psych 230 - unit 9 the visual system: the brain

work by torsten wiesel and david hubel

Nobel prize for work on the anatomy and physiology of the visual cortex. Discovered areas of the visual brain (including thalamus and areas in the occipital cortex) that are specifically sensitive to certain kinds of stimuli.

optic nerve

carries neural impulses from the eye to the brain. Where the pathway for visual information starts

optic chiasm

Area where some of the visual info either stays on the same side or switches sides

optic tract

leads from optic chiasma to terminate in lateral geniculate body

LGN

8 properties (steps)

optic radiation

A collection of axons coursing from the lateral geniculate nucleus to the visual cortex

superior colliculus

function, saccades, smooth eye movements

function of superior colliculus

control of rapid eye movement

saccades

sudden eye movements used to look from one object to another

smooth eye movements

voluntary tracking eye movements

visual cortex

6 layers with the 4th layer having 3 sublayers. Layer 4 receives info from LGN, these pathways don't converge, they stay separate because they pass on very specific, different info.

retinotopic map

Point-by-point relation between the retina and primary visual cortex, every single location on the retina are processed by neurons that are close to each other in the primary visual cortex.

cortical magnification

The allocation of more space in the cortex to some sensory receptors than to others.

visual crowding

Implication of cortical magnification, you're more focused on one specific apple in a fruit stand but you have high visual acuity surrounding the one apple so you can tell what fruits are around it, but you can't tell what is really in the periphery.

bar detector

a cell in the visual cortex that responds most to bars in the visual field

simple cells

cells that detect lines, very sensitive to line

• orienting tuning curve

orientation tuning curve

demonstrates the typical response of a simple cell to stimuli or different orientation

complex cells

• Sensitive to an oriented bar anywhere within their receptive field

• Assemble lines, then small motion

•  can respond to both dark and light lines, unlike simple cells

• Will respond to a line defined by contrast

end-stopped cells

• Neurons that are fired only when the entirety of the stimulus falls inside the receptive fields/stimulus

• Help us understand the end of objects, the corners, the end of surfaces

• Allows us to detect if an object is ending in a particular part of the world

organization of V1: hypercolumn

• As you push down, they all have the same orientation, selectively

• All the layers below it are sensitive to that particular orientation

• If you put their electrode in the neuron right next to the next column and so on (traveling laterally over the surface of V1), there is a continuity over the preferences of the orientations of the self

V2

Involved in representing the world, color and shape and motion processing all occurs here, the neurons that look at if an edge is part of a given object.

ventral (“what”) pathway

color/shape processing, in the temporal lobe

dorsal (“where”) pathway

motion and spatial relations, located in the parietal lobe

experiment on monkeys

• Lesioned parts of the brain to show that these ventral paths and the dorsal paths were involved in these different aspects of our lives

• Interacted with the object and engaged with the objects to understand the spatial relations

• Monkey learned that he had to find the bin that was under the square object

• When they lesioned an area in the infratemporal cortex, the monkey lost the ability to perform that task

where does vision come together?

No single location where info converges, vision happens because of the simultaneous activation across all the visual areas

development of the visual system

a period of development beyond which it is difficult/impossible to change the function of neurons. (cataractclouding of lens, strabism- misalignment of eyes)

the kitten carousel experiment

Cats raised in complete darkness except for 2-3 hours a day, divided into two groups. One were the active kittens (control over their movement, the world moved in direct reaction to their movements) and the passive kittens (in a suspended basket, yolked the movement of the active kitten to the passive kitten, their own movement had no affect on their perception of the world) The active kittens grew up fairly normally Passive kittens had a very strong visual deficiency

critical period: what is it?

in the first 7-8 years for humans—when the brain's visual cortex is highly plastic and requires normal visual input to mature properly

cataract

• Results from the clouding of the lens and doesn’t allow light to enter

• Might become blind as the disease progresses

strabism

a common condition where eyes are misaligned, pointing in different directions due to poor muscle control, often affecting depth perception

visual acuity

• How small are the spatial details that our visual system can resolve?

• the clarity, sharpness, and spatial resolving power of vision

spatial frequency

• how many alternations of black and white can we fit in a fixed amount of space?

• how rapidly image intensity changes across space

development of spatial frequency in children

low spatial frequency (kids reach adult levels in ~9 weeks) and high spatial frequency (kids reach adult levels in 3-4 years)

selective adaptation

Noninvasive procedure to see what sorts of properties the visual brain of humans are respond to. A method used to investigate whether humans have neurons that prefer specific features like specific colors, orientations, or spatial frequencies.

tilt after effect

The vertical bars should appear opposite of the previous orientation

color aftereffect

You continue to see a color after it is removed from a visual field.

spatial frequency aftereffect

If you adapt to a medium spatial frequency, you won't observe an aftereffect. If you present a similar spatial frequency, you will see an aftereffect.

blindsight

unconscious residual visual capacities shown by cortically blind patients or the presence of visual abilities in the absence of the visual cortex.

LGN step 1

• The left visual field projects on the nasal retina of the left eye

• The right visual field projects on the temporal retina of the left eye

• There is a crossed projection of the visual stimulation presented

LGN step 2

• The temporal retina has ipsilateral projections (stays on the same side of the body)

• The nasal retina has contralateral projections (opposite side)

LGN step 3

• Each LGN receives information from both the left and right eye (green layers = right eye, red layers = left eye)

• In other words, each LGN receives ipsilateral and contralateral connections

LGN step 4

• The right LGN processes the left visual field (ABC)

LGN step 5

• The left LGN processes the right visual field (DEF)

LGN step 6

• Information from both eyes is maintained in separate layers in the LGN (green = right eye, red = left eye).

• Separate neurons process the information from the left and the right eye

LGN step 7

• Layers 1-2 receive the information from the M ganglion cells (Part of the magnocellular pathway)

• Layers 3-6 Receive the information from the P ganglion cells (path of the parvocellular pathway)

LGN step 8

• Topographic mapping

• Locations that are next to each other in the real world (and on the retina) are processed by the neurons that are next to each other in the brain