Sensation and Perception (Vision) Flashcards
Layering of the retina
Photoreceptors, then ganglion cells, then axons of the ganglion cells form the optic nerve
Photoreceptors
- Rods and cones
- contain pigments that absorb light energy and turn it to electrochemical energy used in the nervous system
Parallel processing (visual system)
The visual system simultaneously processes different aspects of the visual scene at the same time
Rods
Rods contain the pigment rhodopsin: sensitive to small amounts of light
Rods are located in the periphery of the retina
Many rods feed into ganglion cells
Cones
- 3 types of cones: sensitive to different wavelengths- red, blue, green
- Cones are most densely packed in the fovea
- Only a few cones feed into ganglia
Ganglion Cells
- Have axons that extend to the brain to form the optic nerve
- Many rods feed into a single ganglion cells, very few cones feed into one ganglion
- Two main types of ganglia: M cells (large) and P cells (small)
- the two types of ganglia send input to different parts of the brain
M cells (Magnocellular cells)
The larger ganglion cells
- Responsive to coarse pattern and rapid motion
- goes down tectopulvinar pathway
P cells (Parvocellular cells)
Preserve colour information
The smaller ganglion cells
Receptive Fields
- Specific cells that respond to specific regions in the visual space
- Light strikes different parts of the eye depending on where the eye is facing
- the brain knows where light has struck based on which ganglion cells are excited
Centre-surround receptive fields
Receptive fields have a centre-surround structure
- light in a particular spot will excite the ganglion cell, light in the donut-shaped area surrounding that spot will be inhibited/ weakened
- this enhances contrast in vision
Pathway from the eye to the cortex
- Right visual field goes to the left of each eye and vice versa
- All right visual field information goes to the left of the brain to V1, and vice versa
- Information travels from the eye, through the optic nerve, to the optic chiasma (where information crosses over), reaching the Lateral Geniculate Nucleus (LGN), and finally, the Primary Visual Cortex
The Tectopulvinar Pathway
- Receives the majority of input from M ganglion cells
- Fast acting, sensitive to both motion and the appearance of novel objects on the vision periphery
-Sends information directly to the superior colliculus
»> The pathway then extends to the pulvinar nucleus in the thalamus and to cortical areas that process information about visual motion.
»> Superior colliculus also sends projections to motor regions that control eye & head movements
Superior Colliculus
Part of the tectum (in the midbrain), alongside the inferior colliculus
SC is visual, IC is auditory
SC sends projections to motor regions that control eye and head movements
The Geniculostriate Pathway
90% of optic fibres project to this
- Axons terminate in the LGN of the thalamus
— information continues to the straite (V1)
— enables colour and detail perception
— information on the right sides of both retinas is sent to the right side of the brain + vice versa
- Once optic nerve fibres cross (at the optic chiasm), they are referred to as the optic tract instead of the optic nerve
Lateral Geniculate Nucleus (LGN)
6 main layers, stacked on each other, then folded into a knee shape
- additional minilayers between each layer: konicellular layers
- Each layer receives input from only one eye, all layers receive information from the contralateral visual field
- Has 2 Magnocellular layers and 4 Parvocellular layers
— Koniocellular layers recieve input from bistratified ganglion calls + superior colliculus
Each layer contains a retinotopic map of the visual world, which helps organize information
