Liana Machado Eye Section Flashcards
what is the pupil
the opening that allows light to enter the eye and reach the retina
what is the iris
a circular muscle that controls the size of the pupil (the coloured part)
what is the cornea
the transparent surface that covers the pupil and iris
what is the sclera
the “white of the eye”, it is continuous with the cornea
what is the lens
this helps focus rays of light on the retina
what is the retina
the internal lining of the rear two thirds of the eye, it converts images into electrical impulses that are sent to the brain
what is the macula
the central area of the retina that is specialised for vision
what is the fovea
this marks the centre of the retina and macula, the visual image received here is the least distorted.
what is the optic nerve
this is made up of axons and retinal ganglion cells, it carries impulses for vision from the retina towards the brain.
what is light to the eyes
light is electromagnetic energy that is emitted in the form of waves and is visible to the eyes.
what wavelengths are visible to the naked human eye
400-799 nm
how does visual information flow within the retina
photoreceptors - bipolar cells - ganglion cells
what does the retina convert
light energy to neural activity
what are the two types of photoreceptors
rods and cones
what are rods
rod-shaped structures that are specialised for low lighting.
what are cones
these are conical-shaped structures that are specialised for higher light levels and colour vision.
which part of the retina has more rods
the peripheral retina
which part of the retina has more cones
there is a higher concentration of cones in the central retina.
what is the process of visual information in the retina
- light enters
- information about the light flows from photoreceptors to bipolar cells to ganglion cells that project axons out of the eye.
- axons of retinal ganglion cells carry information from eye to brain.
why are bipolar and ganglion cells displayed laterally
to allow light to strike the foveal photoreceptors directly.
where is the blind spot
where the axons of the retinal ganglion cells exit the retina, there are no photoreceptors so sensation of light cannot occur.
what does our brain do to counteract the blind spot in our visual field
fill in our perception of these areas.
are images inverted on the retina
yes
the half of the retina that is closest to the nose is called the
nasal hemiretina
the half of the retina that is not close to the nose is called the
temporal hemiretina
at which degrees is the blind spot located in the temporal hemifield
15 degrees eccentrically.
because the optic disk is located in the nasal hemiretina, what affects the temporal hemiretina
the blindspot
the axons of the ganglion cells located in each nasal hemiretina go where
they cross the midline via the optic chiasm
the axons of the ganglion cells located in each temporal hemiretina go where
they dont cross the midline, they stay on their own side.
what happens if the optic chiasm is transected
peripheral vision will be lost bilaterally
what are axons of ganglion cells called before they cross at the optic chiasm
the optic nerve
what are axons of ganglion cells called after they cross the optic chiasm
the optic tract
where do the axons of the optic tract project to
superior colliculus
lateral geniculate nucleus of the thalamus
for subcortical vision, what is located in the retinotectal pathway
the retina and superior colliculus
for cortical vision, what is located in the retinogeniculostriate pathway
retina
thalamus (LGN)
primary visual cortex
what % of ganglion cells in the retina project to the superior colliculus
10%
what is the map in the superior colliculus
retinotopic map
where are the left and right LGN located
in the thalamus
what are the right and left LGN major targets of
the two optic tracts
where do most retinal ganglion cells synapse on to
LGN neurons
is the right LGN receives information, this comes from…
the left half of the visual field
where do most neurons in the LGN project their axons to
the primary visual cortex
what were the results of the ecstasy and V1 excitability study?
- that participants in the ecstasy group has a significantly lower phosphene threshold than participants in the control group. the frequency of ecstasy use correlated negatively with phosphene threshold.
- within the ecstasy group, the phosphene threshold of participants who hallucinated was significantly lower than the phosphene threshold of participants who didn’t hallucinate.
what was the phosphene threshold
the minimum intensity that evokes phosphenes
what occurs if the TMS coil is placed over the primary visual cortex
when places over the occipital lobe, TMS can elicit light sensation (phosphenes) in the absence of visual stimuli
what is the ventriloquist illusion
the concept that speech seems to be coming from the puppets mouth rather than the puppeteers mouth
why does the ventriloquist illusion occur
occurs due to the sound source being mislocalised towards a synchronous by spatially discrepant visual event (in this case, the puppets mouth).
what is the visual cortex
this lies beyond the striate cortex in the extrastriate areas.
what can researchers identify with the use of single cell recording
they can identify the representational characteristics of neurons in different visual areas.
what is the experiment of single cell recording in the MT.
use of monkeys, are MT, looking at the activity of a single neuron being recorded when a white bar is passed through the neurons receptive field.
the found the neuron fired lots when the bar moved downward toward the left.
this meant that neurons in are MT are selective for the direction of motion.
what are the two cortical visual pathways of projection routes from primary visual cortex (V1) to extrastriate visual cortex
the dorsal stream and ventral stream.
what does the dorsal stream code for?
motion and location
what does the ventral stream code for
it processes detailed stimulus features and object identity
where is V4 located
along the ventral stream
what do the neurons in V4 respond to
they respond to mainly colour, but also form
where is V5 located
it is located along the dorsal stream
what do the neurons in V5 respond to
these neurons are selective for the direction of motion and speed of motion.
what can damage to V5 do
this can disrupt motion perception which means the ability to discriminate the direction in which a stimulus is moved
what % of axons in the optic tract target the retinogeniculostriate pathway
90%
what are some general conclusions about the superior colliculus
- the superficial layers of the SC contain retinotopic maps of the visual field.
- the retinotopic map in the left SC represented the right hemifield.
- the retinotopic map is distorted, with more neurons devoted to analysis of the central portion of the visual field.
what is the sprague effect
this is the restoration of orienting toward the cortically blind hemifield
what is a basic summarisation of the Sprague effect
he lesioned the superior colliculus on the opposite side of the initial brain injury in hope to restore lost visual abilities because there is a reduction in the overactivity of the one side of the SC, helping the brain reroute an alternative visual pathway
in the experiment of visual cortex vs superior colliculus damage, what two things were rodents trained to do
a localization task (turning their head toward a sunflower seed in the experimenters hand)
a discrimination task (running down a two-arm maze and entering the door which hid a sunflower seed.
what occurred in the localisation task for the rodents with the lesions in the visual cortex
they performed normally for this, but not normally in the discrimination task.
the rodents with the bilateral disruption of the retinotectal pathway struggled on the localisation task but were fine on the discrimination task.
what is blindsight
this the phenomenon where people who are blind in part of their visual field (usually due to brain damage) can still respond to visual information in the blind area even though they cant consciously see anything there.
what happens when there is unilateral damage to primary auditory cortex (A1)
there is a surprising degree of normal auditory function retained.
where are retinal ganglion cells located
they are located in the layers of the superior colliculus
what is a saccade
this is a rapid eye movement
neurons in deeper layers of the superior colliculus have …. field.
movement field - part of the visual field to which the eyes move in response to activity in the cells
the movement fields of collicular neurons code for?
they code for eye movements in the contralateral hemifield
neurons in the superficial layers recieve information from where
from retinal ganglion cells and contain a retinotopic map.
the characteristics of the cells in the superior colliculus make them idea for?
detecting the location of visual events and triggering orientation responses.
what is a reflexive saccade
a rapid eye movement in response to stimuli appearing the the periphery.
what do reflexive eye movements help promote?
survival
what is an exogenous eye movement
this is an eye movement driven by an external response
exogenous =
external
reflexive saccade =
exogenous saccade
cells in deeper layers of the SC discharge during what
during saccades
because of the organisation of cells, where are the smallest saccades represented
in the rostral superior colliculus
because of the organisation of cells, where are the largest saccades represented
in the caudal superior colliculus
what is the fixation reflex triggered by
an external visual stimulus projecting on to central vision.
when a stimulus is presented at the fixation point, cells in which portion of the superior colliculus are activated?
in the rostral (front) area.
what does FOE stand for
Fixation offset effect
What does FOE provide
it provides a measure of the responsiveness of the fixation reflex, which a large FOE indicating a strong fixation reflex and a small FOE indicating a small one.
what is an endogenous eye movement
this is a voluntary eye movement that is initiated internally
what eye movements can be generated even in the absence of a visual stimuli
endogenous eye movements
the superior colliculus which receives information directly from the retina projects down to what?
saccade generators in the brain stem
what is the FEF
the frontal eye field
where does the FEF project to
saccade generators in the brain stem
reflexive eye movements depend on what structures
subcortical structures.
voluntary eye movements depend on what structures
cortical structures in the brain.
do reflexive eye movements require fewer or more neural connections compared to voluntary eye movements
they require fewer because there is less processing required.
the superior colliculus is important for what type of reflexes.
oculomotor reflexes.
in newborns, are subcortical or cortical structures already mature
subcortical structures
What is FOE
this is a measure of how quickly you can shift your attention from one object to another
at what age do infants often exhibit prolonged periods of fixation
at about 1 - 2 months old
immaturity of cortical pathways in infants is also reflected in
reflected in their natural orienting behaviours.
immaturity of the frontal cortex contributes to what in newborns
contributes to the fact that they exhibit a poverty of strategic behaviours, and instead are largely controlled by external stimuli
at what age does the frontal lobes finally fully develop
around 15 - 20 years old
what occurs in the anti-saccade task
you fixate on the centre, when a stimulus appears in the periphery, move your eyes in the opposite direction as soon as you can then return your eyes to the centre.
the anti-saccade task requires the inhibition of what saccade?
a reflexive saccade.
an abnormally slow correct reaction times on the anti-saccade task would suggest more of what?
more of a struggle in imposing voluntary control over reflexive behaviours.
what is one part of the visual field that can come at a cost of neglecting other parts
attention
overt shifts of attention involve what
they involve the movement of the eyes.
covert shifts of attention involves what
they involve a mental shift of attention that doesn’t require the movement of the eyes
exogenous shifts in attention are elicited by
by an external stimulus.
what part of the brain is important for reflexive movements of attention
the superior colliculus
what type of neurons are important for voluntary movements of attention
cortical neurons
what does attention facilitate
responses
inhibition of return is thought to facilitate what
facilitate efficient visual search by discouraging orienting towards recently attended locations.
what is inhibition of return
this is the phenomenon where, after you briefly pay attention to a specific spot, you become slower to return your attention to it.
inhibition of return provides an example of
reflexive mechanism of attention.
what can the flanker task be used to assess
the efficacy of strategic control over attention (i.e., how easily distracted the participant it).
what are the instructions of the flanker task?
maintain fixation on the centre of the screen. when a stimulus appears at the centre, indicate its identity by pressing the appropriate button as quickly as you can.
the formation of what nervous system occurs during prenatal development
the central nervous system.
the structure of the brain develops in what three steps
- cell division
- cell migration
- cell differentiation
cell division is what
the first step in wiring cerebral cortex by generating cells
cell differentiation refers to what process
the process, by which, after migrating, new cells take on the appearance and characteristics of a neuron or glial cell.
within the wiring of the brain, neurons extend their axons to the appropriate targets to form…
interneuronal connections
what is plasticity
this refers to the ability of the nervous system to change.
is the adult or the postnatal brain more plastic
the postnatal
what is the concept of plasticity
learning, growing the brains connections through retaining the information that we learn
fine-tuning of the wiring of the brain is driven by…
neuronal activity
do both eyes receive the same visual information?
no
what is the background anatomy of the auditory system:
neurons in the inferior colliculus (IC) send their axons to the medial geniculate nucleus of the thalamus (MGN) which in turn send their axons to the primary auditory cortex (A1):
IC -> MGN -> A1
