The Visual System Flashcards
See what you can see
light entering the retina moves at
300,000km/hr
we can see electromagnetic energy between
380 and 760 nanometers in length
wavelength relates to
role in colour perpception
intensity relates to
perception of brightness
our pupil dilation is a compromise btw
sensitivity and acuity
behind the pupil is the
lens
the lens does what?
focuses incoming light on the retina
tension on the lens is adjusted by
the ciliary muscles
accommodation is done by
the lens adjusting to focus
turning eyes slightly in
convergence
the diff in position of the same image on the two retinas
binocular disparity
Binocular disparity is greater when things are
closer
first 3 steps of light entering the eye
pupil
lens
retina
what does the retina do?
converts light to neural signals, conducts to the CNS, helps process signals
name the 6 types of retinal cells or I’ll burn your house down
IN ORDER!!!
Rods
Cones
Horizontal
Bipolar
Amacrine
Retinal Ganglion
axons that project outside the eyeball and end in bundle
Retinal ganglion
what is the center of the retina
the fovea
how does the visual system fill in the retinal gaps?
completion
Cones are good for
colour, good light, high acuity
Rods are good at
low light
rods are ___receptors,
scotopic
cones are ___ receptors
photopic
cones have hundreds of outputs that converge on a single RGC
T or F?
FALSE
Suuuuper false
so false
the fovea only has
cones
what happens at the edge of the fovea?
cones drop off, rods increase
cones can’t see colour, TF????
Falllseeee
in the Purkinge effect…
low light- blues seem brighter
high light red and yellow seem brighter
light to neural signal is
visual transduction
a red pigment that lose it’s ability to absorb in intense light
Rhodopsin
our sensitivity to various wavelengths is due to
Rhodopsin’s ability to absorb them
When Rhodopsin molecules are indarkness their ___are partially open
sodium channels
signals in the Retina-geniculate-striate system reach both sides of of the visual cortex
ipsilaterally and contralaterally
Retina-geniculate-striate is organized
retinotopically
there are ___ pathways from the eyes to the cortex
4
the nasal hemiretinas cross over at the
optic chiasm
the temporal hemiretinas cross over at the ?
THEY DO NOT CROSS OVER!! Trick question
they are ipsalateral motherfucker!!
Parvocellular layers are__ and are for
small cell body neurons and are for colour, fine pattern, slow, still objects
Magnocelluar layers are __ and are for__
large cell body neurons, for movement
cones go to which channel in the lateral gen?
Parvocellular!
Rods go to which channel in the lateral gen?
Magnocelluar
Bipolar cells get their edge info from
cones
bipolar cells enhance
center vision
Neural signals are carried from the retina to the lateral geniculate nuclei by
the axons of RGCs
photopigment of rods is
rhodopsin
non-existent stripes running at the edges, make edges easier to see
mach bands
how did Hubel and Weiss map receptive fields?
microeletrode near single vis system neuron
eye moves blocked with paralytic
images on screen focused on retina
record repsonses of Neuron to various simple stims
when an achromatic light was shone onto the receptive fields of the RGS pathway
on off firing depending on location in field
based on off center or on center
on center cells in the retinal-geniculate-striate respond to
light in central vision field with ON firing and lightst in the peripheral with inhibition
simple striate cells respond best to
straight line borders, bars of light,
complex striate cells respond best to
stim to both eyes, retinal disparity,
the primary vis cortex is organized into
vertical right angles to the cortical layers
each vertical column of the PVC reps to
stim on the same retinal area, same eye
- the complexity of the preference of cortical cells progresses from the
retina, to thalamus to the lower IV levecl of the PVC
PVC neurons resp to
texture
line orientation
line movement
periodic patterns
spatial gradients
3 types of colour receps (cones), each with diff spectral sensitivity, colour is encoded by ratio of activity in the 3 types of cones
trichromatic
two classes of cells in vis system
Brightness and colour
opponent process
in opponent process red is green as blue is
yellow
the colour vision in most primates is
trichromatic
the fact that perceived colour of an object is not a simple function of the reflected wavelengths
colour constancy
the colour of an object is determined by it’s reflectance- the ratios of light of diff wavelengths it reflects on it’s surface
Retinx theory
the PVC gets most of it’s input from
the lateral geniculate nuclei (in the thalamus)
the PVC is mostly hidden by the
longitudinal fissure
the 2ndary PVC is mostly in the
prestriate cortex (band around the PVC)
the biggest association cortex for vis is in the
posterior parietal cortex
the order of the vis cortexes is
PVC- 2ndary, association
area of blindness in corresponding contralateral visual field of both eyes
Scotoma
the dorsal stream runs from the
PVC- Dorsal prestriate-posterior parietal cortex
the dorsal stream resp strongly to
WHERE??? location and time
the ventral stream runs from
PVC- ventral prestriate- inferotemporal cortex
Ventral stream responds strongly to
WHAT???
colour and shape
clusters of vis neurons with classes for objects, face, animals are in the
ventral stream
dorsal mediates
interaction
ventral stream directs
conscious perception
visual agnosia for faces (dev or acquired)
Prosopagnosia
failure to recognize faces is
Agnosia
what causes issues with facial recognition?
damage to the fusiform gyrus
- can’t see moving objects smoothly
Akinetopsia
Complexity
Hierarchy
Parallel Processing
Functional Segregation/specialization
are the
principles of visual system organization
principles of visual system organization
Complexity
Hierarchy
Parallel Processing
Functional Segregation/specialization
patching the good eye after corrective surgery is for treatment of
amblyopia
