Visual system: the brain

Visual Processing pathway

1. optic nerve

2. Lateral Geniculate Nucleus (LGN)

3. Primary Visual cortex (V1)

4. Secondary visual Cortex (V2)

5. Inferior temporal cortex (ITC) or Posterior temporal cortex (PTC)

Lateral Geniculate Nucleus (LGN)

part of the thalamus specialized for visual perception; acts as a gate to control how much visual info reaches the cortex

• If all visual info reached the cortex, it would be a fuckign mess

Ex. When I am focused on playing alcross, I am not processing what is happening in my periphery

Primary Visual Cortex (V1)

(one per hemisphere) Receives information from the LGN; the first level of cortical processing of visual info, contains 2 types of cells

• simple cells

• complex cells 8

Simple cells

Responds to bars/edges with a particular width, location, orientation

Ex. A cell might fire a TON for horizontal lines; it doesn’t really gaf about vertical lines

Complex cells

have elongated receptive fields; respond to patterns of light/stimuli movement in a certain direction

Ex. a cell fires A LOT of an object goes down

receptive field

part of the visual field that either excites or inhibits the cells (2 on each side of teh brain)

V1 Hieracheal model

the idea that complex events are built on input from simpler ones; the brain “assembles” a visual by breaking it down and building it back up

• limited bc we don’t have a cell for every single object; this kinda crumbles

Spacial frequency

How fine/corase a detail is

Spacial frequency filter model

Some V1 cells seem to detect “bars and edges” and are tuned into spatial frequencies bc they can detect fine edges

• The V1 cells break scenes into coarse to fine pieces, and then assemble them back together

V1 cortex organization features (4)

1. location in the visual field

2. ocular dominance

3. oritation/spatial frequency

4. color

“Location in the visual field” (organization feature)

map of the visual world; more cortex is dedicatied to processing central vision vs. peripheral vision

occular dominance

The brain prefers input from one eye over the other

• Apparently, my brain does not heavily fuck with my left eye

orientation/spatial frequency (oranization prescne)

angle/fineness of lines

Higher order visual processing in the cortex

visual info first enters cortex at V1, then extends beyond V1 into other cortical areas

• V2

• ITC/PTC

Dorsal Stream

Visual parthway into the parietal cortex; processes motor, location, the “where”

Dorsal Pathway

V1 → V2 →Middle Temporal area/V5

Middle Temporal Area (V5)

region in occipital lobe, reponds to motion in particualr directions/speeds, key arae ofr motion perception

Motion Blindness

Inability to recognize if objects are moving, what direction they’re moving in, ect

• Normally caused by damage to MT

Blindsight

you can’t detect an object but you know it’s moving

• Occurs with V1 damage but MT still intact

Ventral stram

Visual pathways into the temporal lobe, recognizes objects and faces, the “what”

Secondary Visual Cortex (V2)

processes info further, sends it to other areas

V4

Receives info from V2; responds to radial spiral figures, important for color perception/color constancy

Posteroir Temportal Cortex (PTC)

acts as hub for language, sensory integration

Interior temporal cortex (ITC)

Continues to process shapes and color, responds selectivly to complex shapes

Visual Agnosia

Inability to recognize objects despite normal vision; can be caused by damage to ventral pathways (usually ITC)

• Ex. I know what a chair is. If I look at a chair, I have no fucking clue what that is

Prosopagnosia

inability to specifically recognize faces; caused by damage to face-selective areas of the ITC

Association cortical areas

areas that recive converging sensory and motor infomation

• Ex. Prefrontal cortex, posteroir partial cortex