“Intuition tells us that the brain is complicated. We do complicated things, in immense variety. We breathe, cough, sneeze, vomit, mate, swallow, and urinate; we add and subtract, speak, and even argue, write, sing, and compose quartets, poems, novels, and plays; we play baseball and musical instruments. We perceive and think. How could the organ responsible for doing all that not be complex?”

Eye Brain and Vision : David Hubel

Visual Signal Processing: 2

Visual Information Processing:

Touch : Mono frequency system

1. Modality

2. Location

3. Timing

4. Intensity

Hearing: Multi-frequency system

Bheraghat Jabalpur MP

Visual Signal Processing

1. Modality - EM

2. Location Form, shape, depth

3. Timing - Motion

4. Intensity -

Retina

Rods and Cones

Cones RodsLight Low High

Pigment Less More

Response Fast Slow

Use Day

Loss Blindness Night Blindness

Acuity High Low

Saturation Intense light Day light

Color Yes No

Fovea All Absent

Population Low High

Phototransduction

LightDark

Receptive Field

Receptive field

Receptive field: Lateral Inhibition

Receptive Field: Ganglion Cells

Stimulus M Cells P CellsColor No YesContrast High Low

Spatial Low High

Temporal High Low

Ganglion Cell : Contrast discrimination

Lateral Geniculate Nucleus

Lateral Geniculate Ganglia

Organization of Visual Cortex

Visual Cortex Architecture

Visual Cortex Architecture

Recording from Visual Cortex

Simple Cell

Complex Cells

Complex Cell

Complex Cells

Hypercomplex Cells

Significance of Movement Cells

Orientation Column

Orientation column of visual cortex

Illusion of Edges: V2 in Monkey

Inferior Temporal neuron response to Form

Face and Complex Form Recognition ITC

Blobs

40μm thick layer of upper cortex that has been processed histochemically to reveal the density of cytochrome oxidase, a mitochondrial enzyme involved in energy production

Ocular dominance column

Visual Cortex Architecture

Motion in the visual field

PET scan of MT area for Motion Processing

Depth of vision

Neuronal basis of stereoscopic vision

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 intraparietalarea.) (Based on Merigan and Maunsell 1993.)