Vision 1 Flashcards
What is light?
Electromagnetic radiation: ripples in an electric field .
What determines the colour of light?
The frequency composition
How is an image produced on the retina?
Light from source reflected off object is focused onto the retina by the cornea and the lens
What happens to the eye for distant vision?
Ciliary muscles relax, fibres taut and lens at a minimum
What happens to the eye . for close vision?
Tightening of ciliary muscles, allowing the . pliable . crystalline lens to become more rounded
What are light rays like for distant objects?
nearly parallel and don’t need as much refraction to bring them into focus .
what are light rays like for close objects?
they diverge and require more refraction for focusing
What are quick eye movements called?
Saccades
What happens in visual transduction?
signals carried by light waves are converted into electrical impulses in neurons: the language of the brain.
When light strikes the cells, a chemical reaction occurs that generates electrical signals that are carried to the brain via the optic nerve .
How many different types of cones are there?
3, containing three different colour-sensitive pigments (roughly red, green, blue)
What are rods?
Scotopic (nightime) vision- high sensitivity allowing for vision to dim light. More convergence than the cone system, increasing sensitivity while decreasing activity.
What are cones:
Photopic (daytime) vision –> High acuity colour information in good lighting, only cones are found in the fovea.
What are ganglion cells?
Optic nerve fibres
What do ganglion cells do?
Combine the electrical outputs of the rods and cones
What is visual coding form?
The ganglion cells combine the outputs of the rods and cones to form receptive fields with a centre-surround antagonism.
What are receptive fields?
the region of the visual field in which light stimuli evoke responses in the ganglion cell
What are neural pathways?
- The optic nerve carries info to the thalamus (lateral geniculate nucleus)
- The LGN projects the primary visual cortex with different neurons carrying information about different places in the image on the retina.
What is orientation sensitivity?
In the primary visual cortex, the outputs of the neurons from the eye are combined to produce neurons that respond best to edges and bars at particular orientations.
What is the primary visual cortex?
Ø In the primary visual cortex, the shapes of objects are well represented, and the brain has already started analysing features, such as edges at particular orientations.
What is perception of depth: convergence?
When the position of the two eyes required to focus the image on the fovea is a cue to depth (works only for close objects)
What is perception of depth: Stereopsis?
The two eyes get slightly different views of the world, providing another cue to depth (used to make 3D)
What is the flow of visual information?
Primary visual cortex
Secondary visual cortex
Visual association cortex
What happens to receptive fields of neurons as information flows through the hierarchy?
They become longer and they respond to more complex and specific stimuli
According to the what vs where theory what does the dorsal stream specialise in?
Visual Spatial perception
According to the what vs where theory what does the ventral stream specialise in?
Visual Pattern recognition
According to the control of behaviour vs conscious perception theory what does the dorsal stream specialise in?
Visually guided behaviour
According to the control of behaviour vs conscious perception theory what does the ventral stream specialise in?
Visual perception
