Vision Flashcards
Contain photopigments, which break down in presence of light
Retina has two light-sensitive receptors
- is extremely sensitive to light
- function well in dim light, poorly in bright light
- do not distinguish color
- In peripheral retina
Rods contain rhodopsin
-requires bright light to function
-do well in daylight, not dim light
-3 types, each responds to different wavelength
-In central retina (fovea)
Cones contain iodopsin
-Amacrine cells
-Horizontal cells
Two types of lateral processing cells
contact bipolar and ganglion cells
Amacrine cells
contact photoreceptors and bipolar cells
Horizontal cells
All cell types except ganglion cells generate graded potentials
Ganglion cells fire action potentials
how much of the visual world one receptor can see
Receptive fields of rods and cones
-receptive fields of GCs are large
-many share a ganglion cell
-enhances their already greater sensitivity to light
-reduces their acuity
Rods
-receptive fields of GCs are small
-fewer attach to each ganglion cell
-in the fovea, each has its own ganglion cell
-visual acuity-ability to see details-is high
Cones
When light strikes rhodopsin
Retinal is activated
-RPE65 is defective; photoreceptors degenerate
-gene therapy can treat this disease
Leber’s congenital optic degeneration
-light closes sodium channels
-hyperpolarizes
-turns rods off
Transduction
Mary Cassatt
Mach effect
Inhibiting one’s neighbors produces contrast
Lateral inhibition
- Retina
- Optic chiasm
- Lateral geniculate nucleus (thalamus)
- Visual cortex (occipital lobe)
Visual pathways
- An on-center/off-surround cell
- An off-center/on-surround cell
Neurons in retina have two types of receptive fields
- LGN (thalamus)
- Visual cortex (V1-V5)
- Secondary Visual Cortex
Three stages of vision processing
-Parvocellular
-Magnocellular
-Koniocellular
LGN has 3 cell types
-small cells
-small receptive fields
Parvocellular
-large cells
-large receptive fields
Magnocellular
-layers with very small cells
-between main layers
Koniocellular
Where pathway
Parietal Cortex
What pathway
Infero-temporal Cortex (IT)
Where most visual information first arrives
Primary visual cortex (V1) in occipital cortex
Brain maps of visual space are mostly devoted to
Fovea
-simple cortical cells
-complex cortical cells
Brain maps of visual space are mostly devoted to the fovea
Respond to an edge or bar of a particular width, orientation, and location
Simple cortical cells
Respond to a bar of a particular width and orientation, but it may be anywhere in the visual field (location independent)
Complex cortical cells
Classified as simple or complex, depending on their receptive fields
V1 cells are
receive input from neurons in the lateral geniculate
simple cortical neurons
receive input from simple cortical cells
Complex neurons
Perceives objects so it is needed to form all visual images
V1 (primary visual cortex)
perceive complex form
V2, V4, and the inferior temporal lobe
Specialized for motor perception
V5
Organized in columns and slabs
V1 is
A region of cortex with greater synaptic input from one eye
Ocular dominance column
Color, shape, location
3 inputs of vision at once
-Parallel processing
-V1 breaks down the visual image into components
Primary Visual Cortex
Breaks down the visual image into components
V1
-“fills in the gaps”
-much of vision is extrapolating (predicting) from what is actually ‘seen’
V2
-respond to concentric and radial stimuli
-involved in color perception
V4
A regular polygon of infinite number of sides
Circle
-Spatial location and action
-where pathway
Dorsal Pathway
-characteristics of objects
-what pathway
Ventral Pathway
-dorsal pathway
-MT, V2
Parietal lobe
-ventral pathway
-V4, V2
Temporal lobe
