Vision

Question 1

The Eye

Answer 1

Pupil: light enters eye
Iris: adjustable aperture, constricts in high light to make pupil smaller
Cornea and lens: focuses light on retina
Accomodation: ciliary muscles change shape of lens to bring objects
Light focuses on the fovea - most densely pact area of photo receptors. Muscles in the eye change the shape of the lease to focus light here.

Question 2

Retina and photoreceptors

Answer 2

Photoreceptors: light sensitive photopigments in outer segments. changes chemical properties when light hits it
Rods: 1 type of receptor: contain rhodispin, respond in dim light, none in fovea. more widely distributed. detect movement
Cones: 1 type of receptor: three types with photopigments most sensitive to different wave lengths (long medium short), daytime vision. Used for fine detail, densely packed in the fovea

Question 3

Retinal Ganglion Cells

Answer 3

neurons that connect to the photoreceptors 
Last stage in retinal processing 
Larger Parasol ganglion cells
Small Midget ganglion cells 
Code different properties 
Cells have ‘receptive fields’

Midget (parvocellular) cones - only connect to a few cones. responsible for fine detail
Parasol (magnocellular) rods - and connect to larger patch of the retina so connect to many

Question 4

Ganglion cell receptive fields (ones connected to cones)

Answer 4

If theres no light shone in the receptive field of G cells it responds at baseline. if you fill the RF it only spikes occasionally

If there is a small patch of light in the middle of the visual field that ganglion cell goes crazy (third picture)
If there is a circle of light outside its receptive field it doesn’t fire at all
It’s all connected to the photoreceptors on the outside its inhibitory and on the inside its excretory

Question 5

Retinal Ganglion cell processing

Answer 5

The cells responsidn to the upper left of the image theres barely any change it doesn’t fire (top left image) When its black the cell isn’t firing but when its white its firing dramatically

(Face picture) The cells are filtering the image for edge information

Throwing away gradual changes and keeping info about the edges e.g. useful in identifying things in the world

Question 6

Optical Chasm

Answer 6

left and right visual field cross over this and go to their respective fields

Question 7

Visual Cortex

Answer 7

50% of the cortex is dedicated to vision (visual cortex)
Primary Visual Cortex/V1/straite cortex (mean the same thing)
The first place the information arrives at is the V1

Question 8

Retinotopy

Answer 8

How info is organised in V1
Calcarun sulcus - runs through the middle of the two hemispheres and thats where the information goes
Retinotopy - part of the visual field is mapped onto the surface of the brain
Centre is mapped at the occipital pole
Upper bank of the sulcus is where the lower visual field is mapped

Question 9

Streams of Processing

Answer 9

nfo arrives in the primary visual cortex and then flows out in different directions

Dorsal - from PVC and up over top of the brain and goes towards the motor system. At each stage the info is changing into more motor representation e.g. how you might move muscles in your arm to grasp something. Automatically computed.