Optic Shit- Exam 2 Flashcards
The physical property of a wavelength is psychologically converted into what?
Colour perception
What two types of ways to describe light? And what is more common in psychology?
Wave length and particles called photons. Wavelengths more appropriate in psyc
The physical property of intensity is converted into what psychologically?
Brightness perception
What is the function of the iris?
Regulates amount of light reaching the retina.
When an image is in close vision, the pupils are…
Constricted
pupils dilate for what two conditions?
Small amounts of light and far objects
What is the function of the lens?
Focussing light onto retina
What part of the eye converts light into neural signals and conducts them toward the CNS?
The retina
Light hits the back of the eye first and then travels forward towards the retinal ganglion cells for neural transportation, what two problems does this create in vision?
- Light is lost in absorption by other cells
2. The ganglion cells leaving the eye creates a hole in vision called “the blind spot”
How is the “blind spot” fixed?
By “filling in”. The brain takes the information from the surrounding images to perceive an image where the blind spot image should be
What part of the eye fixes the light absorption problem caused by inside out processing of light?
Fovea- curvature that allows cell body’s and layers to thin out in the retina area.
What are the two types of vision receptors are there and what do each of them specialise in?
Rods and cones.
Rods- poor colour coding and image resolution but good for being able to see in the dark
Cones- good colour and image resolution but poor in the dark.
Photopic vision relates to high amounts of what receptor?
Cones
Scotopic vision relates to high amounts of what photoreceptors ?
Rods
What is visual transduction?
The conversion of light into neural signals
What pigament underpins rod-mediated vision?
Rhodopsin
Explain lateral inhibition. Give an example.
Helps determine the edge of one object from the edge of another by over-compensating in differences of brightness. E.g. Mach bands
If I wanted to bring an object into sharp focus, what would I have to do with my lens?
Bend lens or make more cylindrical to refract light
I would have a flat lens when…
Focusing on distant objects
What is the first point of organisation of neural signals of vision?
The lateral geniculate nucleus (LGN)
What are the basic 3 stages from retina to primary visual Cortex?
Retina- Lateral Geniculate Nuclei (thalamus) - primary visual cortex
How many layers are in the LGN?
6
The parvocelluar layers make up how many lateral geniculate nuclei layers? Give basic information about parvocelluar system.
First 4 layers.
Parvo= small therefore contains small cell bodies
Is responsible for colour and stationary objects and therefore receives information mostly from cones
The magnocellular layers make up how many lateral geniculate nuclei layers? Explain the magnocellular layers function.
Last 2 layers.
Magno= large therefore contains large cell bodies
Responsible for motion and large receptive field, it receives most of its info from rods.
What is occlusion?
When a darker object is placed in front of an opaic object to make it seem closer.
What is stereopsis?
The appreciation of the 3rd dimension after the brain has perceived the images from each eye.
What is a pro of binocular summation?
The eyes are more sensitive to dim light.
At what region in the eye has the highest spatial aquity ?
Fovea
What happens when both eyes converge at the same spot in each fovea?
Images are perceived to full capacity
Is an object is close to the eyes:
What type of angle do the two eye tractorys make?
Therefore, the eyes ……
A large angle so they Converge
If an object is far away for the nose:
What angle do the joining of each eyes tractory make?
Therefore, the eyes….
A small angle, they diverge
What is binocular disparity?
When there are slight differences of image from each eye
What layer of the retina contains the visual receptors?
The last layer
Where does the light exit the eyeball?
The retinal ganglion cells
What happens in the optic chaism?
Half of visual neurons dessucate.
What visual nuerons dessucate in the optic chaism and which ones don’t ?
The cells in medial half of retina dessucate- cells in lateral half of retina do not.
What 2 stages of the visual process comes after the optic chaism?
The optic tracts and then the lateral geniculate nucleus
What is a reintopic pathway?
Spatial relations are equal throughout visual process. From retina to primary visual cortex.
Where is the primary visual cortex located?
In the occipital lobes, hidden in the longitudinal fissure
In what two regions are the secondary visual cortexs located?
Prestraite and inferotemporal cortex
Where is the prestriate Cortex located?
In a band that surrounds the primary visual cortex (straite cortex))
Where is the inferotemporal cortex located?
In the inferior region of the temporal cortex
What two routes does visual perception either take?
The dorsal or the ventral route
What is the function of the dorsal
Route?
Perception of motion and location
What is the role of the ventral route?
Perception of colour and form
What is the association area of the visual pathway, what route does it belong to and what is it’s role?
Posterior parietal cortex- dorsal route- role in location and motion
When does zero disparity occur?
When objects fall on corresponding retinal points
What is a horopter? Name one.
A horopter is a circle of vision where all objects that fall on this circle have zero disparity and are perceived identically. An example is the vieth-muller circle.
Explain what happens when an object falls beyond the fixation point?
It is called uncrossed disparity as the eyes “uncross” or diverge. The object in each eye falls medial to the fixation point.
What is crossed disparity?
Crossed disparity is when an object falls closer than the fixation point causing the eyes to “cross” or converge. The object is therefore projected laterally to the fixation point in each eye.
Explain absolute disparity.
Absolute disparity is the difference in the angles between the fixation point and an object between both eyes. (aL-aR)
What is relative disparity?
Relative disparity is the difference between two objects and can be worked out by taking the absolute disparity for one of the objects and minusing it from the other. (aL-aR)- (bL-bR)
What happens if an object is outside panums fusional range?
Double vision occurs- but depth can still be perceived
Where is the first point of binocular convergence?
LGN
What type of cone colour system do humans have?
A 3 cone system called trichromatic cones.
What are the 3 classes of cones that we have?
S, M, L
What is an S cone responsible for?
An S cone standards for short wavelengths and therefore it’s maximum absorption is at blue
What are M cones responsible for?
M cones have medium wavelengths and maximumly absorb green light
What are L cones?
L cones are coded for long wavelengths and have maximum absorption at red.
What is the name of the condition where you are unable to see green/red?
Protanopia or deuteranopia
What is the name of the condition where you are unable to see yellow/ blue?
Tritanopia
Explain the young- helmoltz trichromatic theory.
The young- helmholtz theory is based on the fact that we have 3 cone receptors that code for blue, green and red and together we can make all the colours necessary.
What challenges the young- helmoltz theory?
The fact that if you stare at a colour for too long it turns into it’s opposite colour
What is the opponent process theory and who made it?
the proposal that colours are paired in antagonist ways so that once when colour starts to fade the opposite will regenerate it. Hering made it
At what level is the opponent process theory true?
The Ganglion cells and LGN level
At what level is the young-helmholtz trichromatic theory true?
The receptor cell level
Considering both theories are true, what is the knew name for this theory?
The dual process theory.
Similarly to light- how are the excitatory/inhibitory receptive responsive?
To different wavelengths
Looking at the columnar layout of the primary visual cortex: how do colours appear within it?
Colours appear as blobs randomly throughout it.
If you go down the columns vertically (in regards to colour processing) what will you find?
Same colour processes
