Hubel Wiesel

Neuronal architecture of mammalian visual system

Visual receptor

Retina Functional organization

Photoreceptors Rod and Cone

Anatomical Distribution of Rods and Cones

Phototransduction

Ganglion Cell : Contrast discrimination

Receptive Field

Receptive fields of photoreceptors and their connections. (A) The receptive field center provides a direct input from the photoreceptors to the bipolar cell, and the receptive field surround provides indirect input from the photoreceptor to the bipolar cells via horizontal cells. (B) 1: Photoreceptor cell; 2: on-center bipolar cell; 3: off-center bipolar cell; 4: on-center ganglion cell; 5: off-center ganglion cell.

Receptive field of bipolar cells

Receptive field

Responses of retinal bipolar and ganglion cells to darkness and illumination in the receptive field center.A) Changes in the electrical activity of the photoreceptor and on- and off-center bipolar and ganglion cells when the photoreceptor receptive field center is in the dark. (B) Changes in the electrical activity of the photoreceptor and on- and off-center bipolar and ganglion cells when the photoreceptor receptive field center is illuminated

Lateral inhibition mechanism

Responses of retinal bipolar and ganglion cells to darkness and illumination in the receptive field surround. (A) Changes in the electrical activity of the photoreceptor and on- and off-center bipolar and ganglion cells when the photoreceptor receptive field surround is in the dark. (B) Changes in the electrical activity of the photoreceptor and on- and off-center bipolar and ganglion cells when the photoreceptor receptive field surround is illuminated.

Receptive field of two ganglion cells overlap

Two neighboring retinal ganglion cells receive input over the direct path from two overlapping groups of receptors. The areas of retina occupied by these receptors make up their receptive-field centers, shown face on by the large overlapping circles.

Ganglion Cells

Characteristics M Cells P Cells

Color No Yes

Contrast High Low

Spatial Low High

Temporal High Low

Population 5% 90%

Action Potential Phasic, fast Tonic, slow

Function Movement Shape

Receptive field Large Small

Retinal mapping Periphery Fovea

Central Projections of Retinal Ganglion Cells

Lateral Geniculate Ganglia

Retinal projection to Lateral Geniculate Nucleus

Central retinal pathway

LGN Projection to Occipital Cortex

Occipital lobe

LGN to Visual Cortex projection

Receptive field of a simple cell in the primary visual cortex

Simple cell of visual cortex

Complex Cell

What Primary Visual Cortex do?

Projection of LGN to V1

A, sends a signal to many simple

cells, each with different

orientations. In this figure, cell A

shares its information with 3 simple

cells. If there were a simple cell for

each 5 deg change in orientation,

the same cell A would provide

information to 36 simple cells (180

deg/ 5 deg = 36).

Complex Cells

Retinal image of an object

Significance of Movement Cells

A rough indication of physiological cell types found in the different layers of the striate cortex.

The ocular dominance columns

Ocular Dominance Columns

Ocular dominance remains constant in vertical microelectrode penetrations through the striate cortex. Penetrations parallel to the surface show alternation from left eye to right eye and back, roughly one cycle every millimeter.

Ocular Dominance Column input from LGN

R L

The overlap and blurring of ocular-dominance columns beyond layer 4 is due to horizontal or diagonal connections.

Orientation column of visual cortex: Optical imaging

Organization of Blobs

Primary Visual Cortex Architecture

Hypercomplex CellsEnd Stopping cells

V2-3: Assembling simple features into objects.

V1V2

Binding Problem

Binding Problem

Illusory contour

What we perceive depends not only on the visual image but also on our interpretation of what we see

Interpretation based on our memories modifies what we see. For example if we expect to see the letter m in “exanple” we may not notice that is has been misspelled.

Visual Area Beyond V2

Evidence for dorsal and ventral pathway

Inferior Temporal neuron response to Form

Face and Complex Form Recognition ITC

Fusiform face area

Columnar organization of IT area

IT has a columnar organization Cells within a column are activated by the same object. Neighboring columns respond best to objects of a similar shape as in a and b.

Central Visual Pathways

AIT = anterior inferior temporal area; CIT = central inferior temporal area; LIP = lateral intraparietal area; Magno = magnocellular layers of the lateral geniculate nucleus; MST = medial superior temporal area; MT = middle temporal area; Parvo = parvocellular layers of the lateral geniculate nucleus; PIT = posterior inferior temporal area; VIP = ventral intraparietal area.) (Based on Merigan and Maunsell 1993.)