Visual System Flashcards
The aperture or gap that controls the amount of light entering the next chamber of the eye. Size is controlled by the iris.
pupil
Bring visual images into sharp focus by acting as a fine adjustment to the cornea. Behind the pupil.
lens
Small round window that enables light to enter the eye
cornea
A ring of muscles that gives the eye its colour
iris
Tough white tissue that covers the eye
sclera
How many rods are there?
120 million
How many cones are there?
6 million
Cones are used to see
light and colour
Rods are used to see in the
dark
Most of the rods are located in the
periphery
Most cones are in the centre or in the
fovea
Which cells project laterally or sideways and interconnect the photoreceptors?
horizontal cells
Both rods and cones contain special chemicals called
photopigments
What do photopigments do?
absorb light and transduce it into neural information
What is the response of an on-centre cell?
on response when light is in centre of field, off response when light is in periphery of the field.
What is the response of an off-centre cell?
off response when light is in the centre of the field, on response when the light is in the periphery of the field
The sensory area detected by a group of photoreceptors that converge onto an individual ganglion cell and contribute to its neural activity is known as?
receptive field
What is the colour opponent theory?
Each detector produces 2 colour sensations which also oppose each other (red-green, yellow-blue, black-white)
What links the bipolar and ganglion cells?
amacrine cells
Bipolar cells project to what cells?
ganglion cells
What is the optic nerve made out of?
axons of the ganglion cells
The part where two optic nerves cross over each other is called the?
optic chiasm
Where does 80% of visual information terminate?
lateral geniculate nucleus
what cells is the lateral geniculate nucleus composed of?
magnocellular and parvoocellular cells
the superior colliculus is responsible for?
saccadic eye movement
The optic tract that doesn’t go to the lateral geniculate nucleus branches out to:
suprachiamatic nucleus, pretectum, superior colliculus.
A simple cell in the visual cortex has a receptive field (at the retina) that is
Elongated with on and off components (responding best to a stationary line in the correct orientation)
A complex cell in the visual cortex:
Responds maximally when a line is anywhere in its receptive field providing it is in the correct orientation
A hypercomplex cell responds best to?
a line in a specific orientation and of a certain length
We have 2 eyes (left and right) but one visual world. This convergence of visual input is called?
occular dominance
The dorsal pathway is where?
parietal lobe
the ventral pathway is where?
temporal lobe
The dorsal pathway is also known as the
where pathway
the ventral pathway is also known as the
what pathway
Prosopagnosia is when you can’t
recognise faces
Simultanagnosia is when you are unable to
put a scene together and make sense of it
Someone who has ocular apraxia is unable to
make a systematic scan and has wondering eyes
optic ataxia is?
unable to reach for objects
someone with associative agnosia can’t identify
what
someone with appercetive agnosia can’t identify
where (man who mistook wife for a hat)
Cells in the blobs found in the visual cortex are involved in?
colour perception
Orientation detection is first coded by
simple cortical cells
The range of electromagnetic energy visible to humans falls between
400 and 750 nm
Which cell type responds to high contrast and colour?
P cells
Motion information is conveyed by
M cells
Four of the six LGN layers contain ?
Parvocellular layers
common in older people and the reduced ability of the lens to accommodate is called
presbyopia
Myopia is?
unable to see things clearly from far away
