Visual system Flashcards
Define decussation?
Criss cross of orientation info from sensory field to opposite side of brain
- left visual field to right cortex
- right visual field to left cortex
Is vision partially or fully desuccated? Explain.
Partially.
50% of optic nerve fibres go to opposite side of brain by crossing at the optic chiasm.
What is an optic nerve?
Nerve that transports visual info from the eye to the optic chiasm
Has bilateral visual field
What is an optic tract?
Nerve that transports visual info from the optic chiasm to the brain
Unilateral visual field
Define retinotopic? True/false It is maintained throughout the visual processing hierarchy?
Adjacent points in the visual field that line up with adjacent points in the retina. True
Define cortical magnification?
More cortex dedicated to central visual field than periphery - convergence
What is the role of the eye in visual processing?
Forms an image
Generates a neural signal
Early neural processing of the signal
Transmits visual signal to brain
What is the cornea and what is it’s role in visual processing?
Transparent outer layer of eye
Most refraction of light occurs here
What is the lens and what is it’s role in visual processing?
Bouncy elliptical, clear ball behind iris that fine tunes image formation
Adjustable
Stiffens with age
What is the iris and pupil and what are they responsible for?
Size of the opening (pupil) regulated by contractile tissue (iris)
Varies light but most importantly focal length
What parts of the eye are involved in transduction?
Retina and fovea
What is the retina and what is it responsible for?
Layers of neurons for early processing of the signal
Receptors to transduce light signal to neural signal
Retinal ganglion cells final layer - axons to brain
What is the fovea and what is it responsible for?
Small specialised high acuity central vision
Solves the backward wiring problem by having less RGCs than rest of retina
What are the items responsible for transmission of visual info to brain?
Optic disc and optic nerve
What is the optic disc and what is it’s job?
Point on the retina where retinal ganglion cell axons leave to become the optic nerve
Blind spot-no receptors
What is the optic nerve and what is it’s job?
Optic tract beyond the optic chiasm
Partial desiccation at the optic chiasm
Neural transmission to brain
What are simple cortical cells
Centre-surround cells in layer 4 project to simple cells in layer 3
Detect line segments
Simple cells (and LGN and RGCs) are monocular
What type of stimuli do simple cortical cells prefer?
- Type of edge
- bars of light in a dark field
- dark bars in a light field
- single straight edges between dark and light - Orientation
- Location (retinotopic)
What is a scotoma and how does it affect visual perception?
Blind spot in contralateral field of both eyes caused by damage to V1
Often no consciousness awareness due to completion
What are receptive fields? What do they reveal about the function of the neuron?
Regions on the retina and the features that excite or inhibit the neuron. Nature of receptive field gives clues about the cell’s function.
What are the characteristics of an RF?
Small (high spatial resolution) or large (low spatial resolution), have both excitatory and inhibitory areas
Define photopic and scotopic vision
Photopic vision is vision under well-lit conditions. It allows vision of colours and details.
Scotopic vision is vision under dimly lit conditions. It allows vision of light and dark contrast.
What is lateral inhibition?
The ability of a neuron to tone down the activity of neighbouring neurons in the lateral direction.
What are Mach bands? How does our brain interpret them?
Bands of contrast that are decreasing in intensity. Our brain interprets them using contrast enhancement where perception of edges stronger to detect contrast better.. Firing rate proportional to intensity of light and each neuron decreases activity of its lateral neighbours. Inhibition greater with more intensity and greater inhibition for closest neighbours.
