Vision Flashcards
Cornea
Refracts light at the retina
Lens
Changes shape to fine-tune the image and further refract light towards the retina
Rods
More common and see in the dark
Cones
Less common but high acuity and see in the day
Horizontal cells
Contact photoreceptors and bipolar cells
Amacrine cells
Contact bipolar and ganglion cells
Order of visual processing
Rods/cones> bipolar cells> ganglion cells> optic nerve
Fovea
Centre region of the retina that has a high density of smaller, tightly packed cones with high acuity
Retina
A layer of neurons at the back of the eye
Optic nerve
the collection of ganglion cell axons that extends from the retina to the occipital cortex of the brain.
Optic chiasm
The point at which parts of the two optic nerves cross the midline.
Optic tract
The axons of retinal ganglion cells (form optic nerve) after they have passed the optic chiasm. Most of these axons terminate in the lateral geniculate nucleus.
V1
Where most visual information arrives first
V2
Adjacent to V1, can respond to illusory boundaries and complex relations among parts of the receptive field4
V4
Strong responses to the frequency gratings
V5
Specialized for the perception of motion and its direction
On-centre receptive field
Light hits the cone and causes glutamate release to decrease, depolarizing the on-centre bipolar cell and increasing its neurotransmitter release. This goes to the on-centre ganglion cell which increases its firing rate.
Off-centre receptive field
Light hits the cone and causes glutamate release to decrease, hyperpolarizing the off-centre bipolar cell and decreasing its neurotransmitter release. This goes to the off-centre ganglion cell which decreases its firing rate.
Hubel & Wiesel’s theoretical model of visual analysis
Is hierarchical.
More complex receptive fields are built up from inputs of simpler ones.
Visual acuity
Sharpness of vision
Adaptation
Each photoreceptor adjusts its level of sensitivity to match the average ambient level of light.
Lateral inhibition
The phenomenon by which interconnected neurons inhibit
their neighbours, producing contrast at the edges of regions.
Trichromatic hypothesis
Three different types of cones (RGB) that each respond to a specific part of the spectrum. Each has its own separate pathway to the brain and color is recognized based on which receptors are activated.
Opponent-process hypothesis
Four unique hues (blue, green, yellow, red) and three opposed pairs of colours (b&y, g&r, b&w).
Dorsal stream
Assessing the location of objects (where) and guiding our movements towards them
Ventral stream
Identifying objects (what)
Rhodopsin
The photopigment in rods that responds to light.
Lateral geniculate nucleus (LGN)
The part of the thalamus that receives information from the optic tract and sends it to visual areas in the occipital cortex.
on-center bipolar cell
A retinal bipolar cell that is excited by light in the center of its receptive field. know how they work
off-center bipolar cell
A retinal bipolar cell that is inhibited by light in the center of its receptive field.
on-center ganglion cell
A retinal ganglion cell that is activated when light is presented to the center, rather than the periphery, of the cell’s receptive field.
off-center ganglion cell
A retinal ganglion cell that is activated when light is presented to the periphery, rather than the center, of the cell’s receptive field.
Amblyopia
Reduced visual acuity not caused by optical or retinal damage
Optic ataxia
Difficulty using vision to reach for and grasp objects
Simple cortical cells
“Bar detectors” respond to edge or bars of a particular width that is in a specific location in the visual field
Complex cortical cells
Responds best to bar of a particular width that is in motion anywhere in the field
Lateral inhibition
Sensory receptor cells inhibit information from the neighbouring receptor cells
Scotopic system
Rods
Photopic system
Cones
Myopia (nearsightedness)
Difficulty seeing distant objects
