopagnosia

Visual agnosia type Deficit

The M channel: Agnosia for depth & movement

Visual spatial agnosia Movement agnosia

Stereoscopic vision Discerning object movement

Area of lesion

18, 1Q, 37 on right 18, 1Q, 37 bilaterally

The P channel:: Agnosia for form and pattern:

Object agnosia

Agnosia for drawings Prosopagnosia

The P channel: Agnosia for color:

Color agnosia Color anomia Achromatopsia

Naming, understanding purpose recognition of real objects Recognition of drawn objects Recognition of faces

Association of colors with objects Naming colors Distinguishing hues

18, 19, 20, 21 on left & corpus callosum 18, 19, 20, 21 on right

20, 21 bilaterally

18, 19 on right

Speech zones or connections from 18, 19, 37 on left 18, 19, 37

FIGURE 14 The visual agnosias. Visual area 1 (V1) corresponds to Brodmann's area 17 (dark blue). From V1 information passes in separate channels into the visual association areas located in Brodmann's areas 18, 19, and 37 (lighter shades of blue). The M channel projects in a series of steps toward the parietal lobe, carrying spatial and movement information. The P channel passes down toward the temporal lobe as it processes form, pattern and color. In the temporal lobe, the P channel associates vision with higher order functions such as naming objects. The many visual maps in the visual cortex process different aspects of the visual world, and damage to one of these can produce an isolated deficit, leaving the rest of vision intact.

Color Vision

A. Photoreceptor types in the human retina

S-cone 430 nm rod 500 nm

M-cone 530 nm blue sensitive green sensitive green sensitive

L-cone 560nm red sensitive

B. Absorption spectra of the human rod and three cones.

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