PSYC2020 Practice Questions - Wk5 Visual System Flashcards
How much visual information goes to the superior colliculus, and not to visual processing?
10%
What are the 3 steps to visual pathway (overview)?
- Image formation - eye
- Transduction - retina
- Visual processing
what is the difference between optic tracts and optic nerves?
Nerves = bilateral visual fields
Tracts = unilateral visual fields
How much of optic nerve fibres cross a the optic chiasm? And what is the effect of this?
50%
information from the nasal hemiretina crosses over to the cortex that process that respective visual field
What’s the difference between optic nerves and optic tracts? And what does this mean for potential damage?
Bilateral vs unilateral information, respectively. So if you cut one you’ll lose either both fields or just one.
What does the term retinotopic mean?
Adjacent points in the visual field map onto adjacent points on the retina. and this mapping maintained through the processing hierarchy
What does cortical magnification refer to?
More cortex is dedicated to processing the central visual field (near the fovea) than the periphery
What is a receptive field?
The regions on the retina which excite or inhibit a cell. So a neuron has an area in space which it will respond to.
What are possible characteristic of Receptive Fields? 4
They can have small or large spatial resolution.
They have both an excitatory and inhibitory region.
What shape are centre surround cells (1) and simple cells (1)? 2
Round and rectangular, respectively.
What are four things that happen in the eye?
- Form an image
- Generate a neural signal through transduction
- Early neural processing !
- Transmit the visual signal to the brain
Where does the visual spectrum of light lie on the whole spectrum?
Between ultraviolet and infrared light
what is the cornea and what does it do?
A transparent outer layer of the eye. It refracts (bends) light
what does the lens do in the eye?
Fine tunes the image. It stiffens with age
What is the accomodation reflex of the eye lens?
Lens shape automatically changes depending on what you are looking at
What do the pupil and iris do?
The opening (pupil) is regulated by contractile tissue (iris). It varies light and thereby focal length.
What is the fovea?
High acuity part of the eye, lots of cones. Where RGCs are cleared away
what is the backward writing problem and how is it solved?
Light has to pass through the processing layers before the receptors, meaning it will pass through all the nerves. The fovea clears away most of the wiring in the center to allow more clarity of light.
Where does the optic nerve go?
To LGN
What is the optic disc?
The blind spot where nerves and blood vessels exit the eye.
What does it mean if each eye has a blind spot but there is no black hole in vision?
Vision is construction
In completion what happens to edges, and what happens to surfaces?
Continued, interpolated respectively
What cells in the eye contribute to lateral communication?
What is lateral communication?
Horizontal and amacrine cells. Early processing
What is photopic vision?
Well lit vision
Why do cones have low convergence? What does this mean?
RGCs are connected to very few cones, so there is better positional acuity
Where does colour perception come from?
Cones
What does high convergence in rods mean?
Many rods feed an RGC, so low positional acuity but high sensitivity to light
What is the benefit of convergence?
Simple processing is done whilst the reducing the amount of axons to the brain
What are Mach bands?
Contrast enhancement for edge detection
how does lateral inhibition work?
Each receptor fire based on intensity AND neighbour inhibition
what myelinated the optic nerves?
ODCs not Schwann cells; because it’s CNS not PNS
Why does albinism result in poor depth perception?
Disruption of melanin synthesis in development causes more decussation (more visual signal crosses over than is needed)
What type of receptive fields do retinal ganglion cells have?
Centre-surround
What do centre surround cells respond to?
Contrast rather than light detection
What happens to the visual stream in the LGN?
Left and right eyes are separated into different layers (3 each) and P and M channels
Where do axons from the LGN project to in the striate cortex?
Lower layer 4
How do you start detecting edges from dots?
Centre surround cells connect to a simple cortical cell with a rectangular RF
What are simple cells about? 2
Monocular. Detecting line segments
What are the preferences a simple cortical cell can have? 3
Type of edge.
Orientation
Location (retinotopic)
What triggers the best response in a simple cortical cell?
An appropriate bar leaving an OFF region and entering an ON region
What is contour integration?
we are looking for edges and lines rather than regularity. This is what pops out to us because the visual system is looking for it.
What is lateral facilitation?
Lateral connections between directionally similar and retinotopic ally adjacent simple cells. These connections enhance each other
What do low and high spatial frequency give?
Texture and edges
What is the relationship between simple cell subfields and spatial frequency?
Low SF activates cells with wide subfields. High SF activates cells with narrow subfields.
What do complex cells most respond to?
Movement.
Where is depth perception calculated?
Complex cells - because they fire more intensely if both eyes have same input
What is ocular dominance in complex cells?
Complex cells respond more vigorously to one eye.
What is blindsight?
Scotomas which still respond without conscious awareness
What is the difference between damage to the dorsal and ventral stream?
Dorsal: can describe but cant grab object
Ventral: can grab, but not describe
What are the receptive fields of the dorsal and ventral streams?
dorsal: large RF mostly outside fovea
ventral: Large RFs, all include fovea
Where is processing for object location or direction of motion?
Dorsal stream
Where is processing for colour and shape (characteristics) of objects?
Ventral stream
What are the difference between the “what vs where” and “action vs perception” hypotheses?
Difference in kind of information vs difference in how the information is used (functional)
What is a dysfunction associated with the dorsal stream?
Akinetopsia - motion blindness (cant see motion)
What is processed in the dorsal stream?
Spatial attention and selective attention?
What is processed in the ventral stream?
Object centred visual experience
What is processed in the anterior and posterior stages of the ventral stream?
Knowledge of object.
Features of objects combined
What is the difference between apperceptive and associative agnosia?
Apperceptive = loss of perception, impaired naming and drawing
Associative = loss of meaning, unimpaired drawing & impaired naming
What happens first in the chain, apperceptive or associative agnosia?
Apperceptive then associative (can draw)
What area is related to prosopagnosia?
Fusiform face area (right inferior temporal lobe)
