Vision Flashcards
what is feature detection
sensory neurons detect colour/edges/lines
what is the role of the iris
regulate amount of light reaching retina
what is the role of pupil size
regulate sensitivity and acuity
what happens when pupils constrict
reduced light - increased sensitivity = sharp and great depth
what happens when pupils dilate
more light enter eye - sacrifice depth and acuity
what happens when more light enters the eye
image is more blurry and less acuity
what is the role of the cornea
help focus incoming light
what % is the cornea of the eye focusing power
75%
what is the lens help in place by
ligaments called zonules
what is the role of the lens
bends light to change focal distance
what is the process called to bend light to change focal distance
accomodation
what is the effect of a flatter lens
thinner = increased focal distance for distance objects
what is the effect of a rounder/thicker lens
bends light to reduce focus distance - short distance for sharper objects
what is retinography
imaging process of a retina
used by opticians
define transduction
light into neural code
what is the centre of the retina
macula
state characteristics of the macula
contains fovea
high concentration of photoreceptor cells
what effect occurs on the macula as age increases
macula degenerates - loss of central vision
what is the role of the fovea
site of sharpest vision
why does the fovea have sharp vision
contains lots of photoreceptor cells
what is the role of photoreceptor cells
convert light to neural signals
process of transduction
what is another name of the blind spot
optic disk
what is surface interpolation
perceived surface and fill in gaps of blind spot
what is sclera and its function
white of eye
protective tissue layer
what percentage of nerve fibres make up the fovea
50%
which region of the eye is densely packed with cones
fovea
what is the function of the blood vessels at the side of the fovea
reduce distortion of light
why is light distorted when it enters the human eye
human retina is inside out hence why black spots occur
is light distored in octupus
no because their retina is the right way round
what is choroid and its function
tissue between retina and sclera
provides oxygen and glucose to retina cells
what is the reflective tissue in nocturnal animals
tapetum lucidum
why does red eye occur from camera flash
flash reflected from blood in choroid
how is a blind spot filled
info from receptor is used to fill gap from blind spot
state 3 layers which compose the retina
photoreceptors
bipolar cells
retinal ganglion cells
state the two types of photoreceptors
rods and cones
why do stars seem to disappear at night
few roads in the fovea
state the follow characteristics of rods
- lighting
- type of vision
- level of convergence, sensitivity and acuity
rods = scotopic operate in dim lighting peripheral vision high levels of convergence poor acuity high sensitivity
what is the term used to describe people with 3 cones
trichomats
state the following characteristics of cones
cones= phototopic operate best in good lighting central vision poor sensitivity low convergence high acuity
state the 3 types of cones
red
blue
green
define phototopic and which type of photoreceptor it links to
phototopic = vision in daylight or bright light
CONES
Define scotopic and which type of photo receptor it links to
scotopic = vision in dim light
RODS
what effect does more photoreceptors have on colour
more photoreceptors means better colour resulting power
which type of lighting is rhodosin active in
bright lihght
what effect does active rhodosin have
- cyclic GMP broken down
- sodium channel close
- cell becomes hyper polarised
- glutatmate release decreases
what effect occurs when rhodosin is not active in the dark
- sodium channels open
- cell becomes depolarised
- number of rods increase
- glutamate release increases
define deuteranamoly
partial loss of green colour vision
becomes harder to distinguish between red and green
what percentage of men and women experience colour blindness
.5% women
8% men
define colour blindness
altered sensitivity in cones or absence of cones
what is the function of bipolar cells
process input from photoreceptor cells
what do interneurons aid bipolar cells to do
allows low level signal processing of input from the photoreceptors
describe the process of input and output of info in vision
input to photoreceptors
bipolar cells
retinal ganglion cells
output
what is the function of ganglion retinal cells
facilitate detection of edges of images
what cells are retinal ganglion cells linked up to
bipolar cells
what is the basis for edge detection in retinal ganglion cells
maximise contrast to detect edges
what colour does a single photoreceptor detect
greyscale
what can 2-3 photoreceptors do
detect the difference between wavelength and intensity
where was lateral inhibition first observed
horse shoe crab
what is the ommatidia
large visual receptors
define lateral inhibition
lateral inhibition is the capacity of an excited neuron to reduce the activity of its neighbors
what effect does lateral inhibition cause in mach bands
causes contrast enhancement
what is the link between light and firing intensity
amount of firing is proportional to light intensity
what effect do sideways projections have as a result of lateral inhibition
inhibit activity of neighbour
what is the hermann grid
white spots of light appear when not looking at target zone
what causes the effects of the hermann grid
lateral inhibition
why do the white squares appear in the hermann grid illusion
white squares appear at intersection when foveated
surrounded by more active receptor fields
what is the process that occurs when eyes foveate
- light intensity projected to photoreceptors
2. retinal ganglion cells pass info on to form output
what do horizontal cells do?
inhibit other cells when activated
where are on centre cells responsive to light
centre of receptive field
in on centre cells what would happen to firing in periphery field
firing in periphery field would be off
no light in periphery field
where are off centre cells response to light
periphery receptive field
what is the function of off centre cells
respond with inhibition
how do off centre cells maximise contrast
maximise firing between centre and periphery field
centre surround difference
what occurs to neighbours which experience high levels of inhibition
lower levels of firing due to inhibition from neighbours
define receptive field
area of visual field where the visual stimulus can influence firing of neuron
what kind of influences can the receptive field have on firing of the neuron
increase or decrease firing rate
what did hubel and wiesel measure
3 layers of the retina geniculate striate pathway
what are the 2 categories of neurons in the receptive field
simple cells and complex cells
state characteristics of complex cells in the receptive field
- role in depth perception
- rectangualr receptive field
- binocular
what do complex and simple cells respond best to
responsive best to straight line stimuli
what type of receptors do simple cells have
antagonistic on and off receptors
what type of organisation is the primary visual cortex composed of
corticol organisation made up of functional vertical columns
what is needed for scene analysis
higher receptive field properties
what is the perceptual binding problem
different stimuli are processed in different corticol areas
what does V2 process
shape characteristic
what is the function of V3
motion and depth perception
what is the function of V4
colour and form perception
what is the function of v5
motion perception
where does info in the dorsal stream travel to
parietal lobe
what type of info travels in the dorsal stream
process spatial locations
what type of info and where does the info travel in the ventral system
object identity and scene analysis info travel to temporal lobe
define visual agnosia
able to see object but can’t define or recognise it
what is prosopagnosia
can’t recognise faces
which brain region is damaged in prosopagnosia
fusiform face area
what is visual neglect
people unaware of existence of part of their visual field
define blindsight
person is conciously blind but retain visual ability or awareness
what is meant by columnar organisation in vision
neural signals flow from simple to complex receptive fields
specific hierachy
what is the horizontal electrode track
orientation of neurons at tip - shift systematically
what vision function is the horizontal electrode track linked with
spatial location of receptive field
which type of track are V1 neurons linked with
vertical electrode track
where is the vertical electrode track grouped in
functional vertical columns
define vergence
movement of image further away or closer to eyes
what are projections to brain stem nuclei responsible for
responsible for visual reflexes eg. accomodation, vergence and pupil control
where does the left visual field project to
right visual cortex
where does the retino tectal pathway project to and what does it control
project to superior colliculus to orientate head and eyes
what is another name for the superior colliculus
optic tectum
what are the neurons in the superior colliculus sensitive to
luminate change
what is the role of the retino-geniculate pathway
provide input to identify objects and scene analysis
what are parvocellular cells and what are their function
small cell bodies
responsive to colour and stationary objects
what are magnocellular cells and what is their role
large cell bodies
responsive to luminate change - on off movement
which photoreceptor provide input for M and P cells
cones = input for P cells rods = input for M cells
what is the role of the lateral geniculate nucleus
thalamic relay for M and P channels
what is retinotopic mapping proportional with
activity in the retina
what is the activity in the retina disporportional to
disproportional to activity in visual cortex
what does the right visual field project to
left primary cortex
what does contralateral projections mean
projections from left visual field would go to right cortex
what type of projections does the temporal hemiretina have
one way = ipsilateral
what type of projections does the nasal hemiretina have
contralateral
where does info that is projected contralaterally seperate
optic chiasm to superior colliculus and visual cortex
state the key findings of hubel and wiesel
- receptive field is smaller in fovea than periphery
- receptive field has both excitory and inhibitory area
- receptive field is circular and monocular
