Lecture 15: Vision Flashcards
what is the 7 step hierarchy of the visual system
eye and retina (photoreceptors)
optic nerve
optic chiasm
optic tracts
thalamus
Optic radiations
primary visual cortex
what is the retina
Receives light from the lens and converts it into neural signals that the brain can understand.
what are photoreceptors
cells in the retina that respond to light
what are the two kinds of photoreceptors
rods
cones
where are rods found
in the peripheral retina
what are rods
Achromatic (don’t process colour)
High light sensitivity, so we use these for Nighttime vision
a lot more rods than cones
where are cones found
in the central retina (fovea)
what are cones
High-acuity and colour vision during day-time when light levels are higher.
what is the optic disc
Region where the axons leaving the retina gather to form the optic nerve
*no photoreceptors here > blind spot
what is the region of the retina with the HIGHEST visual acuity
the fovea
what are the 2 kinds of ganglion cells
Parasol Ganglion Cells
Midget Ganglion Cells
what are Parasol Ganglion Cells
- Gross stimulus features and movement
- Large cell bodies, large receptive fields, large axons
what are Midget Ganglion Cells
- Fine visual detail and color
- Small cell bodies, small receptive fields, smaller axons…. More NUMEROUS
what is Age-Related Macular Degeneration
Damage to macula. Central vision affected.
what is Diabetic Retinopathy
Excess blood sugar damages retinal blood vessels. Patchy vision loss throughout visual field.
what is Cataracts
Loss of lens transparency.
what is Glaucoma
Increased intraocular pressure = damage to optic nerve (often peripheral deficits).
how is what we see changed
its flipped and inverted by the type it reaches the optic nerves
once information has been flipped and upside down, where does it go
the optic chasm where 60% of fibres cross
where does information go after the optic chiasm
the optic nerves become the optic tracts, which each have information from both eyes
what is the path for anything to do with motion/spatial analysis
it goes through the parasol cells, then to the magnocellular layers of thalamus
it stays in its own channel
what is the path for anything to do with form and colour
it goes through the midget cells, then to the parvocellular layers of thalamus
it stays in its own channel
what is the retina-geniculate pathway
the primary visual pathway used for conscious vision
Information from the retina projects to four important subcortical regions in the thalamus
what are the 3 extra-geniculate pathways
don’t go to thalamus, for subconscious vision
pretectum
superior colliculus
hypothalamus
what are the where/what pathways
once information reaches the primary visual cortex, it can either go:
up to the parietal stream (where- analysis of motion and spatial relations)
down to the temporal stream (what-analysis of form and colour)
what is Prosopagnosia
inability to recognize faces
issue with the “what” pathway
what is Homonymous field deficits
a part of the visual field is missing
common after stroke
what are the 6 muscles responsible for moving the eyes
Lateral Rectus
Medial Rectus
Superior Rectus
Inferior Rectus
Superior Oblique
Inferior Oblique
what are brainstem gaze centres
responsible for the automatic control of our extra- ocular muscles
Direct the movements of two eyes together
Connected to output nuclei by inter-nuclear pathways (circuits)
what is paramedian pontine reticular formation (PPRF)
the horizontal gaze center
gives information to the medial longitudinal fasciculus or MLF to yoke the right and left eye
what are saccades
Rapid eye movements to bring targets of interest into the field of view
Refocus image on the fovea
what are the 2 kinds of saccadic eye movements
reflexive (loud sound)
voluntary (looking for someone)
what is Smooth pursuit
Require moving stimulus; cannot be carried out voluntarily without a stimulus
eyes track something as it moves
what is Optokinetic Nystagmus
- Slow phase (smooth pursuit) in one direction
- Fast phase (saccade-like) eye movements in the other
“Train nystagmus”
what is the Vestibulo-ocular reflex (VOR)
Eye movements maintain fixation on target when the head moves
