Lecture 3: Visual System Flashcards
What are the 6 steps in the retino-geniculate-striate pathway
- Eyes
- Retina
- Thalamus
- Primary Visual Cortex (Occipital lobe)
- Extrastriate cortex (Occipital lobe)
- Extended Cortex (Temporal and Parietal lobe)
What are the three main phases of seeing something?
- Image formation
- Transduction - image is transducted into signals
- Visual process - understanding the image
What is decussation?
Where the left visual field reaches the right cortex and the right visual field reaches the left cortex
Bilateral visual fields are _____ and unilaterial visual fields are ______
Optic nerves are responsible for bilateral visual fields, optic tracts are responsible for unilateral visual fields
40% of the optic nerves fibres cross at optic chiasm, T/F
False! 50% do
Explain retinotopic
Retinotopic is the idea that adjacent points in the visual field map onto adjacent points on the retina, i.e., mapping of visual information from visual field to retina to brain. This mapping is maintained through visual processing
Explain cortical magnification
More cortex is dedicated to processing the central visual field than the periphery, i.e., fovea disproportionately represented with high acuity, compared to periphery
Explain what is occuring when a neuron fires with light in the centre and dark surround it, and when the same neuron suppresses when light surrounds dark spot
This process is termed receptive fields. The neuron is stimulated (excited) by this image due to its features and where the light lays (region), and is inhibited by the opposite of what stimulate it. This assists with mapping. The neuron describe in the example is a centre-surround cell.
Where does refraction of light occur?
Cornea
What is the role of the lens?
The lens focuses on a light through a process named accomodation reflex, that is, changing its shape to focus
How does the iris and pupil work in conjunction?
The iris controls the size of the pupil, moderating the amount of light the eye receives
Explain the process of how images are formed
An image is formed through light passing through the cornea, which is refracted. The light then passes through the pupil, in which the iris moderates the amount of light it receives by controlling the size of the pupil. Afterwards, the light reaches the lens which focuses the light onto the retina.
Which part of the eye is responsible for transduction?
Retina. Receptors transduce light signals into neural signals
What is the RGC?
Retinal ganglion cells, the final layer of axons to the brain
Fovea is responsible for the small and low acquity central vision, t/f
False! Fovea is responsible for small and HIGH acuity of the central vision
What is the optic disc?
Point of retina where RGC axons leave to become optic nerve
Optic nerve is responsible for…
The neural transmission to the thalamus
How does the fovea solve the backward wiring problem?
The fovea is a solution to the backward wiring problem because due to the fact that light has to pass many layers to reach photoreceptors, the fovea creates an area of high resolution by “pealing through the layers of photoreceptors”
Name the 5 layers of different types of neurons and briefly describe their functions
- Receptors, receives light and transduces
- Horizontal cells, lateral communication
- Bipolar cells, signals pass through and processes
- Amacrine cells, lateral communication
- Retinal ganglion cells (RGC), transmits signal to brain
What is the difference between rods & cones
Cones: Responsible for colour vision and high positional acuity, due to their low convergence. They are low in sensitivity and thus require more well-lit scenes (photopic vision).
Rods: responsible for low position acuity, due to their high convergence (lots of rod cells converging into one area). And as well, due to their high sensitivity, they’re better suited for low light situations
The retina is a ___ _______ ______, convergence is _____ _________, reducing axons to brain. Responsible for ____ detection & ______ detection
low processing centre, early processing. Edge & motion
What is lateral inhibition? How does this occur and how does this create enhancement of edges?
Lateral inhibition is the proess of contract enhancement for edge detection. Each receptor inhibits its neighbours with inhibition being greater when there is increased intensity. If a dim light and an intense light are adjacent, the receptor A receive intense light will inhibit receptor B, and thus enhancing an edge
Optic nerve transmit to….
Thalamus, (lateral geniculate nucleus)
Describe the key processes of V1
The key function of V1 is to identify object boundaries, done by simple cells, and motion information, done by complex cells