Receptor processes:
1. reception: absorption of physical energy; in sensory receptors.
2. transduction (see above)
Receptive fields:
- Is the area of the retina from which the activity of a cell is influenced (
-> or also part of the space (around the observer) within which a light stimulus
triggers the action potential
- Receptive fields = part of the retina that transmits information to the downstream
neuron
-> e.g. each ganglion cell receives input from rods or cones, but via intermediate cells
Type Explanation
Simple center-surround type cells - in ganglion cells & LGN.
- Positive response in the center area, negative response in the outer area
- ON-center ganglion cells = exposure of receptive field leads to excitation in cell, on
exposure of periphery inhibition
- OFF-center ganglion cells = just the opposite, lateral inhibition to sharpen contrasts.
Simple cortex cells - orientation specific response, depending on orientation of light
stripe.
- Also excitatory & inhibitory zone, right next to each other
Complex cortex cells - movement (of a correctly oriented bar).
- Selective response of receptive fields, but independent of where exactly the
stimulus is found in the receptive field -> stimulus by direction of movement.
End-inhibited (hyper-complex) cortex cells - corners, angles, bars of specific length
moving in specific direction
- Length of light bar also relevant
Lateral inhibition / inhibition
- Enhanced contrasts due to reciprocal inhibition of cells.
-> When a receptor fires, it inhibits its nearest neighbors
- Difference central vs. peripheral vision
-> Exact edge vs. imaginary shadow
-> Narrow (cones) vs. large-scale (rods) connectivity / inhibition
Visual pathways and organization of the visual cortex
Visual field Explanation
Right Left sides of the two retinas, signals in the left visual cortex.
Left Right sides of both retinas, signals in right vis. cortex Cortex
Retino-geniculo-striate visual pathway
- Runs from the eye via the optic nerve of the respective eye; partially crosses in the
optic chiasm (ipsilateral = not crossed)
- Runs further in the contralateral side of the brain as an optic tract (no longer optic
nerve) to the LGN (part of the thalamus)
- Right field of vision falls on left sides of both retinae (in both eyes), left field of vision
falls on right sides
- Further from the LGN via the so-called optic radiation (black lines in the picture) to
the primary visual cortex in the occipital lobe
- In the LGN separation between magnocellular pathway and parvocellular pathway
1. reception: absorption of physical energy; in sensory receptors.
2. transduction (see above)
Receptive fields:
- Is the area of the retina from which the activity of a cell is influenced (
-> or also part of the space (around the observer) within which a light stimulus
triggers the action potential
- Receptive fields = part of the retina that transmits information to the downstream
neuron
-> e.g. each ganglion cell receives input from rods or cones, but via intermediate cells
Type Explanation
Simple center-surround type cells - in ganglion cells & LGN.
- Positive response in the center area, negative response in the outer area
- ON-center ganglion cells = exposure of receptive field leads to excitation in cell, on
exposure of periphery inhibition
- OFF-center ganglion cells = just the opposite, lateral inhibition to sharpen contrasts.
Simple cortex cells - orientation specific response, depending on orientation of light
stripe.
- Also excitatory & inhibitory zone, right next to each other
Complex cortex cells - movement (of a correctly oriented bar).
- Selective response of receptive fields, but independent of where exactly the
stimulus is found in the receptive field -> stimulus by direction of movement.
End-inhibited (hyper-complex) cortex cells - corners, angles, bars of specific length
moving in specific direction
- Length of light bar also relevant
Lateral inhibition / inhibition
- Enhanced contrasts due to reciprocal inhibition of cells.
-> When a receptor fires, it inhibits its nearest neighbors
- Difference central vs. peripheral vision
-> Exact edge vs. imaginary shadow
-> Narrow (cones) vs. large-scale (rods) connectivity / inhibition
Visual pathways and organization of the visual cortex
Visual field Explanation
Right Left sides of the two retinas, signals in the left visual cortex.
Left Right sides of both retinas, signals in right vis. cortex Cortex
Retino-geniculo-striate visual pathway
- Runs from the eye via the optic nerve of the respective eye; partially crosses in the
optic chiasm (ipsilateral = not crossed)
- Runs further in the contralateral side of the brain as an optic tract (no longer optic
nerve) to the LGN (part of the thalamus)
- Right field of vision falls on left sides of both retinae (in both eyes), left field of vision
falls on right sides
- Further from the LGN via the so-called optic radiation (black lines in the picture) to
the primary visual cortex in the occipital lobe
- In the LGN separation between magnocellular pathway and parvocellular pathway
